A crash course in
Mesh Networking
Victor Bahl
Microsoft Research
bahl@microsoft.com
http://research.microsoft.com/~bahl/
© 2007 Victor Bahl. All Rights Reserved.
Notice
These lecture notes are for educating. Feel free to incorporate these
slides in your presentations but please cite the source on each
borrowed slide and as a courtesy to the author please inform him of
such use. Do not post a copy of these slides, or slides derived from
these on a web site without the author’s written permission.
The contents of this deck may change without notice
© 2007 Victor Bahl. All Rights Reserved.
Foreword
• Mobile ad hoc networking and mesh networking is a thriving area of
research. The number of solutions & results are simply too large to
cover in a short tutorial.
• This is not a tutorial on (1) wireless communications (2) MAC
protocols, and (3) multi-hop routing protocols.
• This is crash course on what I know about building mesh networks.
Exhaustive & deep treatment of all existing results is not provided.
• These notes are an attempt to describe the main problems & the
general idea behind some of the promising solutions. At the end of
this tutorial you should have a reasonably good understanding of the
state-of-art in mesh networking.
• I would appreciate your pointing out any mistakes you may find.
© 2007 Victor Bahl. All Rights Reserved.
Acknowledgements
Some of the work presented in this tutorial is a result of the research
conducted in my group at MSR. I want to particularly acknowledge my
colleagues Jitu Padhye, Ranveer Chandra, Richard Draves, and Sharad
Agarwal in MSR. I consulted with my colleagues in academia as well. Special
thanks to Edward Knightly (Rice University), Brian Levine (University of
Massachusetts), Suman Banerjee (University of Wisconsin), Bhaskaran
Raman (IIT Kanpur), and Yair Amir (Johns Hopkins University) for providing
me the details of their testbeds. Finally, thanks to our interns Pradeep
Kyasanur (UIUC), Krishna Ramachandran (UCSB) Saumitra M. Das (Purdue)
whoes research results are incorporated in this tutorial.
© 2007 Victor Bahl. All Rights Reserved.
Course Roadmap
1. Mesh Networking & Applications
2. Basics of Radio Frequency Communications
3. Multi-hop Wireless Networking
–
–
Historical background
Challenges: Mesh networking with 802.11
4. Handling the Challenges
–
Capacity Enhancement & Calculation
MMAC, SSCH, BFS-CA, HMCP, MUP, Network Coding, conflict graphs, ….
–
Routing Protocols & Link Quality Metrics
RFC 2501, RFC 3626, RFC 3684, RFC 3561, RFC 4728, ETX, LQSR, EXoR, HWMP, ETT, WCETT
–
Security & Network Management
5. Mesh Deployments – Discoveries & Innovations
–
MSR’s Mesh, MIT’s RoofNet, IIT’s DGP, Rice’s TFA, UMASS’s DieselNet, UCSB’s Mesh, Madcity’s Mesh, JHU’s
SMesh
6. Mesh Networking Standards
–
IEEE 802.11s (IETF standards covered previously)
7. References
© 2007 Victor Bahl. All Rights Reserved.
Mesh Networking & Applications
Wireless Mesh Networking
Definition
A wireless mesh network is a peer-to-peer multi-hop wireless network
in which participant nodes connect with redundant interconnections
and cooperate with one another to route packets.
– Unlike Mobile Ad hoc NETworks (MANETs) where routings node are
mobile, in mesh networks routing nodes are stationary.
– Mesh nodes may form the network's backbone. Other non-routing mobile
nodes ("clients") may connect to the mesh nodes and use the backbone to
communicate with one another over large distances and with nodes on the
Internet
© 2007 Victor Bahl. All Rights Reserved.
Characteristics of a Mesh Network
Mesh Network
–
–
–
–
–
Classic Hub & Spoke Network
Grows “organically”
Does not require infrastructure support
Is fault tolerant
Requires distributed management
Offers higher capacity (via spatial diversity & power
management), but
• Too many nodes  shared bandwidth may suffer due to interference
• Too few nodes  route maintenance difficult disconnections possible
– Identity and security management is a challenge
© 2007 Victor Bahl. All Rights Reserved.
The Mesh Networking World
Mesh Node
Mesh
Node
Web
Content
Mesh
Node
Corporate
Data
Communication
Mesh
Node
Games
Mesh
Node
Shopping
Mesh
Node
Media
Internet
Broadband
Neighbourhood
Traditional Last Mile Territory
© 2007 Victor Bahl. All Rights Reserved.
Home Mesh
Scenario 1: Broadband Internet Access
Internet
•
Last Mile
Equipment capital cost
The scale of touching / maintaining so many endpoints
The physics of running cable large distances over unfriendly terrain
Political, social and territorial implications
Wireless mitigates these issues but introduces others
–
–
–
–
•
Middle Mile
Cost of middle and last miles make physical wired infrastructure not an option in
rural areas and many countries
–
–
–
–
•
Backbone
Range
Bandwidth
Spectrum availability
Cost & maintenance issues of new hardware / standards
Mesh networking makes wireless workable
–
–
Range & bandwidth addressed by shorter links
Cost & maintenance addressed by building on commodity standards
© 2007 Victor Bahl. All Rights Reserved.
Scenario 2: A Community Mesh Network
Organic – Participants own the equipment and the network
© 2007 Victor Bahl. All Rights Reserved.
Community Mesh Network Applications
•
•
•
•
•
•
Shared broadband Internet access
Neighborhood watch (e.g. video surveillance)
Shared media content (e.g. neighborhood DVR)
Medical & emergency response
Neighborhood eBay (garage sales, swaps)
Billboards (babysitter/service recommendations, lost cat, newsletter)
 Bits produced locally, gets used locally
 Social interaction
• Distributed backup
Internet use increased social contact, public participation and size of social
network. (social capital - access to people, information and resources)
Prof. Keith N. Hampton (author of “Netville Neighborhood Study”)
URL: http://www.asanet.org/media/neville.html
© 2007 Victor Bahl. All Rights Reserved.
Scenario 3: Home Mesh
Services
Entertainment
Entertainment
E-Business, Services
Pre-Recorded Content
Personal Media
Broadband
•
•
•
Extend Access Point (AP) coverage
Better spectrum (re)use  greater capacity
Automatic discovery, plug-and-play networked home devices:
– AV equipment (Cameras, TV, DVD, DVR, satellite/cable)
– Phones (Cellular and POTS)
– Traditionally disassociated smart devices (PDAs, AutoPC)
– Home infrastructure items (Light switches, HVAC controls)
© 2007 Victor Bahl. All Rights Reserved.
Scenario 4: Blanket City-wide Wireless Coverage
Philadelphia picks Earthlink for City Wireless, TechNew World, October 5, 2005
San Francisco Keeps Pushing City Wide WiFi, CNET News.com, August 17, 2005
“San Francisco Mayor Gavin Newsom wants to make Wi-Fi coverage in the city as ubiquitous as the fog that blankets
its neighborhoods.”
Wi-Fi Hits the Hinterlands, BusinessWeek Online, July 5, 2004
“Who needs DSL or cable? New “mesh” technology is turning entire small towns into broadband hot spots”, Rio Rancho
N.M., population 60,000, 500 routers covering 103 miles2
NYC wireless network will be unprecedented, Computerworld, June 18, 2004
“New York City plans to build a public safety wireless network of unprecedented scale and scope, with a capacity to
provide tens of thousands of mobile users”
Rural Areas need Internet too! Newsweek, June 7, 2004 Issue
“EZ Wireless built the country's largest regional wireless broadband network, a 600-square-mile Wi-Fi
blanket, and activated it this February”, Hermiston, Oregon, population 13,200, 35 routers with 75
antennas covering 600 miles2
Mesh Casts Its Net, Unstrung, January 23, 2004
“Providing 57 miles2 of wireless coverage for public safety personnel in Garland Texas”
PCCW takes Wireless Broadband to London, The Register, September 2, 2005
“Prices for the service in UK start from £10 / month for 256 Kbps to £18 /month for 1 Mbps”
Anacapa and Firetide Bring Free Wireless Internet to La Semaine Italienne in Paris, France ,
Business Wire, 24 May, 2005
Bell Canada and Nortel Networks launch Project Chapleau,
designed to evaluate broadband in rural Canada, Optical Networks Daily, 18 July 2005
© 2007 Victor Bahl. All Rights Reserved.
Scenario 5: All-Wireless Office
• Older buildings
• No wires
• For small offices (~100 PCs) • No switches
• No APs
– Rapid deployment
– Low cost
– Short-term offices
• Not a replacement for wire
© 2007 Victor Bahl. All Rights Reserved.
Scenario 6: Spontaneous “Mesh”
Definition
A temporary ad-hoc multihop wireless network for exchanging voice, video or
data, for collaboration in a locally distributed environment, when no permanent
infrastructure or central control is present. Usually between portable wireless
devices.
1. Peer Calling & Party Lines
– P2P calling within local groups – conferences, events, school campus,…
2. Public Safety
Fire and rescue teams need ad-hoc
communication at incident sites
3. Real Time Advisory
Drivers need traffic information and
advisories generated in real time
© 2007 Victor Bahl. All Rights Reserved.
Grass Roots Mesh Deployments
Academia
– The Roofnet Project (MIT, USA) - http://pdos.csail.mit.edu/roofnet/doku.php
802.11 mesh network for broadband IA in cities
– The CITRIS TIER Project (UC Berkeley, USA) - http://tier.cs.berkeley.edu/
Technology and Infrastructure for emerging regions
– The Digital Gangetic Plains Project (IIT Kanpur, India) - http://www.iitk.ac.in/mladgp
802.11-based low-cost Networking for rural India
– The TFA Project (Rice University, USA) - http://taps.rice.edu/index.html
Technology for All Project
– ….
Community Mesh Networks
– Community Network Movement - http://www.scn.org/commnet/
– Seattle Wireless - http://www.seattlewireless.net/
– Champaign-Urbana Community Wireless Network - http://www.cuwireless.net/
– Kingsbridge Link, U.K. - http://www.kingsbridgelink.co.uk/
– ….
© 2007 Victor Bahl. All Rights Reserved.
Industry Breakdown
Infrastructure Based
Infrastructure-less
Internet
UNIVERSITY
Internet
101
Bus Stop
206
Poletop Radio
Gas Station
(Internet TAP)
Mesh Router 7
EXIT
90
Mesh Router 5
Mesh Router 2
Mesh Router 3
MeshStreet
Zone
Any
SkyPilot, Flarion, Motorola (Canopy)
Invisible Networks, RoamAD, Vivato,
Arraycomm, Malibu Networks,
BeamReach Networks, NextNet
Wireless, Navini Networks, etc.
Mesh Router 1
Mesh End Device
End Device
(Guest to Router 1)
Meshnetworks Inc.,Radiant Networks,
Invisible Networks, FHP, Green Packet Inc.,
LocustWorld, etc.
Architecture effects design decisions on
Capacity management, fairness, addressing & routing, mobility
management, energy management, service levels, integration with the
Internet, etc.
© 2007 Victor Bahl. All Rights Reserved.
Industry Deployment Scenarios
http://www.unstrung.com/insider/
March 2005, Source: Unstrung Insider
© 2007 Victor Bahl. All Rights Reserved.
What about WiMAX?
IEEE 802.16d for developing/rural use (.16e targets mobile scenarios)
– Still needs market momentum around hardware optimisation: size, power,
efficiency and most important—cost
WiMAX as a last-mile solution?
– In low-density areas, WiMAX requires high-power towers or lots of
towers: (=> cost goes up)
– In NLOS environments, range impacts bandwidth through reduced
modulation
– WiMAX CPE expensive in next 3-5 years (~ $150-250)
WiMAX feeding a mesh can be a good solution
– Mesh extends WiMAX tower reach
– Mesh simplifies the financials by greatly reducing equipment cost
– Mesh is robust and deal with network vagaries
© 2007 Victor Bahl. All Rights Reserved.
WiMAX + Mesh
WiFi Meshes can add value to WiMAX in several ways:
– Reduce CPE costs
– Extend range of WiMAX tower without compromising speed
– Replace high-price WiMAX towers with cheaper mesh nodes
WiMAX
Only
WiMAX
with
Mesh
16
QAM
8PSK QPSK
FSK
A
© 2007 Victor Bahl. All Rights Reserved.
16
QAM
16
QAM
16
QAM
16
QAM
A
Radio Frequency Communications Basics
© 2007 Victor Bahl. All Rights Reserved.
RF Communications
Radio Frequency (RF) waves are effected by
– Distance between the transmitter and receiver
 Inverse power law
– Reflection (e.g. ground reflection)
– Diffraction (e.g. from building)
– Scattering (e.g. from trees)
Path Loss
Multipath Fading
– Links may not be bi-directional
 A can hear B, but B can’t hear A (e.g. because of
receiver sensitivity)
– Radio waves may be blocked (absorbed) by objects
 e.g by buildings, humans, rain, walls, glass windows
Shadowing
Degree of attenuation generally depends on frequency
© 2007 Victor Bahl. All Rights Reserved.
Radio Frequency Wave Propagation
101
A
P
101
Access Point 1
House
House
House
House
Building 1
A
P
Access Point 1
House
Tree
Tree
House
Tree
Tree
Tree
Tree
Condos
Tree
Tree
Tree
Tree
Condos
Hospital
Tree
Gas station
Shadowing
Multipath Fading
- caused by multiple reflections
- caused by physical obstructions
© 2007 Victor Bahl. All Rights Reserved.
Multipath Fading
What causes multipath fading?
–
–
–
–
Transmitter radiates power in many directions
Receiver collects power from many directions
Signals are reflected by various objects
Many different paths exists between transmitter & receiver
Results in
– Delay spreads
 Signals along different paths arrive at different times
 One “symbol” bit may overlap with another
– Time varying signal amplitudes at receiver
Types of Fading
– Fading can be fast or slow (rapid fluctuation of signal)
– Fading can be flat or frequency-selective
– All four combinations possible
© 2007 Victor Bahl. All Rights Reserved
Multipath is not all bad
• The multipath phenomena can be exploited to increase data
throughput and range by reducing bit error rates
• From information theory, channel capacity increase is proportional to
the number of transmit and receive antennas
– MIMO (Multiple-Input Multiple-Output)
• MIMO techniques are the key reason for higher data rates in IEEE
802.11n and IEEE 802.16 standards
• Signals arriving via different paths are picked up at different strengthlevel by the different antennas and combined to form a cleaner &
stronger signal
– The correlation between antennas must be de-couple by DSP algorithms
Statistical Models for Propagation Effects
– Rayleigh Fading
 Each reflected wave may have a different phase
 Signals arriving out of phase may cancel each other
 Models RF propagation in heavily built-up urban environments
– Rician Fading
 Essentially like Rayleigh, except that there is one dominant (line of
sight) wave
 Models RF propagation inside buildings
– Doppler Shifts
 Movement creates shifts in frequency
 Different path lengths have different shifts
 Introduces random frequency modulation at receiver
Challenge in using these models is what parameters should you use
© 2007 Victor Bahl. All Rights Reserved.
Effect of Frequency
At higher frequency
– signals are absorbed more rapidly by water in the air
 attenuate faster
– signals are blocked by objects
 do not refract; leave a complete shadow behind obstacles
 lower frequency signals refract (bend) around obstacles
Friis Transmission Equation
Free-space path loss
Lfs  32.44  20 log d  20 log 10f  GT  GR
Where, Lfs is the loss in dB; f is the frequency in MHz; GT & GR are the
transmitter & reciever antenna gain in dBi; and d is the distance in Km at which the
loss is calculated
© 2007 Victor Bahl. All Rights Reserved.
Range Calculations
Link budget calculations for line of sight communication with free space loss
PR  PT  Lfs  LT  LR
where PR & PT are received & transmitted powers in dBm; Lfs is path loss;
LT & LR are signal loss at the transmitter & receiver in dB
•
When the receiver sensitivity is known, link budget calculations can provide an
estimate of the range.
•
The formula captures the fact that range is effected by frequency, distance,
transmission power, antenna gains, and losses at the transmitter and receiver.
•
For non-line of sight communications (e.g. indoor). The formula has to be
modified [out of scope for this tutorial]
© 2007 Victor Bahl. All Rights Reserved.
Should know “The Decibel”
• The dB is a dimensional-less logarithmic unit used to describe a ratio.
• In RF communications dB used to describe the ratio between two
measurements of power. Mathematically,
 the difference in decibels between two powers = 10 log10 (P2/P1)
• dBm (or dBmW) is the absolute unit of measured power referenced to 1
mW
– 3 dBm is 2 (= 103/10) mW
– 0.01 mW is -20 (= 10log10(0.01)) dBm
• The receiver sensitivity of typical 802.11 wireless cards ranges between
-60 dBm and -80 dBm, i.e. they can decode RF signals received at
power levels between 0.000001 mW and 0.0000001 mW
© 2007 Victor Bahl. All Rights Reserved.
Summing up observations about the RF channel
• Radio channel exhibits unpredictable behavior
– Signal strength fluctuates rapidly and widely
– Error rates are high
– Fading varies with time and causes attenuation
• Understanding it’s characteristics leads to better system
design (e.g. MIMO, Routing protocol design,…)
• Statistical models should be used in simulations
• Interference is hardest to deal with and can limit
performance severely
• Transmission power control & frequency reuse are
important techniques for capacity enhancement
© 2007 Victor Bahl. All Rights Reserved.
Channel Access Protocols: Wired vs. Wireless
Wired networking protocols such as Ethernet perform
poorly when used in wireless communication
– Why? Because of media dependent differences
Should know:
– Hidden terminal problem
– Exposed terminal problem
– Collision detection problem
– Interference problem
– Deaf-time problem
 Turn-around time between Rx/Tx can have significant effect on the design of the MAC
layer
© 2007 Victor Bahl. All Rights Reserved.
The Hidden Terminal Problem
Consider the following scenario
–
–
–
–
Tobagi-Comm-1975
B is within range of A and C; A and C are out of range of each other
 i.e. A and C are hidden from each other
A sends a packet to B
C sends a packet to B
The packets collide at B
 results in reduction of throughput
CSMA doesn’t work
–
C can’t know that it has to wait
since it can’t hear A
B
A
C
Solution: RTS/CTS - with intended transmission
duration Karn-CNC-1997
© 2007 Victor Bahl. All Rights Reserved.
The Exposed Terminal Problem
Consider the following:
– C is within range of B’s transmitter
– B sends a packet to A
– C wants to send a packet to D but doesn’t, since C is exposed to B
(Note: transmitter B must be protected because it expects an ACK from A)
CSMA doesn’t work
– C thinks it should wait since
it can hear B
– C waits needlessly
 results in reduction of throughput
A
C
B
Can transmit,
but doesn’t
D
© 2007 Victor Bahl. All Rights Reserved.
The Collision Detection Problem
No collision detection in wireless communications
In wireless can’t listen while you send
– Generally hardware is not flexible enough
– All you hear is your own signal
 Your own signal at your antenna is much stronger than anyone else’s
signal
n
 do 
– The power law Pr  Pt  
 dr 
Consequently,
– wireless can’t do collision detect like Ethernet
© 2007 Victor Bahl. All Rights Reserved.
Things to know about Spectrum Use (US View)
•
WLANs operate in the 2400 – 2483.5 MHz (2.4 GHz), 5150 – 5250 MHz (lower U-NII),
5250 – 5350 MHz (mid U-NII), and 5725 – 5825 MHz (upper U-NII) bands under FCC’s
Part 15 “unlicensed” rules
•
Part 15 operation is subject to no harmful interference caused to; and interference
accepted from, licensed services, other unlicensed devices, ISM equipment, and
incidental radiators
•
IEEE Standards operating in these bands include:
–
–
–
•
Other Part 15 devices and Part 18 ISM devices that also use these bands:
–
–
•
802.11{b,g} in the 2.4 GHz band; 802.11a in the U-NII band
802.15 WPAN (Bluetooth) in the 2.4 GHz band
802.16 WirelessHUMAN in the mid and upper U-NII bands
Field disturbance sensors, cordless telephones, low power devices, and microwave ovens
Non-802.11 Part 15 devices: cordless telephones, A/V repeaters, security cameras, baby
monitors, & digital data links
Licensed services that operate in these bands include:
–
Amateur radio in the 2.4 GHz and upper U-NII bands; fixed microwave in the 2.4 GHz band; and
satellite in the lower U-NII band
© 2007 Victor Bahl. All Rights Reserved.
2.4 GHz Band Allocation (“The junk” band)
802.11b&g WLAN
802.15 – Bluetooth WPAN
15.209 – Generic Unlicensed
15.245 – Field Disturbance Sensors
15.247 – Spread Spectrum
15.249 – Low Power
Part 18 – ISM
Part 90 – Private Land Mobile
Part 97 – Amateur
Part 101 – Fixed Microwave
Government
2400 MHz
2450 MHz
© 2007 Victor Bahl. All Rights Reserved.
5.3 GHz Band Allocation (US View)
5.3 GHz Band
802.11a – WLAN
802.16a –
WirelessHUMAN
15.209 – Generic
Unlicensed
15.4XX – U-NII
Part 25 – Satellite
Part 87 – Aviation
Government
5150 MHz
5200 MHz
5250 MHz
5300 MHz
© 2007 Victor Bahl. All Rights Reserved.
5350 MHz
5.8 GHz Band Allocation (US View)
802.11a – WLAN
802.16a – WirelessHUMAN
15.209 – Generic Unlicensed
15.245 – Field Disturbance Sensors
15.247 – Spread Spectrum
15.249 – Low Power
15.4XX – U-NII
Part 18 – ISM
Part 97 – Amateur
Government
5725 MHz
5775 MHz
© 2007 Victor Bahl. All Rights Reserved.
5825 MHz
The Interference Problem
Following rules and regulations but….
802.11 in presence of BT
Phone on
TCP download from a 802.11 AP
Panasonic 2.4GHz Spread Spectrum
Phone 5 m and 1 wall from receiver
Performance worsens when there are large
number of short-range radios in the vicinity
Badly written rules: Colliding standards
© 2007 Victor Bahl. All Rights Reserved.
Things to know about IEEE 802.11{b,g}
22 MHz channels, K = 1 … 11
– Channels are 5 MHz apart. Center frequencies: 2412 + 5 (K-1) MHz
– Channels 1, 6, 11 are non-overlapping (“orthogonal”)
Transmit power limit is 1 Watt (30 dBm)
.11g data rates
Data Rate
(Mbps)
Modulation
Sensitivity
(dBm)
1, 2
DSSS
-80
5.5
CCK
-80
Sensitivity
(dBm)
6
BPSK
-82
9
BPSK
-81
.11b data rates
Data Rate
(Mbps)
Modulation
1, 2
DSSS
-80
11
CCK
-76
5.5
CCK
-80
12
QPSK
-79
11
CCK
-76
18
QPSK
-77
24
4-QAM
-74
36
4-QAM
-70
48
16-QAM
-66
54
16-QAM
-65
© 2007 Victor Bahl. All Rights Reserved.
Things to know about IEEE 802.11a
Channelization & Data Rates
Channel
(20 MHz
width)
Center Freq
(MHz)
40 mW
(2.5 mW/MHz)
36
40
44
48
5180
5200
5220
5240
200 mW
(12.5 mW/MHz)
52
56
60
64
5260
5280
5300
5320
149
153
157
161
5745
5765
5785
5805
Power
Limits*
U-NII Lower Band
(5150 – 5350 MHz)
U-NII Mid Band
(5250 – 5350 MHz)
U-NII Upper Band
(5725 – 5825 MHz)
800 mW
(50 mW/MHz)
Data Rate
(Mbps)
Modulation
Sensitivity
(dBm)
6
BPSK
-82
9
BPSK
-81
12
QPSK
-79
18
QPSK
-77
24
16-QAM
-74
36
16-QAM
-70
48
64-QAM
-66
54
64-QAM
-65
Range:
Path loss at 5765 MHz is 20 x log10[5765/2437] = 7.5 dB greater than at
2437 MHz independent of distance (Remember Friis’s formula!)
© 2007 Victor Bahl. All Rights Reserved.
Summarizing: Wireless Communications is Hard
Unlicensed spectrum is not pristine
 Current spectrum etiquette rules are insufficient
Available spectrum is limited => Capacity is limited
 Shannon’s Law: can pack only n bits / m Hz (Hz is not getting bigger)
Transmit power is strictly regulated
 Limits the operational range
Channel is unpredictable
 Wide & rapid fluctuation of signal strengths, high error rates, and attenuation
depends heavily on environment (fading, multipath, absorption,…)
Wireless is a broadcast channel
 Snooping is easy
Battery technology is not following Moore’s law
 Limits usage, battery power doubles once every 35 years!
Node mobility stresses protocols
© 2007 Victor Bahl. All Rights Reserved.
Powers-Proc-1995
Solution Space is Large
•
•
•
•
•
•
Microelectronics
Modulation schemes
Error correction
Signal processing
Smart antennas
Energy conservation
•
•
•
•
•
•
Channel access protocols
Routing protocols
Transport protocols
Operating system support
Application adaptation
Human interface
A simple tweak in any one of these results in a paper 
© 2007 Victor Bahl. All Rights Reserved.
A word about the
Integrity & Credibility of Mesh Simulations
Andel-Computer-2006
Is it repeatable?
– Document all setting; provide freely available code, models & app. traffic
Is it statistically valid?
– Use the Central Limit Theorem to determine the no. of independent runs; Address
sources of randomness (e.g. pseudo number generator); delete transient values or
eliminate by preloading routing tables, queues etc.
Is the radio model reasonable?
– Use two-ray and shadowing models rather than free-space model
Did you use the correct traffic type?
– Traffic generation should be based on target applications, CBR may be incorrect
Did you perform sensitivity analysis?
– Use analysis of variation (ANOVA) technique to understand significance of a
particular parameter setting
Did you validate against real implementation?
– When possible, validate simulation runs on real testbed, even if at a smaller scale
Did you try to compare?
– Use simulations to understand general behavior, not to compare protocols
© 2007 Victor Bahl. All Rights Reserved.
Multi-Hop Wireless Networking
Historical Perspective
Packet Radio Network (PRNET), 1972-1982
•
Band: 1718.4-1840 MHz; Power: 5 W; Range: 10 km; Speed:100-400 Kbps, Addressing: Flat;
Routing: Distance Vector; Scale: 50+
Survivable Adaptive Networks (SURAN), 1983-1992
•
Band: 1718.4-1840 MHz; Power: 5 W; Range: 10 Km; Speed: 100-400 kbps, Addressing:
Hierarchical; Routing: Distance Vector; Scale: 1000+ (Low cost packet radio)
Global Mobile Information Systems (GLOMO), 1995-2000
•
e.g. NTDR, Band: 225-450 MHz; Power: 20 W; Range: 11-20 Km; Speed: 300 kbps,
Addressing: Flat; Routing: Link-state / 2-level clusters; Scale: 400+
IETF Mobile Ad Hoc Networks (MANET) Working Group, 1997 –
•
RFC 2501 (Eval), RFC 3561 (AODV), RFC 3626 (OLSR), RFC 3684 (TBRPF), Drafts – DSR,
DYMO, Multicast, OLSRv2
PRNET Van
IEEE 802.11s Working Group, 2004 -
© 2007 Victor Bahl. All Rights Reserved.
Challenge:
Mesh Networking with IEEE 802.11
When does a viable mesh form?
Problem Formulation
How many nodes have to sign
up before a viable mesh
forms?
Answer depends on
–
–
–
–
Definition of “viable”
Wireless range
Neighborhood topology
Probability of participation
Example Scenario:
Community Mesh Network
Viable mesh: group of at least 25
homes that form a connected
graph
Topology: A North Seattle
Neighborhood. 8214 houses, 4Km
x 4Km
Wireless range: 50, 100, 200 and
1000 meters
Houses decide to join at random,
independent of each other. We
consider 0.1% to 10%
participation rates.
© 2007 Victor Bahl. All Rights Reserved.
Mesh Formation Results
•
5-10% subscription rate needed
for suburban topologies with
current wireless ranges (> 100 m)
•
Once a mesh forms, it is usually
well-connected
– i.e. number of outliers are few
(most nodes have > 2
neighbors)
•
Need to investigate other joining
models
•
Business model considerations
are important
Increasing range is key for good mesh connectivity
© 2007 Victor Bahl. All Rights Reserved.
But…The Range Problem
5 GHz:
• Bandwidth is good,
• Published 802.11a
ranges (Yellow circles)
decent
• Measured range (red
circle) poor
• Range is not sufficient
to bootstrap mesh until
installed % is quite high
The Antenna Problem
Need software steerable antennas to reduce interference & increase range
Challenges
Advantages
– Directional high gain antenna
makes long-range meshes
viable.
– Topology control minimizes
interference
– High gain, low sidelobe design
may enable indoor placement
– Exacerbates hidden terminal
problem
 Solution requires control
channel and omni antenna
– Must change FCC reqs for ERP
 Currently set up to preclude
neighborhood mesh
– Cost increment over omni
 Separate band/radio for
control
 High gain antenna is more
expensive
– Software steerable
© 2007 Victor Bahl. All Rights Reserved.
Antenna Evaluation – Sample Study
Study Objective
Can directional antennas reduce interference, increase spatial reuse, and
increase capacity in indoor meshes
Antenna characteristics
– 6.5// diameter; 3// height; 1.85 lbs
– Continuously steerable via software on a PC
– Gain: 5.5 - 6.0 dBi; Frequency 2.4-2.497 GHz;
– Azimuth Beamwidth: 50o ; Elevation Beamwidth: 90o
– Beam position transition time 1 msec
© 2007 Victor Bahl. All Rights Reserved.
Indoor Performance of Directional Antenna
Interior effectiveness severely limited by multi-path
© 2007 Victor Bahl. All Rights Reserved.
Indoor Performance of Directional Antenna
Interior effectiveness severely limited by multi-path
© 2007 Victor Bahl. All Rights Reserved.
Indoor Performance of Directional Antenna
Interior effectiveness severely limited by multi-path
© 2007 Victor Bahl. All Rights Reserved.
Indoor Performance of Directional Antenna
Interior effectiveness severely limited by multi-path
© 2007 Victor Bahl. All Rights Reserved.
Indoor Performance of Directional Antenna
Interior effectiveness severely limited by multi-path
© 2007 Victor Bahl. All Rights Reserved.
Implications of Antenna Study
Study Objective:
Can directional antennas reduce interference, increase spatial reuse, and
increase capacity in indoor meshes
Results:
– Wide azimuth beamwidth (50o) antenna do not work when placed
indoors
reflections and multipath compromise directional gain
– MIMO is better for indoor and dense apartment complexes
– Antenna placement is critical
– We have no 5 GHz antennas to experiment with (FCC rules?)
– We don’t have good antenna solutions yet
© 2007 Victor Bahl. All Rights Reserved.
The MAC Problem – Packets in Flight Example
RTS
RTS
RTS
RTS
1
2
3
RTS
4
5
6
7
8
9
10
CTS
CTS
Backoff window doubles 
2 packets in flight! Only 4 out of 11 nodes are active….
© 2007 Victor Bahl. All Rights Reserved.
11
Throughput: Internet Gateway Example
Internet
RTS
RTS
RTS
CTS
Backoff window doubles
© 2007 Victor Bahl. All Rights Reserved.
Backoff window doubles
The Scheduling Problem
Conflict graph
A
B
A
A
B
B
D
D
A
C
B
D
C
E
D
E
1
Choice 1
Choice 2
D
 yes
A
B
0
1
1
D
C
D
A
B
A
D
D
 yes
B
A
C
A
B
E
E
B
D
D
B
C
A
B
A
E
If future traffic is not known, which one do you schedule first?
© 2007 Victor Bahl. All Rights Reserved.
The Fairness Problem
A
1
B
C
2
D
Jinyang-MobiCom-2001
Information Asymmetry
– A & C do not have the same information
 C knows about flow 1 (knows how to contend)
 A does not know about flow 2
– Flow 2 always succeeds, Flow 1 suffers
 When RTS/CTS is used
– A’s packets are not acknowledged by B
» A times out & doubles it’s contention window
 When RTS/CTS is not used
– A’s packet collide at B, but Flow 2 is succesful
» A times out & double it’s contention window
– Downstream links suffer
© 2007 Victor Bahl. All Rights Reserved.
Gambiroza-MoiCom-2004
The Fairness Problem (2)
ITAP
Camp-DC-2005
•
Location closest to gateway gets the more packets
•
Nodes farthest from the gateway get very little bandwidth and can get starved
•
Possible solution: Rate control on each node with fairness in mind
– Need topology & traffic information to calculate fair amount
– Global vs. distributed solution
© 2007 Victor Bahl. All Rights Reserved.
The Fairness Problem (3)
MAC attempts to provide fairness at packet level not flow level
Capture phenomena
 Winner of competing flows has a higher chance of winning contention again
Different levels of interference at different links (different neighborhood)
 Highly interfered flows can be drowned
Nandagopal-MobiCom-2000
Qiu-MSRTR-2003
A
C
B
F1
F2
O
P
D
F3
Q
E
F
F4
R
G
F5
S
T
U
Flow1
Flow2
Flow3
Flow4
Flow5
2.5 Mbps
0.23 Mbps
2.09 Mbps
0.17 Mbps
2.55 Mbps
Active area of research
- MACAW, WFQ, DFS, Balanced MAC, EBF-MAC, PFCR, ….
© 2007 Victor Bahl. All Rights Reserved.
The Path Length Problem
Experimental Setup
Impact of path length on throughput
• 23 node testbed
10000
9000
One IEEE 802.11a radio per node
(NetGear card)
• Randomly selected 100 senderreceiver pairs (out of 23x22 =
506)
8000
Throughput (Kbps)
•
7000
6000
5000
4000
3000
2000
1000
0
• 3-minute TCP transfer, only one
connection at a time
0
1
2
3
4
5
6
Byte-Averaged Path Length (Hops)
If a connection takes multiple paths over lifetime,
lengths are byte-averaged
Total 506 points.
© 2007 Victor Bahl. All Rights Reserved.
Robert Morris’s Rooftnet MSR Mesh Summit 2004 Presentation
The Collision Problem
Actual Roofnet b/w is often much lower
Multi-hop collisions cut b/w by about 2x
Expected multi-hop b/w based on single-hop b/w
The Node Density Problem
Round trip delay versus node density
Average RTT
avg_rtt = 0.1*curr_sample + 0.9*avg_rtt
One sample every 0.5 seconds
0.2
0.18
0.16
Average RTT
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
0
20
40
60
80
100
120
140
160
180
Time
A new 100Kbps CBR connection starts every 10 seconds,
between a new pair of nodes. All nodes hear each other.
© 2007 Victor Bahl. All Rights Reserved.
The Power Control Problem
Tight power control reduces interference and increases throughput
A
D
B
C
– A & B do not detect RTS/CTS exchange between C & D
– B does not detect data transmission from D to C
– B’s transmission to A results in packet collision at C
© 2007 Victor Bahl. All Rights Reserved.
The Power Control Problem (2)
Tight power control reduces interference & increases overall throughput
A
D
B
C
But it also disconnects the network. So what’s the “right” power control
algorithm?
A
D
B
C
© 2007 Victor Bahl. All Rights Reserved.
The Capacity of Mesh Nodes
What is the maximum achievable capacity of a mesh network with N nodes?
Gupta-IEEEIT-2000
Optimal Case
Average Case
– Nodes are optimally
located, destinations are
optimally located
– Randomly located nodes and
destinations
– Traffic pattern are random
– Traffic patterns are fixed
– Optimally spatio-temporal
scheduling, routes, ranges
for each transmission
– As
n
each node obtains
 1  bits/sec

O
– Each node chooses same
range
– Each n   node obtains

1  bits/sec
O
 n


© 2007 Victor Bahl. All Rights Reserved.
 n log n 


The Capacity Calculation Problem
Gupta and Kumar 2000
– Theorem for stationary ad hoc nodes in the worst case traffic scenario
Determines asymptotic, pessimistic bounds on performance
– Every node in the mesh is active (either transmitting or receiving)
Does not answer:
– What is the capacity of a mesh which is using multiple channels,
directional antennas, tight power control?
© 2007 Victor Bahl. All Rights Reserved.
What is the Real Capacity of a Chain?
…but the radio’s interferance range is > radios communication range
Source
1
Destination
2
3
4
5
6
With Ideal MAC, Chain Utilization = 1/3
With interferences, Chain Utilization = 1/4!
Jinyang-MobiCom-2001
….but this is achievable only with optimum scheduling and optimum offered load!,
…with random scheduling and random load, utilization ~ 1/7 !
© 2007 Victor Bahl. All Rights Reserved.
The Path Selection Metric Problem
Several link quality metrics to select from
– Hop count
–
–
–
–
–
Round trip time
Packet pair
Expected data transmission count incl. retransmission
Weighted cumulative expected transmission time
Signal strength stability
–
–
–
–
Energy related
Link error rate
Air Time
…
Which to select? We still don’t have a interference-aware metric! We still
don’t know how to measure interference…..
© 2007 Victor Bahl. All Rights Reserved.
Baseline comparison of Metrics
Single Radio Mesh
Experimental Setup
Median path length:
HOP: 2, ETX: 3.01, RTT: 3.43, PktPair: 3.46
• 23 node testbed
1600
One IEEE 802.11a radio per node
(NetGear card)
• Randomly selected 100
sender-receiver pairs (out of
23x22 = 506)
• 3-minute TCP transfer, only
one connection at a time
Draves-MobiCom-2004
1400
Median Throughput (Kbps)
•
1200
1000
800
600
400
200
0
HOP
ETX
RTT
PktPair
ETX performs the best
© 2007 Victor Bahl. All Rights Reserved.
Baseline Comparison of Metrics
Two Radio Mesh
Draves-SIGCOMM-2004
Experimental Setup
Median path length:
HOP: 2, ETX: 2.4, WCETT: 3
• 23 node testbed
Median Throughput of 100 transfers
• 3-minute TCP transfer
• Two scenarios:
– Baseline (Single radio):
 802.11a NetGear cards
– Two radios
 802.11a NetGear cards
 802.11g Proxim cards
3500
2989.5
3000
Throughput (Kbps)
• Randomly selected 100
sender-receiver pairs (out of
23x22 = 506)
Single Radio
Two Radios
2500
2000
1601
1379
1500
1508
1155
844
1000
500
0
WCETT
ETX
Shortest Path
WCETT utilizes 2nd radio better
than ETX or shortest path
© 2007 Victor Bahl. All Rights Reserved.
But with different traffic pattern….
226
Trace Capture
• 1 workstations connected via Ethernet
• Traces captured during 1-month period
227
Erickson-MobiSys-2006
225
219
EL32
Trace Replayed
• Testbed of 22 mesh computers in office environment
• 2 IEEE 802.11a/b/g cards per computer
215
217
220
218
216
214
211
210
209
UP
DN
208
207
204
205
~ 76 m
206
203
202
~ 32 m
Similar performance
© 2007 Victor Bahl. All Rights Reserved.
201
The Multicast Problem
A multicast group is defined with a unique group identifier.
Nodes may leave or join the group anytime
 In wired networks physical network topology is static
 In ad hoc multi-hop wireless networks physical topology can change often
– Need to Integrate with unicast routing protocols
Many proposals [Tree-based, Mesh-based, Location-based] which one
to use?
- ABAM (On-Demand Associatively-Based Multicast)
- FGMP (Forwarding Group Multicast Protocol)
- ADMIR (Adaptive Demand-Driven Multicast Routing)
- LAM (Lightweight Adaptive Multicast)
- AMRIS (Ad hoc Multicast Routing utilizing Increased id-numberS)
- MAODV (Multicast AODV)
- DCMP (Dynamic Core Based Multicast Routing)
- MCEDAR (Multicast CEDAR)
- AMRoute (Adhoc Multicast Routing)
- MZR (Multicast Zone Routing)
- CAMO (Core-Assisted Mesh Protocol)
- ODMRP (On-Deman Multicast Routing Protocol)
- CBM (Content Based Multicast)
- SPBM (Scalable Position-Based Multicast)
- DDM (Differential Destination Multicast)
- SRMP (Source Routing-based Multicast Protocol)
- DSR-MB (Simple Protocol for Multicast and Broadcast using DSR) - …
-…
© 2007 Victor Bahl. All Rights Reserved.
The Interference Detection Problem
When two systems operate on overlapping frequencies, there exists a
potential for harmful interference between them
– Performance degradation on both systems
Conflict graph is determined by the “Interference Graph”
To determine the Interference Graph, require
– Knowledge of packet transmission from nodes that are not “visible”
– Knowledge of physical location of nodes within the network
– Knowledge of whether or not multiple transmissions increase ot decrease
interference?
Interference Graph can change
– as rapidly as the environment
– when a node leaves or join the network
© 2007 Victor Bahl. All Rights Reserved.
The Transport Layer Problem
• Majority of the Internet traffic is TCP
• Packet losses & delays in wireless can occur due to
– Environmental fluctuations resulting link failures
– Stochastic link performance due to rapidly changing error rates
– CSMA/CA assumes loss is due to congestion and back-off’s
• TCP assumes packet losses are due to congestion
– Times out when no ACK is received
– Invokes slow start, when instead the best response would be to retransmit
lost packets quickly
• RTT calculation can change as rapidly as the environment (link)
changes
Can we solve this problem without changing the end-to-end semantics?
© 2007 Victor Bahl. All Rights Reserved.
The Security Problem
Two type of attackers:
– External malicious node (no crypto keys)
– Compromised node (attacker captures legitimate node and reads out all
cryptographic information)
Attacks
– Selfish behavior, do not forward other node’s packets
– Denial of Service (DoS)
 Jamming
 Resource consumption attack
 Routing disruption (e.g. Wormhole attack)
 Inject malicious routing information
Hu-MobiCom-2002
Ongoing Research
–
Possible solutions: SEAD, Ariadne, SRP, CONFIDANT, …
Bucheggar-MobiHoc-2002
© 2007 Victor Bahl. All Rights Reserved.
The Spectrum Etiquette Problem
Local behavior affects Global Performance!
Doesn’t care
Node D
Node E
100 meters
Node A
Node B
200 meters
Node C
200 meters
120
Packets get dropped!
Normalized Percentage
100
80
60
40
20
0
Base
One TCP
© 2007 Victor Bahl. All Rights Reserved.
10% Drop rate
Consequently we…..
Must Increase Range and Capacity
Single radio meshes built on 802.11 technologies are not good enough. We must extend
the range of radios; we must understand the achievable capacity in an ideal wireless
mesh and we must build technology to approach this capacity?
Must Improve Routing Performance
Routing protocols based on shortest-hop are sub-optimal. We must build a routing
protocol that adapts quickly to topology changes, incorporates wireless interference and
link quality.
Must Provide Security and Fairness
Is it possible to ensure fairness and privacy for end-users and security for the network?
We must ensure that no mesh nodes starves and that the mesh guards itself against
malicious users.
Must Provide Self Management
An “organic network” should be both self-organizing and self managing? To what extent
can we remove the human out of the loop?
.
Must Develop a Resilient Framework for Applications
In a environmentally hostile environment, we must provide a framework for applications to
work robustly.
© 2007 Victor Bahl. All Rights Reserved.
Handling the Challenges
© 2007 Victor Bahl. All Rights Reserved.
Strategies for increasing Capacity
Strategy 1: Use all available channels
–
Avoid spectrum waste
Strategy 2: Improve modulation, reception, and coding
–
Today ~ 2.5 bits/Hz (.11g), Soon ~ 4.5 bits / Hz (.11n)
–
Network coding
Strategy 3: Improve spatial reuse by reducing interference
–
Fine grain transmit power control
–
(Steerable) directional antennas and directional MACs
Strategy 4: Navigate around harmful interference
–
Interference aware least cost routing
© 2007 Victor Bahl. All Rights Reserved.
Will not
cover
Strategy 1: Multi-Channel Communications
Goal
Assign n non-interfering channels to n pair of nodes such that n packet
transmissions can occur simultaneously.
Knobs
Single
Channel
Single Radio
Multiple Radio
Multiple Channels
Today
☺
X
☺
© 2007 Victor Bahl. All Rights Reserved.
Single Radio – Multiple Channels (SR-MC)
Distributed: Use a modified RTS/CTS sequence to negotiate channels
– Problem
 How does the sender know which channel the receiver is listening on?
– Solutions
 Receive on all channels simultaneously
– Simplest solution but too costly - will not consider here
 Use a dedicated rendezvous channel
 Use a synchronized hopping protocol
 Provide multiple rendezvous opportunities
Centralized: Compute channel assignments using global knowledge
Scope of Coverage
We will cover schemes that work on commodity radios only
© 2007 Victor Bahl. All Rights Reserved.
Packets-in-Flight Example Revisited
Negotiating Channel with RTS / CTS
RTS (C1,C3,C7)
C2
1
RTS (C3,C5,C7,C11)
C1
2
3
C2
4
5
6
C11
7
CTS (C1, C7)
8
C1
9
CTS (C11)
10 nodes are active, 5 packets in flight, 150% improvement!
© 2007 Victor Bahl. All Rights Reserved.
10
11
Note: Hidden Terminal – Multi-Channel Case
Let C1 be the rendezvous channel
γ can hear traffic on C1 only, doesn’t hear the CTS from β consequently doesn’t
know anything about traffic on C6 (δ is too far to hear anything from β)
α
γ
β
C1
RTS
C1
C6
C6
CTS
Data
C6
C6
on
Data
(C 6)
on C
6
C6
Data on C6
Time
(C 6)
CTS
C1
C11
C1
RTS
δ
Collision
Possible solution: Use multiple radios
© 2007 Victor Bahl. All Rights Reserved.
So-MobiHoc-2004
Implementation Option for SR-MC
Buffer packets, switch between channels
Chandra-INFOCOM-2004
Channel switching speed:
Today - 5 milliseconds
Possible - 80 microseconds
Application Layer
User-level
Kernel-level
TCP/IP, Network Stack
802.11 Device Driver
Switching logic
Packets for C1
Packets for C11
Firmware
802.11 hardware
Packets for C6
Multi-Channel Medium Access Control (MMAC)
Idea: Periodically rendezvous on a fixed channel to decide the next channel
• Divide time into beacon intervals
• Divide a beacon interval into two phase
So-MobiHoc-2004
– Negotiation Phase: All nodes switch to a pre-defined common channel
and negotiate the channel to use
– Transfer Phase: Once a channel is selected, the source & receiver switch
to this channel and data transfer occurs during this phase
Issues
• Requires tight clock synchronization
• Packets to multiple destinations can incur high delays
• Congestion on the common channel
• Common channel goes bad, everything goes bad
• Not able to handle broadcasts
© 2007 Victor Bahl. All Rights Reserved.
Slotted Seeded Channel Hopping (SSCH)
•
•
Divide time into slots
At each slot hop to a different channel
–
•
•
Bahl-MobiCom-2004
Nodes hop across channels to distribute traffic
Senders and receivers probabilistically meet & exchange schedules
Senders loosely synchronize hopping schedule to receivers
Characteristics

Distributed: every node makes independent choices

Optimistic: exploits common case that nodes know each others’
channel hopping schedules

Traffic-driven: nodes repeatedly overlap when they have packets to
exchange
© 2007 Victor Bahl. All Rights Reserved.
SSCH Rendezvous
Divide time into slots: switch channels at beginning of a slot
New Channel = (Old Channel + seed) mod (Number of Channels)
seed is from 1 to (Number of Channels - 1)
(1 + 2) mod 3 = 0
Seed = 2
Seed = 1
1
0
2
1
0
2
1
0
0
1
2
0
1
2
0
1
3 channels
E.g. for 802.11b
Ch 1 maps to 0
Ch 6 maps to 1
Ch 11 maps to 2
(0 + 1) mod 3 = 1
• Enables bandwidth utilization across all channels
• Does not need control channel rendezvous
© 2007 Victor Bahl. All Rights Reserved.
SSCH Syncing Seeds
• Each node broadcasts (channel, seed) once every slot
• If B has to send packets to A, it adjusts its (channel, seed)
Seed 2
2
2
2
2
2
2
2
2
2
1
0
2
1
0
2
1
0
3 channels
B wants to start a flow with A
Seed
1
2
0
2
1
0
2
1
0
1
1
2
2
2
2
2
2
2
Follow A: Change next (channel, seed) to (2, 2)
Stale (channel, seed) info simply results in delayed syncing
© 2007 Victor Bahl. All Rights Reserved.
Using all Available Channels with SSCH
In current IEEE 802.11 meshes
1
3
2
5
4
6
Only one of 3 pairs is active @ any given time
With proper use of channels
Ch 1 1
2
1
4
5
4
Ch 6 3
4
5
2
1
6
Ch 11 5
6
3
6
3
2
10 msecs
10 msecs
10 msecs
© 2007 Victor Bahl. All Rights Reserved.
…
SSCH Performance
100 nodes, IEEE 802.11a, 13 channels, every flow is multihop
Total System Throughput
Avg. per node Throughput
4
80
Throughput (Mbps)
60
SSCH
50
40
30
SSCH
3
2.5
2
SSCH
1.5
IEEE 802.11
20
IEEE 802.11a
10
Throughput (Mbps)
3.5
70
1
SSCH
0.5
0
10
20
30
Number of Flows
40
50
M802.11
IEEE 802.11a
0
10
20
30
40
50
Number of Flows
Significant capacity improvement when traffic load is on multiple separate flows
© 2007 Victor Bahl. All Rights Reserved.
How many Channels can we really use?
Banerjee-SIGMETRICS-2006
2.4 GHz ISM band use in 802.11b
Ch 1
Ch 6
Ch 11
• IEEE 802.11{b,g} partitions the allocated 83.5 MHz
spectrum into 11 channels
– Only channels 1, 6 and 11 are mutually non-overlapping
• But…using only these channels may waste spectrum
© 2007 Victor Bahl. All Rights Reserved.
How many Channels can we really use?
Ch 1
Ch 4
Ch 6
• Can we use more channels by using partially-overlapped
channels?
• Caution: may increase interference and cause more harm
than good
• Need an appropriate model to capture interference-effects
and make correct choices
Overlapped Channels do work!
Link A, Channel 1
Distance
(X-axis)
Link B, Channel Y
UDP Throughput (Mbps)
6
ChSep = 5
ChSep = 2
ChSep = 1
5
4
ChSep = 0
3
0
10
20
30
40
50
Distance (meters)
LEGEND
• Minimum distance between links for different choices
of channel
Non-overlapping channels, A = 1, B = 6
5
separation
Partially Overlapped Channels, A = 1, B = 3
2
Partially
Overlapped
Channels,
A
=
1,
B
=
2
1
• For every channel separation there is a minimal distance
0
Same channel, A = 1, B = 1
• Model-based algorithmic approach for channel assignment in wireless
Channel Separation
mesh networks
© 2007 Victor Bahl. All Rights Reserved.
60
Notes on Single Radio – Multiple Channels
•
Single radio solutions can be applied to multi-radios nodes since in most
cases the number of channels is greater than the number of radios in the
node.
•
Compared to multi-radio solutions, single radio solutions are power efficient –
but power is not the primary concern in most mesh networks
•
Single radio solutions are less costly than multi-radio solutions but radios are
fairly inexpensive
•
Switching speeds and mute-deaf-time is a problem in single radio solutions
but switching speeds are being reduced dramatically
•
When distance between nodes is large, need not restrict operation to nonoverlapping channels only
…so now lets look at multi-radio solutions
© 2007 Victor Bahl. All Rights Reserved.
Single Node Multiple Radio - Interference Study
Question:
Do two radios operating on non-overlapping channel interfere?
Experimental setup:
HOP 1
A
TCP
B
6” separation between B & C radios
C
TCP
HOP 2
© 2007 Victor Bahl. All Rights Reserved.
D
802.11a/g Interference Results
40.00
35
Hop 2
Netgear: A to B Hop
TCP Throughput (Mb/Sec)
30
Throughput (Mb/sec)
Netgear: C to D Hop
25
20
15
10
5
35.00
Hop 1
30.00
25.00
20.00
15.00
10.00
5.00
0.00
0
64,64
60,64
Channels
56,64
Hop1 = A, Hop2 = G
52,64
Same channel or channel
separation of 4 causes
46% - 49% reduction in overall
throughput
Hop1 = G, Hop2 = A
802.11a link causes a 22%
reduction in overall throughput,
and a 63% reduction in
throughput on the 802.11g link.
Surprise: 802.11g does not affect 802.11a
Implications
• Interference even when radios are placed 6” apart is significant
• Significant RF hardware shielding work is needed
© 2007 Victor Bahl. All Rights Reserved.
Single Node Multiple Radios
Channel 1
Channel 11
t1
Source
Mesh Box
Destination
Let’s assume we can build “mesh-boxes” with enough separation /
shielding between radios that performance does not suffer.
Then interesting problem to consider
(1) How should we assign channels to each interface?
 Don’t want to cause network partitions
(2) Which interface should we send the packet on?
 State-of-art metrics (hop count, ETX, SRTT, packet-pair) are not
suitable for multiple radio / node. As they do not leverage channel,
range, data rate diversity.
© 2007 Victor Bahl. All Rights Reserved.
Multiple Radios - Multiple Channels
Options to consider
Static Assignment
One channel / radio for all time
 Suboptimal use of spectrum
 Some routes may be suboptimal
Dynamic Assignment (all SR-MC strategies apply)
Channels assigned to match traffic patterns and/or to reduce interference
 Interference patterns can change,
network may get disconnected
Hybrid Assignment
One channel to one radio for all time, for all other radios, channels are
assigned dynamically to match traffic patterns and/or reduce interference
© 2007 Victor Bahl. All Rights Reserved.
Static Assignment (1)
2 radios / node
Draves-MobiCom-2004
All nodes use common set of channels
A
11
1
B
11
1
11
1
11
1
D
11
C
1
E
11
F
© 2007 Victor Bahl. All Rights Reserved.
Suboptimal use of
spectrum
Static Assignment (2)
2 radios / node, 4 channels
Raniwala-Infocom-2005
Different nodes use different channels
A
52
56
52
B
52
60
C
60
Some routes may
be suboptimal
(e.g. B->F)
D
60
E
64
F
© 2007 Victor Bahl. All Rights Reserved.
Dynamic Assignment
N radios / node; M channels; N < M
Interfaces can switch channels as needed
A
B
C
Coordination may be
needed before each
transmission
D
• MMAC
• SSCH
• BFS-CA
E
F
See section on single radio – multiple channels
© 2007 Victor Bahl. All Rights Reserved.
Dynamic Assignment
Breadth First Search – Channel Assignment (BFS-CA)
Ramachandran-Infocom-2006
Goals:
– External interference can severely degrade mesh performance
 Measure & avoid external interference
– Internal interference between mesh links should be avoided
 Assign orthogonal channels to any two interfering mesh links
Nodes periodically estimate surrounding interference levels
– A radio per-node monitors 802.11 data and control traffic
– Channels ranked from least interfered to most interfered
– Ranking sent to centralized channel assignment server
Distributed channel sensing and channel assignment
can break network connectivity
– A radio per-router is tuned to a common channel to
ensure connected mesh
© 2007 Victor Bahl. All Rights Reserved.
BFS-CA Interference-Aware Channel Assignment
• Multi-radio conflict graph models interference between mesh links
• Breadth first search algorithm selects channels for mesh radios
• Significant performance improvement over static channel assignment
in the presence of varying interference levels
Issues
– Interference patterns can change rapidly
– Dependence on existance of traffic patterns to determine interferance
 Incorrect channel assignment possible
© 2007 Victor Bahl. All Rights Reserved.
Hybrid Assignment
Hybrid Multichannel Control Protocol (HMCP)
• Each node has two interfaces (1 fixed, 1 switch-able)
– Connectivity is maintained + all channels used
Kyasanur-WCM-2006
• Every node picks a channel as it’s fixed channel
– Different nodes use different fixed channels
• Sender tunes it’s “switchable” interface to receiver’s fixed channel to
send packets
– Once a “connection” is made, there may not be a reason to switch
channels again for that particular flow.
© 2007 Victor Bahl. All Rights Reserved.
HMCP Channel Selection
Challenge: Nodes in a neighborhood should use different fixed channels
Fixed Channel Selection
– On startup pick a random fixed channel
– Periodically send a “hello” pkt. containing fixed channel & 1-hop neighbors
info. on all channels (using the switchable interface)
– Maintain a NeighborTable containing fixed channels being used by
neighbors
– Select the channel with fewest nodes as a candidate
 Use 2-hop neighbor information
– Change fixed channel to candidate channel probabilistically to avoid
oscillations
Issues
– High overhead for broadcast packets
© 2007 Victor Bahl. All Rights Reserved.
Which Interface should we send the packet on?
Note: Must use off-the-shelf wireless NICs
A Simple Approach: Multi-Radio Unification Protocol (MUP)
– For every transmission select the interface with the “best” channel & transmit on it
Pros:
- Locally optimizes use of available spectrum
- Does not require changes to routing protocols or application-level software
- Interoperates with legacy hardware
- Does not require global topology information
Cons:
– For one-hop ad hoc – works great. For meshes need metrics that combine
link selection metrics into a path selection metric (will see)
© 2007 Victor Bahl. All Rights Reserved.
MultiRadio Unification Protocol (MUP)
Illustration of Channel Switching
Goal
Allow nodes with multiple radios to locally
optimize use of available spectrum and
hence increase capacity
Ch. 0
0
MUP Enabled
1
Operation
• Set the network interface cards on different
frequency channels
Ch. 1
• Periodically monitor channel / Link
quality on each interface
• Select the interface with the “best” channel
and transmit packets
Does not require global topology
information
Adya-BroadNets-2004
© 2007 Victor Bahl. All Rights Reserved.
MUP in a Neighborhood
252 houses in a Seattle neighborhood
(Green Lake Area)
Mesh formation among 35
randomly selected houses
Web surfer
40-50% reduction in delay
compared to a one-radio network
ITAP
Routes via RFC 3561 (AODV)
© 2007 Victor Bahl. All Rights Reserved.
Why MUP is not enough?
MUP is a link metric not a path metric. Routing protocols that use MUP do not
– Leverage channel diversity
 A two hop path with hops on different channels is better than a path with both
hops are on the same channel.
– Leverage range and data rate diversity
 A path with two 6 Mbps hops is better than a path with a single 1 Mbps hop. MUP
will take the 1Mbps path.
 …..but a path with four 6 Mbps hops is worse than a path with a single 2 Mbps
hop. MUP and metrics like ETX may take the four-hop path, depending on delay
& loss rate.
Note: Striping protocols are not enough
–
–
–
Packet-level striping results is packet reordering, and hence poor TCP throughput
Flow-level striping requires a routing algorithm!
MUP may work, but only if radios have identical range.
Bottom Line: Need a routing protocol / metric that takes bandwidth, loss rate, and channel diversity into
account.
© 2007 Victor Bahl. All Rights Reserved.
Strategy 2: Higher Capacity by Improving Coding
= 4 transmissions in the air
A
C
A
R
Throughput (Mbps)
UDP (A→C, C→A)
11.02
TCP (A→C, C→A)
10.91
TCP (C →A)
10.55
© 2007 Victor Bahl. All Rights Reserved.
C
Network Coding Improves Capacity
C
A
= 3 transmissions in the air
broadcast
XOR
C++ A
Throughput (in Mbps)
A
R
w/o Network Coding
Network Coding
UDP (A→C, C→A)
11.02
18.13 (+64%)
TCP (A→C, C→A)
10.91
13.97 (+28%)
TCP (C →A)
10.55
12.11 (+15%)
© 2007 Victor Bahl. All Rights Reserved.
C
Calculating Mesh Capacity
•
Gupta & Kumar focused on
determining asymptotic,
pessimistic bounds on
performance.
– O(1/sqrt(N))
•
Want to answer the questions
about achievable capacity for
specific topologies with specific
traffic pattern and node specific
configurations
Example: 4 houses talk to the
central ITAP. What is the maximum
possible throughput?
Asymptotic analysis is not useful in this case
© 2007 Victor Bahl. All Rights Reserved.
Calculating Mesh Capacity (2)
Analytical Approach
Jain-MobiCom-2003
Create a connectivity graph
– Each vertex represents a wireless node
– Draw a directed edge from vertex A to vertex B if B is within range of A
– We can incorporate more sophisticated connectivity models
– Capacity of each edge is determined by wireless technology in use
Create a conflict graph that shows which wireless links interfere with each other
– Each edge in the connectivity graph represented by a vertex
– Draw an edge between two vertices if the links conflict with each other
© 2007 Victor Bahl. All Rights Reserved.
How does it work?
• Create a linear program that solves the basic MAXFLOW problem on
this connectivity graph
• Cliques in conflict graph
– At most one of the links can be operating at any given instant
– Sum of utilization of links belonging to a clique is <= 1
– MAXFLOW LP can be augmented with Clique constraints to get a better
upper bound
• Independent sets in conflict graph
– All links belonging to an independent set can be active at the same time.
– MAXFLOW LP can be augmented with constraints derived from
independent sets to get a lower bound
– Lower bound is always feasible.
• If upper and lower bounds converge, we have optimal answer
© 2007 Victor Bahl. All Rights Reserved.
Sample Result
Mesh Example: 4 houses talk to the central ITAP. What is the maximum possible throughput?
1
0.9
Upper Bound
0.8
Lower Bound
Throughput
0.7
0.6
0.5
0.4
Optimal Throughput
0.3
0.2
0.1
0
0
50
100
150
200
Effort
Houses talk to immediate neighbors, all links
are capacity 1, 802.11-like MAC, Multipath
routing.
Better results with more computation time
© 2007 Victor Bahl. All Rights Reserved.
The “What if” Analysis
What if we double the range?
1
0.9
Upper Bound
0.8
Lower Bound
0.9
Upper Bound
0.8
Lower Bound
0.7
0.7
0.6
0.6
Throughput
Throughput
1
0.5
0.4
0.5
0.4
0.3
0.3
0.2
0.2
0.1
0.1
0
0
0
20
40
60
80
100
120
140
160
0
20
40
Effort
Original scenario
60
80
100
Effort
Doubling the range provides
no benefit in this scenario!
© 2007 Victor Bahl. All Rights Reserved.
120
Conflict Graph Analytical Framework
Advantages
– Scenario based numbers instead of asymptotic bounds
– Framework is flexible. It can accommodate:






Multiple radios on multiple channels
Directional antennas
Single path or Multi-path routing
Different ranges, data rates
Different wireless interference models
Different topologies
– We can also include fairness criteria, pricing.
– Great for “what if” analysis
Limitations
– Requires time to generate accurate results. Not suitable for making on-the-fly routing
decisions.
– Problem of finding optimal throughput is NP-Hard. Best we can do is to find upper and
lower bounds and bounds may not always converge
– Requires global knowledge of network topology
© 2007 Victor Bahl. All Rights Reserved.
Problem: How to Determine the Conflict Graph
We know that
– Interference degrades performance
– Conflict graph captures link interference
– Conflict graph is necessary for capacity estimation, better routing,
channel assignment & power management
Question: How should we determine the conflict graph?
– How should we study the structure and the stability of the interference
graph?
– How can we understand the relationship between interference graph and
the communication topology of the network?
© 2007 Victor Bahl. All Rights Reserved.
An attempt at Determining Interference
•
Establish a base maximum sending rate for each node
•
Select two or more nodes to simultaneously broadcast packets as fast
as possible
•
Study the sending rate and the reception rate at every node
– Calculate Broadcast Interference Ratio (BIR)
 Approximates Link Interference Ratio (LIR)
– O(n2) experiments suffice to estimate O(n4) LIR values
•
Vary the transmit power, PHY data rate etc.
– Repeat the experiment
•
BIR needs to be calculated regularly as interference patterns change
over time.
© 2007 Victor Bahl. All Rights Reserved.
Determining Interference
Pairwise Interference
Measure A’s receive rate @ B = M
Measure A’s receive rate @ B = M/
Calculate BIR: (M/ + N/) / (M + N)
=1
no
interference
A
B
< 1 interference
= 0 severe interference
C
D
Measure C’s receive rate @ D = N
Measure C’s receive rate @ D = N/
© 2007 Victor Bahl. All Rights Reserved.
Padhye-IMC-2005
Interference – IEEE 802.11a (Indoors)
620
6000
600
5000
580
4000
560
3000
540
2000
520
1000
500
0
480
460
12
Link Quality
440
420
10
400
450
500
550
600
650
Carrier Sense Interference
700
750
8
Observation:
The difference between the
interference and the communication
range is small for 802.11a
6
4
We may be able to get a reasonable
approximation for the interference
graph from the communication graph
using simple heuristics
2
0
0
10
20
30
40
© 2007 Victor Bahl. All Rights Reserved.
50
60
70
80
90
Interference – IEEE 802.11b (Indoors)
650
1000
900
800
700
600
500
400
300
200
100
0
600
550
500
450
2
Link Quality
Carrier Sense Interference
1.8
400
1.6
200
300
400
500
600
700
800
1.4
1.2
Observation
1
The relationship between the
interference and the communication
range is difficult to characterize in
802.11b.
0.8
0.6
0.4
0.2
0
0
20
40
© 2007 Victor Bahl. All Rights Reserved.
60
80
100
120
140
…about routing in mesh networks
The Routing Problem
Why not simply use traditional routing protocols
(RIP/OSPF/etc)?
• Network topologies are dynamic due to router mobility &
environmental fluctuations
– Dynamic topology may prevent routing protocol convergence
• Many links are redundant (routing updates can be large)
• Periodic updates may waste bandwidth & batteries
• Computed routes may not work due to unidirectional links
• Wireless makes routing protocols easy to attack
• Link quality, spectrum utilization and interferences are uniquely
important for path selection
© 2007 Victor Bahl. All Rights Reserved.
Desirable Qualitative Properties
•
•
•
•
•
•
•
Distributed operation
Loop-freedom
Corson-RFC2501-1999
Demand-based operation
Proactive operation
Attack resistant & Secure
“Sleep” period operation (friendly to power management)
Unidirectional link support / asymmetric link support
Implementation
– Layer 3 - traditional “network layer” / IP layer
 Interoperable internetworking capability and consistency over a heterogeneous networking
infrastructure.
– Layer 2.5
 Agnostic of IPv4 or IPv6 issues and can incorporate link quality measures more easily
 Capable of handling multiple wireless & wired networking technologies
© 2007 Victor Bahl. All Rights Reserved.
Routing and Addressing
Many choices, which is the best one?
– Flat addressing - Each node runs the routing protocol; node’s address is
independent of its location (e.g. PRNET, TORA, DSR, AODV,..)
– Clustering – Only cluster heads run routing protocol; addressing is flat
and independent of node’s location (NTDR, CEDAR,..)
– Hierarchical – Only cluster heads run routing protocol, a node’s form
subnets, each node acquire’s address of its subnet (SURAN).
Many protocols to consider
–
–
–
–
Proactive based on traditional distance vector (DSDV, OLSR, TBRPF)
Reactive or on-demand (DSR, AODV)
Hybrid: proactive + reactive (ZRP)
Geographical (LAR)
Multiple path routing
– Many choices: MSDR, AOMDV, AODV-BR, APR, SMR, ROAM, ….
© 2007 Victor Bahl. All Rights Reserved.
Proposals: Unicast Ad Hoc Multi-hop Routing Protocols
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
ABR (Associativity-Based Routing Protocol)
AODV (Ad Hoc On Demand Distance Vector)
ARA (Ant-based Routing Algorithm)
BSR (Backup Source Routing)
CBRP (Cluster Based Routing Protocol)
CEDAR (Core Extraction Distributed Ad hoc Routing)
CHAMP (CacHing And MultiPath routing Protocol)
CSGR (Cluster Gateway Switch Routing)
DART (Dynamic Address Routing)
DBF (Distributed Bellman-Ford)
DDR (Distributed Dynamic Routing)
DNVR (Dynamic Nix-Vector Routing)
DSDV (Dynamic Destination-Seq. Dist. Vector)
DSR (Dynamic Source Routing)
DSRFLOW (Flow State in the DSR)
DYMO (Dynamic Manet On-Demand)
FORP (Flow Oriented Routing Protocol)
FSR (Fisheye State Routing)
GB (Gafni-Bertsekas)
GLS(Grid) (Geographic Location Service)
GPSAL (GPS Ant-Like)
GSR (Global State Routing)
Guesswork
HARP (Hybrid Ad hoc Routing Protocol)
HSLS (Hazy Sighted Link State)
HSR (Hierarchical State Routing)
HSR (Host Specific Routing)
IARP (Intrazone Routing Protocol)
IERP (Interzone Routing Protocol)
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
LANMAR (LANdMARk Routing Protocol)
LAR (Location-Aided Routing)
LBR (Link life Based Routing)
LCA (Linked Cluster Architecture)
LMR (Lightweight Mobile Routing)
LQSR (Link Quality Source Routing)
LUNAR (Lightweight Underlay Network Ad hoc
Routing)
MMRP (Mobile Mesh Routing Protocol)
MOR (Multipoint On-demand Routing)
MPRDV (Multi Point Relay Distance Vector)
OLSR (Optimized Link State Routing)
OORP (OrderOne Routing Protocol)
DREAM (Distance Routing Effect Algorithm for
Mobility)
PLBR (Preferred Link Based Routing)
RDMAR (Relative-Distance Micro-discover Ad hoc
Routing)
Scar (DSR and ETX based)
SSR (Signal Stability Routing)
STAR (Source Tree Adaptive Routing)
TBRPF (Topology dissemination Based on ReversePath Forwarding)
TORA (Temporally-Ordered Routing Algorithm)
WRP (Wireless Routing Protocol)
ZHLS (Zone-Based Hierarchical Link State)
ZRP (Zone Routing Protocol)
….
© 2007 Victor Bahl. All Rights Reserved.
Popular Taxonomy
Multihop Routing Protocols
Proactive
Reactive
Hybrid
Hierarchical
© 2007 Victor Bahl. All Rights Reserved.
Geographical
Power Aware
Mapping Protocols to Taxonomy
Multihop Routing
Protocols
Proactive
Reactive
CSGR
DBF
DSDV
Guesswork
HSLS
HSR
IARP
LCA
MMRP
OLSR
STAR
TBRPF
WRP
Hybrid
ARA
ABR
AODV
BSR
CHAMP
DSR
DSRFLOW
DNVR
DYMO
FORP
GB
IERP
LBR
LMR
LQSR
LUNAR
MOR
MPRDV
RDMAR
SrcRR
SSR
TORA
PLBR
ZRP
Hierarchical
Geographical
CBRP
CEDAR
DART
DDR
FSR
GSR
HARP
HSR
HSR
LANMAR
OORP
Power
Aware
DREAM
GLS(Grid)
LAR
GPRS
GPSL
ZHLS
© 2007 Victor Bahl. All Rights Reserved.
ISAIAH
PARO
EADSR
PAMAS
Common Metrics for Comparing Routing Protocols
• Route Acquisition Time
– Time required to establish route(s)
Broch-MobiCom-1998
• Routing Overhead
– Total number of routing packets transmitted (for discovery & maintenance) for a
fixed amount of transfer over multiple hops with random node mobility.
• Path Optimality / End-to-End Throughput
– TCP & UDP data throughput and delay
 Previously path optimality was measured in terms of the difference between the number of
hops a packet took to reach it’s destination and the length of the shortest path that
physically existed through the network when the packet originated. However, the hop
count metric has been overshadowed by other link metrics when it came to end-to-end
throughput
• Packet Delivery Ratio
– Ratio between the number of packets originated by the application layer and the
number of packets received by the sink at the final destination
© 2007 Victor Bahl. All Rights Reserved.
Context for Comparing Metrics
• Network size
Corson-RFC2501-1999
Measured in terms of the number of nodes
• Network connectivity
Measured in terms of avg. node degree (i.e. the avg. number of neighbors)
• Topological rate of change
Speed with which a network's topology changes
• Link capacity
Effective link speed in bps, after accounting for losses due to multiple access, coding, framing, etc.
• Fraction of unidirectional links
Transmission ranges of radios may be different
• Traffic patterns
Long-lived versus bursty non-uniform
• Mobility
Described in terms of dwell time, movement direction, speed etc.
• Fraction and frequency of sleeping nodes
© 2007 Victor Bahl. All Rights Reserved.
Most Studied
Proactive (periodic)
– Each node maintains route to each other network node (Global state)
–
–
–
–
–
Routes are determined independent of traffic
All topology changes propagated to all nodes
Periodic routing advertisements (neighbor discovery is beacon based)
Generally longer route convergence time
Examples: Distance vector and link state (DSDV, OLSR, TBRPF)
Reactive (on-demand)
– Actions driven by data packet requiring delivery
– Source builds route only when needed by “flooding” (Route Discovery)
– Maintain only active routes (Route Maintenance)
– Pro: Typically less overhead, better scaling properties
– Cons: Route acquisition latency
– Examples: DSR, AODV
© 2007 Victor Bahl. All Rights Reserved.
Conventional Wisdom
• Proactive protocols perform best in networks with low to moderate
mobility, few nodes and many data sessions
– E.g. OLSR (RFC 3626), TBRPF (RFC 3684)
• Reactive protocols perform best in resource-limited, dynamic networks
where nodes are mobile. Tradeoff routing overhead for start-up delay
– E.g. AODV (RFC 3561), DSR (IETF Draft)
© 2007 Victor Bahl. All Rights Reserved.
Courtesy: David B. Johnson
RFC 4728: Dynamic Source Routing (DSR)
Reactive / On demand
– When node S wants to send data to node D, but does not have a route to it
IETF Experimental RFC 4728
Properties:
–
–
–
–
–
Johnson-Draft-2004
All aspects operate entirely on-demand
Ignores all topology changes not affecting you
Overhead scales automatically with movement
No overhead when stationary and found routes
Supports unidirectional links & asymmetric routes
Johnson-RFC4728-2007
Divides routing problem into two parts:
– Route Discovery: Find route only when don’t have one and need one
– Route Maintenance: Fix a broken route only while you’re actually using it
© 2007 Victor Bahl. All Rights Reserved.
DSR Basic Route Discovery Overview
To discover a route to some address:
– Broadcast a ROUTE REQUEST with a unique id
– When receiving a ROUTE REQUEST:
 If destination IP address is yourself
Return the recorded route to the initiator in a ROUTE REPLY
 Else if recently seen this id
Drop the REQUEST
 Else
Append your own address and rebroadcast the ROUTE REQUEST
Notes:
– Nodes overhearing source routes learn topology
– Nodes can answer ROUTE REQUEST using cached routes
 Speeds up discovery and reduces propagation of ROUTE REQUEST
– Can store multiple routes to same node
© 2007 Victor Bahl. All Rights Reserved.
DSR Basic Route Maintenance Overview
After transmitting a packet to the next hop:
– Listen for link-level per-hop acknowledgement, or
– Listen for that node sending packet to next hop, or
– Set a bit in the packet to request explicit next-hop acknowledgement
When a problem with forwarding is detected:
– Send a ROUTE ERROR to original sender
– Sender removes the broken link from its cache
© 2007 Victor Bahl. All Rights Reserved.
DSR Issues
• Scalability: Packet header size grows with route length
– Can be an issue specially when data packets are small (e.g. VoIP)
• Route Caching: Each node caches a route it learns
– Pros: Can speed up route discovery & reduce route request propagation
– Cons: Stale routes can adversely affect performance
 TCP applications suffer the most
• ROUTE REQUEST flooding
Ni-MobiCom-1999
– Broadcast storm problem
 Collisions between (redundant) route requests by neighbors
– Solutions: (1) re-broadcast Route Request with probability p (2)
re-broadcast by using classical collision avoidance techniques,
e.g. introducing random delays (3) …
© 2007 Victor Bahl. All Rights Reserved.
RFC 3561 Adhoc On-Demand Distance Vector
• Table driven Reactive / On demand
Perkins-RFC3561-2003
• IETF Experimental RFC 3561
• Like DSR, but maintains routing tables at the nodes
– data packets do not have to carry routes
• Sequence numbers are used for route freshness and loop prevention
• Protocol divided in Route Discovery and Route Maintenance
– Maintains active routes only
• Popular routing protocol, many public implementations available
– Check out: http://moment.cs.ucsb.edu/AODV/
© 2007 Victor Bahl. All Rights Reserved.
AODV Basic Route Discovery Overview
To discover a route to some address D:
– Broadcast a ROUTE REQUEST (RREQ)
– On receiving a ROUTE REQUEST
 If destination IP address is yourself
– Create a ROUTE REPLY (RREP)
– Unicast RREP to node from which RREQ was received
 Else, If have a route to D, and the seq # for route to D is >= D’s seq # in
RREQ
– Create a RREP
– Unicast RREP to node from which RREQ was received
 Else
– Make a reverse entry for Source IP address
– Rebroadcast RREQ
© 2007 Victor Bahl. All Rights Reserved.
AODV Basic Route Discovery Overview (2)
To discover a route to some address D (cont.):
– On receiving a ROUTE REPLY
 If Source IP address is yourself
– Make forward route entry to D
<Destination IP address, next hop IP Address, HopCount to
Destination>
 Else
– Make a forward route entry to D
– Unicast RREP to node from which RREQ was received
© 2007 Victor Bahl. All Rights Reserved.
AODV Basic Route Maintenance Overview
When a intermediate node detects a link problem:
– It invalidate the route to destination
– Creates a ROUTE ERROR (RERR) message
 Lists all destinations that are unreachable
 Sends to upstream neighbors
On Receiving ROUTE ERROR
– If Source IP is yourself
 if node sending RERR is it’s next hop to destinations
– Delete route(s) to destination(s)
– Restart Route Discovery if needed
– Else
 If node sending RERR is it’s next hop to destination
– Deletes route(s) to destination
– Forwards RERR to source address
© 2007 Victor Bahl. All Rights Reserved.
AODV Optimizations
Expanding Ring Search
– Prevents flooding of network during route discovery
– Control Time to Live (TTL) of RREQ to search incrementally larger areas
of network
 Less overhead when successful
 Longer delay if route not found immediately
Local Repair
– Repair breaks in active routes locally instead of notifying source
– Use small TTL because destination probably hasn’t moved far
– If first repair attempt is unsuccessful, send RERR to source
 Repairs links with less overhead, delay and packet loss
 Longer delay and greater packet loss when unsuccessful
© 2007 Victor Bahl. All Rights Reserved.
AODV Issues
• AODV assumes symmetric (bi-directional) links
– The intermediate nodes set up reverse paths towards source
• AODV does not support multiple routes between source / destination
pair
• Routes can expire even when topology does not change
© 2007 Victor Bahl. All Rights Reserved.
Link / Path Selection Metrics
Min. hop count results in lower-quality links
© 2007 Victor Bahl. All Rights Reserved.
Path Selection Metrics
• Link Metric: Assign a weight to each link
– Prefer high bandwidth, low-loss links
– RTT, Packet Pair, ETX
• Path Metric: Combine metrics of links on path
– Prefer short, channel-diverse paths
– WCETT
© 2007 Victor Bahl. All Rights Reserved.
Expected Transmission Count (ETX)
Couto-MobiCom-2003
• Each node periodically
broadcasts a probe
• The probe carries information
about probes received from
neighbors
• Each node can calculate loss
rate on forward (Pf) and reverse
(Pr) link to each neighbor
• Selects the path with least total
ETX
ETX 
1
(1  Pf) * (1  Pr)
Advantages
– Explicitly takes loss rate into
account
– Implicitly takes interference
between successive hops into
account
– Low overhead
Disadvantages
– PHY-layer loss rate of broadcast
probe packets is not the same as
PHY-layer loss rate of data packets
 Broadcast probe packets are
smaller
 Broadcast packets are sent at
lower data rate
– Does not take data rate or link load
into account
© 2007 Victor Bahl. All Rights Reserved.
Expected Transmission Time (ETT)
Link loss rate = p
–
Expected number of transmissions (ETX) = 1/(1-p)
Mean Packet size = S, Link bandwidth = B
–
Each transmission lasts for S/B
Lower ETT implies better link
S
ETT    * ETX
B
© 2007 Victor Bahl. All Rights Reserved.
Expected Transmission Time (ETT)
Taken the MAC delays into account
– Min backoff window CWmin
ETT  ETxmit  ETbackoff
where,
ETxmit
S

B(1  p)
i 7
f(p)  1   2
i 0
(i 1)
ETbackoff
p
CWmin f(p)

2(1  p)
i
© 2007 Victor Bahl. All Rights Reserved.
Path Selection Metric in Multi-Radio Mesh
• Link metrics such as shortest path, Packet Pair, RTT, ETX & ETT do
not leverage channel, range and data rate diversity
• In multiradio meshes, need a path metric that does.
• This metric should
• avoid unnecessarily long paths
– bad for TCP performance
– bad for global resources
• know that all hops in the path on the same channel interfere
• Path throughput is dominated by the maximum of these sums
© 2007 Victor Bahl. All Rights Reserved.
WCETT = Combining link ETTs
Given a n hop path, where each hop can be on any one of k channels,
and two tuning parameters, a and b:
Path throughput is dominated by the max
of the sum of ETTs of path links on the
same channel
Sum of ETTs of all links on the path
- Favors short paths

a *  ETT   b * max
WCETT 
n
i 1
i
1 j  k
X
j

ab
where
X 
j
Draves-MobiCom-2004
 ETT
hop i is on channel j
i
Sum of ETTs of all links on the path that are on the same channel
Select the path with min WCETT
© 2007 Victor Bahl. All Rights Reserved.
Incorporating Link Quality Metrics
into Routing Protocols…
Extremely Opportunistic Routing (ExOR)
Probabilistic Broadcast
Biswas-SIGCOMM-2005
– Decides who forwards after reception
 Desirable: node closest to destination should forward
 Challenge: avoid duplicate transmissions
How to determine who is closest
– Nodes periodically flood ETX “link state” measurements
 Path ETX is weighted shortest path (Dijkstra’s algorithm)
– Closest node is determined by sorting via ETX metric
To avoid duplicate transmissions
– Packets includes a priority list of forwarder in ExOR header
– One node sends at a time, ordered from higher priority to lower priority
Layer 2.5 design
© 2007 Victor Bahl. All Rights Reserved.
Link Quality Source Routing (LQSR)
• Derived from Dynamic Source Routing Protocol
Draves-SIGCOMM-2004
• Optimizations for sporadic node mobility at the virtual link layer
• Incorporates 5 different link selection metrics:
– Hop count, RTT, Packet Pair, ETX, WCETT
• A layer 2.5 protocol
– For the protocols above looks a like virtual adapter on virtual link
– For the drivers below binds to physical adapters that provide next-hop
connectivity
– Inserts a new L2.5 header
• Why Layer 2.5?
– Works over heterogeneous links (e.g. wireless, powerline)
– Transparent to higher layer protocols.
• works equally well with IPv4 and IPv6
– ARP etc. continue to work without any changes
© 2007 Victor Bahl. All Rights Reserved.
Hybrid Wireless Mesh Protocol (HWMP)
• Proposal for default routing protocol in IEEE 802.11s meshes
• On-demand with option for pro-active routing
IEEE-Mesh-2006
• Support multiple path selection metrics
– vendor defined (by default, Airtime)
• On-demand version
– RM-AODV
 Essentially RFC 3561
 RM is for Radio Metric (or link metric)
• Pro-active version
– Distance-vector routing tree from a root portal (e.g. an AP as root)
 Avoid unnecessary discovery flooding
© 2007 Victor Bahl. All Rights Reserved.
Path Length and Throughput
Eriksson-MobiSys-2006
Which metric is best? (“Wireless Office Study”)
WCETT
Experimental Setup
ETX
HOP
3.5
•
•
23 node testbed
Randomly selected 100 senderreceiver pairs (out of 23x22 = 506)
3-minute TCP transfer (transmit as
many bytes as possible in 2
minutes, followed by 1 minute of
silence)
For 1 or 2 hop the choice of
metric doesn’t matter
2.5
2
1.5
1
0.5
0
A
C
D
E
F
Testbed Configuration
WCETT
ETX
HOP
4000
Throughput (Kbps)
•
Hop Length
3
3500
3000
2500
2000
1500
1000
500
0
A
C
D
E
Testbed Configuration
© 2007 Victor Bahl. All Rights Reserved.
F
Comparison of Metrics
Eriksson-MobiSys-2006
Wireless Office Scenario
23 node indoor testbed. Two radios (both 802.11a) per node.
11 active clients, 4 servers.
Heavy Office Traffic
1 hour, 308 sessions, 587.5 MB total
Light Office Traffic
1 hour, 415 sessions, 19.72 MB total
10000
1000
474
100
10
89
120
179
82
11
4
6
4
5
3
8
3
6
ETX
HOP
PKTPAIR
1000
RTT
590
862
943
31
30
3
3
ETX
HOP
100
27
10
4
2
1
WCETT
Additional Delay (ms)
Additional Delay (ms)
10000
1
WCETT
PKTPAIR
Relatively light traffic means performance is okay for all metrics.
WCETT does better under heavy load (worst case delay)
© 2007 Victor Bahl. All Rights Reserved.
RTT
Summarizing
• Many routing protocols to choose from
• Protocols that take link quality into account show most promise
• A link quality metric that incorporates interference is still needed
• Adaptive protocols that change behavior in different environments
might be best
© 2007 Victor Bahl. All Rights Reserved.
Securing & Managing Meshes
Network management is a process of
controlling a complex data network so
as to maximize its efficiency and
productivity
Network Management a Practical Perspective
Addison Wesley 1993
Security & Privacy Requirements
• Only “authorized” nodes should be allowed to route through mesh
– Packet level authentication
• Authentic route setup (e.g. Ariadne, Sead)
• Robust & adaptive forwarding in face of malicious or congested
nodes or links
• Detect malicious nodes who promised to route during the route
setup, but actually don’t forward
• Limit the resource consumption of greedy nodes
– Rate control/policing
• Preserve the anonymity of communicating parties
© 2007 Victor Bahl. All Rights Reserved.
MSR’s Mesh Security Architecture
For Wireless Office and Community Networks Scenario
Philosophy
Internet
Mesh is open to all, however,
people who contribute resources
to the mesh get priority.
Internet
Gateway
Goals
Certificate
•
Guard against faulty or hacked
mesh nodes
•
Defend against disruption (e.g.,
denial-of-service attacks) by
malicious end devices
•
Protect mesh traffic privacy
•
Laptop
Certificate
Snooper
Server
Neighborhood
File Server
Protect access to network
resources
Compromised
Mesh Box
Assumptions
•
End Device
Difficult to hack into a “Mesh Box”
(similar to cable modems)
End Device
Malicious
End Device
© 2007 Victor Bahl. All Rights Reserved.
Regulations handle malicious RF Interference attacks
Certificate
Basic Security Framework
Certification
Encryption & Anonymity
•
•
Traffic between mesh nodes is
encrypted to foil eavesdroppers
•
Misbehaving mesh nodes have their
certificates “blackballed”
•
Traffic from uncertified end devices
is prevented from disrupting certified
traffic
•
Mesh nodes have built-in publickey certificates for authenticating
to each other
Authenticated mesh nodes issue
certificates to end devices
•
Mesh nodes accept certificates
issued by any mesh node within
range
•
Access to resources is controlled
based on policy and end device
certificate
© 2007 Victor Bahl. All Rights Reserved.
Troubleshooting Wireless Meshes
The least well understood area of research
Difficult because:
Network is hostile
 Unpredictable physical medium, Dynamic topology, Overhead
limitations, Link vulnerabilities, …..
Root cause fault identification is hard
 Determining normal behavior is difficult
– Just knowing link statistics is insufficient
– Typical signature based techniques don’t work
– Handling multiple faults
» Complicated interactions between faults and traffic
» Among faults themselves
© 2007 Victor Bahl. All Rights Reserved.
Mesh Management Design
Reactive and Pro-active
– Investigate reported performance problems
 Time-series analysis to detect deviation from normal behavior
– Localize and Isolate trouble spots
 Collect and analyze traffic reports from mesh nodes
– Determine possible causes for the trouble spots
 Interference, or hardware problems, or network congestion, or
malicious nodes ….
Respond to troubled spots
–
–
–
–
Re-route traffic
Rate limit
Change topology via power control & directional antenna control
Flag environmental changes & problems
© 2007 Victor Bahl. All Rights Reserved.
Management Workflow
Mesh Configuration & Setup
(scope out network)
Initialiazation
Gather & Distribute
Data
Step 1
Clean & Analyze
Data
Determine Physical
Topology
Step 2
Model Network
Behavior
“What-if”
Analysis
Detect
Anomaly
Improve Routing/
Capacity
Locate Hot Spots
& Inform
Step 3
Step 4
Diagnose
Problem
Suspect software/
hardware
Poor local
connectivity
Inform/Fix
Reconfigure
Topology
Suspect attack
Congestion
Rate Limit
Perform Security
Analysis
© 2007 Victor Bahl. All Rights Reserved.
Step 5
Some Approaches
Data distribution protocols for network management


ANMP Chen-JSAC-1999
Guerrilla
Shen-Milcom-2002
Network monitoring to detect routing and MAC misbehavior


Watchdog & Pathrater
MACMis Kyasanur-TMC-2005

Filtering and graph dependency analysis
Marti-MobiCom-2000
Fault detection, isolation & root cause analysis

Badonnei-JNM-2005
Qiu-CCR-2006
On-line modeling based analysis
© 2007 Victor Bahl. All Rights Reserved.
Qiu-MSRTR-2003
Step 1: Monitor & Distribute Data
Monitoring: What should we collect?
– Link Info: Noise level, signal strength, loss rate to direct neighbor (packet
retransmission count)
– Connectivity Info: Network topology / connectivity Info (Neighbor Table)
– Traffic Info: Load to direct neighbor
– …
Distribution: Minimize (overhead) bandwidth consumption
– Dynamic scoping
 Each node takes a local view of the network
 The coverage of the local view adapts to traffic patterns
– Adaptive monitoring
 Minimize measurement overhead in normal case
 Change update period
 Push and pull
– Delta compression
– Multicast
© 2007 Victor Bahl. All Rights Reserved.
Step 2: Clean & Analyze Data
Data may not be pristine. Why?
– Liars, malicious users
– Missing data
– Measurement errors
Clean the Data
– Detect Liars
 Assumption: most nodes are honest
 Approach:
– Neighborhood Watch
– Find the smallest number of lying nodes to explain inconsistency
in traffic reports
– Smoothing & Interpolation
© 2007 Victor Bahl. All Rights Reserved.
Step 2: Clean & Analyze: The Watchdog
B
S
C
S sends a packet to B; If B doesn’t forward packet to C; S assumes B is malicious
Nodes may not forward packets
Marti-MobiCom-2000
– Because they are malicious
– Because they are selfish (e.g. to conserve energy, or get greater bandwidth)
Watchdog
– When a node drops more than a Threshold number of packets, Watchdog can
inform the sender of the misbehaving node
Limitations
– Ambiguous collisions, partial dropping, collution, environmental fluctuations, false
misbehaviour reporting, etc.
© 2007 Victor Bahl. All Rights Reserved.
Resiliency against Liars/Lossy Links
Qiu-CCR-2006
Problem
•
Identify nodes that report incorrect
information (liars)
Detect lossy links
Assume
•
•
Nodes monitor neighboring traffic, build
traffic reports and periodically share info.
Most nodes provide reliable information
1
0.8
0.6
0.4
0.2
0
NL=1
NL=2
Challenge
NL=8
Watchdogs
Find the smallest number of lying nodes to
explain inconsistency in traffic reports
Use the consistent information to estimate
link loss rates
NL=10 NL=15 NL=20
false positive
Detect lossy links
Fraction of lossy links
identified
Approach
•
NL=5
coverage
Wireless links are error prone and unstable
•
•
Qiu-MSRTR-2003
Detect liars
Fraction of lying nodes
identified
•
Simulation Results
1
0.8
0.6
0.4
0.2
0
NL=1
NL=2
NL=5
NL=8 NL=10 NL=15 NL=20
coverage
© 2007 Victor Bahl. All Rights Reserved.
false positive
Guarding against Attacks - Corrupted Routers
•
Monitor router behavior when
throughput problems are detected
•
The original router queries each
downstream router in turn, obtaining
verifiable traffic throughput
information
Internet
Internet
Gateway
Certificate
Laptop
Certificate
Snooper
•
•
A “bad” link, where traffic isn’t getting
through, can be identified
Server
Neighborhood
File Server
Which end of the bad link is
misbehaving can be investigated outof-band, or the link can simply be
avoided
End Device
Compromised
Mesh Box
End Device
Malicious
© 2007 Victor Bahl. All Rights
Reserved.
End
Device
Certificate
Qiu-CCR-2006
Step 3 & 4:
Model Network Behavior & Perform Root Cause Analysis
Faults
Directory
Root
Cause
Inject
Candidate
Faults
Collect Data
Raw
Data
Agent Module
• SNMP MIBs
• Performance Counters
• Routing Table
• Native WiFi
Clean
Data
Topology
Link Loads
Signal Strength
Simulate
Network
Delay
Diagnosis Module
© 2007 Victor Bahl. All Rights Reserved.
Estimated
Link Layer
Performance
Compare
Measured
Link Layer
Performance
Troubleshooting Framework
Challenges [in Online Simulation based Diagnostics]:
–
–
Accurately reproduce the behavior of the network inside a
simulator
Build a fault diagnosis technique using the simulator as a
diagnosis tool
Advantages
–
–
Flexible & customizable for a large class of networks
Captures complicated interactions



–
–
within the network
between the network & environment, and
among multiple faults
Extensible in its ability to detect new faults
Allows what-if analysis
© 2007 Victor Bahl. All Rights Reserved.
Handling the Challenges
Reproducing network behavior
•
•
•
•
Identify the set of traces to collect
Rule out erroneous data from the trace
Drive the simulator with the cleaned traces
Self-correct performance with feedback circuitry
Building fault diagnosis
• Use performance results from trace-driven simulation to
establish normal behavior
• Deviation from normal behavior indicates a potential fault
• Identify root cause by efficiently searching over fault space to
re-produce symptoms
© 2007 Victor Bahl. All Rights Reserved.
Step 5: Mitigation
Responding to troubled spots
–
–
–
–
Re-route traffic
Rate-limit
Change topology via power control & directional antenna control
Flag
 environmental changes & problems
 Malfunctioning hardware
– Launch DoS attacks against the possible attacker
– etc.
© 2007 Victor Bahl. All Rights Reserved.
Sample Performance
25 node random topology
Number of
faults
4
6
8
10
12
14
Coverage
1
1
0.75
0.7
0.92
0.86
False
Positive
0
0
0
0
0.25
0.29
Faults detected:
- Random packet dropping
- MAC misbehavior
- External noise
© 2007 Victor Bahl. All Rights Reserved.
Mesh Deployments
Discoveries & Innovations
CMU’s Monarch Testbed
•
•
•
•
•
•
Motivation: Study multi-hop routing protocols & their interaction with MobileIP
Scale: 6 car-mounted nodes, 2 fixed Internet gateways
Access: 900 MHz WaveLAN CSMA/CA (pre-802.11)
Routing: DSR, MobileIP
Applications: VANETs with car speeds of 0-50 KPH; rtk-GPS (< 1 cm)
When: 1998-1999
© 2007 Victor Bahl. All Rights Reserved.
CMU’s Monarch Innovations
•
MANETs outside the military!
–
–
•
Integration of MANET with Internet
–
•
Node could roam from WLAN, to cellular IP service (CDPD), to DSR MANET cloud
MANET/Internet gateway served as Foreign Agent
MIP/DSR integration made MNs full members of the MANET
Evaluation of predictive hand-off
–
•
All nodes on the Internet via gateway
Integration with MobileIPv4
–
–
–
•
Supported a mix of data
 voice data with PTT (walkie-talkie) quality, GPS updates, situational awareness data
 Telemetry: serial-line replacement, bulk file transfer
Topology changes every 4 s, each link lasted at most 220 s
Looked at both GPS/topology/predicted-trajectory and RSSI
Identified routing problem caused by wireless propagation that is transiently
better than expected
© 2007 Victor Bahl. All Rights Reserved.
MSR’s Mesh Network Project
http://research.microsoft.com/mesh
•
Motivation: Alternative broadband technology for Internet access
•
Scenarios: Initial focus: NeighborNet (“community network that grows
organically”) Longer term: WirelessOfficeNet, WirelessVillageNet,
WirelessCityNet
•
Testbeds: MSR Redmond Offices, Redmond Apartment Complex, MSR
Cambridge Offices - DVB distribution system
•
Design Objectives
–
–
–
–
In-expensive (use .11-like radio - same PHY, possibly different MAC)
Self managing - no truck-toll, take the human operator out of the equation
High capacity – multi Mbps in the backbone, .11{a,b,g} on access links
Coverage – typical suburban neighborhoods
•
Success Metric: Point of irrefutably, catalyst for wide-spread broadband Internet
availability
•
When: 2003-2005
© 2007 Victor Bahl. All Rights Reserved.
MSR’s Mesh Architecture
End Device
– Connects to a Mesh
Router
– Standards Compliant
Network Interface
Two Tier Architecture
Internet
ITAP
101
Bus Stop
206
Gas Station
(Internet TAP)
Mesh Router 7
EXIT
90
Mesh Router 5
Mesh Router / MeshBox
– Routes traffic within the
mesh and to the
neighborhood Internet
Gateway
– Serves as access point for
end devices
Mesh Router 2
Mesh Router
Mesh Router 3
MeshStreet
Zone
Any
Mesh Router 1
Mesh End Device
End Device
(Guest to Router 1)
End Device
Neighborhood Internet Gateway
– Gateway between the
mesh nodes and the
Internet
Key: Multiple radios, cognitive software
MSR’s Multi-Radio Mesh Box
CPU
800 MHz VIA C3 Eden
133 MHz FSB
DISPLAY
Trident Blade 3D
2 PCI Slot Riser
NORTH BRIDGE
VIA Apollo PLE133
Video & RAM
RAM
512 MB PC133 SDRAM
PCI Bus
LOW-FREQUENCY M ESH
SOUTH BRIDGE
VIA VT8231
Audio, ATA, USB, Ethernet,
Serial, Parallel, PS/ 2
HIGH-FREQUENCY M ESH
802.11a
D-Link DWL-AG520
802.11a
Linksys WMP55AG
900 M Hz
tbd
900 M Hz
tbd
NETWORK
VT6103
AUDIO
VT1612A
TV OUT
VT1621
USB
HDD
512 MB Flash Card
EPIA 800 M AINBOARD
© 2007 Victor Bahl. All Rights Reserved.
MSR’s All-Wireless Office (Testbeds 1 & 2)
Details
201
Testbed 1: 23 to 30 nodes; Testbed 2: 45 to 60
nodes
Inexpensive desktops (HP d530 SF)
Two radios in each node
–
–
–
210
220
205
203
226
204
NetGear WAG or WAB
Proxim OriNOCO
Cards can operate in a, b or g mode.
227
221
207
Verification of the mesh software stack
–
–
–
–
Routing protocol behavior
Fault diagnosis and mesh management
algorithms
Security and privacy architecture
Range and robustness @ 5 GHz with
different 802.11a hardware
Study of Wireless Office Scenario
Stress Testing
Approx. 61 m
Purpose
206
208
225
211
223
209
214
215
217
219
Various methods of loading testbed:
–
–
–
224
Harpoon traffic generator (UWisconsin)
Peer Metric traffic generator (Internal tool)
Ad-hoc use by researchers
© 2007 Victor Bahl. All Rights Reserved.
218
216
Approx. 32 m
MSR’s Community Network (Testbed 3)
Apartments in Redmond, WA
Road
B
UNIT FF
B
UNIT GG
B
31
B
UNIT BB
B
A
a
FF102
FF203
BB103
a
B
b
A
ControlApt
GG302
b
GG202
Parking Lot
32
B
BB302
ControlApt
GG302
Bellaire Apts
B
A
B
BB201
Carport
A
A
A
HH301
Microsoft
Campus
B
A
A
= MeshBox
UNIT CC
Road
Control Apt GG302
Mesh Box
20 Feet
UNIT HH
Mesh Hall (Kitchen)
© 2007 Victor Bahl. All Rights Reserved.
B
MSR’s Cambridge UK Trial (Testbed 4)
10 node 802.11a mesh
Worked with ehome team to create a media
sharing demo in collaboration with ZCast DVB trial
MSR-Cambridge - 1st
Floor, Mesh box Locations
UK3Gtwy
UK6
UK-MCE20 is the
Kiosk with posters.
= Mesh Box location
= Mesh Box location
© 2007 Victor Bahl. All Rights Reserved.
UK1 UK8
UK
MCE20
UK2
MSR’s Mesh Discoveries
•
Certain applications are not as attractive as were initially thought
– Neighborhood distributed backup met with great suspicion
•
Percentage of node participation doesn’t have to be high for viable meshes to
be formed
– Low frequency meshes & high gain antennas can compensate for lower densities
•
Multi-radio meshes are necessary for reasonable capacity
– A new link & interface selection metric is required for path selection
•
Performance largely dictated by Internet gateway placement
– P2P applications work well regardless
•
Qiu-ICNP-2004
Hooks for management of the network have to be part of the design
requirement
– Monitoring, automatic alerts & root-cause analysis
Qiu-CCR-2006
© 2007 Victor Bahl. All Rights Reserved.
MSR’s All-Wireless Office Discoveries
Eriksson-MobiSys-2006
Hardware
–
802.11 hardware can result in 2.5x difference in performance
 Hardware from different vendors performs very differently
Channel selection
–
Selection of 802.11 band can lead to 2x difference
 Automatically sniffing & selecting channels where there are fewer competing wireless
networks helps
Topology
–
Server placement can have up to 3x difference
 Experiment performed with central, distant, and random server placement
Routing metrics
–
–
Hop count works as well as WCETT under light loads
With lots of cross traffic routing metrics matter
802.11 MAC
–
Enabling RTS and CTS has minimal benefit
 No benefit of spatial reuse, hidden node avoidance
Most configurations – median delay <30ms
© 2007 Victor Bahl. All Rights Reserved.
MSR’s MCL Innovations
•
Software steerable directional antenna
Kuga-NRSM-2004
– 8x8 dipole array, 20o beam-width, coplaner waveguide phase shifter, new form factor
for indoor wall mounting, low loss feed network
•
Multi-radio meshboxes
– Two radios on different channels for simultaneous rcv/send on the backbone, a third
radio for standard’s based client connections, a forth radio for control & management
channel
•
Dual Frequency Meshes
– Lower (< 1 GHz) frequency mesh when node density is low, higher frequency mesh
(2.4 GHz, 5 GHz) mesh when density and capacity reuqirement is higher
•
Multi-radio link selection metric – Weighted Cumulative ETT (WCETT)
– Reduces to ETT for single radio case. Recognizes self-interference.
•
Link Quality Source Routing (LQSR)
Draves-SIGCOMM-2004
Draves-MobiCom-2004
– Layer 2.5 design - hardware and upper protocol agnostic (supports both IPv4 and IPv6)
– Includes multiple metrics incl. Hop-count, PacketPair, RTT, ETT, WCETT
© 2007 Victor Bahl. All Rights Reserved.
MSR’s MCL Innovations
• Conflict-graph framework for calculating mesh capacity
Jain-MobiCom-2003
– Allows “what-if” analysis when hardware / software node configurations
and network density is changed
• Single radio-channel hopping protocol for better spectrum utilization
and improved capacity (SSCH) Bahl-MobiCom-2004
• A split-MAC control channel based protocol (C2M)
Kyasanpur-Broadnets-2005
– Channel contention with advanced reservations for packet chains on lowbandwidth control channel; data transmission on the high bandwidth data
channel
• Academic toolkit
– Source code and tools for 440 Universities world-wide using it
–
http://research.microsoft.com/mesh/kit/
© 2007 Victor Bahl. All Rights Reserved.
MIT’s Roofnet
http://pdos.lcs.mit.edu/roofnet/
•
•
•
•
•
•
Motivation: Unplanned community mesh network
Location: Cambridge, Massachusetts, USA
Scale: ~ 20 mesh nodes operational at any time, 3 sq. km coverage, 100+ users
Access: IEEE 802.11b network
Routing: ExOR with ETT
Applications: Broadband Internet Access
Briket-MobiCom-2005
© 2007 Victor Bahl. All Rights Reserved.
MIT’s Roofnet Discoveries
Aguayo-SIGCOMM-2004
•
For organic networks, with no network planning lossy radio links are common
– sometimes need to handle as much as 70% loss
•
Signal to Noise Ratio (SNR) does not predict delivery probability
– Bursty noise can corrupt packets without affecting SNR
 But most links aren’t bursty
•
In single-radio meshes, multi-hop collisions cut bandwidth by greater than 2x
•
Minimum hop-count routing metric uses low-quality links.
– More hops with better quality links generally perform better
•
Routing protocols should
– incorporate link quality metrics (such as ETX, WCETT)
– Opportunistic transmissions (MAC, ExOR)
– Multicast distribution
© 2007 Victor Bahl. All Rights Reserved.
MIT’s Roofnet Discoveries
• Higher node density improves connectivity and throughput
– Even though the hop count increases
• Even with 9 hops, were able to achieve reasonable throughput
– Avg. TCP throughput: 152 Kbps, latency: 121 msec
• N mesh Internet gateway nodes give better throughput than N (hotspots”) APs connected to the Internet
– In mesh often use a sequence of short high-quality links rather than a
single long low-quality link.
© 2007 Victor Bahl. All Rights Reserved.
MIT’s Roofnet Innovations
•
Self-installation kit
– 8dBi Antenna, PC, .11b card, 50 ft. low (3 dB / 100 ft) loss
cable, easy to install Linux based software
•
Link quality metric - Expected Transmission Count (ETX)
– Predicts the total amount of time it would take to send a data
packet along a route.
Couto-MobiCom-2003
•
Link quality aware source routing protocol (SrcrRR)
– Tries to find the highest-throughput route between any pair of
nodes.
•
Rate Selection Algorithm (SampleRate)
– Selects bit-rate that will provide the highest throughput based
on delivery probabilities measured at the different bit-rates.
•
Opportunistic routing (ExOR)
Biswas-SIGCOMM-2005
© 2007 Victor Bahl. All Rights Reserved.
Roofnet Kit
Courtesy: Bhaskaran Raman
IIT’s Digital Gangetic Plains (DGP) Project
http://www.cse.iitk.ac.in/users/braman/dgp.html
•
•
•
•
•
•
Motivation: WiFi for rural India
Bhagwat-HotNets-2003
Location: Kanpur and vicinity, India
Scale: 13 backbone mesh nodes, longest link ~ 39 Km, with multi-hop ~ 80 Km
Access Speed: > 1 Mbps, Backhaul links: 11 Mbps
Routing: Bridging
Application: Phone service (Ashwini Project: video-based services: distance-education,
tele-health, & agricultural advice)
Mar ‘03
Mar ‘04
Point-to-Point
802.11 link
Rasoolabad
Sep ‘02
Safipur
802.11 for last-hop
access within a village
5
Km
17.3 Km
22.5 Km
Mandhana
12 Km
Jun ‘02
Nov ‘02
Bithoor
0.9 Km
5.1 Km 12 Km
Mohanpur
Sep ‘04 3.5 Km
Apr ‘02
IITK
Rajajipuram/
Lucknow
39 Km
Dec ‘02
Sarauhan
Jun ‘03
Banthar
2004 - present
End to end
distance ~80 Km
23 Km
22 Km
Dec ‘03
2.3 Km
Lodhar
Dhaura
17.5 Km
37 Km
MS3
Jun ‘02
Aug ‘04
Sawayajpur
Land-line access point (close to
high-population density area)
© 2007 Victor Bahl. All Rights Reserved.
River Ganges
IIT’s DGP Discoveries
• Links seemed to sensitive to multi-path
Chebrolu-MobiCom-2006
– Off-the-shelf hardware designed for indoor delay spreads (~100 ns max)
doesn’t to too well outdoors ~ 1 microsec delay spread
• System cost reduction is more important than spectral efficiency in
rural settings
• Careful network planning is necessary for predictable performance in
long distance links
– Line of sight necessary for long-distance links
• 802.11 CSMA/CA is unsuitable for long-distance communication.
– Timing parameters (need to account for RF propagation speeds)
– Arbitrary contention resolution needs to be replaced by simple hop-by-hop
scheduling
• Interference causes drastic reduction in performance
• Power conservation necessary. Turn off equipment when link idle
– Wake-on-WLAN
© 2007 Victor Bahl. All Rights Reserved.
IIT’s DGP Project Innovations
For long distance connectivity
WiFi
Radio
– Built towers since line of sight is necessary
 Towers were expensive, function of
height (45 m ~ $5K)
– Antenna selection & transmit power made a
big difference
WiFi
Radi
o
Antennae at
Mandhana
802.11 (CSMA/CA) Issues
– Single channel operation - only one link
operational per node
 Designed a simple scenario-based
scheduling
– Tweaked MAC parameters to handle long
distance links
802.11b/g
Z
X
Raman-MobiCom-2005
RF switch
or splitter
Sensor Mote
12 V
Battery
Energy preservation via wake-on-WLAN
– A second low-power radio
Antenna
 IEEE 802.15.4 Sensor mote
 Clear channel when received energy is
below threshold
© 2007 Victor Bahl. All Rights Reserved.
Soekris
Power Switching
Circuit
Courtesy: Edward Knightly
Rice’s Technology for All (TFA) Project
http://www.tfa-wireless.ece.rice.edu/
•
•
•
•
•
Motivation: “Empower low income communities through technology”
Location: Houston’s East End
Scale: 15 nodes deployed, 2 Km2 coverage, 700+ users
Access Speed: > 1 Mbps, Backhaul links > 3 Mbps
Application: Education and work-at-home
Two-Tier Architecture
•
•
•
Limited gateways wired to Internet
Backhaul tier - Mesh
Access tier – Client to mesh node
Coverage map with location of mesh nodes
© 2007 Victor Bahl. All Rights Reserved.
Rice’s TFA Discoveries
• Don’t believe the manufacturer’s specifications
Camp-MobiSys-2006
– Radio & antenna specifications severely optimistic
• Measure before deploying. Deployment cost may be reduced if you have
– Accurate knowledge of the RF Propagation environment
 Measured path loss = 3.3 (specified 2 to 5)
– Knowledge of throughput-signal-strength function
 manufacturer values over-estimate link range by 3 times yielding disconnected
network
• When measuring always take concurrent traffic patterns into account
• Only small number of measurements required for good prediction
• Identification of the “Parking-Lot Fairness” Problem
• Placement of Internet Gateway has a significant effect on mesh
performance
© 2007 Victor Bahl. All Rights Reserved.
Rice’s TFA Innovations
Programmable, single-radio mesh
node with storage
Client node
Specifications:
• 200 mW 802.11b
• LocustWorld Mesh SW
• VIA C3 1Ghz
• 5 GB Hard Drives
• 4 GB Flash to run Linux
• HostAP driver
• 15 dBi Omni-directional Antenna
Specifications:
• 200 mW 802.11b
• 3 dBi Omni at 2 m
• Ethernet Port
Similar functionality to
DSL or cable modem
Camp-DC-2005
•
Layer 2 rate-limiting algorithm for handling the parking lot fairness problem
– Spatial Bias
 Nodes closer to the wired gateway obtain higher throughput
 Starvation occurs in nodes farthest from the gateway
–
Overhead of RTS/CTS outweighs slight gains for starved nodes
© 2007 Victor Bahl. All Rights Reserved.
Courtesy: Mark Corner and Brian Neil Levine
UMASS’s DieselNet
http://prisms.cs.umass.edu/diesel/
•
•
•
•
•
Motivation: Disruption-tolerant mesh networking
Location: Amherst, Massachusetts, USA
Scale: 40 buses, 14 Mesh APs, 4 Throwboxes, 150 miles2
Access Speed: 802.11a/b, GPRS, MaxStream, XTend, CC1000
Applications: Mesh/DTN synergy, vehicular networking
Amherst downtown and UMass
© 2007 Victor Bahl. All Rights Reserved.
DieselNet: Bus Equipment
• 40 equipped buses, routes spanning 150 sq. mi.
• Town center (4 sq.mi.) is hub of network.
• Each bus:
– HaCom Open Brick computer
(577MHz CPU, 256MB RAM)
– 802.11b USB dongle
– Linksys/Netgear 802.11b AP
– GPS Receiver
– 40GB drive
– XTend radio
– GPRS
– Custom software
© 2007 Victor Bahl. All Rights Reserved.
Dieselnet Innovations: ThrowBox
•
•
•
•
TelosB Mote (sensor)
900 MHz XTend radio
8 Mhz microcontroller
Stargate
- 802.11b CF card
- 400Mhz PXA255 Xscale
- 64 MB ram, 32MB store
• Java 1.3
• DieselNet code
• AA rechargeable batteries / solar power
© 2007 Victor Bahl. All Rights Reserved.
DieselNet’s Throwbox Use
DieselNet’s Discoveries
•
Real deployments must build in a strong software update and data logging
mechanism.
•
Routing: Information about the network allows routing protocols to manage
resource constraints correctly. (Use as much bandwidth as necessary during a
short-lived DTN contact opportunity to exchange meta-data.)
•
DTNs are a failure mode for meshes; Meshes are a performance benefit for
DTNs.
•
Two fundamental “Throwboxes” challenges:
– Placement: Throwbox deployment that incorporates knowledge about
contact opportunities performs better than deployment that ignores this
knowledge.
– Power management: long-range radio coupled with Mote used for
discovery and mobility prediction; normal-range radio and Stargate used
for transfer and routing.
© 2007 Victor Bahl. All Rights Reserved.
MadCity’s Madison Broadband Downtown Mesh
•
•
•
•
•
Motivation: Commercial endeavor, local ISP, $20/month to cover the entire city
Location: Madison, Wisconsin, USA
Scale: 200+ mesh nodes (not all completely functional), coverage 9 miles2
Access Speed: 802.11a speed in the backbone, 802.11b access link
Applications: Broadband Internet Access
© 2007 Victor Bahl. All Rights Reserved.
MadCity’s Mesh Network
• Carefully planned network
– Grid-like topology. Every mesh node has at least one other mesh node win it’s line
of sights
• Two-tier network
– 5.8 GHz (for the mesh backbone), 2.4 GHz (for client access)
– Client connect to mesh as if connecting to infra-structure network AP
• Mesh nodes run Cisco’s propriety software
– Tree based protocol with AODV like features
• Injection Points
– A 18 GHz (6-mile) licensed link between a tower and the NOC
 Tower has a 3 ft. diameter antenna and located high above the city
– The tower points to 3 mesh nodes (Internet Gateways)
© 2007 Victor Bahl. All Rights Reserved.
MadCity’s Discoveries
From UW WiNGs Research Group
•
Multi-radio systems are preferable
– Next version may have 3 radios, two for the backbone, 1 for access
•
Foliage has a significant negative impact on data rates
– Performance in winter and summer is significantly different
 Up to factor of 2
– Neighboring mesh nodes have to be approximate in line-of-sight
 Carefully network planning is necessary
 Routing doesn’t change often
•
Directionality can help improve performance
 Use of sector antennas and polarization capabilities
© 2007 Victor Bahl. All Rights Reserved.
Courtesy: Krishna Ramachandran
UCSB’s Multi-Channel Mesh Network
http://moment.cs.ucsb.edu/meshnet/
•
•
•
•
•
•
Motivation: High-capacity multi-channel mesh network design
Location: University of California Santa Barbara department offices
Scale: 20 802.11a/b nodes in a 5 floor office building
Access Speed: > 20 Mbps backhaul
Routing: AODV with Link Metrics
Application: Indoor broadband access (“Wireless Office”)
UCSB MeshNet Map – subscript with node number indicates floor number
© 2007 Victor Bahl. All Rights Reserved.
UCSB’s Discoveries and Innovations
Discoveries
• Commodity radios have imperfect band filters
– Inter-radio interference, such as board-crosstalk and radiation leakage, prevents
construction of a single-unit multi-radio router
– Physical separation alleviates inter-radio interference
Innovations
.11a & .11b
• Split Wireless Router Architecture
– Individual radios on separate
processing nodes
– Modular wireless router architecture
– Backhaul formed using Wired / UWB
.11a
• TIC Multi-Channel Architecture
– Avoids external interference
Ramachandran-Infocom-2006
– Results in high-throughput,
frequency-diversified routes between
APs and mesh gateways
© 2007 Victor Bahl. All Rights Reserved.
.11a
4 radio Split Wireless Router
consisting of 3 processing units
and a 100 Mbps switch as as
interconnect
Courtesy: Saumitra M. Das
Mesh@Purdue: Purdue’s Wireless Mesh Testbed
http://engineering.purdue.edu/MESH/
•
Motivation: Design, study and
evaluate throughput improving
architectures for mesh networks
•
Location: Purdue University CS
Dept.
•
Scale: 32 dual-radio 802.11a/b
routers deployed across 4 academic
buildings with a few outdoor links
•
Access Speed: radio 1: 802.11b (~5
Mbps) radio 2: 802.11a (>20Mbps)
•
Application: Broadband internet
access and community networking
Purdue MAP testbed
© 2007 Victor Bahl. All Rights Reserved.
Purdue’s Discoveries and Innovations
• Directional antennas in multi-radio mesh networks
Das-JSAC-2006
– Spatial + frequency separation (directional antennas with channel assignment) is more
powerful than spatial or frequency separation alone
– Conservative channel assignment based on rough antenna characteristics is effective
• Mitigating the gateway bottleneck using cooperative caching in mesh
networks
– Mesh routers can be leveraged as caches through expandable storage
– Internet traffic exhibits locality. Hit rate 40~50% in traces of small user populations
– Fetching cached content from other mesh routers can improve throughput (reduced
gateway bottleneck, reduced hop count, multiple choices)
Das-mobicom_wintech-2006
• Interference measurements in wireless mesh networks
– Study of the impact of multi-way interference on a link (multiple simultaneous
transmitters) and whether pair-wise interference measurements are adequate
– Significant multi-way interference does occur although in a small fraction of cases.
Protocols that schedule multiple transmitters need to take into account such effects by
being conservative.
© 2007 Victor Bahl. All Rights Reserved.
Standards
The contents of the next set of slides are derived directly from the IEEE 802.11s
presentations made during the various IEEE meetings. The draft standard is a
living document that is constantly being revised. Therefore it is possible that the
contents of these slides may differ from the standard that finally issues.
Reference for these slides:
IEEE Document 802.11-06/0329r2, March 2006
What is IEEE 802.11s?
Protocol specification for unmanaged mesh networks.
– Primary target is a self-configuring multi-hop wireless distribution system that
supports broadcast / multicast and unicast traffic
– Mesh nodes interoperate with legacy nodes.
Guidelines
– Low complexity and to the extent possible, reuse previous technology
 Reuse 4-address frame format for exchanging packets between APs
 Build on top of 802.11i security
 Build on top of 802.11e MAC and power saving options
Initiated in late 2003; Call for proposal ended in July 2005.
Current Status
– Draft Specification
– (hopefully) Letter ballot review in November 2006
– Target completion: First half of 2008
© 2007 Victor Bahl. All Rights Reserved.
IEEE 802.11s Background
History
– Started with 35 proposals, narrowed it down to 6 by July 2005; to 4 by
Sept. 2005, to 2 by Nov. 2005 and to 1 by Mar. 2006
Final Proposal is co-authored by 38 companies. It’s a merge of:
– SEEMesh Proposal (SEE – Simple, Efficient, Extensible)
 Intel, Nokia, Motorola, NTT DoCoMo, and TI
– Wi-Mesh Proposal
 Accton, ComNets, InterDigitial, NextHop, Notel, Phillips, Extreme Networks,
MITRE, Naval Research Laboratory, Swisscom Innovations and Thomson
 http://wi-mesh.org/
The proposal includes flexibility to define protocols / mechanisms and
scenario-specific optimizations. Allows future extensions. The design
supports both single-radio and multi-radio platforms.
© 2007 Victor Bahl. All Rights Reserved.
IEEE 802.11s in a Nutshell
Discovery and Network Formation
– Single-hop & multi-hop neighbor discovery via beacons & probe responses
– Combinations of single radio / multi radio & single channel / multi-channel possible
Inter-networking
– 802.1 (STP) bridging support included
Path Selection and Forwarding
– Hybrid wireless mesh protocol default
– Support for optional protocols (e.g. RA-OLSR)
Security
– 802.11i link security, support for distributed and centralized authentication
MAC Enhancements
– 802.11e (EDCA) with support for congestion control and optional multi-channel
operation
Optional Power Save
– Reduced beaconing, single hop, APSD and ATIM/DTIM
© 2007 Victor Bahl. All Rights Reserved.
802.11s Nomenclature Device Classes
Station (STA)
“Legacy” .11 nodes, allowed to initiate sessions
Mesh Point (MP)
Mesh node
Mesh AP (MAP)
MP + access point for communication with “legacy” nodes
Mesh Portal
Commonly referred to as ITAP or Internet Gateway in research
literature but a little more generic
Light Weight MP (LWMP)
Subset of MP: primarily for neighbor-link communication
© 2007 Victor Bahl. All Rights Reserved.
802.11s Mesh Formation
• Neighbor Discovery is via beacons and probe response frames. A new
Information Element is defined
– Mesh ID
– Name of the mesh
– Mesh Capability Element
– Summary of active protocol & metric
– Channel coalescence mode and channel precedence indicators (see next)
• MPs inform one another about the supported mesh services via IEs
– e.g. Link state announcement, path selection information etc.
• Membership is determined by secure association with neighbors
– Mesh data services can be used by LWMPs without association
© 2007 Victor Bahl. All Rights Reserved.
802.11s Multi-Radio Support
MP may have one or more logical radio interface:
– Each logical interface belongs to one “Unified Channel Graph”
– Two possible modes for each interface:
 Simple channel unification mode
– Follows rules to form a fully connected graph on one channel
 Advanced mode
– Framework for flexible channel selection, algorithms/ policy (out of scope)
– Each Unified Channel Graph shares a channel precedence value
 Channel precedence indicator
– for coalescing disjoint graphs and supporting channel switching
© 2007 Victor Bahl. All Rights Reserved.
802.11s Routing
• All implementations support default mandatory protocol and metric
– Any vendor may implement any protocol and/or metric
– Only one protocol/metric is active on a particular link at a time
– A particular mesh has only one active protocol
• MP uses the Mesh Capability IE to indicate which protocol is in use
• A mesh that is using other than mandatory protocol is not required to
change its protocol when a new MP joins
– (Algorithm to coordinate such a reconfiguration is out of scope)
• Proposal for Path Selection Protocol
– Default: HWMP (RM-AODV or Distance Vector Routing Tree)
– Optional: Radio Aware OLSR (RA-OLSR)
 Based on RFC 3626
© 2007 Victor Bahl. All Rights Reserved.
802.11s Interworking with LAN Segments
Scope
– Connect a 802.11s mesh to a 802.1D bridged LAN
Support
– Transparent forwarding (“Broadcast LAN”) when bridge receives packets
destined for outside the LAN
– Learning by overhearing packets to certain destinations
– Bridge-to-bridge communications using stand bridging techniques
Note: 802.11s meshes support
– Broadcast delivery
– Unicast delivery
– Multicast delivery
© 2007 Victor Bahl. All Rights Reserved.
802.11s Bridging Functionality
Bridges handle packet delivery to a node
–
–
–
in the mesh
outside the mesh
In a the mesh but reachable via another bridge over a LAN segment
leverage layer-2 mesh path discovery to determine if the destination is
inside or outside of the mesh
IF destination inside the mesh
–
ELSE
–
–
Use layer-2 routing to discover route & forward packets
// destination outside the Mesh
Identify the “right” gateway, and deliver packets via unicast
If not known, deliver packets to all mesh portals / gateways
© 2007 Victor Bahl. All Rights Reserved.
802.11s Packet Forwarding at the Bridge
When a packet reaches the MAP, it makes bridging decisions
IF destination is not known
– Send packet on all ports
ELSE
IF destination is reachable via a non-mesh port
–
Deliver to that port
ELSE IF destination is reachable via a mesh port
IF packet came from the mesh
–
Drop it
ELSE IF the packet came from outside the mesh
–
Use mesh delivery
Note: bridge has to know where the destination is located. (out of scope)
© 2007 Victor Bahl. All Rights Reserved.
802.11s Security Goals and Requirements
• Builds on top of 802.11i security mechanisms
– Both distributed & centralized authentication schemes supported
– 802.11i provides link-security, .11s provides link-by-link security
 End-to-end security can be layered on top, e.g. using IPSEC
• Allows association/authentication between neighboring
MPs / MAPs
– Pre-requisite to participating in the mesh
• Protects mesh management & control messages
exchanged between MPs / MAPs
– Allows routing information to be authenticated
© 2007 Victor Bahl. All Rights Reserved.
802.11s Basic Security Model
• Mesh nodes belong to single logical administrative domain
• Authentication schemes
– Distributed
 Credentials are derived from certificates or PSK
– PSK limits security -- no ability to reliably identify source of
messages
– Centralized
 At least one MP can directly access AAA server
– other MPs authenticate via AAA-connected MPs via EAP
 Connection to AAA server built up hop-by-hop
• Authenticated MP can be trusted
– Mesh services (path selection protocol, data forwarding, etc.)
© 2007 Victor Bahl. All Rights Reserved.
802.11s Basic Security Model (2)
• Each MP acts as supplicant & authenticator for each
of its neighbors
– Similar to IBSS security model in 802.11i
• Each MP uses 4-way handshake with each neighbor
to establish session keys
– Each MP uses its own group session key to broadcast/multicast
and pair-wise session keys for unicast
© 2007 Victor Bahl. All Rights Reserved.
802.11s Security Model
Authenticator
Supplicant
security bubble
New participant
Notes:
– Pair-wise keys for unicast communications
– Group key for broadcast / multicast communications
– Authentication can be distributed or centralized
 Compatible with 802.1X and PSK
© 2007 Victor Bahl. All Rights Reserved.
802.11s Media Access Control
Builds on 802.11e (EDCA)
– Compatible with “legacy” devices
– Simultaneously handles multi-hop mesh & single-hop BSS traffic
• Prioritization policies left to vendor
Mesh specific enhancements
– Intra-mesh Congestion Control
• Hop-by-hop congestion control mechanism implemented at
each MP
– Common Channel Framework (Optional)
• Support for multi-channel MAC operation
© 2007 Victor Bahl. All Rights Reserved.
802.11s Congestion Management
Monitoring [Informative]
– Each node actively monitors local channel utilization
– If congestion detected, notifies previous-hop neighbors and/or the neighborhood
Signaling mechanisms are defined
– Congestion Control Request (unicast)
– Congestion Control Response (unicast)
– Neighborhood Congestion Announcement (broadcast)
Rate control [Informative]
– On receiving a congestion notification MP should adjust its traffic generation rate
– Rate control (and signaling) on per-AC basis – e.g., data traffic rate may be adjusted
without affecting voice traffic
– Example: MAPs may adjust BSS EDCA parameters to alleviate congestion due to
associated STAs
© 2007 Victor Bahl. All Rights Reserved.
802.11s Common Channel Framework (Optional)
Common channel is:
– Unified Channel Graph on which MPs and MAPs operate.
– In single radio MPs
 MPs switch from CC to a destination channel & return back.
– In multi-radio MPs
 MPs may use a separate common channel for each interface
Common Channel Framework (CCF) supports channel switching
– After RTX/CTX exchange on common channel, MP pairs switch to a
destination channel and then switch back
– Groups of MPs may switch to a negotiated destination channel
Neighbors discover support for CCF during association
– Using the Mesh Capability IE in the beacon
© 2007 Victor Bahl. All Rights Reserved.
802.11s: Channel Negotiation Protocol
Control Frames
– Request to Switch (RTX)
– Clear to Switch (CTX)
Kyasanur-BroadNets-2005
Channel Negotiation Protocol
– Using RTX, the transmitter suggests a destination channel
– Receiver accepts/declines the suggested channel using CTX
– After a successful RTX/CTX exchange, the transmitter and
receiver switch to the destination channel
– Switching is limited to channels with little activity
– Existing medium access schemes are reused
© 2007 Victor Bahl. All Rights Reserved.
802.11s Accommodating Legacy Behavior
• For devices that do not implement CCF, the common
channel appears as a conventional channel
• Common channel can be used for data transmission
• A MAP with a single radio may use the common
channel for WDS as well BSS traffic
© 2007 Victor Bahl. All Rights Reserved.
802.11s Power Save Mechanisms (Optional)
Mechanisms focused on powersave between neighbors
– MPs that support powersave may enter sleep state
– Sleep-wake cycles are not coordinated across multiple hops
Two approaches
– The Automatic Power Save Delivery (APSD) approach
 Similar to 802.11e APSD
– Periodic APSD
– Aperiodic APSD
– The Announcement Traffic Indication Message (ATIM) / Delivery Traffic
Indication Message (DTIM) approach
– Well known wake times coordinated with well-known specific beacon times
© 2007 Victor Bahl. All Rights Reserved.
802.11s: ATIM based Sleep-Wake Operation
• Guaranteed window of awake time after periodic
DTIM beacons
• DTIM interval is a parameterized multiple of
beacon intervals; globally unique to the mesh
• Control communication in ATIM window
– Indicating pending traffic
– Indicating change in PS state
– Re-instating of stopped flows
• Remain awake after ATIM window depending on
the control communication in it
DTIM Interval
ATIM
window
Beacon
DTIM Interval
ATIM
window
Beacon
© 2007 Victor Bahl. All Rights Reserved.
Time
802.11s: APSD based Sleep-Wake Operation
• Similar to 802.11e APSD solution for wireless LANs
• Periodic-APSD: Sleep-wake times coordinated with
each neighbor separately and independently
– Used for QoS traffic such as VoIP
– Pairs of neighbors setup periodic schedules to wake up at set times
• Aperiodic-APSD : MP in powersave state sends a
packet to an ‘always awake’ neighbor to indicate it is
awake
– Used only with neighbors that are awake all the time
– PS state MP sends a packet to the neighbor to indicate it is awake any time
it wishes
© 2007 Victor Bahl. All Rights Reserved.
802.11s Lightweight Mesh Points (LWMPs)
• Participate in communications with neighbors
– Association is not required when source and destination are neighbors
• Use and provide a subset of mesh services
– Incl. powersave, security, and unicast and broadcast delivery
• Do not provide or use any distribution system services
– Maximum allowed associations = 0
– Advertised routing profile = “Null”
• Lightweight in terms of memory and processing
requirements
© 2007 Victor Bahl. All Rights Reserved.
802.11s Lightweight Meshing
Association is not a pre-requisite
– When the source and destination are neighbors
 When distribution system service is not required
– When maximum number of associations allowed/possible at a MP is exhausted;
 lack of association should not preclude direct communication
Mixed mode operation is okay
– An MP may associate with some of its neighbors, and may
communicate without association with other neighbors
 The DS service may be used through associated neighbors
 Neighbor communication possible with un-associated neighbors
© 2007 Victor Bahl. All Rights Reserved.
Additional Areas of Research
Topics not covered in this tutorial
Due to lack of time I was not be able cover several important research
results that you should also be aware of. Some of these are:





Modulation and PHY techniques like spread spectrum, OFDM etc.
Adaptive antenna technologies like MIMO, beam forming, etc.
TCP over meshes
Multicast routing and group communications
Topology control and power management
 Networking technologies including UWB, IEEE 802.16,…
 Spectrally-agile cognitive radios & networking
 Directional MACs etc
© 2007 Victor Bahl. All Rights Reserved.
Active Areas of Research
–
–
–
–
–
–
–
–
–
–
–
–
Analytical tools for calculating mesh capacity
Flow-level and packet-level fairness
Network management & automatic diagnosis of faults
Network coding for capacity improvement
Routing with directional antennas / routing for network coding
Supporting VoIP & video traffic over meshes
Inexpensive software steerable directional antennas
Smart medium access control
Meshing with cognitive radios
Multi-spectral meshes
Delay tolerant meshing
Usage scenarios
© 2007 Victor Bahl. All Rights Reserved.
Thanks!
For prior work & updates, check out:
http://research.microsoft.com/mesh/
References
Papers are categorized under subject area. Duplication is possible because
some papers include more than one problem/solution pair. This is not a
exhaustive list.
References - Testbeds
UMASS’s DieselNet
•
•
•
•
•
•
•
[Zhao-MASS-2006] Wenrui Zhao, Yang Chen, Mostafa Ammar, Mark Corner, Brian N. Levine, and
Ellen Zegura. Capacity Enhancement using Throwboxes in DTNs, IEEE Intl Conf on Mobile Ad hoc
and Sensor Systems (MASS), Oct 2006.
[Partan-WUWNet-2006] Jim Partan, Jim Kurose, Brian N. Levine, A Survey of Practical Issues in
Underwater Networks. ACM Intl Wkshp on Underwater Networks (WUWNet), September 2006
[Jun-ACHANTS-2006] Hyewon Jun, Mostafa Ammar, Mark Corner, Ellen Zegura. Hierarchical
Power Management in Disruption Tolerant Networks with Traffic-Aware Optimization, ACM
CHANTS. September, 2006.
[Burgess-INFOCOM-2006] John Burgess, Brian Gallagher, David Jensen, and Brian N. Levine.
MaxProp: Routing for Vehicle-Based Disruption-Tolerant Networks, IEEE INFOCOM, April 2006.
[Burns-ICRA-2006] Brendan Burns, Oliver Brock, and Brian N. Levine. Autonomous Enhancement
of Disruption Tolerant Networks, IEEE Intl Conf on Robotics and Automation (ICRA), May 2006.
[Burns-INFCOMM-2005] Brendan Burns, Oliver Brock, and B.N. Levine. MV routing and capacity
building in disruption tolerant networks., IEEE INFOCOM, March 2005.
[Hanna-ICNP-2003] Kat Hanna, Brian N. Levine, and R. Manmatha. Mobile Distributed Information
Retrieval For Highly Partitioned Networks, IEEE ICNP, November 2003.
© 2007 Victor Bahl. All Rights Reserved.
References - Testbeds
IITK’s Digital Gangetic Plains
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[Chebrolu-MobiCom-2006] Kameswari Chebrolu, Bhaskaran Raman, and Sayandeep Sen, LongDistance 802.11b Links: Performance Measurements and Experience, 12th Annual International
Conference on Mobile Computing and Networking (MOBICOM), Sep 2006, Los Angeles, USA.
•
[Raman-MobiCom-2005] Bhaskaran Raman and Kameswari Chebrolu, Design and Evaluation of a
new MAC Protocol for Long-Distance 802.11 Mesh Networks, 11th Annual International Conference
on Mobile Computing and Networking (MOBICOM), Aug/Sep 2005, Cologne, Germany.
•
[Bhagwat-HotNets-2003] Pravin Bhagwat, Bhaskaran Raman, and Dheeraj Sanghi, Turning 802.11
Inside-Out, Second Workshop on Hot Topics in Networks (HotNets-II), 20-21 Nov 2003, Cambridge,
MA, USA.
MIT’s RoofNet
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[Briket-MobiCom-2005] John Bicket, Daniel Aguayo, Sanjit Biswas, and Robert Morris, Architecture
and Evaluation of an Unplanned 802.11b Mesh Network, ACM MobiCom 2005.
[Biswas-SIGCOMM-2005] Sanjit Biswas and Robert Morris, Opportunistic Routing in Multi-Hop
Wireless Networks, ACM SIGCOMM 2005
[Aguayo-SIGCOMM-2004] Daniel Aguayo, John Bicket, Sanjit Biswas, Glenn Judd, Robert Morris,
Link-level Measurements from an 802.11b Mesh Network, SIGCOMM 2004, Aug 2004
[Couto-MobiCom-2003] Douglas S. J. De Couto, Daniel Aguayo, John Bicket, Robert Morris, A
High-Throughput Path Metric for Multi-Hop Wireless Routing, ACM Mobicom 2003
© 2007 Victor Bahl. All Rights Reserved.
References - Testbeds
MSR’s Mesh Network
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[Qiu-CCR-2006] Lili Qiu, Paramvir Bahl, Ananth Rao, Lidong Zou, “Troubleshooting Wireless
Meshes”, ACM Computer Communications Review 2006
[Eriksson-MobiSys-2006] Jacob Eriksson, Sharad Agarwal, Paramvir. Bahl, Jitendra Padhye,
Feasibility Study of Mesh Networks for All-Wireless Offices, ACM/USENIX MobiSys, Uppsala,
Sweden, June 2006
[Kyasanpur-Broadnets-2005] Pradeep Kyasanur, Jitendra Padhye, Paramvir Bahl, On the Efficacy
of Separating Control and Data into Different Frequency Bands, IEEE BroadNets 2005 , Boston,
Massachusetts, USA (October 2005)
[Padhye-IMC-2005] Jitendra Padhye, Sharad Agarwal, Venkata Padmanabhan, lili Qiu, A. Rao,
Brian Zill, “Estimation of Link Interference in Static Multi-hop Wireless Networks”, ACM Internet
Measurement Conference 2005, October 2005
[Kuga-NRSM-2004] Y Kuga, J. Cha, J. A. Ritcey, James Kajiya, Mechanically Steerable Antennas
Using Dielectric Phase Shifters,
IEEE AP-S International Symposium and USNC/URSI National Radio Science Meeting, June 2004
[Qiu-ICNP-2004] Lili Qiu, Ranveer Chandra, Kamal Jain, M. Mahdian, Optimizing the Placement of
Integration Points in Multi-hop Wireless Networks, IEEE ICNP 2004.
[Draves-MobiCom-2004] Richard Draves, Jitendra Padhye, Brian Zill, Routing in Multi-radio, Multihop Wireless Mesh Networks, ACM MobiCom, Philadelphia, PA, September 2004.
[Bahl-MobiCom-2004] Paramvir Bahl, Ranveer Chandra, John Dunagan, SSCH: Slotted Seeded
Channel Hopping for Capacity Improvement in IEEE 802.11 Ad-Hoc Wireless Networks, ACM
MobiCom, Philadelphia, PA, September 2004.
[Draves-SIGCOMM-2004] Richard Draves, Jitendra Padhye, Brian Zill, Comparison of Routing
Metrics for Static Multi-Hop Wireless Networks, ACM SIGCOMM, Portland, OR, August 2004.
© 2007 Victor Bahl. All Rights Reserved.
References - Testbeds
MSR’s Mesh Network
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[Qiu-MSRTR-2003] Lili Qiu, Paramvir Bahl, A. Rao, Lidong Zhou, Fault Detection, Isolation, and
Diagnosis in Multi-hop Wireless Networks, Microsoft Research Technical Report, TR-2004-11
[Jain-MobiCom-2003] K. Jain, J. Padhye, V. Padmanabhan, and L. Qiu, Impact of Interference on
Multi-hop Wireless Network Performance, ACM MobiCom, San Diego, CA, September 2003
Rice’s TFA
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[Camp-MobiSys-2006] Joseph Camp, J. Robinson, C. Steger, Edward Knightly, "Measurement Driven
Deployment of a Two-Tier Urban Mesh Access Network," in Proceedings of ACM MobiSys 2006,
Uppsala, Sweden, June 2006.
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[Camp-DC-2005] Joseph Camp, Edward Knightly, W. Reed, "Developing and Deploying Multihop
Wireless Networks for Low-Income Communities," in Proceedings of Digital Communities 2005, Napoli,
Italy, June 2005.
JHU’s SMESH
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[Amir-MobiSys-2006] Yair Amir, Claudiu Danilov, Michael Hilsdale, Raluca Musaloiu-Elefteri, Nilo
Rivera, “Fast Handoff for Seamless Wireless Mesh Networks”, ACM/USENIX MobiSys 2006, June
2006
© 2007 Victor Bahl. All Rights Reserved.
References - Testbeds
Purdue’s Mesh
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[Das-JSAC-2006] Saumitra M. Das, Himabindu Pucha, Dimitrios Koutsonikolas, Y. Charlie Hu,
Dimitrios Peroulis, “DMesh: Incorporating Practical Directional Antennas in Multi-Channel Wireless
Mesh Networks”, IEEE Journal on Selected Areas in Communications (JSAC 06) special issue on
Multi-Hop Wireless Mesh Networks, 2006.
[Das-mobicom_wintech-2006] Saumitra M. Das, Dimitrios Koutsonikolas, Y. Charlie Hu, Dimitrios
Peroulis, “Characterizing Multi-Way Interference In Wireless Mesh Networks”, ACM MobiCom
International Workshop on Wireless Network Testbeds, Experimental evaluation and
Characterization (MobiCom WiNTECH 06), Los Angeles, CA, September 29, 2006.
© 2007 Victor Bahl. All Rights Reserved.
References - Fairness
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[Nandagopal-MobiCom-2000] Thyagarajan Nandagopal, Tae-Eun Kim, Xia Gao, Vadhuvar
Bharghavan, “Achieving MAC Layer Fairness in Wireless Packet Networks,” ACM MobiCom 2000,
August 2000
[Luo-MobiCom-2000] Haiyun Luo, Songwu Lu, Vadhuvar Bharghavan, “A New Model for Packet
Scheduling in Multihop Wireless Networks”, ACM MobiCom 2000, August 2000
References – Capacity / Channelization
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[MSBA-SIGMETRICS-2006] Arunesh Mishra, Vivek Shrivastava, Suman Banerjee, William Arbaugh,
Partially-overlapped Channels not Considered Harmful, ACM SIGMETRICS, June 2006.
[Ramachandran-Infocom-2006] K. Ramachandran, E. Belding, K. Almeroth, M. Buddhikot,
“Interference-Aware Channel Assignment in Multi-Radio Wireless Mesh Networks”, IEEE Infocom,
Barcelona, Spain, April 2006
[Kyasanur-WCM-2006] Pradeep Kyasanur, Jungmin So, Chandrakanth Chereddi, and Nitin H.
Vaidya, "Multi-Channel Mesh Networks: Challenges and Protocols", IEEE Wireless Communications,
April 2006
[Kyasanur-BroadNets-2005] Pradeep Kyasanur, Jitendra Padhye, and Paramvir Bahl, "On the
Efficacy of Separating Control and Data into Different Frequency Bands", in IEEE Broadnets, Boston,
MA, October 2005
[Raniwala-Infocom-2005] Ashish Raniwala and Tzi-cker Chiueh, “Architecture and Algorithms for an
IEEE 802.11-based Multi-Channel Wireless Mesh Network”, IEEE INFOCOM, 2005
Alicherry-MobiCom-2005] Mansoor Alicherry, Randeep Bhatia, Li Li, “Joint Channel Assignment
and Routing for Throughput Optimization in Multi-radio Wireless Mesh Networks”, ACM MobiCom
2005, September 2005
[Kodialam-MobiCom-2005] Muralidharan Kodialam, Thyaga Nandagopal, “Characterizing the
Capacity Region in Multi-Radio, Multi-Channel Wireless Mesh Networks”, ACM MobiCom 2005,
September 2005
© 2007 Victor Bahl. All Rights Reserved.
References – Capacity / Channelization
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[Kyasanur-MobiCom-2005] Pradeep Kyasanur, Nitin Vaidya, Capacity of Multi-Channel Wireless
Networks: Impact of Number of Channels and Interfaces”, ACM MobiCom 2005, September 2005
[Adya-BroadNets-2004] Atul Adya, Paramvir Bahl, Jitendra Padhye, Alec Wolman, and Lidong
Zhou, “A Multi-Radio Unification Protocol for IEEE 802.11 Wireless Networks”, IEEE BroadNets
2004.
[Bahl-MobiCom-2004] Paramvir Bahl, Ranveer Chandra, John Dunagan, “SSCH: Slotted Seeded
Channel Hopping for Capacity Improvement in IEEE 802.11 Ad-Hoc Wireless Networks”, ACM
MobiCom, Philadelphia, PA, September 2004
[So-MobiHoc-2004], Jungmin So, Nitin Vaidya, “Multi-Channel MAC for Ad Hoc Networks: Handling
Multi-Channel Hidden Terminals Using A Single Transceiver”, ACM MobiHoc 2004, Tokyo, Japan,
May 2004
[Jain-MobiCom-2003] Kamal Jain, Jitendra Padhye, Venkata Padmanabhan, and Lili Qiu, “Impact of
Interference on Multi-hop Wireless Network Performance”, ACM MobiCom, San Diego, CA,
September 2003
[Jinyang-MobiCom-2001] Jinyang Li, Charles Blake, Douglas S. J. De Couto, Hu Imm Lee, and
Robert Morris, Capacity of Ad Hoc Wireless Networks, ACM MobiCom '01), Rome, Italy, July 2001
[Gupta-IEEEIT-2000] Piyush Gupta, P. R. Kumar, “Capacity of Wireless Networks”, IEEE
Transactions on Information Theory, March 2000.
[Wu-ISPAN-2000] S.L. Wu, C.Y. Lin, Y.C. Tseng, J.P. Sheu, “A New Multi-Channel MAC Protocol
with On-Demand Channel Assignment for Mobile Ad Hoc Networks”, International Symposium on
Parallel Architectures, Algorithms and Networks (I-SPAN), 2000
© 2007 Victor Bahl. All Rights Reserved.
References - Routing
IETF Standards
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[Corson-RFC2501-1999] Scott Corson, Joseph Macket, “Mobile Ad hoc Networking (MANET): Routing
Protocol Performance Issues and Evaluation Considerations”, IETF RFC 2501, January 1999
[Perkins-RFC3561-2003] Charlie Perkins, Elizabeth Beilding-Royer, Samir Das, “Ad Hoc On Demand
Distance Vector (AODV) Routing”, IETF RFC 3561, July 2003
[Clausen-RFC3626-2003] T. Clausen, P. Jacquet, “Optimized Link State Routing Protocol (OLSR)”,
IETF RFC 3626, October 2003
[Ogier-RFC3684-2004] R. Ogier, Fred Templin, Mark Lewis, “Topology Dissemination Based on
Reverse-Path Forwarding (TBRPF)”, IETF RFC 3684, February 2004
[Johnson-RFC4728-2007] D. Johnson, Y. Hu, D. Maltz, “The Dynamic Source Routing Protocol (DSR)
for Mobile Ad Hoc Networks for IPv4”, IETF RFC 4728, February 2007
Papers & Drafts
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[Biswas-SIGCOMM-2005] Sanjit Biswas and Robert Morris, Opportunistic Routing in Multi-Hop
Wireless Networks, ACM SIGCOMM 2005
[Draves-SIGCOMM-2004] Richard Draves, Jitendra Padhye, Brian Zill, Comparison of Routing Metrics
for Static Multi-Hop Wireless Networks, ACM SIGCOMM, Portland, OR, August 2004.
[Johnson-Draft-2004] David B. Johnson, David A. Maltz, Yih-Chun Hu, “The Dynamic Source Routing
Protocol for Mobile Ad Hoc Networks (DSR)”, IETF Draft, July 2004
[Ni-MobiCom-1999] S. Ni, Y. Tseng, Y. Chen, J. Chen, “The Broadcast Storm Problem in a Mobile Ad
Hoc Network,” ACM MobiCom ’99, Seattle, Washington, August 1999
© 2007 Victor Bahl. All Rights Reserved.
References - Routing
Papers & Drafts
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[Alicherry-MobiCom-2005] Mansoor Alicherry, Randeep Bhatia, Li Li, “Joint Channel Assignment
and Routing for Throughput Optimization in Multi-radio Wireless Mesh Networks”, ACM MobiCom
2005, September 2005
[Couto-HotNets-2002] Douglas De Couto, Daniel Aguayo, Benjamin Chambers, Robert Morris,
“Performance of Multihop Wireless Networks: Shortest Path is Not Enough”, First Workshop on Hot
Topics in Networks (HotNets-I), October 2002
[Broch-MobiCom-1998] Josh Broch, David A. Maltz, David B. Johnson, Yih-Chun Hu, and Jorjeta
Jetcheva. “A Performance Comparison of Multi-Hop Wireless Ad Hoc Network Routing Protocol”,.
ACM MobiCom'98, Oct. 1998.
[Perkins-CCR-1994] Charlie Perkins and Pravin Bhagwat, “Highly Dynamic Destination-Sequenced
Distance-Vector Routing (DSDV) for Mobile Computers,”, Computer Communications Review 24(4),
Oct. 1994
© 2007 Victor Bahl. All Rights Reserved.
References – Security & Management
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[Qiu-CCR-2006] Lili Qiu, Paramvir Bahl, Ananth Rao, Lidong Zou, “Troubleshooting Wireless
Meshes”, ACM Computer Communications Review 2006
[Badonnei-JNM-2005] Remi Badonnel, Radu State, Olivier Festor “Management of Mobile Ad Hoc
Networks: Information Model and Probe-based Architecture”, International Journal of Network
Management, Vol. 15, Issue 5, September 2005
[Kyasanur-TMC-2005] Pradeep Kyasanur, Nitin Vaidya, “Selfish MAC Layer Misbehavior in
Wireless Networks”, IEEE Transactions on Mobile Computing, Vol. 4, Issue 4, September 2005
[Hu-Infocom-2003] Yih-Chun Hu, Adrian Perrig, David B. Johnson, “Packet Leashes: A Defense
Against Wormhole Attacks in Wireless Ad Hoc Networks,”, IEEE INFOCOM 2003
[Qiu-MSRTR-2003] Lili Qiu, Paramvir Bahl, A. Rao, Lidong Zhou, Fault Detection, Isolation, and
Diagnosis in Multi-hop Wireless Networks, Microsoft Research Technical Report, TR-2004-11
[Shen-Milcom-2002] C.-C. Shen, C. Jaikaeo, C. Srisathapornphat, Z. Huang, “The GUERILLA
Management Architecture for Ad Hoc networks”, IEEE MILCOM 2002, Oct. 2002
[Hu-MobiCom-2002] Yih-Chun Hu, Adrian Perrig, David B. Johnson, “Ariadne: A Aecure OnDemand Routing Protocol for Ad Hoc Networks”, ACM MobiCom 2002, Atlanta, GA
[Bucheggar-MobiHoc-2002] S. Buchegger, J. Y. Le Boudec, “Performance Analysis of the
CONFIDANT Protocol”, ACM MobiHoc 2002
[Marti-MobiCom-2000] Sergio Marti, T. J. Giuli, Kevin Lai, Mary Baker, “Mitigating Routing
Misbehavior in Mobile Ad Hoc Networks”, ACM MobiCom 2000, Boston, MA
[Zhang-MobiCom-2000] Yongguang Zhang , Wenke Lww, “Intrusion Detection in Wireless Ad Hoc
Networks”, ACM MobiCom 2000, Boston, MA
[Chen-JSAC-1999] Wenli Chen, Nitin Jain, Suresh Singh, “ANMP: Ad Hoc Network Management
Protocol”, IEEE Journal on Selected Areas in Communications, Volume 17 Number 8, August 1999
© 2007 Victor Bahl. All Rights Reserved.
References - General
Network Management
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[Badonnel-JTS-2005] Remi Badonnel, Radu State, Olivier Festor, “Self-Organized Monitoring of Ad
Hoc Networks”, Journal of Telecommunications Systems, Vol. 30, No. 1-3, 2005
General
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[Andel-Computer-2006] Todd R. Andel, Alec Yasinsac, “On the Credibility of MANET Simulations”,
IEEE Computer Magazine, pp. 48-54, 2006
[IEEE-Mesh-2006] Joint SEE-Mesh/Wi-Mesh Proposal to 802.11 TGs Overview”, IEEE 802.1106/0329r2, March 6, 2006
[Karn-CNC-1997] Phil Karn, “MACA – A New Channel Access Method for Packet Radio”, in
Proceedings of AARL/CRRL Amateur Radio 9th Computer Networking Conference, Sept. 1997
[Powers-Proc-1995] R. A. Powers. “Batteries for Low Power Electronics”, Proceedings of the IEEE,,
April 1995
[Tobagi-Comm-1975] F. A. Tobag, L. Klienrock, “Packet Switching in Radio Channels: Part II – The
hidden Terminal Problem in a Carrier Sense Multiple-Access Modes and Busy-Tone Solution”, IEEE
Transaction Communications, Vol. COM-23, no. 12, 1975
© 2007 Victor Bahl. All Rights Reserved.