Glenford Mapp
Principal Lecturer, Middlesex University
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2012
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Motivation for the work
Handover Classification
Proactive-Handover
Mathematical Framework
Scenario
Location information
Wireless Footprinting
Implications for future networking
infrastructure
Future Plans
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The Internet will evolve in a physical sense
Core of the network
◦ Super-fast backbone (optical switching, etc)
◦ Fast access networks (MPLS, ATM)
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Peripheral Wireless Networks
◦ Errors due to fading, etc; not just congestion
◦ Handover
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Consequences
 Degradation of end-to-end arguments
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BACKBONE
ACCESS NETWORKS
WIRELESS NETWORKS
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Devices will have more than one wireless
interface.
Vertical handover – switching between
different network interfaces to provide
seamless connectivity
Vertical handover is good but it introduces a
lot of QoS issues because the different
wireless networks have different qualities of
service
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Affects your connections
◦ Some protocols react badly with respect to
handover.
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Affects your applications
◦ Need to think through how Quality-of-Service
affects applications
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Encapsulate these ideas in a Framework
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New framework
◦ We need to control network interfaces generically
◦ Make mobility support explicit
 Vertical handover can have tsunami effects
◦ Merge network and transport services
◦ Make QoS support explicit
 Provide a way for applications to negotiate with the
network
◦ Security
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Goal: Integration of Communication, Mobility,
Quality-of-Service and Security
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PERIPHERAL NETWORK
SECURITY LAYERS
APPLICATION ENVIRONMENTS
QOS LAYER
END SYSTEM TRANSPORT
POLICY MANAGEMENT
VERTICAL HANDOVER
NETWORK ABSTRACTION
(MOBILE NODE)
HARDWARE PLATFORM
(MOBILE NODE)
SAS
QBS
NTS
NAS
CORE NETWORK
SERVICE PLATFORM
NETWORK QOS LAYER
CORE TRANSPORT
NETWORK MANAGEMENT
CONFIGURATION LAYER
NETWORK ABSTRACTION
(BASE STATION)
HARDWARE PLATFORM
(BASE STATION)
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Can’t explain everything about Y-Comm
 It’s too big
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Several people at Middlesex work on it:
◦ Mahdi Aiash : Security
◦ Fragkiskos Sardis: Mobile environments
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Also Cambridge, Loughborough and USP
Concentrate on the Handover
◦ Ferdinand Katsriku & MSc students
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See Y-Comm Research Webpage:
http://www.mdx.ac.uk/research/areas/softw
are/ycomm_research.aspx
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Hard vs Soft Handovers
◦ Hard: - break before make
◦ Soft – make before break
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Network vs Client Handovers
◦ Network – network in control (current)
◦ Client – future (Apple’s patent)
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Upward vs Downward
◦ Upward – smaller to bigger coverage
◦ Downward – bigger to smaller
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HANDOVER
ALTERNATIVE
IMPERATIVE
NETPREF
REACTIVE
UNANTICIPATED
SERVICES
USERPREF CONTEXT
PROACTIVE
ANTICIPATED
KNOWLEDGE-BASED
MODEL-BASED
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HIGHER LAYERS
Interface Information
L2 Triggers
INPUT/OUTPUT LAYER
POLICY LAYER (PONDER)
HANDOVER EXECUTION LAYER
WLAN
GPRS
LAN
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Proactive Policy Management
◦ The mobile node can know or estimate the
network state at a given point before it arrives at
that point
◦ Proactive Policies allow us to maximize the use of
available channels provided you know the amount
of time a channel will be available.
◦ That time is known as:
 Time before vertical handover (TBVH)
 Can significantly reduce packet loss during all vertical
handovers
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Proactive policies can themselves be divided
into 2 types
Proactive knowledge-based systems
◦ Knowledge of which local wireless networks are
operating at a given location and their strengths at
that point
◦ We also need a system to maintain the integrity,
accessibility and security of that data
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Knowledge-based approach
Gather a database of the field strengths for
each network around Cambridge
Need to maintain the database and also know
how the results might be affected by seasonal
effects
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Using a simple mathematical model
Define a radius at which handover should
occur
Find out how much time I have before I hit
that circle, given my velocity and direction
Calculate TBVH
 Used simulation (OPNET)
 Can be used in the real world as well as in simulation
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Handover
threshold circle
Exit threshold
circle
Threshold Circle
coverage
Real coverage
Exit coverage
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Movement of MS under BBS coverage (upward vertical
handoff)
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Introduction of additional
functionality to Base Station at
network boundary (BBS).
Distance between MS and BBS
derived from location
co-ordinates or
RSSdB  10 log(l )
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BBS
r
d x
z
MS
Estimated TBVH
r 2  d 2 sin 2 x  d cos x
TBVH 
v
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TBVH simulation in OPNET Modeler:
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Extends Fatema’s work which only looked at
upward handover
Looks at providing a complete mathematical
framework
Uses the Law of Cosines
Needs accurate location information plus
handover radius
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NET A
NET A
NET A
NET B
NET B
NET B
Complete Coverage
Two Networks Intersect
Networks are Separate
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Fatema Shaikh’s work
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CF from upward handover
CE, EG, GH from downward handover
EF = CF – CE = Intersection Distance
Maximum Coverage
PQ = AQ – AP
PQ = R1 – (AB – R2)
PQ = R1 + R2 - AB
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A
R1
R2
B
For Separate Networks
AB > R1 + R2
(Hard Handover)
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Scenario
Three WLANs in a single UMTS cell
NET A
A
NET B
S
B
NET C
C
T
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Analysis
C1
E1
Y2
Z1
A
S
Y1
H1
Y3
C2
B
E2
C
E3
H3
H2
T
Z2
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Z3
2012
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If the mobile node knows:
◦ Its location, direction and velocity
 Via GPS, accelerometers
◦ The location of networking infrastructure
 Type of radio network, position of the Access Points
◦ A good estimation of the Handover Radius
 Hard to do
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Then we can calculate the optimal time to
handover over a large area using this
mathematical framework
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Mobile Operators
◦ Location of Base-Stations tends to be difficult to
obtain.
 Commercially sensitive
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Location of WLANs
◦ Ad-hoc arrangements
◦ Almost impossible; need to do wardriving
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Growing need to address this issue
 IEEE 802.21:Media Independent Information Service
(MIIS)
 Cognitive Radio is also going to change this
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Need 4 things
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Location of the Transmitter
The power at the transmitter
Propagation model
The signal threshold at which handover should
occur
 Depends on the wireless receiver in the Mobile Node
 More expensive the better
 Most WLAN receivers can do -70-85dB
 Mobile phones: around -120 dB
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Need better propagation models
Propagation Models
◦ Semi-static Models:
 Free Space, Okumura and Hata Models
 Less dependent on specific conditions
◦ Finite-element propagation models
 Arshad and Katsriku
 They take into account surroundings and specific
conditions
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Need for a more dynamic approach
◦ More context and location awareness
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Let mobile nodes store information about
their location, the signal strengths and other
measurements in the core network
Make information on previous journeys
available
Also this information to be shared with other
mobile uses
◦ Need to make sure that we don’t forget privacy
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Developed at USP
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System has been built and can be used. So we
put the software on mobile phones and it
uses the WF Server
This will allow us to look at building a better
propagation model that is more tuned to
location and context of mobile nodes
More dynamic; based on continuous
measurements
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Explore the effect of TBVH and NDT on
channel allocation strategies
Could be the real game-changer for mobile
operators
A mobile node is able to say much more
when requesting a channel
◦ Will also know TBVH and NDT
◦ Allow better channel allocation
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GPS
Location,
Speed, direction
Connections
(QoS)
NDT
TBVH
New QoS
New IP
Polling
CORE NETWORK
Done
POLICY MANAGEMENT LAYER
DECISION HANDOVER
(BASE-STATION, 3G, QOS, TBVH, NDT)
NETWORK MANAGEMENT LAYER
Send to Mobile
TOPOLOGY, RESOURCES, QoS
DO IT
CONFIGURABLE LAYER
VERTICAL HANDOVER LAYER
ACQUIRE CHANNEL
ACQUIRE RESOURCES
( 3G Base-station, QOS, TBVH, NDT)
(3G Base-station , QOS, TBVH, NDT)
DO IT
NETWORK ABSTRACTION LAYER
NETWORK ABSTRACTION LAYER
BASE-STATION
CHANNEL ACQUIRED
DATA CHANNNEL = 3G
3G=ACTIVE WLAN=PASSIVE WiMAX= PASSIVE
L2 events
Media Info
3G
WLAN
WiMax
3G
WLAN
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WiMax
2012
REQ (Time , TBVH, NDT)
A
A
WIRELESS
NETWORK
B
REQ (Time , TBVH, NDT)
B
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MNA needs channel at (Time + TBVH)
A
MNA releases channel at (Time + TBVH +
NDT)A
MNB needs channel at (Time + TBVH)B
MNB releases channel at (Time + TBVH +
NDT)B
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No Contention
◦ (Time + TBVH)A < (Time + TBVH)B
◦ (Time + TBVH + NDT)A < (Time + TBVH)B
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Contention: Two Types: Partial and Total
◦ (Time + TBVH)A < (Time + TBVH)B
◦ (Time + TBVH + NDT)A > (Time + TBVH)B
◦ Partial Contention
 (Time + TBVH + NDT)A < (Time + TBVH + NDT)B
◦ Total Contention
 (Time + TBVH + NDT)A >= (Time + TBVH + NDT)B
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Request Granted as requested
◦ Channel granted at (Time + TVBH)A
◦ Channel released at (Time + TBVH + NDT)A
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Request Granted but modified (for B)
◦ Channel granted at (Time + TBVH + NDT)A
◦ Channel released at (Time + TBVH + NDT)B
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Request not granted
◦ Force handover to other network(s)
◦ MN node no longer stuck in queue
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Much better use of core resources
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Basic mathematical framework
◦ Develop a program for mobile phones
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Better propagation models
◦ Use Wireless Footprinting
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Investigate the implications for the core
infrastructure
◦ New multi-channel allocation scheme based on
TBVH and NDT
◦ Quantify improvement
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Show mobile operators how they can provide
much better services in this new context
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