When Dynamic Source Routing (DSR)
meets IEEE 802.11 Power Saving Mode
(PSM)
Sunho Lim (Ph.D., Assistant Professor)
T2WISTOR: TTU Wireless Mobile Networking Laboratory
Dept. of Computer Science
Texas Tech University
Lubbock, TX 79409
sunho.lim@ttu.edu
Computer Science Department Seminar, Fall 2012
Preliminary:
know Your
Professor
New department homepage
http://www.depts.ttu.edu/cs
About what I am doing?
Teaching & Service
Personal website
Research
Research group website
About me?
Personal website
More information about me?
Curriculum Vitae
Computer Science Department Seminar, Fall 2012
Source: CS Department Website
T2WISTOR: TTU Wireless Mobile
Networking Laboratory
“We design and develop algorithms and
communication protocols in the level of Link
and Network layers.”
Mobile Ad Hoc Networks (MANETs)
RandomCast: Energy Efficient Randomized Communication
CMM: Clustered Mobility Model
Internet-based Mobile Ad Hoc Networks (IMANETs)
Aggregate Caching and Data Access Strategies
Cooperative Caching Strategies
Single-hop Wireless Networks
ConSens: Opportunistic Data Access
Wireless Sensor Networks (WSNs)
Vibration-Sensitive Energy Harvesting
Google Android-based Mobile Software
eSCORT: I am not alone
Mobile Education
Cybersecurity
Counter DoS Attacks
Source: Mobile Communication, J. Schiller
Computer Science Department Seminar, Fall 2012
Research Motivation:
Energy Conservation & Routing
Efficiency
One of the most critical issues in MANETs is energy conservation.
Exploiting low-power state is the key to maximize the energy efficiency.
Device
Idle / Listening
Low-Power
Lucent IEEE 802.11
WaveLAN-2
1.15 W
0.045 W
TR 1000, used in
Berkeley Motes
13.5 mW
0.015 mW
IEEE 802.11 PSM (Power Saving Mechanism) cannot be both energy-efficient &
routing performance-efficient in multihop networks.
e.g., DSR heavily relies on overhearing.
Heart of this problem is semantic discrepancy: A node transmits a unicast
packet, but it wishes that all its neighbours overhear it.
Computer Science Department Seminar, Fall 2012
Why Mobile Ad Hoc Networks
(MANETs)?
Sometimes there is NO infrastructure!
remote areas, ad-hoc meetings,
disaster areas
cost can also be an argument against
an infrastructure!
Ease of deployment, speed of deployment,
decreased dependence on infrastructure
Main topic: routing
every node should be able to forward
no default router available
Many Applications:
Personal area networking
Military environments
Civilian environments
Emergency operations
A
B
C
Source: Mobile Communication, J. Schiller
Source:Tactical Wireless Networking, General Dynamics
Computer Science Department Seminar, Fall 2012
Dynamic Source Routing:
Route Discovery
Y
Z
S
E
F
B
C
M
J
A
L
G
H
K
D
I
N
Represents a node that has received RREQ for D from S
Computer Science Department Seminar, Fall 2012
Source: Prof. Nitin Vaidya in UIUC
Dynamic Source Routing:
Route Discovery (cont.)
Y
Broadcast transmission
[S]
S
Z
E
F
B
C
M
J
A
L
G
H
D
K
I
N
Represents transmission of RREQ
[X,Y]
Represents list of identifiers appended to RREQ
Computer Science Department Seminar, Fall 2012
Source: Prof. Nitin Vaidya in UIUC
Dynamic Source Routing:
Route Discovery (cont.)
Y
Z
S
E
[S,E]
F
B
C
A
M
J
[S,C]
H
L
G
D
K
I
N
• Node H receives packet RREQ from two neighbors:
potential for collision
Computer Science Department Seminar, Fall 2012
Source: Prof. Nitin Vaidya in UIUC
Dynamic Source Routing:
Route Discovery (cont.)
Y
Z
S
E
F
B
[S,E,F]
C
M
J
A
L
G
H
[S,C,G]
I
D
K
N
• Node C receives RREQ from G and H, but does not forward
it again, because node C has already forwarded RREQ once
Computer Science Department Seminar, Fall 2012
Source: Prof. Nitin Vaidya in UIUC
Dynamic Source Routing:
Route Discovery (cont.)
Y
Z
S
E
[S,E,F,J]
F
B
C
M
J
A
L
G
H
D
K
I
[S,C,G,K]
N
• Nodes J and K both broadcast RREQ to node D
• Since nodes J and K are hidden from each other, their
transmissions may collide
Computer Science Department Seminar, Fall 2012
Source: Prof. Nitin Vaidya in UIUC
Dynamic Source Routing:
Route Discovery (cont.)
Y
Z
S
E
[S,E,F,J,M]
F
B
C
M
J
A
L
G
H
D
K
I
N
• Node D does not forward RREQ, because node D
is the intended target of the route discovery
Computer Science Department Seminar, Fall 2012
Source: Prof. Nitin Vaidya in UIUC
Dynamic Source Routing:
Route Reply
Y
Z
S
RREP [S,E,F,J,D]
E
F
B
C
M
J
A
L
G
H
K
I
D
N
Represents RREP control message
Computer Science Department Seminar, Fall 2012
Source: Prof. Nitin Vaidya in UIUC
Dynamic Source Routing:
Data Delivery in DSR
Y
DATA [S,E,F,J,D]
S
Z
E
F
B
C
M
J
A
L
G
H
D
K
I
N
Packet header size grows with route length
Computer Science Department Seminar, Fall 2012
Source: Prof. Nitin Vaidya in UIUC
Dynamic Source Routing:
Use of Route Caching
[S,E,F,J,D]
[E,F,J,D]
S
[F,J,D],[F,E,S]
E
F
B
[J,F,E,S]
C
[C,S]
A
M
J
L
G
H
[G,C,S]
D
K
I
N
Z
[P,Q,R] Represents cached route at a node
(DSR maintains the cached routes in a tree format)
Computer Science Department Seminar, Fall 2012
Source: Prof. Nitin Vaidya in UIUC
Use of Route Caching:
Can Speed up Route Discovery
[S,E,F,J,D]
[E,F,J,D]
S
[F,J,D],[F,E,S]
E
F
B
C
[C,S]
A
[J,F,E,S]
[G,C,S]
M
J
L
G
H
[K,G,C,S]
I
D
K
RREP
N
RREQ
Z
When node Z sends a route request
for node C, node K sends back a route
reply [Z,K,G,C] to node Z using a locally
cached route
Computer Science Department Seminar, Fall 2012
Source: Prof. Nitin Vaidya in UIUC
Use of Route Caching:
Can Reduce Propagation of Route
Requests
[S,E,F,J,D]
Y
[E,F,J,D]
S
[F,J,D],[F,E,S]
E
F
B
C
[C,S]
A
[J,F,E,S]
[G,C,S]
M
J
L
G
H
I
[K,G,C,S]
D
K
RREP
N
RREQ
Z
Assume that there is no link between D and Z.
Route Reply (RREP) from node K limits flooding of RREQ.
In general, the reduction may be less dramatic.
Computer Science Department Seminar, Fall 2012
Source: Prof. Nitin Vaidya in UIUC
Dynamic Source Routing:
Route Error
Y
RERR [J-D]
S
Z
E
F
B
C
M
J
A
L
G
H
K
D
I
N
J sends a route error to S along route J-F-E-S when its attempt to forward the
data packet S (with route SEFJD) on J-D fails
Nodes hearing RERR update their route cache to remove link J-D
Computer Science Department Seminar, Fall 2012
Source: Prof. Nitin Vaidya in UIUC
IEEE 802.11:
Two Power Modes
Active mode (AM)
Power saving mode (PS)
A node periodically wakes up during the packet advertisement period (ATIM
window) to see if it has data to receive.
When a node receives an advertised packet (ATIM message) that is not destined to
itself,
It switches to a low-power state during the data transmission and thus, saves
energy.
Beacon Interval
Data transfer
ATIM Window
Computer Science Department Seminar, Fall 2012
IEEE 802.11 PSM:
In One-hop Ad-hoc Networks
For a unicast msg to R1
(needs to be acked)
S1
ATIM
SIFS
R1
S2
For a broadcast msg
(needs no ack)
Contention period
Mandated by CSMA
ACK
DIFS
All five nodes
remain awaken
ATIM
R2
R3
ATIM window (e.g. 50 msec)
Actual data transfers
Beacon interval (e.g. 250 msec)
One unicast and one broadcast message:
All five nodes remain awaken during entire beacon interval.
Computer Science Department Seminar, Fall 2012
IEEE 802.11 PSM:
In One-hop Ad-hoc Networks (cont.)
For a unicast msg
(needs to be acked)
S1
ATIM
SIFS
R1
S2
Contention period
Mandated by CSMA
ACK
DIFS
Four nodes
remain awaken
ATIM
SIFS
R2
R3
ACK
R3 sleep
ATIM window (e.g. 50 msec)
Actual data transfers
Beacon interval (e.g. 250 msec)
Two unicast messages:
All nodes except R3 should remain awaken during entire beacon interval.
Computer Science Department Seminar, Fall 2012
IEEE 802.11 PSM:
In Multi-hop Ad-hoc Networks
802.11 with overhearing
802.11 without overhearing
Multihop routing algorithms complicate the situation (e.g., DSR).
DSR improves the routing efficiency via overhearing.
Because nodes need to eavesdrop other communications
to gather route information.
DSR with the IEEE 802.11 PSM.
With overhearing “enforced”.
Nodes should not sleep, but receive all the routing and
data packets transmitted in their vicinity.
Routing performance is O.K., but energy consumption
is large.
Without overhearing
Network performance degrades significantly.
Computer Science Department Seminar, Fall 2012
DSR Protocol:
Overhearing Perspective
D
S
Route Request Packet (RREQ)
Route Reply Packet (RREP)
Route discovery & maintenance.
Data transmission in wireless networks is broadcast in nature.
Intermediate relaying nodes & other nearby nodes also learn
the path to the destination via overhearing. But it incurs high
energy cost.
Computer Science Department Seminar, Fall 2012
DSR Protocol:
Redundant Overhearing
D
S
DATA
Sending multiple data packets over the same path
Nearby nodes overhear redundant path information and
thus, waste more energy
Computer Science Department Seminar, Fall 2012
DSR Protocol:
Stale Route Problem
D
broken link !!
S
Route Error Packet (RERR)
Stale route problem in DSR.
Nodes in DSR aggressively collect route information but RERR
propagates negative information to a limited range, causing a
serious stale route problem.
Overhearing aggravates the problem.
Computer Science Department Seminar, Fall 2012
DSR Protocol:
Load Unbalance Problem
S1
overloaded !!
A
B
S2
overloaded !!
D
S
Route Request Packet (RREQ)
Route Reply Packet (RREP)
DATA
Load unbalance problem in DSR.
Nodes play an role as a router to forward packets.
An overloaded node becomes more overloaded.
Overhearing aggravates the problem.
Computer Science Department Seminar, Fall 2012
RandomCast:
Randomized Communication
Mechanism
A message overhearing mechanism: RandomCast
Every node operates in PS mode.
Sender: A sender can specify the desired level of overhearing when it advertises a
packet.
No overhearing
Unconditional overhearing
Randomized overhearing
Receiver: Upon receiving a packet advertisement during an ATIM window, a node
makes its decision whether or not to overhear based on the specified overhearing
levels.
Computer Science Department Seminar, Fall 2012
RandomCast:
Randomized Communication
Mechanism (cont.)
D
S
(i) No overhearing
C
S
D
S
A
B
(ii) Unconditional overhearing
D
In the randomized overhearing:
Some of the neighbors overhear,
but others do not.
These nodes switch to the low-power
state during the transmission period.
(iii) Randomized overhearing
Computer Science Department Seminar, Fall 2012
RandomCast:
Randomized Communication
Mechanism (cont.)
Key idea of RandomCast:
Temporal locality:
Overheard route information will probably be overheard again in the near
future.
Spatial locality:
Even though a node misses particular route information, it is highly probable
that one of its neighbours overhears.
Neighbour nodes can offer the information when the node asks for it.
Computer Science Department Seminar, Fall 2012
RandomCast:
Design and Implementation Issues
When a node has a unicast packet to send,
Q1:Which overhearing method to choose?
Q2: How to specify its decision?
When a node receives an ATIM frame for a unicast packet that is not destined to it but
requires randomized overhearing,
Q3: How to determine whether to overhear or not?
Computer Science Department Seminar, Fall 2012
The RandomCast Issues (Q1):
Which Overhearing Method to Use?
DSR employs three control packets:
RREQ (broadcast), RREP (unicast), and RERR (unicast)
In addition, DATA (unicast)
We use the overhearing mechanism for these unicast packets.
Randomized overhearing for RREP/DATA packets
Unconditional overhearing for RERR packet
Can a broadcast packet, RREQ, be RandomCasted?
e.g. In dense networks, it would avoid redundant rebroadcasts of the same packet.
However, the overhearing decision must be made conservatively to make sure that
the packet is propagated correctly until it reaches the final destination.
Computer Science Department Seminar, Fall 2012
The RandomCast Issues (Q2):
How to Specify it? - ATIM Frame
Format of an ATIM frame (length in octets)
FC
DI
2
2
DA
SA
6
6
BSSID
6
SC
Frame body
2
0 (null)
FCS
4
DI: Duration/Connection ID
DA, SA, BSSID: Addresses of destination, source, and IBSS
SC: Sequence control
Frame body: Null for ATIM frame
FCS: Frame check sequence
FC: Frame control (length in bits)
Protocol
version
Type
Subtype
To
DS
2
2
4
1
From More
Retry
DS
Frag
1
1
1
Pwr
Mgt
1
More
WEP Order
Data
1
1
1
Type: 00 for management frame such as ATIM frame
Subtype: 1001 for ATIM frame (No overhearing) Original ATIM frame subtype.
1111 for ATIM frame (Unconditional overhearing)
1101 for ATIM frame (Randomized overhearing)
Computer Science Department Seminar, Fall 2012
The RandomCast Issues (Q3):
How to Determine it?
Balanced energy consumption
Low energy consumption per node
Computer Science Department Seminar, Fall 2012
When a node receives an ATIM frame for a unicast packet,
Check destination address (DA) and subtype ID.
The node remains awaken if the node,
is the intended destination
is not the destination, but the sender wants
unconditional overhearing (ID = 11112)
is not the destination, but the sender wants
randomized overhearing (ID = 11012) and the node
decides to overhear
For this, each node maintains a probability (PR)
Simply use the number of neighbors (PR = 1 /
number of neighbors).
Can be extended to consider mobility, and
remaining battery energy
Any Questions?
Computer Science Department Seminar, Fall 2012