E-ODMRP: Enhanced ODMRP with Motion Adaptive Refresh

Soon Y. Oh, Joon-Sang Park, Mario GerlaComputer Science Dept.

UCLA

2

Multicasting in ad hoc nets Why multicast in ad hoc nets?

Group (1-to-many) communication Wireless “broadcast” medium

ODMRP: On Demand Multicast Routing Protocol One of the most widely used ad hoc

multicast routing protocol Simple yet high-performing

3

Join Query Join Reply Forwarding NodeLinkMulticast Route

On-demand approach: A source initiates JOIN QUERY flooding only when it has data to send The sender periodically floods JOIN QUERY control messages All intermediate nodes set up route to sender (backward pointer) Members send Join Reply messages following backward pointers Routes from sources to receivers build a mesh of nodes called “forwarding group”.

S

R

R

R

R

Forwarding Group

ODMRP: Initialization Phase

F

FF

F

4

Generalize to multiple sources

To make the procedure scalable to large number of sources: stagger “join query” floods aggregate join replies

S

R

R

R

R

S1

S2

Forwarding Group

F

FF

F

5

Source broadcasts data packet to neighbors Forwarding Group nodes forward multicast packets via

“restricted” flooding on the forwarding mesh Soft state

No explicit receiver join/leave messages Forwarding nodes clear state upon timeout

Extremely robust to mobility, fast fading, obstacles, jamming

S

R

R

R

R

S2

Forwarding Group

ODMRP: operation

6

Comparison: Packet Delivery Ratio

8

Problem: Forward Group maintenance

Mesh is very resilient to: Short term disruptions (jamming, fading, obstacles) Medium term (connectivity) disruptions, eg FG node

moving out of field FG maintenance

To overcome connectivity disruptions, need frequent mesh refresh

Short refresh interval (proportional to FG node longevity) needed to keep connectivity in the face of motion

Problem: Short refresh interval leads to high overhead

Refresh rate is a key performance parameter

9

Adaptive route refreshing Route refresh rate is adjusted on-the-fly to

environment, i.e., node mobility Adjustment is based on receivers’ loss reports to

source

Local route recovery Receiver estimates packet interval and calculate

time out eg. Interval * n If time out expires, the disconnected node

proactively grafts onto the FG mesh instead of waiting until next route refresh

Solution: motion adaptive refresh + local route recovery

10

Local Route RecoveryRing search with limited TTL

Disconnected node (say node A) floods RECEIVER JOIN locally, e.g. set packet TTL to 1

On reception of RECEIVER JOIN, a Listener node, a neighbor of any forwarder or receiver nodes, sets itself up as a Temporary Forwarders and start forwarding next several data packets

Node A sends passive ACKs to one of Temporary Forwarders (say node B)

Node B becomes a Forwarder and others clear their status and go back to Listeners

11

Local Route Recovery

Source

Forwarders

Receivers Listeners

Receiver Join

Data flow

A

B

C

D

12

Local Route Recovery

A

B

C

D

Source

Forwarders

Receivers Listeners

Receiver Join

Data flow

13

Local Route Recovery

A

B

C

Source

Forwarders

Receivers Listeners

Receiver Join

Data flow

D

14

Local Route Recovery (Cont.)

If failed Local Recovery, the disconnected node floods entire network with REFRESH REQUEST

On reception of REFRESH REQUEST, sources refresh FG by flooding JOIN QUERY

15

Adaptive Route Refresh Refresh interval varies between min and max

value, e.g. 3 sec and 30 sec On reception of REFRESH REQUEST (RR),

refresh interval is adjusted to: Max > Rfr >Min ( route lifetime/F, 3 sec) Route lifetime is the time difference between

the two events: last JOIN Query arrival and link breakage detection

F is a reduction coefficient, e.g. F=2 If no RR during a refresh interval, linearly and

slowly increase refresh interval

16

Passive ACK and Pruning Intermediate nodes overhear packet

transmission from downstream nodes Data packets serve as passive ACKs If a Forwarder misses several passive ACKs, it

prunes itself from the mesh Passive ACK suppression technique; a leaf

node skips sending a passive ACK if it receives duplicated packets Other node may send a passive ACK A leaf node is changing a upstream forwarder due

to mobility

17

Passive ACK Suppression & Pruning

Forwarders

Receivers

Passive ACK

Data flow

18

Passive ACK Suppression & Pruning

Forwarders

Receivers

Passive ACK

Data flow

19

Passive ACK Suppression & Pruning

Forwarders

Receivers

Passive ACK

Data flow

20

Simulation Results Settings

NS2.1b8 100 nodes on 1200x800m2

Random Way Point mobility model 512 byte/packet Constant bit rate traffic (4 packet/sec) 300 seconds simulation time Scenario 1: Varying mobility

Varying max speed (1 ~ 30m/s) and 0 sec pause time

1 group, 1 source, and 20 receivers

21

Simulation Results (Cont.) Scenario 2: Varying number of receivers

Varying number of receivers (10 ~ 50) 20 m/s max speed and 0 sec pause time

Scenarios 3: Varying data rate Varying data rate 4pkts/sec ~ 30pkts/sec 20 m/s max speed and 0 sec pause time 1 group, 1 source, and 20 receivers

Scenarios 4: Varying number of sources Varying number of sources (1 ~ 6) 20 m/s max speed and 0 sec pause time 1 group and 20 receivers

22

Results in various mobility cases

Packet Delivery Ratio

E-ODMRP maintains PDR degradation within 1% to ODMRP and surpasses ADMR’s PDR

23

Results in various mobility cases

Normalized Packet Overhead

E-ODMRP reduces the normalized overhead by 50% to ODMRP’s

24

Results in various group sizePacket Delivery Ratio

E-ODMRP scales with the number of receivers and shows best PDR with 50 receivers

25

Results in various group sizeNormalized Packet Overhead

E-ODMRP normalized overhead is superior to ODMRP and ADMR

26

Results in various Data RatePacket Delivery Ratio

E-ODMRP outperforms ODMRP and ADMR in high packet sending rate

27

Results in various Data RateNormalized Packet Overhead

E-ODMRP keeps lowest normalized overhead in high packet sending rate

28

Results in various number of Sources

Packet Delivery Ratio

PDR lines decrease by different factors and E-ODMRP surpasses others when there are more than three sources

29

Results in various number of Sources

Normalized Packet Overhead

E-ODMRP overhead is near-flat line, but ADMR’s overhead slope suddenly change

30

Conclusion E-ODMRP : Enhanced ODMRP with

motion adaptive refresh E-ODMRP reduces normalized packet

overhead up to 50% yet keeping similar PDR compared to ODMRP

E-ODMRP surpasses ADMR in any case

E-ODMRP achieves high packet delivery ratio with low overhead