Jabbour, Psota, Radul 6.829 Final Project

A Probabilistic Routing Protocol for Mobile Ad Hoc

Networks

Abdallah Jabbour • James Psota • Alexey Radul

{ajabbour, psota, axch}@mit.edu

Jabbour, Psota, Radul 6.829 Final Project 2/25

Routing in Ad Hoc Networks• Most routing protocols…

– Use fixed route to send all packets from a given source to a given destination• Send along path with minimum hop count

– Use two main types of packets• Data packets• Control (routing) packets

• Can we do better?

Jabbour, Psota, Radul 6.829 Final Project 3/25

Outline• Related Routing Protocols

– DSDV, DSR, AODV– Probabilistic routing protocols

• Shortcomings of related protocols• Protocol description• Simulation environment • Measures of evaluation• Simulation results• Conclusions and future work

Jabbour, Psota, Radul 6.829 Final Project 4/25

Related Routing Protocols• Destination-Sequenced Distance Vector

(DSDV)– Hop-by-hop distance vector protocol– Routes tagged with sequence numbers– Proactive

• Dynamic Source Routing (DSR)– On-demand source routing– Floods route requests– Maintains routes by link breakage notification

• Ad Hoc On-Demand Distance Vector (AODV)– Borrows sequence numbers from DSDV and the

Route Discovery mechanism from DSR– Uses RREQ, RREP, RREP ACK, RERR and HELLO

packets

Jabbour, Psota, Radul 6.829 Final Project 5/25

Probabilistic Routing Protocols

• Routing table entries have probability values corresponding to each destination-neighbor pair

• Control packets (“ants”) sent randomly• Data forwarded deterministically along

path with best metric (number of hops)• Examples

– Ant-Based Control (ABC)– AntNet– Ant-Colony-Based Routing Algorithm (ARA)

Jabbour, Psota, Radul 6.829 Final Project 6/25

Drawbacks and Limitations of Above Protocols

• Routing packets hinder performance– Decrease available bandwidth– Increase transmission latency

• High recovery latency due to static routes– DSDV, DSR, AODV

• Probabilistic protocols incorrectly assume symmetric traffic

• Above protocols use shortest hop routes– Tend to pick routes with less capacity than

optimal ones– Tend to use marginal links

Jabbour, Psota, Radul 6.829 Final Project 7/25

Questions That Need Answers• Is it possible to minimize routing packets?

– Especially those interfering with data traffic• How can nodes cooperate with little or no

control traffic?• Can nodes make forwarding decisions

based on a better measure of network state?

• How can nodes better cope with link outages?

• Which is better: random routing or deterministic routing?

Jabbour, Psota, Radul 6.829 Final Project 8/25

Our Answers…

Jabbour, Psota, Radul 6.829 Final Project 9/25

Protocol Overview• Minimize control packets by prepending

protocol-level headers onto all data packets– Both when originating and forwarding a packet

• Nodes cooperate by promiscuously listening to all traffic, using protocol headers to update their state

• Routing decisions based on link loss ratios– ETX used instead of minimum hop count

• Probabilistic routing modularized– Choice of metric – Choice of metric-to-probability mapping– Choice of routing strategy (random or

deterministic)

Jabbour, Psota, Radul 6.829 Final Project 10/25

Node State• Nodes maintain the following state

– Dynamically-updated set of neighbors– Loss ratios to and from each neighbor– Routing state

• Metric values for each destination and each destination-neighbor pair

• Probability of forwarding to a certain neighbor in order to reach a desired destination

– Requests for information about destinations that this node must make and those that it must answer

Jabbour, Psota, Radul 6.829 Final Project 11/25

Protocol Header Contents• Each originated or forwarded packet contains

the following protocol-level header:

Jabbour, Psota, Radul 6.829 Final Project 12/25

State Update• Nodes update state

– Upon sending– Upon receiving– Periodically

• Refresh stale state and, if needed, alert neighbors that you’re still alive

• Probability distribution updates– Probability distribution and metric values

updated along with other node state– Values evolve in response to changes in link

quality and to nodes entering and leaving the system

Jabbour, Psota, Radul 6.829 Final Project 13/25

p3 = 0.5

Probabilistic Routing• Nodes forward probabilistically to neighbor ni with probability pi

• Update forwarding probability upon link breakage (nodes see infinite loss ratio on link)

ddest n1 n2 n3

d 0.10.3

0.40.0

0.50.7

n1

n3

n2

p1 = 0.3

p3 = 0.7

p1 = 0.4s x x xxlink breaks!

routing tablep1 = 0.1

• Route is not fixed, so packets can still reach destination immediately upon link breakage

Jabbour, Psota, Radul 6.829 Final Project 14/25

Node Joins with HELLO packets

n4

n1

n3

n2

Jabbour, Psota, Radul 6.829 Final Project 15/25

dest n4

n4 1.0

dest n1 n3 n4

n4 0.05 0.15 0.8

dest n2 n3

n4 0.5 0.5

dest n1 n2 n4

n4 0.05 0.2 0.75

Protocol in Steady State

n4

n1

n3

n2

Jabbour, Psota, Radul 6.829 Final Project 16/25

Probabilistic Routing Strategies• Random: node forwards

probabilistically to neighbor ni with probability pi

• Deterministic: node forwards ALL data packets along path with highest pi

• Our flexible infrastructure allows simulation of both

• No one else has compared random and deterministic routing

Jabbour, Psota, Radul 6.829 Final Project 17/25

Simulation Environment• ns-2 with Monarch wireless and mobility

extensions• Compare the new protocol to DSDV, DSR and

AODV• 50 mobile nodes in a 1500m x 300m area• Random waypoint movement model• 900s simulation time• Use UDP (CBR) sources

– TCP’s inconvenience: conforming load• We investigate different…

– Pause times– Node speeds– Connection patterns

Jabbour, Psota, Radul 6.829 Final Project 18/25

Measures of Evaluation• Packet delivery ratio / goodput• Packet delivery latency• Routing packet overhead• Total bytes of overhead• Path length optimality• Route acquisition latency

Jabbour, Psota, Radul 6.829 Final Project 19/25

Simulation Results• We have built a complete simulation

infrastructure, and simulated three protocols for comparison with ours– AODV, DSR, DSDV

• We have not finished ironing out the bugs in our protocol implementation– Our protocol simulates for short time…– We loosely expect to finish and simulate

by Monday

Jabbour, Psota, Radul 6.829 Final Project 20/25

Delivery Ratio vs. Pause Time

10 connections

Jabbour, Psota, Radul 6.829 Final Project 21/25

Routing Packets Sent vs. Pause Time

10 connections

Jabbour, Psota, Radul 6.829 Final Project 22/25

Routing Packets Sent vs. Number of Connections

averaged over all pause times

Jabbour, Psota, Radul 6.829 Final Project 23/25

Route Acquisition Latency vs. Pause Time

10 connections

Jabbour, Psota, Radul 6.829 Final Project 24/25

Route Acquisition Latency vs. Number Connections

averaged over all pause times

Jabbour, Psota, Radul 6.829 Final Project 25/25

Conclusions and Future Work• Our routing protocol is feasible (and

even nearly done)• We believe randomized routing is

competitive with deterministic routing

• We will continue our quest to implement and simulate the protocol

Jabbour, Psota, Radul 6.829 Final Project

A Probabilistic Routing Protocol for Mobile Ad Hoc

Networks

Abdallah Jabbour • James Psota • Alexey Radul

{ajabbour, psota, axch}@mit.edu

Jabbour, Psota, Radul 6.829 Final Project 27/25

Jabbour, Psota, Radul 6.829 Final Project 28/25

dest n1 n3

n4 0.5 0.5

Protocol in Steady State

n4

n1

n3

n2

dest n1 n2 n4

n4 0.05 0.2 0.75

dest n4

n4 1.0

dest n1 n2 n4

n4 0.05 0.15 0.8