1. A Probabilistic Routing Protocol for Mobile Ad Hoc Networks
Abdallah Jabbour • James Psota • Alexey Radul
{ajabbour, psota,
Jabbour, Psota, Radul
6.829 Final Project

2. Outline Related Routing Protocols Shortcomings of related 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

3. 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

4. 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

5. 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

6. Questions that need answers
Is it possible to minimize routing packets?
- Especially those interfering with traffic
How can nodes cooperate with little or no control traffic?
Can one make forwarding decisions based on a better measure of network state?
How can one better cope with link outages?
Which is better: random routing or deterministic routing?
our goals are to increase performance by…
Jabbour, Psota, Radul
6.829 Final Project

7. The answers!
Control packets are minimized 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 are based on link loss ratios
ETX used instead of minimum hop count
Probabilistic routing is made modular
- choice of metric
- choice of metric-to-probability mapping
- choice of routing strategy (random or deterministic)
Jabbour, Psota, Radul
6.829 Final Project

8. Protocol Header Contents
Each originated or forwarded packet contains the following protocol-level header:
Jabbour, Psota, Radul
6.829 Final Project

9. 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 and fulfillments thereof information about destinations
Jabbour, Psota, Radul
6.829 Final Project

10. State Update Nodes update state Probability distribution updates
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

11. Probabilistic Routing
routing table
p1 = 0.1
dest p1 p2 p3 d
0.1
0.4
0.5 n1 n2 n3 d
0.1
0.4
0.5
dest p1 p2 p3 d
0.1
0.4
0.5 s n2 d
p1 = 0.4
p3 = 0.5 n3
Route is not fixed, so packets can still reach destination immediately upon link breakage
Jabbour, Psota, Radul
6.829 Final Project

12. Probabilistic Routing
routing table
p1 = 0.3 n1 n2 n3 d
0.1
0.3
0.4
0.0
0.5
0.7 x s n2 d
p1 = 0.4 x x x
link breaks!
p3 = 0.7 n3
Update forwarding probability upon link breakage
Jabbour, Psota, Radul
6.829 Final Project

13. 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 allowed simulation of both
First to compare random to deterministic routing
Jabbour, Psota, Radul
6.829 Final Project

14. Simulation Environment
ns-2 with Monarch mobility extensions
Compared the new protocol to DSDV, DSR and AODV
50 mobile nodes in a 1500m x 300m area
Random waypoint movement model
900s simulation time
Used UDP(CBR) sources
TCP’s inconvenience: conforming load
We investigated different…
Pause times
Node speeds
Connection patterns
Packet sizes
Jabbour, Psota, Radul
6.829 Final Project

15. 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

16. Simulation Results
Jabbour, Psota, Radul
6.829 Final Project

17. Conclusions and Future Work
Jabbour, Psota, Radul
6.829 Final Project