1. Ad Hoc Wireless Routing
Different from routing in the “wired” world
Desirable properties of a wireless routing protocol
Distributed operation
Loop freedom
Demand-based operation
Security
“Sleep” period operation
Unidirectional link support
Corson M., Macker, J. “Mobile Ad hoc Networking (MANET): Routing Protocol Performance Issues and Evaluation Considerations.” IETF Internet Draft. issues-01.txt

2. Overview of Ad hoc Routing Protocols
Globally precomputed, table based
DSDV – Destination-Sequenced Distance Vector
WRP – Wireless Routing Protocol
GSR – Global State Routing
FSR – Fisheye State Routing
HSR – Hierarchical State Routing
ZHLS – Zone-based Hierarchical Link State Routing Protocol
CGSR – Clusterhead Gateway Switch Routing Protocol

3. Overview of Ad hoc Routing Protocols
On-Demand, source initiated
AODV – Ad Hoc On-demand Distance Vector Routing
DSR – Dynamic Source Routing
TORA – Temporally Ordered Routing Algorithm
CBRP – Cluster Based Routing Protocols
ABR – Associativity Based Routing
SSR – Signal Stability Routing

4. DSDV, DSR, AODV, TORA
These four protocols were chosen for further study for several reasons:
Submitted to MANET for approval
Implemented in ns-2
Multiple performance studies have been done on these protocols

5. Dynamic Destination-Sequenced Distance Vector (DSDV)
C. Perkins and P. Bhagwat. “Highly dynamic Destination-sequenced distance vector routing (DSDV) for mobile computers” ACM SIGCOMM '94 p ,
Each node knows the state and topology of the entire network
Routes are chosen by a metric (least delay, best signal strength, etc..)
Periodically and when triggered transmits the entire routing table to neighbors
Full dumps
Incremental dumps
Avoids loops by using sequence numbers

6. DSDV Recovery When a link loss is detected at node N:
the metric of the route to the destination through the lost link is advertised as infinity (the worst value), and
An incremental update is flooded to the neighbors

7. DSDV Evaluation Loop avoidance
Constant routing overhead versus mobility
Overhead increases as the number of nodes increases
DSDV can no longer find a route reliably when there is high mobility (< 300s pause times)

8. Ad Hoc On-Demand Distance Vector (AODV)2
C. Perkins. “Ad Hoc On-Demand Distance Vector (AODV) Routing” IETF Internet Draft. manet-aodv-10.txt.
Each node only keeps next-hop information
Source broadcasts ROUTE REQUEST packets
Each node that sees the request and forwards it creates a reverse route to the source
If the node knows the route to the destination, it responds with a ROUTE REPLY
All nodes along the reply route create a forward route to the destination

9. AODV Recovery When a link loss is detected at node N
any upstream nodes that have recently sent packets through this node are notified with an UNSOLICITED ROUTE REPLY with an infinite metric for that destination

10. AODV Evaluation
Routing overhead increases as mobility increases, but not as the number of nodes increases
Sends many packets, but they are small
Costs to access the medium (RTS/CTS packets)
Always delivers at least 95% of packets sent in all cases (Broch, et. al.)

11. Temporally Ordered Routing Algorithm (TORA)
V. D. Park and M.S. Corson. “A Highly Adaptive Distributed Routing Algorithm for Mobile Wireless Networks.” Proceedings of INFOCOMM ’97 April routing-infocom97.pdf.
Discovers multiple routes to destination
Separate logical copy of the algorithm for each destination exists on each node
Creates a Directed Acyclic Graph with the destination as the head of the graph
Requires IMEP (Internet MANET Encapsulation Protocol) – guarantees reliable in-order delivery of routing messages

12. TORA (cont)
Each node keeps a reference value and a height for each destination
QUERY packets are sent out until one reaches the destination or a node with a route to the destination
This node sends an update to its neighbors listing its height for that destination

13. TORA Recovery The node, N which discovers the link loss:
Does nothing because other routes still exist, or
If the lost link is the last downstream link of this node:
changes its height to be the local maximum and
transmits update packets to look for new routes

14. TORA Evaluation Congestion feedback loop
Can contain routing loops for short periods of time
High routing overhead
Does not try to find the shortest path
When there are large numbers of sources transmitting simultaneously, TORA cannot find paths
Congestion feedback loop
When there is too much congestion, IMEP loses packets and tells TORA that the link is down
TORA sends out more UPDATE packets to reconfigure
More congestion is created

15. Dynamic Source Routing(DSR)
David B. Johnson, Davis A. Maltz, “The Dynamic Source Routing Protocol for Mobile Ad Hoc Networks” October IETF Internet Draft.
Routes are kept in each packet
Routes to that point in REQUEST packets
Full routes in data packets
Routes are cached at each node to limit flooding of REQUEST packets
Any route that is seen through a node is cached
Source sends out REQUEST packets
Any node which is the destination of a node which has a route to the destination replies with a route reply

16. DSR Recovery A Route ERROR is sent to the Source
All nodes along the path remove that route
Source uses a cached alternate route to destination or sends out request packets for a new route

17. DSR Evaluation
Always delivers at least 95% of all packets sent in all cases (Broch, et. al.)
Routing packets are large because of the source routing

18. Performance
Broch, et al. “A Performance Comparison of Multi-Hop Wireless Ad Hoc Network Routing Protocols” MOBICOM ’98 p85-97, 1998.
Measurements are from simulations with 50 nodes, pause times from 0s (constant motion) to 900s (no motion), transmission rates of 4 packets/s, and speed of nodes at 1m/s and 20 m/s
Load was 10 sources transmitting simultaneously, 20 sources, and 30 sources
Simulated in ns-2 on top of complete implementation of the Medium Access Control (MAC) protocol Distributed Coordination Function (DCF)

19. Performance Convergence
Convergence is the ability of the routing protocol to quickly “stabilize” the routes it knows
DSR & AODV always deliver at least 95% of the packets sent in all cases
TORA fails to converge at less than ~500s pause time for the 30 source experiments, but always converges for 10 and 20 sources.
Congestion feedback loop
DSDV does not converge with a pause time less than ~300s when nodes are moving at 20 m/s

20. Performance Routing Overhead
Broch, et al. “A Performance Comparison of Multi-Hop Wireless Ad Hoc Network Routing Protocols” MOBICOM '98 p85-97, 1998.

21. NS-2, JavaSim Evaluations
Looking for:
Basic network/TCP implementation
Ability to implement an application layer routing protocol (Gnutella)
NS-2 is a popular network simulator
JavaSim was recommended by a group doing similar research
OMNet++ was pushed to the side because of the constant recompilation needed to run simulations

22. NS-2 and JavaSim Similarities
Event driven simulators
tcl like interface
Capable of network simulation
Outputs to NAM and xgraph formats
Can also output to any format that's been programmed into it
Bad documentation
JavaSim: no documentation other than javadoc
ns-2: documentation does not match code

23. Differences ns-2 was designed as a network simulator
Built in wireless medium support
Uses octcl as an interface
Does not handle application layer data well
Designed as an all purpose simulator
No known wireless support
Uses jacl as an interface
Full support for application layer data exchange

24. NS-2 octcl interface is easy to use and set up simulations
Code is confusing written in both C++ and tcl, no standard for what should be written in each
octcl must be installed as a separate program

25. JavaSim Jacl interface is “built-in” to the simulator
Jacl scripts are difficult to understand and not easy to set up simulations
Can use actual Java applications as components