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. http://www.ietf.org/internet-drafts/corson-draft-ietf-manet- issues-01.txt

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

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

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

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 p234-244, 1994. 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

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

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)

Ad Hoc On-Demand Distance Vector (AODV)2 C. Perkins. “Ad Hoc On-Demand Distance Vector (AODV) Routing” IETF Internet Draft. http://www.ietf.org/internet-drafts/draft-ietf- 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

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

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.)

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 1997. http://www.ics.uci.edu/atm/adhoc/paper-collection/corson-adaptive- 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

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

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

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

Dynamic Source Routing(DSR) David B. Johnson, Davis A. Maltz, “The Dynamic Source Routing Protocol for Mobile Ad Hoc Networks” October 1999. IETF Internet Draft. http://www.ietf.org/internet-drafts/draft-ietf-manet-dsr-10.txt. 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

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

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

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 802.11 Medium Access Control (MAC) protocol Distributed Coordination Function (DCF)

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

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

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

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

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

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

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