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Ad Hoc Wireless Routing

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

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Ad Hoc Wireless Routing

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

  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. 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

  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 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

  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 • 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 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

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

  19. PerformanceConvergence • 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. PerformanceRouting 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. Designed as an all purpose simulator No known wireless support Uses jacl as an interface Full support for application layer data exchange 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

  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

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