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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
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.
overview of ad hoc routing protocols
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 protocols1
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
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
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
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
Ad Hoc On-Demand Distance Vector (AODV)2
  • C. Perkins. “Ad Hoc On-Demand Distance Vector (AODV) Routing” IETF Internet Draft.
  • 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
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
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
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.
  • 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
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
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
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
dynamic source routing dsr
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.
  • 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
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
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
  • 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
PerformanceRouting 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
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
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
Designed as an all purpose simulator

No known wireless support

Uses jacl as an interface

Full support for application layer data exchange

  • 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
  • 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
  • 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