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Aug2Presentation-routingProtocols-take2ppt - Ad Hoc Wireless Routing

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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
   –   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
•   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   • Designed as an all
  network simulator          purpose simulator
• Built in wireless        • No known wireless
  medium support             support
• Uses octcl as an
  interface                • Uses jacl as an interface
• Does not handle          • Full support for
  application layer data     application layer data
  well                       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

				
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posted:5/24/2010
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