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ODMRP-ASYM(On Demand Multicast Routing Protocol) For Linux Implementation

ODMRP-ASYM(On Demand Multicast Routing Protocol) For Linux Implementation. CS218, Fall 2003, Professor Gerla Eric Bostrom, Jason Lin Tutor: Joon-Sang Park University of California, Los Angeles. Asymmetric Link Problem in On-demand routing. Asymmetric link

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ODMRP-ASYM(On Demand Multicast Routing Protocol) For Linux Implementation

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  1. ODMRP-ASYM(On Demand Multicast Routing Protocol) For Linux Implementation CS218, Fall 2003, Professor Gerla Eric Bostrom, Jason Lin Tutor: Joon-Sang Park University of California, Los Angeles

  2. Asymmetric Link Problem in On-demand routing • Asymmetric link • link with different characteristics in the two directions • link that connects A to B, but not B to A • Sources of asymmetric Links • External interference • Directional antennas • Power control • Asymmetric link problem in on-demand routing • Reverse Path technique does not work! • Two ways to solve the problem • Eliminate or unitize

  3. Asymmetric Links: To eliminate or utilize? • Problem with eliminating asymmetric links: • Network partition! • Asymmetric links’ impact on network topology is not negligible • Our challenge: Exploit asymmetric links!

  4. Forwarding Group FG FG FG FG FG ODMRP: Forwarding Group • Forwarding Group: All the nodes inside the “bubble” forward the M-cast packets via “restricted” flooding • Multicast Tree replaced by Multicast “Mesh” Topology • Flooding redundancy helps overcome displacements and fading • FG nodes selected by tracing shortest paths between M-cast members

  5. ODMRP: Route construction • Similar to other on-demand routing protocols • Consists of a query and a reply phase • A source periodically transmits Join Query packets when it has data to send • Join Query packets can carry data payload to eliminate route acquisition latency • Intermediate nodes forward the packet and set up path back to the source (backward learning) • The destination sends a Join Reply in response to a Join Query

  6. S Asymmetric links ODMRP-ASYM: Overview • ODMRP-ASYM: ODMRP with ASYMmetric link support • Observation: A loop exists when there are two non-identical asymmetric paths between a pair of nodes. • Our strategy: Detect the loop and mark it! Path from S to D A B Loop! E C D Path from D to S

  7. S ODMRP with asymmetric links • Source S floods Join Query toward destination D • Reserve path for relaying Join Reply from D to S is blocked at B due to link asymmetry Join Query A B E C D Join Reply

  8. S ODMRP-ASYM: Loop Detection • On detecting asymmetric link, node B initiates Loop Detect Packet (LDP) flooding • A LDP goes around a loop while collecting node IDs in the loop and returns to B LDP LDP A B CEA E C D

  9. S ODMRP-ASYM: Loop Marking • Once found a loop, B circulates Loop Mark Packet (LMP) to set forwarding group flag on (on node A) • The node closest to the source in the loop (node A) resumes relaying Join Reply to the source • Route Constructed! LMP CEA A B Join Reply E C D

  10. ODMRP-ASYM:Detecting asymmetric links • In ODMRP, every Join Reply is to be ACKed as the reliable delivery of Join Queryis critical for establishing forwarding path. • If Join Reply is not ACKed, it is retransmitted at most two times. • A link is considered to be asymmetric and initiate the loop detection if a Join Reply is not ACKed even for the second retransmission.

  11. ODMRP-ASYM: Linux Implementation • Existing Code for ODMRP in Linux • Written by many different people • Not the entire protocol was implemented to specification • Defined our packet types and added handler code • Hardest part: set up and configure the testbed to run our code

  12. Existing Code • Written by a number of different people over a larger period of time. • Poor commenting • Not fully compliant to specification • Acks and timeouts / some hacks • Large project with many files

  13. Loop Discovery Packet Definition

  14. Our Implementation • Acks and Timeouts still yet to be done • Should have been done in ODMRP • We used a single ack timeout with passive ack • Loops limited to internal nodes • ODMRP actually 2 programs, sender receiver and routing nodes. We only modified the routing nodes protocol • Easily extendible to the end nodes • Implementation supports only 1 loop currently • Loop Marking Packet in progress

  15. S Asymmetric links Testbed • Consists of 5 dell Lattitude laptops with 802.11b Lucent wireless pcmcia cards installed. • Asymmetric Links are made using iptables packet filtering tool Path from S to D A B Loop! C D Path from D toS

  16. Conclusion • ODMRP-ASYM: extending ODMRP to asymmetric links • Implementation on Linux is near completion • We are having some problems with the testbed configurations, acking and timeouts are not fully compliant to specification

  17. Papers • Lee, S.-J., Su, W., Gerla, M.: On- Demand Multicast Routing Protocol in Multihop Wireless Mobile Networks . ACM/Kluwer Mobile Networks and Applications, 2000. • Implementation of On-Demand Multicast Routing Protocol (ODMRP) in Linux. Dept. of Computer Science, UCLA • M. Gerla, Y. Lee, J. Park, and Y. Yi. ODMRP (On Demand Multicast Routing Protocol) on a Topology with Asymmetric Links. Computer Science Dept. UCLA

  18. Questions

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