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

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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

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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

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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!

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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

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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

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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!
C
E
D
Path from D to S
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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
D
C
E
Join Reply
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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
D
C
E
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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
D
C
E
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ODMRP-ASYMDetecting asymmetric links

• In ODMRP, every Join Reply is to be ACKed as the
  reliable delivery of Join Query is 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.

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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

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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

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Loop Discovery Packet Definition
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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

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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
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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

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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

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Questions