Multipath Routing

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Multipath Routing

• CS 522
• F2003
• Beaux Sharifi

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Agenda

• Description of Multipath Routing
• Necessity of Multipath Routing
• 3 Major Components Necessary for Multipath
  Routing
• Example Multipath Routing Model
• Simulation Results

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What is Multipath Routing?

• Multipath Routing is the spreading of traffic
  from a source node to a destination node over
  multiple paths through the network.
• Figure 1. Multipath Routing Model Diagram.

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Importance of Multipath Routing

• The Internet is a significant part of the Global
  communication infrastructure.
• The use of the Internet is growing at an
  incredible rate
• Jan 1999 43 million hosts
• Jan 2003 171 million hosts (source Internet
  Domain Survey)
• QoS, throughput, and delay are difficult problems
  with current single-path routing architecture.
• From queuing theory, we know that through
  increased sharing, overall utilization of the
  entire network is improved.
• Multipath routing provides much better overall
  network performance by allowing better sharing of
  the available network resources.

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3 Major Components

• A Multipath Calculation algorithm to compute
  multiple paths.
• A Multipath Forwarding algorithm to insure that
  packets travel on their specified paths.
• An End-Host Protocol that effectively uses the
  determined multiple paths.

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Path Algorithms

• Generate paths based on a the desired
  characteristics of the path.
• i.e. Maximized throughput or minimized delay
• Generate Multi-Option paths and/or Multi-Service
  paths.
• Path requirements depend on the end-user
  application.
• i.e. Telnet vs. FTP
• Two characteristics of a quality path
• Path Quantity
• Path Independence

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Path Algorithms (cont.)

• Some path algorithms that dont work
• Shortest K Paths, Link Disjoint Paths, Maximum
  Flow
• Two path algorithms that do work
• Maximize Throughput Capacity Removal
• Minimize Latency Discount Shortest Path
• Both algorithms based on Dijkstras Shortest Path
  algorithm.
• Both algorithms produce shortest paths with
  minimal overlap by incrementally adding cost to
  each of the previously found paths.

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Path Forwarding

• Path Forwarding Problem how to specify a
  packets path and then forward packets along that
  path.
• Each router has potentially multiple routes to a
  destination node.
• The destination address is no longer sufficient.
• A Path Identifier is now required for every
  packet.
• Design Requirements for Path Forwarding
• Minimize Packet Overhead
• Minimize router CPU overhead of forwarding
  packets
• Minimize additional router memory

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End-Host Protocol

• Performance gains are only realized if end-hosts
  use the multiple paths effectively.
• Paths can be used concurrently or one at a time.
• The appropriate use of multiple paths is
  application specific.
• Instant Messenger (multi-service)
• Urgent Message (multi-option)

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Example Multipath Routing Model

• Developed by Johnny Chen of Rice University in
  1999.
• Consists of two different routing algorithms
  based on extensions of the traditional routing
  algorithms
• MPDV (MultiPath Distance Vector)
• MPLS (MultiPath Link State)
• Both routing algorithms seek to optimize
  throughput by using a Capacity Removal based
  algorithm.
• Chen develops efficient path forwarding
  algorithms while minimizing packet and router
  overhead.
• Uses a fixed-length packet path ID to provide
  minimal packet overhead and allow efficient
  indexing into router forwarding tables.

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Example Multipath Routing Model (cont.)

• Contains a new transport layer called MPTCP
  (Multipath TCP).
• MPTCP is based on single-path TCP and provides a
  reliable bit stream service.
• MPTCP operates by opening multiple TCP
  connections on different paths and then
  multiplexing data between them.
• The receiving MPTCP layer collects data from each
  of the connections and then restores the original
  message stream.
• MPTCP provides flow and congestion control.
• MPTCP provides increased network performance
  without any changes to user-applications.

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Simulation Results

• Chen compares both MPDV and MPLS using a
  packet-level network simulator xsim from the
  University of Arizona.
• Simulated network is similar to the Internet
  topology with 100 nodes and 195 links across
  multiple clusters.
• Performance is measured in throughput, latency,
  and message drop-off probability.
• Throughput is measured using MPTCP.
• Latency and drop-off probability is measured
  using multipath ping.

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Throughput Results

• Figure 2. Foreground MPTCP Performance using
  MPDV and MPLS.

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Latency and Message-Drop Results

• Figure 3. Latency and Message Drop Percentages
  with MP-ping and SP-ping.

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Summary

• MPDV and MPLS demonstrate that multipath routing
  provides higher performance than their
  single-path counterparts.
• Performance results are consistent across
  different network topologies and network
  utilization levels.
• The cost incurred by implementing a multipath
  routing algorithm doesnt outweigh the added
  performance benefits.

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References

• Chen, Johnny. New Approaches to Routing for
  Large-Scale Data Networks. Rice University,
  Houston, Texas PhD Thesis, June 1999.
• Nua Internet How Many Online. Nua.com 11 Dec.
  2003 lthttp//www.nua.ie/surveys/how_many_online/gt
• Tanenbaum, Andrew S. Computer Networks, Fourth
  Edition. Upper Saddle River, New Jersey
  Prentice Hall PTR, 2003.

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Questions?