Network Architecture (R02) IP Multipath

1
Network Architecture (R02)IP Multipath Path
SelectionCC

• Jon Crowcroft,
• http//www.cl.cam.ac.uk/jac22
• http//www.cl.cam.ac.uk/teaching/1213/R02/

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Multipath

• Could be useful load balancing
• When Traffic Matrix deviates from expected
• How to assign rates to alternate paths
• IP or Application Layer
• CDN, especially P2P (Torrent or Storm) already
  effectively multipath at App
• Current IP routing mainly only corner cases

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Multipath IP Routing

• Simplest case is equal-cost multipath
• Can be seen as simple bonding technique
• Combines with multihoming/resilience
• For any metric, in an interdomain protocol, can
  do k-shortest paths
• Problem 1 is path metric bottleneck link
  capacity and round trip time are both important
• Problem 2 is BGP

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This paper concentrates on rate/path problem

• Sidesteps the question of route computation for
  now.
• Starts off from the BitTorrent example
• Looks at a MPTCP/MPIP model in contrast
• Builds an convex optimisation style framework (as
  per previous Frank Kelly et al) F. P. Kelly and
  T. Voice. Stability of end-to-end algorithms for
  joint routing and rate control. ACM SIGCOMM
  Computer Communication Review, 35(2)512,
  2005.see
• So max utility subject to path constraints

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BitTorrent behaviour

• Currently, Swarms choose a number of neighbours
  to fetch blocks of a file from, monitor the TCP
  rate achieved, drop the slowest and pick a new
  neighbour at random
• SeeM. Mitzenmacher, A. Richa, and R.
  Sitaraman.The power of two random choices A
  survey of the techniques and results. In P.
  Pardalos, S. Rajasekaran, , and J. Rolim,
  editors, Handbook of Randomized Computing, pages
  255312. 2001

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IP versus Torrent models
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Load balancingc.f. Valiant/data centers
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Two different rate assignments

• TCP is well known to have a 1/RTT dependence in
  the long term throughput of a given (unipath)
  flow.
• So do they allow for this or not in the multipath
  framework? Choice
• Coordinate rates, dont factor in rtt
• Uncoordinated rates, factor in rtt
• See also TCP Friendly rate controlled transport
  protocol work by Handley et al

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Capacity regions
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Note on this version of paper

• This is the shorter, CACM version theres a MSR
  tech report and an Infocom version.
• In Cisco manuals, you can do Multipath BGP, but
  be aware this is mainly just for multihomeing an
  ISP on another (same motive as OSPF-ECM).
• The general problem is very hard, see
• Loop-freeness in multipath BGP through
  propagating the longest path, Van Beijnum,
  Iljitsch (2008) Loop-freeness in multipath BGP
  through propagating the longest path. Masters
  thesis, University Carlos III of Madrid, Madrid,
  Spain

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Other missing architectural pieces

• How to indicate at a sender a packet from a
  coordinated flow belongs on a particular
  sub-path, in general (if the end system isnt
  multihomed)?
• How to tell at a receiver which subpath a packet
  arrived over?
• What about short lived flows?

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Obvious deployment scenarios

• Smart phone with wifi 3G
• Data center networks

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Reference/credit for diagrams

• _at_articleKey2011PSM1866739.1866762, author
  Key, Peter and Massouli\'e, Laurent and
  Towsley, Don, title Path selection and
  multipath congestion control, journal Commun.
  ACM, issue_date January 2011, volume 54,
  number 1, month jan, year 2011, issn
  0001-0782, pages 109--116, numpages 8,
  url http//doi.acm.org/10.1145/1866739.1866762
  , doi 10.1145/1866739.1866762, acmid
  1866762, publisher ACM, address New
  York, NY, USA,