Network Architecture (R02) IP Multipath – Path Selection&CC Jon Crowcroft,

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

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

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):5{12, 2005.see So max utility subject to path constraints

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 255{

IP versus Torrent models

Load balancing…c.f. Valiant/data centers

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, don’t factor in rtt Uncoordinated rates, factor in rtt See also TCP Friendly rate controlled transport protocol work by Handley et al

Capacity regions

Note on this version of paper This is the shorter, CACM version – there’s 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

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 isn’t multihomed)? How to tell at a receiver which subpath a packet arrived over? What about short lived flows?

Obvious deployment scenarios Smart phone with wifi & 3G Data center networks …

Reference/credit for 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 = { }, pages = { }, numpages = {8}, url = { 2}, doi = { / }, acmid = { }, publisher = {ACM}, address = {New York, NY, USA}, }