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Fast TCP Doesn’t Matter to ISPs (What Am I Missing?)

Fast TCP Doesn’t Matter to ISPs (What Am I Missing?). Albert Greenberg Microsoft. Traffic and Cost. Consumer Broadband >> Business Consumer broadband growth trends are stable Individual consumer broadband flows have little impact on ISP backbones

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Fast TCP Doesn’t Matter to ISPs (What Am I Missing?)

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  1. Fast TCP Doesn’t Matter to ISPs(What Am I Missing?) Albert Greenberg Microsoft

  2. Traffic and Cost • Consumer Broadband >> Business • Consumer broadband growth trends are stable • Individual consumer broadband flows have little impact on ISP backbones • Transmission rates per broadband subscriber are tiered and rate limited • High speed access costs are high • TCP is likely not the factor stopping a Disney from last minute distribution of content to theatres world wide

  3. Fast TCP A Win for ISPs? • What if I’m wrong? • Biggest deal = file transfer size • Downloading (stored content) >> Streaming on the Internet • Fast TCP might increase consumer bandwidth demand • Economic wins • Bandwidth is the killer app, so this brings more revenue for ISPs • Fast, robust download protocols have potential to help video-on-demand services in IPTV framework • What would the impact be on network engineering?

  4. Backbone • Sources of router stress • PPS: high rates of little packets (e.g., VoIP), yet Fast TCP won’t promote this • Protocols: stresses CPU, yet this is in the control plane not the data plane • Congestion: yet backbone physical pipes >> individual flow • Caveat: stat mux trouble could arise if using a set of parallel links for higher capacity • Core link load is low under normal conditions • Backbones dimensioned to handle rare failure conditions • Tremendous stat mux gains on backbones – 40Gbps links rolling in now • A 1Gbps flow is still 1/40th of this Backbone Backbone Backbone Could be this: Traffic sea level (after high speed TCP) Not this: Traffic sea level (after high speed TCP) Traffic sea level

  5. Access • Access is where the cost is, and where the potential for problems is • Few 100 broadband subs per 1st aggregation router • Few QoS mechanisms deployed between the first IP aggregation router and broadband subscriber router • Higher speed access attracts subs who are early-adopters/power users, and who increase overall burstiness • E.g., Kensuke Fukada, Kenjiro Cho, Hiroshi Esaki, The Impact Of Residential Broadband Traffic On Japanese ISP Backbones, ACM SIGCOMM Computer Communication Review, Vol. 35, Issue 1, 2005, pp. 15-22. • Yet TCP dynamics are constrained by the access links • Access is rate limited, per sub • Fast TCP still backs off • QoS mechanisms in the last mile are available (to date generally not needed) • Capacity planning practice, which is largely empirical, can be adapted to accommodate increased burstiness; • E.g., Matthew Roughan, Charles R. Kalmanek, Pragmatic Modeling of Broadband Access Traffic, Computer Communications, Volume/Number: 26(8), May, 2003, pp.804-816.

  6. Takeaways • Impact on Internet health • Don’t see potential downside • Impact on Internet economics • See potential upside • Impact on network engineering? • Access >> Backbone • Attendant increase in sluggishness in TCP feedback loop (more bytes shipped per RTT) risks potential for: • TCP synchronization and oscillation • QoS impact (jitter, loss) on legacy TCP flows • QoS impact of jumbo frames (if fast TCP becomes common, jumbos may as well)

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