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The Internet “Community” has adopted TCP-like
behaviour as a Gold Standard: |
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This talk is about why this may be very
detrimental to future choice |
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We’ll use examples from transport protocol
requirements |
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Other arguments are also possible |
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What is TCP like behaviour exactly? |
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What other requirements might there be on
transport protocols? |
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What impact (if any) does this have on IP
(routers)? |
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Are there other implications? |
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Basic rule is that on an end-to-end time scale,
a flow should try to achieve fairness (e.g. Raj Jain’s fairness definition)
with TCP – two approaches are |
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implement AIMD |
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Use TCP equation (1/rtt*sqrt(loss) |
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Has been made “respectable” by Kelly, Maulloo
& Tan |
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Proportional fairness includes link (if 1/RTT ==
link cost) as well as max-min share of pipe over timescale of adaptation… |
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Has a bug: needs user choice of route over short
timescale… |
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Has a missing middle (risk?) |
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Multicast |
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Mobile |
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Link cost varies (CDMA) |
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Striped flows |
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etc |
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Microsoft use a 1.2Gbps link 24*365 |
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Jim Gemmell computes if they multicast each
thing once, and used PGMcc (or RLC) they’d only need a 10kbps link |
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BUT your download would take 1 yearJ |
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Sweet spot is a function of receivers
timescales/needs and the number of receivers |
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Non trivial rate selection |
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Multi-rate is better but not ideal – still
complex |
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Need to consider sender, and network topology
has least implicitly |
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If I move, the link share with other people
varies |
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Why should my rate vary? |
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Why should theirs? |
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What if my path is predictable? |
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CDMA nets share is affected directly but other
users use looks like noise |
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What if I do multi-hop radio net, but can
dynamically choose size of cell/hop? |
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What if I can choose whether to be a router or
not dynamically? |
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Sometimes my access link is fast (e.g. GRID)
1.2Gpbs, but each path on a route is slower |
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What if I Stripe data |
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Much the same as the layered multicast case,
only perhaps a tad easier… |
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Local FIFO+drop or ECN gives a shadow packet (or
bit if virtual buffer) price |
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TCP equation. is proportional fairness |
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Can in principle translate all the previous
problems into a form of this |
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But users may not want to (c.f. audio/video
adapt price, not rate? What about session level price stability
preferences?) |
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Need to consider enforcement – M3I model is to
do this via money and admission (per packet, per flow, per aggregate) –
maybe other permits could be allowed |
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Need to implement hierarchical monitoring |
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Risks need understanding |
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In practice, provisioning enforces capacity
rules in most ISPs (tier 1 core’s over provisioned compared to access ISPs
access links, but access ISPs are 3-1 to7-1) |
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In practice, scheduling & queue management
in the net are pretty chaotic…at the whim of vendor/provider |
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Need to reshape the agenda |
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Hard to do (the IETF is dominated by dogma just
like ISO and ITU were 10-20 years ago) |
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But hey, we are researchers, so just do it! |
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M3I has a metering/edge admission architecture |
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Need to quantify set of costs and distribute
them from within net |
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Need to talk to router people about deploying
smarter ECN like stuff |
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Need a break… |
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Notes
