[Bloat] [Ecn-sane] [iccrg] Fwd: [tcpPrague] Implementation and experimentation of TCP Prague/L4S hackaton at IETF104

Jonathan Morton chromatix99 at gmail.com
Fri Mar 15 15:32:06 EDT 2019

> On 15 Mar, 2019, at 8:36 pm, Mikael Abrahamsson <swmike at swm.pp.se> wrote:
> Having a "lower-than-best-effort" diffserve codepoint might work, because it means worse treatment, not preferential treatment.
> The problem with having DSCP CPs that indicate preferential treatment is typically a ddos magnet.

This is true, and also why I feel that just 2 bits should be sufficient for Diffserv (rather than 6).  They are sufficient to express four different optimisation targets:

0: Maximum Throughput (aka Best Effort)
1: Minimum Cost (aka Least Effort)
2: Minimum Latency (aka Maximum Responsiveness)
3: Minimum Loss (aka Maximum Reliability)

It is legitimate for traffic to request any of these four optimisations, with the explicit tradeoff of *not* necessarily getting optimisation in the other three dimensions.

The old TOS spec erred in specifying 4 non-exclusive bits to express this, in addition to 3 bits for a telegram-office style "priority level" (which was very much ripe for abuse if not strictly admission-controlled).  TOS was rightly considered a mess, but was replaced with Diffserv which was far too loose a spec to be useful in practice.

But that's a separate topic from ECN per se.

 - Jonathan Morton

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