Re: [quicwg/base-drafts] PMTUD (#64)

[martinduke <[e-mail]>]

> What's the benefit of relying on ICMP responses vs. doing MTU discovery at the QUIC layer ("packetization layer PMTUD" RFC 4821)?

Thanks for the reference; I had not seen that RFC.

Though ICMP messages have their disadvantages, there are four advantages over a loss-based scheme.
1) Immediate reporting of the actual PMTU, rather than a search process that is likely to undershoot the actual PMTU.
2) Precision only comes with many probes -> many losses that must be retransmitted.
3) Loss is an overloaded signal, meaning congestion or RF problems in different contexts. Therefore there is the possibility of error in interpreting a loss.
4) In many cases, detecting a loss will take much longer than an ICMP message sent from an in-path router.

Meanwhile, a MTU underestimate has not only packet overhead considerations, but also directly impacts the gross throughput possible via congestion control (which operates in multiples of the MSS).

-- 
You are receiving this because you are subscribed to this thread.
Reply to this email directly or view it on GitHub:
https://github.com/quicwg/base-drafts/issues/64#issuecomment-266607124