How does QUIC multiplexing differ from that of HTTP/2

Question

How does QUIC & HTTP/3 multiplexing (over UDP) differ from that brought by HTTP/2 (over TCP)?

Lior Cohen · Accepted Answer · 2019-07-05 18:02:24Z

9

Great question!

HTTP/2 over TCP suffers from a slight inefficiency caused by TCP. Consider the following example: Suppose you have 3 streams A, B and C. Denote packets (frames) of each stream by lower case letters (a, b, c) and a sequence number. Let's have a look at what happens with HTTP/2 over TCP when the following sequence is sent:

server ---> a2, c2, b2, *c1, b1, a1 ---> client

Where the *c1 means that this frame was lost. The receiving end (client) must wait for a re-transmission of the lost *c1 frame before it can pass later frames to the application layer (namely b2,c2,a2), because the communication is over TCP and TCP guarantees in-order delivery!

That is in contrast to HTTP/3 & QUIC, where over UDP these are just independent packets, thus the loss of *c1 would not delay the delivery of b2, c2 and a2 to the application layer!

edited Jul 5, 2019 at 18:02

answered Jul 5, 2019 at 15:31

Lior Cohen

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