TCP streaming problem, I'm puzzled

From: Roland Kuhn (rkuhn@e18.physik.tu-muenchen.de)
Date: Wed Jul 30 2003 - 06:33:17 EST


Hi!

When trying to understand why xmms stops playing internet radio sometimes I
came across this trace (hope the lines didn't wrap):

[snipped]
21:16:15.985224 server.http > client.40944: . 22482048:22483456(1408) ack 1 win 4096 <nop,nop,timestamp 9339837 306263695>
21:16:15.985263 client.40944 > server.http: . ack 22483456 win 34816 <nop,nop,timestamp 306420832 4369676> (DF)
21:16:16.004022 server.http > client.40944: . 22483456:22484864(1408) ack 1 win 4096 <nop,nop,timestamp 13126582 306263695>
21:16:16.010153 server.http > client.40944: . 22484864:22486272(1408) ack 1 win 4096 <nop,nop,timestamp 14356128 306263695>
21:16:16.010182 client.40944 > server.http: . ack 22486272 win 34816 <nop,nop,timestamp 306420834 13126582> (DF)
21:16:16.047752 server.http > client.40944: . 22486272:22487680(1408) ack 1 win 4096 <nop,nop,timestamp 21891150 306263695>
21:16:16.053473 server.http > client.40944: . 22487680:22489088(1408) ack 1 win 4096 <nop,nop,timestamp 23038224 306263695>
21:16:16.053539 client.40944 > server.http: . ack 22489088 win 34816 <nop,nop,timestamp 306420839 21891150> (DF)
21:16:16.091888 server.http > client.40944: . 22489088:22490496(1408) ack 1 win 4096 <nop,nop,timestamp 30643705 306263695>
21:16:16.097608 server.http > client.40944: . 22490496:22491904(1408) ack 1 win 4096 <nop,nop,timestamp 31792380 306263695>
21:16:16.097634 client.40944 > server.http: . ack 22491904 win 34816 <nop,nop,timestamp 306420843 30643705> (DF)
21:16:16.122534 server.http > client.40944: . 22491904:22493312(1408) ack 1 win 4096 <nop,nop,timestamp 36774422 306263695>
21:16:16.135614 server.http > client.40944: . 22493312:22494720(1408) ack 1 win 4096 <nop,nop,timestamp 39395154 306263695>
21:16:16.135643 client.40944 > server.http: . ack 22494720 win 34816 <nop,nop,timestamp 306420847 36774422> (DF)
21:16:16.165856 server.http > client.40944: . 22494720:22496128(1408) ack 1 win 4096 <nop,nop,timestamp 45475469 306263695>
21:16:16.178931 server.http > client.40944: P 22496128:22496256(128) ack 1 win 4096 <nop,nop,timestamp 48127090 306263695>
21:16:16.178960 client.40944 > server.http: . ack 22496256 win 34816 <nop,nop,timestamp 306420851 45475469> (DF)
21:16:43.983271 server.http > client.40944: . ack 1 win 4096 <nop,nop,timestamp 1310109814 306263695>
21:16:44.343712 server.http > client.40944: . ack 1 win 4096 <nop,nop,timestamp 1382101841 306263695>
21:16:44.387442 server.http > client.40944: . ack 1 win 4096 <nop,nop,timestamp 1390874982 306263695>
21:16:44.431578 server.http > client.40944: . ack 1 win 4096 <nop,nop,timestamp 1399659928 306263695>
21:16:44.475305 server.http > client.40944: . ack 1 win 4096 <nop,nop,timestamp 1408415462 306263695>
...
[snipped several similar lines, approx. 20/sec]
...
21:16:49.531716 server.http > client.40944: . ack 1 win 4096 <nop,nop,timestamp 2418974192 306263695>
21:16:49.575850 server.http > client.40944: . ack 1 win 4096 <nop,nop,timestamp 2427784709 306263695>
21:16:49.619988 server.http > client.40944: . ack 1 win 4096 <nop,nop,timestamp 2436619683 306263695>
21:16:49.664124 server.http > client.40944: . ack 1 win 4096 <nop,nop,timestamp 2445444979 306263695>
21:16:49.708258 server.http > client.40944: . ack 1 win 4096 <nop,nop,timestamp 2454259018 306263695>
21:16:49.752395 server.http > client.40944: R 22496256:22496256(0) ack 1 win 4096
[nothing after that]

Most of the stops are caused by the server simply stopping sending data after
finishing a chunk (i.e. after the PUSH packet), but I don't understand why in
this instance the server sends so many ACK packets when there's clearly
nothing to be acknowledged...

Would somebody please try to enlighten me?

Ciao,
                                        Roland

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