1017263@MCMASTER.BITNET (05/26/86)
Here is a problem from the world of TCP/IP. Why does the Vax retransmit a
packet which has been acknowledged ? Also if the PC does window shrinking and
the window size becomes zero at the point of transmitting the character, the
retry time can be about 30 seconds.
The following is a true log of packets between the Vax and the PC. Only the
names have been changed to protect my innocence.
From PC From Unix/Vax
(Using BWTEL)
Characters = 82
Seq # = 207
Ack # = 32
Characters = 0
Seq # = 32
Ack # = 289
Characters = 82
Seq # = 289
Ack # = 32
*** Character transmitted before last packet processed
Characters = 1
Seq # = 32
Ack # = 289
Characters = 0
Seq # = 371
Ack # = 33
This packet is in response to second to last packet, last packet not yet
processed.
Characters = 1 same character as above
Seq # = 32
Ack # = 371
Characters = 0
Seq # = 371
Ack # = 33
Characters = 82
*** Seq # = 289
Ack # = 33
*** Why Does the Vax retransmit ???? ***
Characters = 0
Seq # = 33
Ack # = 371
Characters = 82
Seq # = 371
Ack # = 33
Characters = 0
Seq # = 33
Ack # = 453
- Carl Beame 1017263@MCMASTER.BITNET or
BEAME@MCMASTER.BITNET
P.S> Any comments or explanations are very welcome.CERF@USC-ISI.ARPA.UUCP (05/27/86)
Aside from bugs, there are a couple of reasons for retransmissions (this is a generic comment, not specific to the VAX code): 1. timeout awaiting ACK leads to retransmissions 2. ACK fails to arrive at all (then see 1 above). Do you know what the path was between the source/sink of this TCP connection? Were there any long delay nets (e.g. SATNET)? Network congestion? Overloaded gateways? Vint Cerf