[ns] TCP sequence numbers.

[Jo�o Pedro Oliveira <jpaos@netcabo.pt>]

Hi all Ns people,

I have a question about the full-tcp sequence numbers.

When stablishing the connection we have:

              A   ------> SYN ------> B
              A   <----- SYN+ACK ---- B
              A   ------> ACK ------> B
              A   ------> data -----> B

In my case A it's node 9 and B node 3.

I'm transfering data from B to A and the first's packets I get are(on node 9):

 

r 40.941003 8 9 ack 40 ------- 0 3.18 9.0 0 11137      <-----+
r 41.11559 8 9 ack 1500 ------- 0 3.18 9.0 1 11205     <-----+
r 41.12159 8 9 ack 1500 ------- 0 3.18 9.0 1461 11206
r 41.37391 8 9 ack 1500 ------- 0 3.18 9.0 2921 11284
r 41.37991 8 9 ack 1500 ------- 0 3.18 9.0 4381 11285
r 41.38591 8 9 ack 1500 ------- 0 3.18 9.0 5841 11287
r 41.39191 8 9 ack 1500 ------- 0 3.18 9.0 7301 11288
r 41.72839 8 9 ack 1500 ------- 0 3.18 9.0 8761 11402
r 41.73439 8 9 ack 1500 ------- 0 3.18 9.0 11681 11406
r 41.74039 8 9 ack 1500 ------- 0 3.18 9.0 13141 11407
r 41.740393 8 9 ack 40 ------- 0 3.18 9.0 14601 11409
r 41.740397 8 9 ack 40 ------- 0 3.18 9.0 14601 11411  <----+

r 41.74671 8 9 ack 1500 ------- 0 3.18 9.0 14601 11412 <----+ (?)
r 41.75271 8 9 ack 1500 ------- 0 3.18 9.0 16061 11413
r 41.75871 8 9 ack 1500 ------- 0 3.18 9.0 17521 11414
r 42.045978 8 9 ack 1500 ------- 0 3.18 9.0 20441 11545

Now: only for the first ack packet the tcp seq # increases 1? Is this a bug?

Wasn't I supposed to extract the amount of data transfered by inspecting the sequence numbers...?

Can anyone explain me that?

 

Thanks in advance,

Jo�o.