Subject: Bundling Data and SACK chunks

From: James Noonan <[email-masked]>
Date: Wed, 9 Mar 2005 15:57:42 +0000

I (unsucessfully) sent this mail to the list last week. Randall
Stewart answered.
I am reposting it with RS's answer in-line.

Thanks,
James

Hi,

Can I ask the list is my understanding of bundling SACK's and data
chunks correct. Apologies if this should be the tsvwg list, but it
seems to be more an implementation issue to me.

RS >Yes its probably  better here..

The bundling of SACK's and Data chunks should follow these rules:

Bundling of these two chunks occur when a SACK is delayed, and a data
chunk becomes ready to transmit. 

RS > yep.

However
-  they are  only bundled if the size of the data chunks + SACK  does
not exceed the PMTU. If it does, the SACK is not send.

RS > In general.. yes. However some implementations may, when they
     > realize they need to bundle but can't send two seperate 
     > packets (one with the SACK and one with the data)...

- SACK's are only bundled if the destination address for the bundled
SACK remains the same as if the SACK was not bundled. Bundling does
not change the destination address of a  SACK.

RS > Yep.

In particular I am interested in the second condition.

RS > And of course there may be exceptions to the above.. after
     > all you are NOT required to send the SACK back to the
     > same place that sent you the data... (which is the
     > recomendation).. so you COULD change the SACK to a
     > different address and NOT violate the RFC... I doubt,
     > highly, that most implementations would do this.. but
     > it is legal for them to

Thanks in advance
James