Subject: [Tsvwg] SCTP: Data chunk in flight when a_rwnd = 0

From: Tom George <[email-masked]>
Date: Sat, 03 Nov 2001 16:51:05 -0600

RFC 2960 section 6.1  Transmission of DATA Chunks says:

   A) At any given time, the data sender MUST NOT transmit new data to
      any destination transport address if its peer's rwnd indicates
      that the peer has no buffer space (i.e. rwnd is 0, see Section
      6.2.1).  However, regardless of the value of rwnd (including if it
      is 0), the data sender can always have one DATA chunk in flight to
      the receiver if allowed by cwnd (see rule B below).  This rule
      allows the sender to probe for a change in rwnd that the sender
      missed due to the SACK having been lost in transit from the data
      receiver to the data sender.

My understanding of this is that the "one DATA chunk in flight" would
have to be something other than new data. Am I correct? If I am correct,
then what is it? A retransmission of old data?

Thanks,
tomG.

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From: Randall Stewart <[email-masked]>
Date: Mon, 05 Nov 2001 06:05:59 -0600

Tom:

The intention was the data can be NEW or RETRANSMISSIONS. Otherwise
you have a deadlock scenario which will occur when the
peer SACK's everything but sets the rwnd=0.

R

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Randall R. Stewart
[email-masked] 815-342-5222 (cell phone)