Re: a_rwnd=0 - heartbeat messages allowed?

Des,

This is really an SCTP question (for [email protected]), however,
an SCTP endpoint is allowed to send SACK with rwnd=0.  The
tester may send it; however, the tester must also send HEARTBEAT
ACK in response to HEARTBEAT if it wants to keep the association
alive.

I would guess that the tester is testing zero-window probing by
the SUT, RFC 4960 6.1. A:

  When the receiver's advertised window is zero, this probe is
  called a zero window probe.  Note that a zero window probe SHOULD
  only be sent when all oustanding DATA chunks have been
  cummulatively acknowledged and no DATA chunks are in flight.  Zero
  window probing MUST be supported.

If that is the case, it is expecting DATA not HEARTBEAT, and
this may be why the test case is failing (timing out) rather
than responding properly to the HEARTBEAT with HEARTBEAT ACK.
To be conclusive that the SUT is failing a zero-window probe
test, it needs to be verified that the SUT has DATA oustanding
after receiving SACK (rwnd=0).

One way for the tester to conclude this (if it is unable to do
so by ferry-clip) would be to send HEARTBEAT ACK and SACK
(rwnd=1500) in response to the first HEARTBEAT and see if the
SUT sends DATA immediately, in which case it might conclude that
the SUT has failed a zero-window probe test.

--brian

Des Smyth wrote:                                (Thu, 21 Jan 2010 09:29:12)
> 
>    Hi all
> 
> 
> 
>    I am conformance testing a Sigtran stack and I am trying to figure out
>    if the behaviour described below is correct:
> 
> 
> 
>    Tester                                                      SUT
> 
>                                 <----------                     DATA
> 
>    SACK (rwnd=1500) ----------->
> 
>    SACK (rwnd=0)      ----------->
> 
>    DATA                    ----------->
> 
>                                <-----------                     SACK
> 
>                                <-----------                     HEARTBEAT
> 
>                                <-----------                     HEARTBEAT
> 
>                                <-----------                     HEARTBEAT
> 
>                                <-----------                     HEARTBEAT
> 
>    association down.
> 
> 
> 
>    Should the SUT send a SACK for the DATA with tester rwnd=0?
> 
>    If this is ok, should SUT send HEARBEAT with rwnd=0?
> 
> 
> 
>    Any comments appreciated.
> 
> 
> 
>    Regards,
> 
>    Des

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-- 
Brian F. G. Bidulock
[email protected]
http://www.openss7.org/