Re: I-D Action:draft-ietf-tsvwg-sctp-strrst-08.txt

["t.petch" <[e-mail]>]

Um; I was expecting perhaps a little more on race conditions.

I had a more complex race condition in mind, which will work, I have
convinced myself of that, provided everyone expects it to:-)

A appl requests a reset of streams 2 and 3
A sends Incoming SSN Reset Request Parameter for streams 2 and 3 and starts
timer
A receives Outgoing SSN Reset Request Parameter for streams 1 and 2 with zero
Stream Reset Request Sequence Number
A sends ACK and  has a think about what to do .....
 - waits for Outgoing SSN Reset Request Parameter for streams 2 and 3?
 - resets streams 1 and 2?
 - raises an event for streams 1 and 2?

Meanwhile,
B appl requests a reset of streams 1 and 2
B sends Outgoing SSN Reset Request Parameter for streams 1 and 2 and starts
timer
B receives Incoming SSN Reset Request Parameter for streams 2 and 3
B has timer running so must wait

Therefore
A must reset streams 1 and 2 and send Stream Reset Response Parameter to let B
proceed
B receives Stream Reset Response Parameter and stops timer
B can and must now send Outgoing SSN Reset Request Parameter for streams 2 and 3
with non-zero Stream Reset Request Sequence Number and starts timer
A receives Outgoing SSN Reset Request Parameter for streams 2 and 3 with
non-zero Stream Reset Request Sequence Number and stops timer
A resets streams 2 and 3 and sends Stream Reset Response Parameter
B receives Stream Reset Response Parameter and stops timer

A appl and B appl both receive events, one for reset of streams 1 and 2, the
other for streams 2 and 3 (which may puzzle them).

Of course, a slightly different scenario would be for both A and B to select the
same streams, say 1 and 3 (perhaps as a result of an application level event) in
which case, the scope for getting it wrong is even greater; when A receives
Outgoing SSN Reset Request Parameter with zero Stream Reset Request Sequence
Number, it might send an Error - Bad Sequence Number, which could really confuse
B

Tom Petch

----- Original Message -----
From: <[e-mail]>
To: <[e-mail]>
Cc: <[e-mail]>
Sent: Monday, November 29, 2010 6:30 PM
Subject: I-D Action:draft-ietf-tsvwg-sctp-strrst-08.txt


> A New Internet-Draft is available from the on-line Internet-Drafts
directories.
> This draft is a work item of the Transport Area Working Group Working Group of
the IETF.
>
>
> Title           : Stream Control Transmission Protocol (SCTP) Stream
Reconfiguration
> Author(s)       : R. Stewart, et al.
> Filename        : draft-ietf-tsvwg-sctp-strrst-08.txt
> Pages           : 31
> Date            : 2010-11-29
>
> Many applications that use SCTP want the ability to "reset" a stream.
> The intention of resetting a stream is to set the numbering sequence
> of the stream back to 'zero' with a corresponding notification to the
> upper layer that this has been performed.  The applications that want
> this feature want it so that they can "re-use" streams for different
> purposes but still utilize the stream sequence number so that the
> application can track the message flows.  Thus, without this feature,
> a new use of an old stream would result in message numbers greater
> than expected unless there is a protocol mechanism to "reset the
> streams back to zero".  This document also includes methods for
> resetting the transport sequence numbers, adding additional streams
> and resetting all stream sequence numbers.
>
> A URL for this Internet-Draft is:
> http://www.ietf.org/internet-drafts/draft-ietf-tsvwg-sctp-strrst-08.txt
>
> Internet-Drafts are also available by anonymous FTP at:
> ftp://ftp.ietf.org/internet-drafts/
>
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> Internet-Draft.
>