Re: DATA chunks with an invalid length

Hi Michael

Thanks for taking the time to respond so quickly.

The data chunks have a chunk length which is larger than the actual chunk length. I've tried to show this by editing the format shown in the RFC (the length field is incremented by 1):-

3.3.1.  Payload Data (DATA) (0)

   The following format MUST be used for the DATA chunk:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Type = 0    | Reserved|U|B|E|    Length +1                  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                              TSN                              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |      Stream Identifier S      |   Stream Sequence Number n    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                  Payload Protocol Identifier                  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       \                                                               \
       /                 User Data (seq n of Stream S)                 /
       \                                                               \
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


I hope that this is clear, if not let me know and I'll see if I can provide a capture of an actual message.

Many thanks
Ian


-----Original Message-----
From: Michael Tüxen [mailto:[email protected]] 
Sent: 06 July 2011 19:49
To: Horsham, Ian
Cc: [email protected]
Subject: Re: [Sigtran] DATA chunks with an invalid length


On Jul 6, 2011, at 4:13 PM, Horsham, Ian wrote:

> 
> 
> Hello Everyone
> 
> I wonder if you would be able to help me regarding a question I have 
> about SCTP.
> 
> How should SCTP DATA chunks should be handled if the chunk length is 
> incorrectly set by the sender? Would I be right in thinking that these chunks should be acknowledged and silently discarded or should they be identified as gaps when sending a SACK in response?
The behavior is not explicitly defined in the RFC... Could you be a bit more explicit what is wrong with the length of the DATA chunk you are considering?

Best regards
Michael
> 
> If anyone can help with this I would be very much appreciated.
> 
> Many Thanks and Kind Regards
> 
> Ian Horsham
> 
> 
> 
> 
> 
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