Re: DATA chunks with an invalid length

On Jul 7, 2011, at 10:31 AM, Horsham, Ian wrote:

> 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.
... and the additional byte is not present in the packet, right? (A tracefile (.pcap format) might
be helpful, you can send it privately). Then it would be a partial chunk? Or are the byte
available (either as padding or in a different chunk)?

Best regards
Michael
> 
> 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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