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Re: [SCTP-Discussion] Query


Chronological Thread 
  • From: Andreas Jungmaier <ajung AT exp-math.uni-essen.de>
  • To: discussion AT sctp.de
  • Subject: Re: [SCTP-Discussion] Query
  • Date: Fri Mar 30 12:17:00 2001
  • List-id: SCTP Discussions <discussion.sctp.de>
  • Organization: University of Essen, Germany

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On Friday, 30. March 2001 06:10, you wrote:
> Hi,
>
> I have following queries related to SCTP, RFC 2960.
>
> 1. Why SCTP performs fragmentation of data chuncks when underlying layer
> (IP) does fragmentation ?

IP Fragmentation is not wanted, it may hamper performance.
When *part* of an IP (and SCTP) datagram is dropped (i.e. a
fragment !), the whole datagram needs to be retransmitted.
In case SCTP does the segmentation, only the really necessary
part would be retransmitted.
Also, you will have delays for reassembly in the endpoint,
which is undesired.

> 2. What is difference between comulative TSN ack. and gap ack block ?
Cumulative TSN ack scknowledges TSNs that have arrived at the
endpoint, and are ready to be delivered to the upper layer
or have already been delivered.
Gap ack blocks acknlowedge TSNs that have been received out of the
normal order of TSNs and serve for triggering fast retransmission.

Regards,
- --

Andreas Jungmaier

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void hamlet()
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Andreas Jungmaier, Dipl.-Ing.
University of Essen email:
ajung AT exp-math.uni-essen.de
Computer Networking Technology Group Tel. : +49 (0201) 183-7636
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PGP Public Key and Fingerprint: see http://www.exp-math.uni-essen.de/~ajung
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