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Deepak Rathore wrote:

Hi All, I have following queries in relation to RFC 2960. 1. I'm not able to understand difference between streams and association. My idea is multiple streams are associated with an association but my confusion is whether these streams are maintained between SCTP user and SCTP or between two SCTP end points. In case of streams maintained between two SCTP end points does all streams follow same path  or multiple paths as mentioned in address parameters. In case streams are maintained between SCTP user and SCTP layer. Does SCTP bundles streams to follow common path. In this case what would happen if reachability of end point fails ( through this point ).

    Association is similar to "Connections" in TCP. An Association is a peer to peer connection  and is created and destroyed on request. "Streams " is something new in SCTP which is not in TCP. Actually streams are maintained between peers of an Association. The User of SCTP ( upper layer) will request for the number of streams required. This will be informed to the peer. So both (peers)  will be ready to accept and send the requested streams within an association. Now when data chunks are passed from the upper layer ( with the stream id), it may bebundled with data chunks with different stream id. And all the streams follow the same path ( if there is no path switch in between the association, as SCTP is also Multihomed). In the peer its again unbundled and delivered to the upper layer with the appropriate stream id which is present in the chunk header.
 
  2. What is the function of cumulative TSN ack point variable. If one use initial TSN value as zero what value does cumulative TSN ack point going to hold and how this value is going to change.

        Cumulative TSN ack point is used to maintain the data chunks which are all acknowledged. If the Retransmission timer expires (assuming it is maintained per association ), the SCTP with the Cumulative TSN , finds out what all data chunks are not acknowledged thru SACK till now, and retransmits those data chunks.
        Initially Cumulative TSN will have the same value as the initial TSN value (because nothing was acked till now). If any SACK is received , the Cumulative TSN ack is assigned the value carried in the SACK.
 

 Hope the above explanation answers ur querry.
  Thanks in advance. RegardsDeepak Thanks
-arun
 
    

• [SCTP-Discussion] SCTP query, Deepak Rathore, 04/09/2001
  • Re: [SCTP-Discussion] SCTP query, arun, 04/18/2001
    • Re: [SCTP-Discussion] SCTP query, Dan Gora, 04/18/2001
      • Re: [SCTP-Discussion] SCTP query, Dan Gora, 04/18/2001

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