Subject: [MMUSIC] Reg. RTSP SETUP request

From: "Maruthi Ram namburu" <[email-masked]>
Date: Fri, 18 May 2007 15:58:20 +0530

Hello,

       In the RFC2326 the following is mentioned about the SETUP request

       "A client can issue a SETUP request for a stream that is already
playing to change transport parameters."

       Lets say that there is a NAT device between the client and server
which selectively opens up the ports and also does statistics collection. It
has to track the SETUP request and response to start natting the packets
flowing on the data stream.

      The following situation will arise when the NAT device sees a SETUP
request with a Session ID on the control connection.

       Case 1.  This new SETUP may be sent to change the transport
parameters of the existing data stream. In this case ports
  of the data stream  may change and NAT device may have to modify/cleanup
and recreate the datastructures it was using for the
 address translation so far.

       Case 2.  This new SETUP may be trying to aggregate another stream in
to the current session. In this case there
  will be a new additional datastream and NAT device has to create a new set
of datastructures to NAT the new datastream.

       From my understanding of the RFC I see that NAT device has to
remember the URL to differentiate these two cases.
  If the new SETUP carries the same URL then it is Case 1 otherwise it is
Case 2. But remebering the URL may turnout to
 be memory intensive for the NAT device which has to deal with large number
of connections.

  Is there any other way these two cases can be distiguished in NAT device ?

  In case if this is not the right forum for this discussion can you please
redirect me to the correct one ?

Thanks and Regards,
Maruthi
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---

From: Magnus Westerlund <[email-masked]>
Date: Mon, 21 May 2007 11:12:47 +0200

Maruthi Ram namburu skrev:
> which selectively opens up the ports and also does statistics 
> collection. It has to track the SETUP request and response to start 
> natting the packets flowing on the data stream.
> 
>       The following situation will arise when the NAT device sees a 
> SETUP request with a Session ID on the control connection.
> 
>   of the data stream  may change and NAT device may have to 
> modify/cleanup and recreate the datastructures it was using for the
>        Case 2.  This new SETUP may be trying to aggregate another stream 
> in to the current session. In this case there
>   will be a new additional datastream and NAT device has to create a new 
> set of datastructures to NAT the new datastream.
> 
>   If the new SETUP carries the same URL then it is Case 1 otherwise it 
> is Case 2. But remebering the URL may turnout to
>  be memory intensive for the NAT device which has to deal with large 
> number of connections.

Your summary seems to be right. I think that is the price you have to 
pay for having an RTSP ALG function in your NAT.

>   Is there any other way these two cases can be distiguished in NAT device ?

Not that I can think of.

> 
>   In case if this is not the right forum for this discussion can you 
> please redirect me to the correct one ?
> 

Yes, it is the right forum.

Cheers

Magnus Westerlund

IETF Transport Area Director & TSVWG Chair
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