Subject: [AVT] BYE RTCP packet schedule.

From: "Oren Peleg" <[email-masked]>
Date: Tue, 18 Nov 2003 13:13:42 +0200

According to RFC3550, the BYE packet should be sent no less then a minimum interval from former RTCP packet. This can cause a resource re-usage problems. Shouldn't it be more relaxed (at least for unicast sessions) to enable sending an immediate BYE upon RTP session closing?

Thanks,

Oren Peleg

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From: Magnus Westerlund <[email-masked]>
Date: Thu, 20 Nov 2003 12:56:44 +0100

Hi Oren,

I think you should go re-read section 6.3.7 of RFC 3550. The relaxation 
you ask for exist. The described algorithm needs only to be used if 
there are more than 50 participants in the session. Most unicast 
sessions does not use more than 50 SSRCs in total. Secondly if on has a 
problem to wait the time the derivation algorithm results in then on MAY 
leave without sending a BYE packet.

Quoted from section 6.3.7 of RFC 3550:

    o  When the participant decides to leave the system, tp is reset to
       tc, the current time, members and pmembers are initialized to 1,
       initial is set to 1, we_sent is set to false, senders is set to 0,
       and avg_rtcp_size is set to the size of the compound BYE packet.
       The calculated interval T is computed.  The BYE packet is then
       scheduled for time tn = tc + T.

    o  Every time a BYE packet from another participant is received,
       members is incremented by 1 regardless of whether that participant
       exists in the member table or not, and when SSRC sampling is in
       use, regardless of whether or not the BYE SSRC would be included
       in the sample.  members is NOT incremented when other RTCP packets
       or RTP packets are received, but only for BYE packets.  Similarly,
       avg_rtcp_size is updated only for received BYE packets.  senders
       is NOT updated when RTP packets arrive; it remains 0.

    o  Transmission of the BYE packet then follows the rules for
       transmitting a regular RTCP packet, as above.

Please look at the first bullet. In this you reset a lot of variables. 
This will result in that if no BYE packet you will based on bandwidth be 
able to send pretty quickly. If a min_rtcp_intreval is set then that 
will be halved due to the initial variable being set to true.

Thus the restriction on sending BYE is only required to be used for 
group size over 50 participants. And even then the sending of a BYE is 
prioritized while still being limited to avoid feedback explosion at 
session endings.

I hope this clarifies things for you.

Best Regards

Magnus

Oren Peleg wrote:

> According to RFC3550, the BYE packet should be sent no less then a 
> minimum interval from former RTCP packet. This can cause a resource 
> re-usage problems. Shouldn't it be more relaxed (at least for unicast 
> sessions) to enable sending an immediate BYE upon RTP session closing?
> 
> Thanks,
> 
> Oren Peleg
> 

-- 

Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
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Ericsson AB                | Phone +46 8 4048287
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