Subject: [Sip] Open Issue #23: dynamic PT reuse

From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 22 Aug 2001 18:43:01 -0400

Issue:

Currently, bis says that if you use a dynamic PT once, you can't reuse it
again for a different codec in a re-invite. In other words, lets say A
invites B using GSM codec, dynamic PT number 88. Then A re-invites, changing
that stream to use AMR, with PT 97. Now, A re-invites once more. If it wants
to use a codec other than GSM, it cannot use PT 88. Is that a problem?

Points of discussion:

The reason for this is synchronization of the media and signaling. You
absolutely cannot reuse a PT for a different codec until any packets using
that PT have been guaranteed to have exited the network. Rather than worry
about figuring out a number for this, we just disallow reuse. 

The result is that you cannot cycle through more than 127 codecs in one SIP
call. This is a reasonable restriction, IMHO.

Proposal:

keep this restriction.

There was consensus on this at IETF 51. 

-Jonathan R.

---
Jonathan D. Rosenberg, Ph.D.                72 Eagle Rock Ave.
Chief Scientist                             First Floor
dynamicsoft                                 East Hanover, NJ 07936
[email-masked]                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com

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