[Sip] SDP telephone-event (DTMF) payload negotiation

"RUOFF, LARS (LARS)** CTR **" <lars.ruoff@alcatel-lucent.com> Fri, 18 November 2011 08:22 UTC

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From: "RUOFF, LARS (LARS)** CTR **" <lars.ruoff@alcatel-lucent.com>
To: "sip@ietf.org" <sip@ietf.org>
Date: Fri, 18 Nov 2011 09:22:05 +0100
Thread-Topic: SDP telephone-event (DTMF) payload negotiation
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Subject: [Sip] SDP telephone-event (DTMF) payload negotiation
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Hi all,

New to this list. Apologies if this question has been asked many times before (my searches showed that it has, but i was still unable to find a definitive answer).
The question is about SDP telephone-event (DTMF) payload negotiation.
Imagine the following call setup between A and B:
(among other media formats)
a=rtpmap:101 telephone-event/8000
200 OK B->A
(among other media formats)
a=rtpmap:97 telephone-event/8000
The question is:
Is the above legal? I.e. is B allowed to choose a different PT than proposed y A. 
In case yes, what PT should the telephone-events be sent...
from A to B?
from B to A?
Please corroborate your answers by providing normative references if possible.
I studied RFC 3264 (SDP Offer/Answer Model) intensively, but could not conclude for a definitive answer in that particular case.

Lars Ruoff