SDP telephone-event (DTMF) payload negotiation

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:
INVITE A->B
SDP:
(among other media formats)
a=sendrecv
a=rtpmap:101 telephone-event/8000
 
200 OK B->A
SDP:
(among other media formats)
a=sendrecv
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.

Regards,
Lars Ruoff
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