Media5 Mediatrix 4104, Reference Manual, Page: 304 / 466

Chapter 18 - SIP Protocol Features Offer/Answer Model
282 Mediatrix 4104
Offer/Answer Model
You can define whether or not the Mediatrix 4104 requires strict adherence to RFC 3264 from the peer when
negotiating capabilities for the establishment of a media session.

To define how to process the Offer/Answer model:
1. In the sipExperimentalMIB , set the sipEnforceOfferAnswerModel variable to the proper value.
The sipAllowMediaReactivationInAnswerEnable (see “Allow Media Reactivation in Answer” on
page 282 ) and sipAllowAudioAndImageNegotiationEnable (see “Allow Audio and Image
Negotiation” on page 283 ) variables allow to enable or disable other deviations from the Offer/
Answer model.
Allow Media Reactivation in Answer
You can define the behaviour of the Mediatrix 4104 when receiving a SDP answer activating a media that had
been previously deactivated in the offer.
You can also set this parameter via the web interface, as described in “Interop Parameters” on page 67 .

To define the behaviour when receiving a SDP answer:
1. In the sipExperimentalMIB , set the sipAllowMediaReactivationInAnswerEnable variable with the
proper behaviour.
Standards Supported • RFC 3264 – An Offer/Answer Model with the Session
Description Protocol (SDP)
Table 191: Offer/Answer Model Parameters
Parameter Description
disable The peer can freely:
• Send back a brand new list of codecs or add new ones to the offered
list.
• Add media lines AFTER the ones found in the offer.
As long as at least one codec sent back is supported by the Mediatrix 4104,
the call is allowed to go on. Any media line added by the peer is simply
ignored.
enable The following guidelines from the Offer-Answer Model must be strictly
followed. An answer must:
• Include at least one codec from the list that the Mediatrix 4104 sent
in the offer.
• Avoid adding extra codecs that were not present in the offer.
• Contain the same number of media lines that the unit put in its offer.
Otherwise, the answer is rejected and the unit ends the call. This is the default
value.
Table 192: Media Reactivation Parameters
Parameter Description
Enable A media reactivated in an incoming answer is ignored. This behaviour goes
against the SDP Offer/Answer model described by IETF RFC 3264.
Disable A media reactivated in an incoming answer ends the current media negotiation and
the call. This behaviour follows the SDP Offer/Answer model described by IETF
RFC 3264.