/mcpMultiple Codecs in Answer When a call is routed through Unified Communications Manager, Unified Communications Manager takes the role of selecting a single audio and video codec for the call based on the CAC policy and the codec preference configured in Unified Communications Manager. Therefore, the endpoint can only communicate with the codec specified by Unified Communications Manager. This logic applies to audio and video codec. However, there are endpoints that can support receiving more than one codec within a media channel. Simulcast is one of the applications that can transmit more than one encoded data within an established channel. In order to support such usage, Unified Communications Manager 10.0 release has introduced Multiple Codec in Answer SDP to support this function that Unified Communications Manager will not narrow down to a single codec during negotiation when both parties are capable of handling more than one codec in the SIP answer message. Instead, Unified Communications Manager sends a common set of codecs in the SIP answer message provided the codec offered by the endpoints does not exceed the inter-region bandwidth policies. This feature only applies to endpoints that indicate the support of Multiple Codec in Answer and they have to be homogenous SIP protocol call. The rest of the call scenarios remain to be single codec negotiation as Unified Communications Manager does today. When Unified Communications Manager allows multiple codec to be negotiated, the endpoint can decide which codec to be transmitted and be prepared to receive any codec being offered. The endpoint may choose to transmit more than one media codec depending on the application. Unified Communications Manager will not know which codec has been transmitted inside the RTP channels by the call devices. Unified Communications Manager recognizes the SIP endpoint supporting multiple codecs in answer in several ways: • SIP line device configuration: SIP endpoints, such as Cisco TelePresence EX90, registering to Unified Communications Manager indicates the support of multiple codecs in the answer SDP through configuration. • SIP contact header URI: The endpoint can specify “+multiple-codecs-in-ans” in the Contact header line of the SIP message to indicate the support of multiple codecs negotiation. It is noted that Unified Communications Manager recognizes the tag in the incoming SIP “offer” message only, not in the “answer” message. Contact:sip:84626@172.27.31.84:5060;transport=tcp;video;audio;+multiple-codecs-in-ans> • SIP trunk configuration: In the SIP profile page, under Trunk Specific Configuration, the "Allow multiple codecs in answer SDP" check box was introduced in the SDP Information section. Any endpoint behind a SIP Trunk (that has this check box enabled and SIP Profile assigned) is considered to be able to handle multiple codecs in the SDP answer message. It is noted that Unified Communications Manager still considers that SIP endpoint supports multiple codecs in the answer SDP, if the incoming offer message containing contact header URI as indicated above though this configuration check box is unchecked. • Multiple Codecs Specified in SIP answer Signals: When Unified Communications Manager offers an SIP endpoint with SDP and the endpoint respond with multiple codecs in answer signals, Unified Communications Manager considers that the endpoint is capable of negotiating multiple codec in the answer. This applies to both sip trunk and sip line device regardless if they have hinted the support of multiple codec negotiations by any means discussed above. This operation is performed in the media layer. SIP Line Messaging Guide (Standard Edition) for Cisco Unified Communications Manager 45 SIP Standard Line Interface Multiple Codecs in Answer