Codec List in SIP-Initiated Offer

The CSP can send a list of up to five supported codecs in an offer to an endpoint when establishing a media session. The receiving endpoint selects one codec from that list and reports the selection back in the answer message to the CSP.

Without this feature, the call might not get established because the CSP could include a codec type that the endpoint will not accept.

The host application provides the codec list and sends the list in the Outseize Control message as shown in the next figure:

Use the following TLVs in the Outseize Control message to include the codec types:

The trace below shows how to nest these TLVs in the Outseize Control message. Note that the Outseize Control message cannot exceed 260 bytes.

The following is a message trace for the Outseize Control message followed by the corresponding SIP INVITE message.

Session-Initiation Protocol. A signaling protocol used for establishing sessions in an IP network. A session could be a simple, two-way telephone call, or it could be a collaborative multi-media conference session.

ITU-T standard defines a set of call control, channel setup, and codec specifications for transmitting real-time voice and video over networks that do not offer guaranteed service or quality of service.

Voice over Internet Protocol. The delivery of voice information in digital form in discrete packets rather than in the traditional circuit-committed protocols of the public-switched telephone network (PSTN).

Internet Protocol. Part of the TCP/IP family of protocols used to route messages and tracks the addresses of nodes.

Outgoing call setup during real-time call processing on a specific channel.

A computer, attached to the Excel platform through an RS-232 or Ethernet link, from which you run the telecommunications application that controls the Excel platform.

The point in the Excel platform where a DS0 connects to a network. Also known as a "socket."

Real-Time Transport Protocol. Supports transport of real-time data like interactive voice and video over packet-switched networks.