/mcpCisco Unified Communications Manager Media Endpoint Model Endpoints represent the entities within the Cisco Unified Communications Solutions platform that terminate media, such as IP telephones and gateways. A call from one endpoint to another results in media flowing between the two endpoints. All endpoints in the Cisco Unified Communications Solutions platform transmit voice data by using real-time protocol (RTP). The Cisco Unified Communications Solutions telephones and gateways, for example, include built-in RTP stacks. Applications may also act as endpoints in a Cisco Unified Communications Solutions system; that is, they may terminate media. Because all Cisco Unified Communications Solutions endpoints use RTP, applications also must be able to transmit and receive RTP packets. Payload and Parameter Negotiation In addition to bearer data and payload, each RTP packet contains a header that helps endpoints to determine how to reassemble and decode a sequence of such packets into a media stream. RTP does not provide, however, a means for endpoints to negotiate which payload type to use for a particular stream: for example, audio data that is encoded by using the G.711 standard. Furthermore, RTP does not offer a means of negotiating unique payload type parameters such as the sampling rate of the encoded data or the number of samples that are to be transferred in each RTP packet. Instead, RTP usually gets used in conjunction with another protocol such as H.323, which specifies its own method for endpoints to negotiate these parameters. All such negotiation occurs prior to transmitting RTP packets between endpoints. Cisco Unified Communications Manager, not the endpoints, has responsibility for selecting the payload and encoding parameters for RTP streams. The following five steps that are involved in a typical bidirectional audio telephone call apply: • Initialization • Payload Selection • Receive Channel Allocation • Starting Transmission and Reception • Stopping Transmission and Reception Initialization Upon startup, each endpoint informs Cisco Unified Communications Manager of its media capabilities, that is, G.711, G.723, G.729a, and so on. Startup for an IP phone, for example, occurs when the phone is first turned on, or after it recontacts Cisco Unified Communications Manager after losing its former connection. The endpoint cannot express a preference for one payload type versus another, but it can specify certain parameters for each payload type, such as, packet size. The capability list that the endpoint registers remains exclusive and immutable. If the endpoint specifies that it can support both G.711 and G.723, it implicitly declares that it cannot support G.729a. Moreover, the endpoint must disconnect from Cisco Unified Communications Manager and reinitialize to change the list of capabilities that it supports. JTAPI applications perform this step by registering a CiscoMediaTerminal with Cisco Unified Communications Manager. The CiscoMediaTerminal.register() method allows applications to supply an array of media capability Cisco Unified JTAPI Developers Guide for Cisco Unified Communications Manager, Release 15 and SUs 51 Features Supported by Cisco Unified JTAPI Cisco Unified Communications Manager Media Endpoint Model