| 单词 | ham |
| 释义 | ham communicates with the gatekeeper. Sequencing of audio and video packets is supported through Real-Time Protocol/Real-Time Control Protocol (RTP/RTCP). Endpoints can set quality of service (QoS) levels through Resource Reservation Protocol (RSVP).Terminals optionally may include video codecs,T.120 data conferencing capabilities, and MCU functionality. • Gateways are optional elements used for various levels of protocol conversion.The gateway serves as a protocol converter between devices and networks that have native H.323 capability and those that do not.The gateway also may translate between audio, video, and data formats, and may perform signaling conversions between the H.225 packet protocol and external protocols such as SS7 and Q.931. Alternatively, signaling conversions may be performed by Gatekeepers, call processors, or session border controllers. • Gatekeepers are optional elements that act as the central points in H.323 zones. Endpoints may communicate directly, in either a unicast or a multicast environment, if no gatekeeper is present. If a gatekeeper is present, all endpoints in its zone must register with it.The gatekeeper performs the function of admission control, determining if devices are authorized to connect and if there is sufficient bandwidth to support the call. Gatekeepers serve to translate LAN addresses into IP or IPX addresses, as defined in the RAS specification. Gatekeepers also can act to route H.323 calls through gateways, if necessary, and monitor the network bit rate capacity, with the ability to deny access to a session if programmable bandwidth thresholds have been reached or exceeded. Gatekeepers also can perform certain administrative functions, such as accounting, billing, directory, and collecting network usage data. Gatekeepers may be distinct network elements (NEs), or gatekeeper functionality can be incorporated into MCUs. • Multipoint Control Units (MCUs) support conferencing among three or more participating terminals.The MCU comprises a Multipoint Controller (MC) and optional Multipoint Processors (MPs). The MC is responsible for call control negotiation to achieve common levels of communication.The MP may process either a single media stream or multiple media streams, depending on the nature of the conference. See also bandwidth, bit rate, cable modem, encryption, Internet, IP, IPX, H.225, H.245, ITU-T, LAN, MCU, multicast, NE, Q.931, QoS, RAS, RSVP, RTCP, RTP, set-top box, signaling and control, T.120, and unicast. |
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