RTP实时软件传输协议外文翻译(一).doc

RTP-实时软件传输协议 外文翻译(一) 附录英文原文资料RTP: A Transport Protocol for Real-Time Applications1  Introduction  This memorandum specifies the real-time transport protocol (RTP), which provides end-to-end delivery services for data with real-time characteristics, such as interactive audio and video. Those services include payload type identification, sequence numbering, times tamping and delivery monitoring. Applications typically run RTP on top of UDP to make use of its multiplexing and checksum services; both protocols contribute parts of the transport protocol functionality. However, RTP may be used with other suitable underlying network or transport protocols (see Section 10). RTP supports data transfer to multiple destinations using multicast distribution if provided by the underlying network.  Note that RTP itself does not provide any mechanism to ensure timely delivery or provide other quality-of-service guarantees, but relies on lower-layer services to do so. It does not guarantee delivery or prevent out-of-order delivery, nor does it assume that the underlying network is reliable and delivers packets in sequence. The sequence numbers included in RTP allow the receiver to reconstruct the senders packet sequence, but sequence numbers might also be used to determine the proper location of a packet, for example in video decoding, without necessarily decoding packets in sequence.  While RTP is primarily designed to satisfy the needs of multi- participant multimedia conferences, it is not limited to that particular application. Storage of continuous data, interactive distributed simulation, active badge, and control and measurement applications may also find RTP applicable.  This document defines RTP, consisting of two closely-linked parts: 1. The real-time transport protocol (RTP), to carry data that has real-time properties. 2. The RTP control protocol (RTCP), to monitor the quality of service and to convey information about the participants in an on-going session. The latter aspect of RTCP may be sufficient for “loosely controlled” sessions, i.e., where there is no explicit membership control and set-up, but it is not necessarily intended to support all of an applications control communication requirements. This functionality may be fully or partially subsumed by a separate session control protocol, which is beyond the scope of this document.  RTP represents a new style of protocol following the principles of application level framing and integrated layer processing proposed by Clark and Tennenhouse 1. That is, RTP is intended to be malleable to provide the information required by a particular application and will often be integrated into the application processing rather than being implemented as a separate layer. RTP is a protocol framework that is deliberately not complete. This document specifies those functions expected to be common across all the applications for which RTP would be appropriate. Unlike conventional protocols in which additional functions might be accommodated by making the protocol more general or by adding an option mechanism that would require parsing, RTP is intended to be tailored through modifications and/or additions to the headers as needed. Examples are given in Sections 5.3 and 6.3.3.  Therefore, in addition to this document, a complete specification of RTP for a particular application will require one or more companion documents (see Section 12): 1. A profile specificat