Positional Multiplex Clause Samples

Positional Multiplex. The key function of TIP is to enable multiple media streams, belonging to the same media type, to be transported on the same UDP channel within the boundaries of standards compliance. To accomplish this there needs to be a multiplex point for the multiple streams based on a label, here after referred to as the “position”. This section describes the mechanisms for this multiplex. All SSRC fields MUST be random 32 bit values, that are unique across the RTP session as per the RTP and SRTP standards [4]. Each unique entity that is a RTP or RTCP transmitter should have a unique SSRC value. The TIP positional multiplex value MUST be added to all RTP packets as the first CSRC value. (Note that multiple CSRC values are still allowed, but the first one must contain the TIP positional values.) The RTP CC field should be set appropriately to indicate the addition of the CSRC value. This document will henceforth refer to this value as the MUX-CSRC. The following packet diagram illustrates these rules. TIP RTP Packet TIP multiplexes multiple RTP media streams of the same type (audio or video) on one UDP channel. For the video stream multiplex, typicall all the streams use the same encoding format, H.264. Hence the RTP payload number is the same for all streams. Each video stream identifies its particular media configuration options via use of inband H.264 parameter sets (SPS/PPS). For the audio stream multiplex, the situation is more complex. Depending on device capabilities and the call topology multiple encoding formats such as AAC-LD, and/or G.711 and G722 audio streams may be used. Also any of the audio streams may include DTMF sent via RFC 2833 encoding. Hence multiple RTP payload numbers may be seen within the audio multiplex. The RTP media streams sent on the same UDP channel are multiplexed by using different RTP MUX-CSRC values for each stream. Note that each RTP stream has its own independent RTP sequence number and RTP timestamp space, hence a receiver should be prepared for a change in the value of the SSRC to be accompanied by a change of sequence number and timestamp. Note that multiplexing different ,yet realted, RTP streams of the same media is allowed in RTP as long as certain requirements are met [4]. Such multiplexing is actually the norm in multicast sessions. Additionally, the bits of the MUX-CSRC field are subdivided and assigned specific semantics: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sampling Clock ID | OutPos|Xmit...