control at the receiver. The IP networks usually in- plications, the size of the RTP header is 12 bytes (no troduce packet interarrival jitter. In addition, for video CSRC). V is a 2-bit field that identifies the version of the encoding, it is possible that a video frame will be skipped RTP. P is 1-bit information used to indicate if there are in order to maintain a predefined fixed encoding bit rate. any padding octets at the end that are not part of the By looking at the timestamp, the receiver can properly payload. X is a 1-bit field used to tell if there is any play out the media at the pace when they were originally header extension information. CC means CSRC count, sampled. Timestamp information can also be used to which uses 4 bits in the header and contains the number synchronize the playout of different media, such as audio of CSRC identifiers that follow the header with fixed and video, with the help of RTCP. We will describe audio size. If an RTP session is one to one, such as in a video and video synchronization in more detail in Section telephony application, the CSRC count should be set to 3.6.3.4. zero. PT indicates payload type in 7 bits. It tells the SSRC specifies the synchronization source and has 32 format of the payload that an RTP packet carries. bits. RTP packets generated from the same source, such M is a 1-bit marker and its interpretation is defined by as a camera or microphone, should have the same SSRC. a profile or payload format. For example, RFC 3016 is SSRC can be used to help the receiver group RTP the payload format used for MPEG-4 audio and video. It packets of the same media for playback. CSRC is also IP Header UDP Header RTP Header Audio/Video Data with Payload Format CSRC1 8 bits 8 bits 16 bits 32 bits 32 bits 32 bits Figure 3.6-5 RTP header format. CHAPTER 3.6 Real-time communication over networks a 32-bit field. It indicates the source of a stream of RTP where packets that have contributed to the combined stream produced by an RTP mixer. For one-to-one video tele- D(i-1,i)=