ethod Binary the video decoder to decode a video frame as soon as the Family ITU-T last packet arrives. SN specifies the sequence number of the RTP packet. Transport TCP or UDP It increases by one when one RTP data packet is sent. The Packet loss recovery Through SIP itself Through TCP initial sequence number of the first RTP packet for an RTP session should be randomly generated. For different Capability exchange SDP (simple but H.245 (rich but media, the initial value may be different. For real-time limited) complicated) telephony applications, the receiver can use the sequence Security Through other IETF; Not very good numbers to detect any lost packets. protocols for The timestamp TS reflects the sampling time of the first encryption, octet in the RTP packet payload. The sampling time should authentication, etc. be calculated from a clock that increases monotonically and Features Call holding, call Call holding, call linearly in time to allow synchronization and jitter calcu- transfer, call transfer, call lations. The timestamp may increase at a different pace for forwarding, call forwarding, call different media. For example, speech data are usually waiting, waiting, conferencing conferencing, instant sampled at 8000 Hz and each speech frame can typically messaging have 160 samples. Each RTP packet for speech will have a timestamp increment of 160. For video data sampled at 15 frames per second, the timestamp increment is 6000, fact that IP networks often introduce jitter in packets' based on a 90,000-Hz clock. If an encoded video frame is arrival time and sometimes packet reordering. RTP itself, pack-etized into several RTP packets, each RTP packet will however, does not provide any mechanism to ensure have the same timestamp as the data in each RTP packet are timely delivery or to provide another quality of service. sampled at the same time instant. Figure 3.6-5 shows the format of an RTP packet and A timestamp is particularly useful for media playout its RTP header. Typically, in one-to-one telephony ap- 