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rtp1 - RTP 1 Real-Time Transport Protocol(RTP RTP 2 RTP...

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RTP 1 Real-Time Transport Protocol (RTP) August 12, 2001
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RTP 2 RTP protocol goals mixers and translators control: awareness, QOS feedback media adaptation August 12, 2001
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RTP 3 RTP – the big picture UDP ST-II IPv4/6 Ethernet AAL5 ATM media application control data RTCP RTP encapsulation August 12, 2001
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RTP 4 RTP = Real-time transport protocol only part of puzzle: reservations, OS, . . . product of Internet Engineering Task Force, AVT WG RFC 1889, 1890 (to be revised) initiated by ITU H.323 (conferencing, Internet telephony), RTSP, SIP, . . . support for functions, but does not restrict implementation compression for low-bandwidth networks: CRTP (RFC 2508) August 12, 2001
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RTP 5 RTP goals lightweight: specification and implementation flexible: provide mechanism, don’t dictate algorithms protocol-neutral: UDP/IP, ST-II, IPX, ATM-AALx, . . . scalable: unicast, multicast from 2 to O (10 7 ) separate control/data: some functions may be taken over by conference control protocol secure: support for encryption, possibly authentication August 12, 2001
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RTP 6 Data transport – RTP Real-Time Transport Protocol (RTP) = data + control data: timing, loss detection, content labeling, talkspurts, encryption control: (RTCP) periodic with T population QOS feedback membership estimation loop detection August 12, 2001
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RTP 7 RTP functions segmentation/reassembly done by UDP (or similar) resequencing (if needed) loss detection for quality estimation, recovery intra-media synchronization: remove delay jitter through playout buffer intra-media synchronization: drifting sampling clocks inter-media synchronization (lip sync between audio and video) quality-of-service feedback and rate adaptation source identification August 12, 2001
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RTP 8 RTP mixers, translators, . . . mixer: several media stream one new stream (new encoding) mixer: reduced bandwidth networks (dial-up) appears as new source, with own identifier translator: single media stream may convert encoding protocol translation (native ATM IP), firewall all packets: source address = translator address August 12, 2001
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RTP 9 RTP mixers, translators, . . . SSRC=39 SSRC=17 192.35.149.52 128.119.40.186 192.26.8.84 192.20.225.101 SSRC=5 DVI4 L16 GSM GSM SSRC=5 translator end system end system mixer CSRC= 17 39 August 12, 2001
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RTP 10 RTP packet header opt. opt. opt. timestamp sequence number synchronization source identifier (SSRC) M V(2) 0x00 header extension X P bytes count CSRC contributing source identifiers (CSRC) UDP packet 0 8 16 24 32 bit payload (audio,video,...) payload type August 12, 2001
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RTP 11 RTP packet header Payload type: audio/video encoding method; may change during session SSRC: sychronization source sources pick at random may change after collision ! sequence number: +1 each packet gaps loss P: padding (for encryption) last byte has padding count M: marker bit; frame, start of talkspurt delay adjustment CC: content source count (for mixers) CSRC: identifiers of those contributing to (mixed into) packet August 12, 2001
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RTP 12 RTP timestamp +1 per sample (e.g., 160 for 20 ms packets @ 8000 Hz) random starting value
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