1 / 32

Agenda

Agenda. A brief overview to RTP and RTCP. Real-Time Transport Protocol (RTP). Protocol to the continuous transmission of audiovisual data (streams) over IP-based networks Product of Internet Engineering Task Force, AVT WG Standardized first in 1996 RFC 1889 In 2003, a revised RFC

taji
Télécharger la présentation

Agenda

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Agenda • A brief overview to RTP and RTCP

  2. Real-Time Transport Protocol (RTP) • Protocol to the continuous transmission of audiovisual data (streams) over IP-based networks • Product of Internet Engineering Task Force, AVT WG • Standardized first in 1996 • RFC 1889 • In 2003, a revised RFC • RFC 3550 which obsoletes RFC 1889. :

  3. 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 :

  4. RTP overview • RTP is a packet-based protocol • usually running over UDP • Transport multimedia data streams (audio, video, text, etc.) over networks • Encode • Package • Send • It applies in many areas • IP telephony technologies (H.323, SIP) • RTP is mainly used for transmission of realtime sensitive data flows, while the Real-Time Streaming Protocol (RTSP) manages and controls the data transmission. :

  5. Architecture :

  6. The RTP header • Ver. (2 bits) • Indicates the version of the protocol. Current version is 2. • P  (1 bit) • Indicates if there are extra padding bytes at the packet. • X  (1 bit) • Indicates if protocol extensions are being used in the packet. • CC  (4 bits) • Number of CSRC identifiers that follow the fixed header. • M  (1 bit) • If it is set, data has some special relevance for the application. • PT  (7 bits) • Format of the payload and determines its interpretation by the application. :

  7. What else • Synchronisation Source  • The data source, characterized by an identifier (32 bit) in the header • Mixer • Switching center, which receive RTP packets from one or multiple sources and forward them. • Mix packages (and synchronizes) and can carry out format conversions. • Translator • Don‘t modify packets, but route through firewalls etc. • Reciever • The reciever of the RTP packets sorts them on the basis of the sequence numbers and submits them to the respective application. :

  8. Real Time Control Protocol (RTCP) • Dient der Aushandlung und Einhaltung von Quality of Service (QoS) Parametern durch den periodischen Austausch von Steuernachrichten zwischen Sender und Empfänger • Mittels: • Rückmeldung der bisher erbrachten Dienstqualität, wodurch eine Anpassung der Übertragungsrate erfolgen kann • Identifikation aller Sitzungsteilnehmer, wodurch semantisch zusammenhängende aber getrennt gesendete Medienströme synchronisiert werden können • Steuerung der für RTCP-Pakete verwendeten Bandbreite, damit der Austausch von RTCP-Nachrichten nicht die Übertragung behindert, was bei vielen Sitzungsteilnehmern passieren könnte.

  9. RTCP packet structure

  10. RTCP sender reports (SR) • SSRC of sender: identifies source of data • NTP timestamp: when report was sent • RTP timestamp: corresponding “RTP time”  lip sync • sender’s packet count: total number sent • sender’s octet count: total number sent • followed by zero or more receiver report

  11. RTCP receiver reports (RR) • SSRC of source: identifies who’s being reported on • fraction lost: binary fraction • cumulative number of packets lost: long-term loss • highest sequence number received: compare losses, disconnect • interarrival jitter: smoothed interpacket distortion • LSR: time last SR heard • DLSR: delay since last SR

  12. Questions • Find more on the online slides

  13. Agenda • Streaming Motivation The RTSP/RTP Session Overview Bits from example Session

  14. RTSP • Wikipedia: • The Real Time Streaming Protocol (RTSP), developed by the IETF and created in 1998 as RFC 2326, is a protocol for use in streaming media systems which allows a client to remotely control a streaming media server, issuing VCR-like commands such as "play" and "pause", and allowing time-based access to files on a server. • The sending of streaming data itself is not part of the RTSP protocol. Most RTSP servers use the standards-based RTP as the transport protocol for the actual audio/video data, acting somewhat as a metadata channel. • …

  15. Resources on the Web • Wikipedia is a good start: • http://en.wikipedia.org/wiki/Real_Time_Streaming_Protocol • RFC RTSP: http://tools.ietf.org/html/rfc2326 • RFC RTP: http://tools.ietf.org/html/rfc3550 • Tutorial on RTSP: • http://www.myiptv.org/Articles/RTSP/tabid/72/Default.aspx • Pictures and parts of text taken from: • http://www.cs.columbia.edu/~hgs/rtsp/

  16. Streaming vs. Television • - reuse existing infrastructure • - flexible media: modem, wireless, cable, LAN, . . . • - Quality scales from stamp-size flipbook to HDTV – adaptive • - Side information easy (closed captioning) • - Easy integration with WWW • - Security through encryption • - Cheap authoring, service lots of content

  17. Applications • - Lectures, seminars • - On-demand instruction • - Entertainment: specialty content (cf. youtube) • Voice mail - P2P video streaming

  18. Challenges • bandwidth: 64–128 kb/s for talking heads, 1.5 Mb/s for movies • quality: packet loss, predictability • reliability: makes CATV look good. . . • billing infrastructure: pay-per-view? • cheap receivers: shouldn’t cost more than set-top box

  19. Internet real-time & multimedia protocols • resource reservation: RSVP, … • media transport: RTP, AVP, … • stream control: RTSP • stream description: SDP, … SDP: http://tools.ietf.org/html/rfc4566 AVP: http://www.ece.osu.edu/~zheng/publications/AVP-protocol.pdf

  20. RTSP and HTTP: similarities • Protocol format: text, MIME-headers • Request/response = request line + headers + body • Status codes • Security mechanisms • URL format

  21. RTSP is not HTTP • - Server state needed • - Different methods • - Server client • - Protocol Extension posssible: • Extensions start with “x-”, e.g.: x-historyLog

  22. Agenda • Streaming Motivation The RTSP/RTP Session Overview Bits from example Session

  23. RTSP / RTP Session

  24. RTSP URLs • Whole presentation: • rtsp://media.example.com:554/twister • track within presentation: • rtsp://media.example.com:554/twister/audiotrack • but: name hierarchy != media hiearchy != file system

  25. RTSP Request headers • Accept media description formats • Accept-Encoding encoding of media format • Accept-Language human language • Authorization basic and digest authentication • Bandwidth client bandwidth available • Conference conference identifier • From name of requestor • If-Modified-Since conditional retrieval • Range time range to play • Referer how did we get here? • Scale (play time)/(real time) • Speed speed-up delivery • User-Agent software

  26. RTSP Response headers • Location redirection • Proxy-Authenticate authenticate to proxy • Public methods supported • Retry-After busy, come back later • Server server software • Vary cache tag • WWW-Authenticate request authorization • Hint: • All headers and bodies end with a double carriage return line feed.

  27. Time Formats • smpte=0:10:00 “Society of Motion Picture and Television Engineers” - hour:minute:second:frame - optional • npt=126.315 Normal play time - {hh;mm;ss}.ms • - mandatory • Rtptime= 1324433 Part of RTP, needed to differentiate between emission time and media time • seq=1214324432 part of RTP != time; sequence number of first frame

  28. Agenda • Streaming Motivation The RTSP/RTP Session Overview Bits from example Session

  29. Unicast session: open streams • C->S: SETUP rtsp://audio.com/twister/audio.en RTSP/1.0 • CSeq: 1 • Transport: RTP/AVP/UDP;unicast;client_port=3056-3057 • S->C: RTSP/1.0 200 OK • CSeq: 1 • Session: 12345678 • Transport: RTP/AVP/UDP;unicast; • client_port=3056-3057;server_port=5000-5001 • C->S: SETUP rtsp://video.com/twister/video RTSP/1.0 • CSeq: 1 • Transport: RTP/AVP/UDP;unicast;client_port=3058-3059 • S->C: RTSP/1.0 200 OK • CSeq: 1 • Session: 23456789 • Transport: RTP/AVP/UDP;unicast; • client_port=3058-3059;server_port=5002-5003 Error Codes listed in RFC, but same as HTTP

  30. Unicast session: play • C->S: PLAY rtsp://video.com/twister/video RTSP/1.0 • CSeq: 2 • Session: 23456789 • Range: smpte=0:10:00- • S->C: RTSP/1.0 200 OK • CSeq: 2 • Session: 23456789 • Range: smpte=0:10:00-0:20:00 • RTP-Info: url=rtsp://video.com/twister/video;seq=12312232;rtptime=78712811 • C->S: PLAY rtsp://audio.com/twister/audio.en RTSP/1.0 • CSeq: 2 • Session: 12345678 • Range: smpte=0:10:00- • S->C: RTSP/1.0 200 OK • CSeq: 2 • Session: 12345678 • Range: smpte=0:10:00-0:20:00 • RTP-Info: url=rtsp://audio.com/twister/audio.en;seq=876655;rtptime=1032181 RTP Interaction

  31. Summary • - Internet multimedia-on-demand • Integrated services • Protocol Extensions • - Conferencing • - Telephony • - WebTV as VOD • - Flexible plug and play RTSP/RTP/AVP/SDP ….

More Related