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Multimedia Session Protocols Overview

Explore multimedia session protocols such as RTP and RTCP. Learn about error detection, correction codes, and real-time transmission protocols. Understand the relation between RTP and RTCP for effective multimedia communication.

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Multimedia Session Protocols Overview

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  1. CS 414 – Multimedia Systems DesignLecture 22 – Multimedia Session Protocols Klara Nahrstedt Spring 2014 CS 414 - Spring 2014

  2. Administrative • MP1,HW1, Midterm graded • Pick up your HW1 and midterm from TA during office hours or by appointment • Regrading: meet with TA or email TA asking for regarding • He will facilitate the regarding with the graders • Deadline until Wednesday, March 19 (one week) • If you can’t make the deadline, email to TA and Instructor CS 414 - Spring 2014

  3. Outline • Error Control • Multimedia Protocols – Standards • RTP/UDP/IP – Transmission Protocol • RTCP Control/Negotiation Protocol to RTP CS 414 - Spring 2014

  4. Covered Aspects of Multimedia Audio/Video Presentation Playback Image/Video Capture Audio/Video Perception/ Playback Image/Video Information Representation Transmission Transmission Compression Processing Audio Capture Media Server Storage Audio Information Representation A/V Playback CS 414 - Spring 2014

  5. Error Detection • Ability to detect the presence of errors caused by noise or other impairments during transmission from sender to receiver • Traditional mechanisms: check-summing, PDU sequencing • Checksum of a message is an arithmetic sum of message code words of a certain word length (e.g., byte) • CRC – Cyclic Redundancy Check – function that takes as input a data stream of any length and produces as output a value (commonly a 32-bit integer) – can be used as a checksum to detect accidental alteration of data during transmission or storage • Multimedia mechanisms: byte error detection at application PDU, time detection CS 414 - Spring 2014

  6. Design of Error Correction Codes • Automatic repeat-request (ARQ) • Transmitter sends the data and also an error detection code, which the receiver uses to check for errors, and requests retransmission for erroneous data • The receiver sends ACK (acknowledgement of correctly received data) • Forward Error Correction (FEC) • Transmitted encodes the data with an error-correcting code (ECC) and sends the coded msg. No ACK exists. CS 414 - Spring 2014

  7. Error Control • Error Correction • Traditional mechanisms: retransmission using acknowledgement schemes, window-based flow control • Multimedia mechanisms: • Go-back-N Retransmission • Selective retransmission • Partially reliable streams • Forward error correction • Priority channel coding • Slack Automatic Repeat Request CS 414 - Spring 2014

  8. Go-back-N Retransmission CS 414 - Spring 2014

  9. Internet Multimedia Protocol Stack Media encaps (H.264, MPEG-4) DASH APPLICATION RTSP RSVP RTCP Layer 5 (Session) SIP RTP HTTP Layer 4 (Transport) TCP DCCP UDP KERNEL Layer 3 (Network) IP Version 4, IP Version 6 AAL3/4 AAL5 MPLS Layer 2 (Link/MAC) Ethernet/WiFi ATM/Fiber Optics CS 414 - Spring 2014

  10. Internet Multimedia Protocol Stack Media encaps (H.264, MPEG-4) DASH APPLICATION RTSP RSVP RTCP Layer 5 (Session) SIP RTP HTTP Layer 4 (Transport) TCP DCCP UDP KERNEL Layer 3 (Network) IP Version 4, IP Version 6 AAL3/4 AAL5 MPLS Layer 2 (Link/MAC) Ethernet/WiFi ATM/Fiber Optics CS 414 - Spring 2014

  11. Service Requirements for Real-time Flows (Voice/Video) Sequencing Intra-media synchronization Inter-media synchronization Payload identification Frame indication CS 414 - Spring 2014

  12. Real-time Transmission Protocol (RTP) RTP RTCP Layer 4 User Datagram Protocol Internet Protocol Ethernet 802.13 or Wi-Fi 802.11 PHY (Wired or Wireless) RTP provides end-to-end transport functions suitable for real-time audio/video applications over multicast and unicast network services RTP companion protocol – Real-time Transport Control Protocol (RTCP) CS 414 - Spring 2014

  13. Relation between RTP and RTCP Application Application Decoding Coding Coding Decoding RTP RTCP RTCP RTP UDP/IP UDP/IP CS 414 - Spring 2014

  14. RTCP: Control and Management • Out-of-band control information for RTP flow. • Monitors QoS for RTP in the delivery and packaging of multimedia data • Used periodically to transmit control packets to participants in a streaming multimedia session. • Provides feedback on the quality of service being provided by RTP. • Gathers statisticson media connection • Bytes sent, packets sent, lost packets, jitter, feedback and round trip delay. • Application may use this information to increase the quality of service, perhaps by limiting flow or using a different codec. CS 414 - Spring 2014

  15. RTCP Functions • There are several type of RTCP packets: • Sender report packet, • Receiver report packet, • Source Description RTCP Packet, • Goodbye RTCP Packet and • Application Specific RTCP packets. • RTCP itself does not provide any flow encryption or authentication means. SRTCP protocol can be used for that purpose. CS 414 - Spring 2014

  16. RTP Services • Payload Type Identification • Determination of media coding • Source identification • RTP works with Profiles • Profile defines a set of payload type codes and their mappings to payload formats • Sequence numbering • Error detection • Time-stamping • Time monitoring, synchronization, jitter calculation • Delivery monitoring CS 414 - Spring 2014

  17. RTP Services – Support of Heterogeneity • Mixer service • Allows for resynchronization of incoming audio packets • Reconstructs constant 20 ms spacing generated by sender • Mixes reconstructed audio streams into single stream • Translates audio encoding to lower bandwidth • Forwards lower bandwidth packet streams • Translator service • Allows for translation between IP and other high speed protocols • May change encoding data CS 414 - Spring 2012

  18. Difference between Mixers and Translators S3 S1 R1 M1 M2 T S2 S4 CS 414 - Spring 2012

  19. RTP Common Header Ver – Version 2 P – Padding X – Extension, if set, the fixed head is followed by exactly one header extension CC – CSRC count M – Marker – intended to allow significant events such as frame boundaries to be marked (defined by profile) PT – Payload type SSRS – synchronization source, CSRC – contribution source CS 414 - Spring 2012

  20. Payload Formats • Static Payload formats • Established in RTP Profile • Payload type 0 := µ-law audio codec • Dynamic Payload formats • Applications agree per session on payload format • H.263, JPEG, MPEG CS 414 - Spring 2012

  21. Conclusion RTP usage – in several application audio and video tools (vat, vic) RTP follows the principle of application level framing and integrated layer processing RTP/UDP/IP is being used by the current streaming session protocols such as RTSP Session protocols are actually negotiation/session establishment protocols that assist multimedia applications Multimedia applications such as QuickTime, Real Player and others use them CS 414 - Spring 2014

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