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Unformatted text preview: Data and Computer Communications Communications
Chapter 24 – Internet Applications – Chapter Multimedia Multimedia
Eighth Edition by William Stallings Lecture slides by Lawrie Brown Internet Applications – Multimedia Internet Applications
Prior to the recent explosion of sophisticated research, scientists believed that birds required no special awareness or intelligence to perform their migrations and their navigational and homing feats. Accumulated research shows that in addition to performing the difficult tasks of correcting for displacement (by storms, winds, mountains, and other hindrances), birds integrate an astonishing variety of celestial, atmospheric, and geological information to travel between their winter and summer homes. In brief, avian navigation is characterized by the ability to gather a variety of informational cues and to interpret and coordinate them so as to move closer toward a goal. —The Human Nature of Birds, Theodore Barber Audio and Video Compression Compression multimedia applications need efficient use multimedia of transmission capacity of hence audio/video compression hence algorithms algorithms techniques standardized by MPEG lossless compression loses no information limited by redundancy in original data lossy compression provides acceptable lossy approximation to original (typically use) approximation Simple Audio Compression Simple must first digitize audio signal, eg. PCM sample at twice highest frequency then quantize using fixed number of bits effectively compression algorithm otherwise need unlimited number of bits compress further by reducing sampling compress frequency or number of bits frequency or use more sophisticated approaches as in MPEG Layer 3 (MP3) giving 10:1 compression Effective Audio Compression Effective Video Compression Video moving picture a sequence of still images hence can compress each individually but get greater efficiency by using but similarities between adjacent images similarities encode just differences between them approach used in MPEG MPEG Video Compression MPEG Video Compression MPEG MPEG Video Compression MPEG important features in video compression random access - needs access frames fast forward / reverse - scan stream using fast access frames access prediction interpolation MPEG foundation is motion compensation Prediction Prediction MPEG uses 16x16 pixel macroblocks for MPEG motion compensation motion each block encoded separately each with reference to preceeding anchor frame with most closely matching it most matching block not on 16-pixel boundary compare against decompressed frame MPEG then records motion vector and MPEG prediction error for current frame prediction Interpolation Interpolation have further compression improvement by using have two reference frames two bidirectional interpolation process current against frames before and after encode using: block from before (forward prediction) block from after (backward prediction) average of blocks before and after (averaging) interpolation encodes more info than prediction MPEG Frame Ordering MPEG MPEG uses three types of frames: intraframe (I) predicted (P) bidirectional interpolated (B) balance need for random access and FF/Rev balance with computational complexity and size with noting B frames rely only on I and P frames relative frequency is configurable MPEG Frame Ordering MPEG Real-Time Traffic Real-Time increasing deployment of high-speed nets increasing sees increasing real-time traffic use sees has different requirements to traditional has non real-time traffic non traditionally throughput, delay, reliability real-time more concerned with timing issues with deadline for delivery of data block Real-Time Traffic Traffic Example Real-Time Traffic Profiles Real-Time Real-Time Traffic Requirements Requirements low jitter low latency integrate non-real-time and real-time services adapts to changing network / traffic conditions good performance for large nets / connections modest buffer requirements within the network high effective capacity utilization low overhead in header bits per packet low processing overhead Hard vs Soft Real-Time Apps Hard soft real-time applications tolerate loss of some data hence impose fewer requirements on network can focus on maximizing network utilization zero loss tolerance hence deterministic upper bound on jitter and hence high reliability take precedence over utilization high hard real-time applications Session Initiation Protocol (SIP) (SIP) control protocol for setting up, modifying, control and terminating real-time sessions defined in RFC 3261 five multimedia communications facets: user location user availablility user capabilities session setup session management SIP Design Elements SIP based on earlier protocols HTTP request/response transaction model client invokes server method/function receives at least one response using most header fields, encoding rules, and using status codes of HTTP status DNS like recursive and iterative searches incorporates the use of a Session incorporates Description Protocol (SDP) Description SIP Components SIP SIP Servers and Protocols SIP servers are logical devices may be distinct servers or combined in one user agent uses SIP to setup session iinitiation dialogue uses SIP involving one or nitiation more proxies to relay to remote agent more proxies act as redirect servers if needed consulting location service DB protocol used here outside SIP DNS also important SIP uses UDP for performance reasons can use TLS for security if desired Session Description Protocol (SDP) (SDP) defined in RFC 2327 have SDP encoded body in SIP message specifies information on media encodings parties specifies can and will use can after exchange parties know IP addresses, after transmission capacity, media types transmission may then exchange data using a suitable may transport protocol, eg. RTP transport change session parameters with SIP messages SIP Uniform Resource Identifier (URI) Identifier identifies a resource within a SIP network eg. user, mailbox, phone number, group eg. sip:firstname.lastname@example.org format based on email address may also include password, port number may and other parameters and “sips” for secure transmission over TLS SIP Example SIP SIP Example SIP SIP Example SIP SIP Example SIP SIP Messages SIP SIP a text based protocol, cf. HTTP have request messages first line a method name and request-URI first line a response code have response messages SIP Requests SIP defined by RFC 3261 REGISTER INVITE ACK CANCEL BYE OPTIONS SIP Request Example SIP
INVITE sip:email@example.com SIP/2.0 Via: SIP/2.0/UDP 184.108.40.206:5060 Max-Forwards: 70 To: Bob <sip:firstname.lastname@example.org> From: Alice <sip:email@example.com>;tag=1928301774 Call-ID: firstname.lastname@example.org CSeq: 314159 INVITE Contact: <sip:email@example.com> Content-Type: application/sdp Content-Length: 142 SIP Response SIP Provisional (1xx) Success (2xx) Redirection (3xx) Client Error (4xx) Server Error (5xx) Global Failure (6xx) SIP Response Example SIP
SIP/2.0 200 OK Via: SIP/2.0/UDP server10.biloxi.com Via: SIP/2.0/UDP Via: SIP/2.0/UDP bigbox3.site3.atlanta.com Via: SIP/2.0/UDP 220.127.116.11:5060 To: Bob <sip:firstname.lastname@example.org>;tag=a6c85cf From: Alice <sip:email@example.com>;tag=1928301774 Call-ID: firstname.lastname@example.org CSeq: 314159 INVITE Contact: <sip:email@example.com> Content-Type: application/sdp Content-Length: 131 Session Description Protocol (SDP) (SDP) describes content of sessions includes information on: media streams addresses ports payload types start and stop times originator Real-Time Transport Protocol (RTP) (RTP) TCP has disadvantages for real-time use is point-to-point, not suitable for multicast includes retransmission mechanisms has no timing mechanisms UDP can address some needs but not all have Real-Time Transport Protocol (RTP) defined in RFC 1889 best suited to soft real-time applications data transfer (RTP) & control (RTCP) protocols RTP Protocol Architecture RTP have close coupling between RTP and have application-layer functionality application-layer view RTP as framework used by applications imposes structure and defines common imposes functions functions key concepts: application-level framing application-level integrated layer processing Application-Level Framing TCP transparently performs data recovery have scenarios where more appropriately have done by application layer done when less than perfect delivery acceptable when application can better provide data preserved by lower layer processing form unit of error recovery iif lose part of ADU discard and retransmit f entire ADU entire have application-level data units (ADUs) Integrated Layer Processing Integrated layered protocols have sequential layered processing of functions in each layer processing limits parallel or re-ordered functions instead integrated layer processing allows instead tight coupling between adjacent layers for greater efficiency greater concept that strict layering is inefficient is concept not new, cf. RPC implementation not Integrated Layer Processing Integrated RTP Data Transfer Protocol RTP supports transfer of real-time data amongst participants in a session define session by RTP port (UDP dest port) RTCP port (dest port for RTCP transfers) participant IP addresses (multicast or unicast) iincludes identity of source, timestamp, ncludes payload format payload strength is multicast transmission RTP Relays RTP relay on intermediary system acts as both destination and source to relay data between systems combines streams from multiple sources forwards new stream to one or more dests may change data format if needed simpler, sends 1+ RTP packets for each 1 in simpler, mixer translator RTP Data Transfer Header RTP RTP Control Protocol (RTCP) RTP separate control protocol same transport (eg. UDP) but different port packets sent periodically to all members Quality of Service (QoS), congestion control identification session size estimation and scaling session control RTCP functions: RTCP Packet Types RTCP have multiple RTCP packets in datagram Sender Report (SR) Receiver Report (RR) Source Description (SDES) Goodbye (BYE) Application Specific RCTP Packets RCTP Summary Summary audio and video compression real-time traffic session initiation protocol (SIP) real-time transport protocol (RTP) ...
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This note was uploaded on 04/06/2011 for the course EE 5363 taught by Professor Kang during the Spring '09 term at NYU Poly.
- Spring '09