y H323 Protocols Stack- video coding/decoding H 261: compression/decompression of digital video, specified by ITU in 1990, P 64kbps, mainly in ISDN, (from M777 p52) H263, defined by Itu, compression of the moving picture component of audio-visual service at low bit rates JPEG treats its picture independently( intraframe coding while h261 tries to predict the current picture from the previous one interframe coding) MPEG-Motion Picture Experts Group, belongs a family of Iso/EC (International Electrical Committee MPEG-1 uses the same format as H 261, but allows a greater choice of image size MPEG-2 developed by ISO/EC, ITU, up to 100Mbps for Video supports HDTV MPEG-4 video coding method for low bit rates 202l/1/27 Dr. Zhanqi XU, National Key Lab on ISN, Xidian University
2021/1/27 Dr. Zhanqi XU, National Key Lab on ISN, Xidian University 11 ✓ H.323 Protocols Stack－video coding/decoding H.261: compression/decompression of digital video, specified by ITU in 1990 , P*64kbps, mainly in ISDN, (from M777 p52) H.263, defined by ITU, compression of the moving picture component of audio-visual service at low bit rates. JPEG treats its picture independently( intraframe coding) while H.261 tries to predict the current picture from the previous one (interframe coding) MPEG-Motion Picture Experts Group, belongs a family of ISO/IEC (International Electrical Committee ) MPEG-1 uses the same format as H.261, but allows a greater choice of image size MPEG-2 developed by ISO/IEC, ITU , up to 100Mbps for Video, supports HDTV MPEG-4 video coding method for low bit rates
yH.323 Protocols Stack-RTP/RtCP comments RTP comments. Sequencing: sequence nu. for detecting lost packets Sync. timestamps to compensate the different delay jitter, needed by player-out buffers Payload: identified the encoding of media, to change the encoder of media dynamically due to the bandwidth availability Source identification: identifier for the originator of the frame in multicast session RTCP comments. In RTP session, the participants periodically send RTCP packets to obtain Qos info, etc QoS feedback: no. of lost packets, round-trip time, jitter, etc Session CTRL: leaving a session by sending BYe packet Identification: info such as e-mail, name, phone Intermedia Sync: synchronizing the video and audio for receiver play
2021/1/27 Dr. Zhanqi XU, National Key Lab on ISN, Xidian University 12 ✓ H.323 Protocols Stack-RTP/RTCP comments RTP comments: Sequencing: sequence nu. for detecting lost packets Sync. : timestamps to compensate the different delay jitter, needed by player-out buffers. Payload: identified the encoding of media, to change the encoding of media dynamically due to the bandwidth availability. Source identification: identifier for the originator of the frame in multicast session. RTCP comments: In RTP session, the participants periodically send RTCP packets to obtain QoS info, etc. QoS feedback: no. of lost packets, round-trip time, jitter, etc. Session CTRL: leaving a session by sending BYE packet Identification: info. such as e-mail, name, phone Intermedia Sync.: synchronizing the video and audio for receiver to play
√SIP# Developed by IETF MMUSIC (Multi-Party Multimedia Session Control work group evolved from Http SIP features Open, simple, and lightweight protocol Text- based protocol(text:文本、明文) Internet heritage- easier to integrate with telephony/video and Internet functions Already implemented on most soft-switches and gatew Advanced extensibility Transport independent-TCPor UDP (reliability for both) SIP Architecture(next page) 202l/1/27 Dr. Zhanqi XU, National Key Lab on IsN, Xidian University
2021/1/27 Dr. Zhanqi XU, National Key Lab on ISN, Xidian University 13 –SIP features • Open, simple, and lightweight protocol • Text –based protocol (text: 文本、明文) • Internet heritage – easier to integrate with telephony/Video and Internet functions • Already implemented on most soft-switches and gateways • Advanced extensibility • Transport independent-TCP or UDP (reliability for both) –SIP Architecture (next page) ✓ SIP# Developed by IETF MMUSIC (Multi-Party Multimedia Session Control) work group, evolved from HTTP
√ SIP Architecture Control and management Micro- deo phone Application Videolaudio coding SIP RTCP RTP Request TCP Response NIC Redirect Location Server 7 Service Agent server SIP Proxy 10 12 SIP Client 1 SIP Client 2 SIP Proxy 202l/1/27 Dr. Zhanqi XU, National Key Lab on ISN, Xidian University
2021/1/27 Dr. Zhanqi XU, National Key Lab on ISN, Xidian University 14 NIC IP 7 SIP Proxy Control and management ✓ SIP Architecture Redirect Server 2 3 4 6 8 9 10 11 SIP Client 1 Request Response 12 1 Agent Server Location Service 5 SIP Client 2 SIP Proxy SIP Terminal TCP UDP Video/Audio coding RTCP RTP Application
Y SIP Components o Clients Redirect server End systems Network"server: redirects Send sIP requests users to try other server Usually contain SIP (user agent may act as a user agent server redirect server) ● User Agent Server ● Proxy server Listens for call Network Server Proxies requests request to another server Prompts user or (user agent also may do this executes program to can“ fork"request to multiple servers, creating a determine response search tree 注解:agen近用户, proxy-般远离用户;(仅对SP)前者翻译为 “用户代理”,后者译为“网络代理”; what is your better idea about their translations
2021/1/27 Dr. Zhanqi XU, National Key Lab on ISN, Xidian University 15 ✓ SIP Components ⚫ Clients – End systems – Send SIP requests – Usually contain SIP user agent server ⚫ Redirect Server – “Network” server; redirects users to try other server (user agent may act as a redirect server) ⚫ User Agent Server – Listens for call requests – Prompts user or executes program to determine response ⚫ Proxy Server – “Network Server” Proxies request to another server (user agent also may do this) – Can “fork” request to multiple servers, creating a search tree 注解：agent接近用户，proxy一般远离用户；（仅对SIP）前者翻译为 “用户代理”，后者译为“网络代理”；what is your better idea about their translations?