Streaming multimedia:HTTP multimedia file retrieved via HTTP GET send at maximum possible rate under TCP variable rate,x(t) video TCP send TCP receive application file buffer buffer playout buffer server client fill rate fluctuates due to TCP congestion control, retransmissions (in-order delivery) larger playout delay:smooth TCP delivery rate HTTP/TCP passes more easily through firewalls Multimedia Networking 9-16
Streaming multimedia: HTTP ▪ multimedia file retrieved via HTTP GET ▪ send at maximum possible rate under TCP ▪ fill rate fluctuates due to TCP congestion control, retransmissions (in-order delivery) ▪ larger playout delay: smooth TCP delivery rate ▪ HTTP/TCP passes more easily through firewalls variable rate, x(t) TCP send buffer video file TCP receive buffer application playout buffer server client Multimedia Networking 9-16
Multimedia networking:outline 9.I multimedia networking applications 9.2 streaming stored video 9.3 voice-over-IP 9.4 protocols for real-time conversational applications 9.5 network support for multimedia Multimedia Networking 9-17
Multimedia networking: outline 9.1 multimedia networking applications 9.2 streaming stored video 9.3 voice-over-IP 9.4 protocols for real-time conversational applications 9.5 network support for multimedia Multimedia Networking 9-17
Voice-over-IP (VolP) VolP end-end-delay requirement:needed to maintain "conversational"aspect higher delays noticeable,impair interactivity ·<I50msec:good ·>400 msec bad includes application-level (packetization,playout), network delays session initialization:how does callee advertise IP address,port number,encoding algorithms? value-added services:call forwarding,screening, recording emergency services:9II Multimedia Networking 9-18
Voice-over-IP (VoIP) ▪ VoIP end-end-delay requirement: needed to maintain “conversational” aspect • higher delays noticeable, impair interactivity • < 150 msec: good • > 400 msec bad • includes application-level (packetization, playout), network delays ▪ session initialization: how does callee advertise IP address, port number, encoding algorithms? ▪ value-added services: call forwarding, screening, recording ▪ emergency services: 911 Multimedia Networking 9-18
VolP characteristics speaker's audio:alternating talk spurts,silent periods. 64 kbps during talk spurt pkts generated only during talk spurts 20 msec chunks at 8 Kbytes/sec:160 bytes of data application-layer header added to each chunk chunk+header encapsulated into UDP or TCP segment application sends segment into socket every 20 msec during talkspurt Multimedia Networking 9-19
VoIP characteristics ▪ speaker’ s audio: alternating talk spurts, silent periods. • 64 kbps during talk spurt • pkts generated only during talk spurts • 20 msec chunks at 8 Kbytes/sec: 160 bytes of data ▪ application-layer header added to each chunk ▪ chunk+header encapsulated into UDP or TCP segment ▪ application sends segment into socket every 20 msec during talkspurt Multimedia Networking 9-19
VolP:packet loss,delay network loss:IP datagram lost due to network congestion (router buffer overflow) delay loss:IP datagram arrives too late for playout at receiver delays:processing,queueing in network;end-system (sender,receiver)delays typical maximum tolerable delay:400 ms loss tolerance:depending on voice encoding,loss concealment,packet loss rates between 1%and 10%can be tolerated Multimedia Networking 9-20
VoIP: packet loss, delay ▪ network loss: IP datagram lost due to network congestion (router buffer overflow) ▪ delay loss: IP datagram arrives too late for playout at receiver • delays: processing, queueing in network; end-system (sender, receiver) delays • typical maximum tolerable delay: 400 ms ▪ loss tolerance: depending on voice encoding, loss concealment, packet loss rates between 1% and 10% can be tolerated Multimedia Networking 9-20