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Computer Networking: A Top Down Approach lecture notes
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Computer Networking: A Top Down Approach 6 th edition Jim Kurose, Keith Ross Addison-Wesley March 2012
ranging from a simple inter-office intercom to complex multi-point teleconferencing / shared screen environments.
IP Network Multimedia PC Multimedia PC Initially, PC to PC voice calls over the Internet PSTN (DC) Gateway PSTN (NY) Gateway Public Switched Telephone Network Gateways allow PCs to reach phones …or phones to reach phones
Complex multi-point teleconferencing Shared screen environments
Model 7960 Executive set: 6 programmable line /feature 4 interactive soft keys:
MCS-7835 Call Mgr. Telecomm MCS-7835 Call Mgr. NERDC MCS-7835 Call Mgr. OIR 7960 7960 DDF/CETS 7960 7960 C3524-PWR C3524-PWR C3524-PWR C3524-PWR PSTN Service CI SCO V G V OICE GATEW (^200) AY P OWE R RP S ACTI VIT Y VG Analog Gtwy - Analog Gtwy - UF Campus Core UF AVVID Campus Pilot PRI (future) Cisco Architecture for Voice, Video and Integrated Data (AVVID) (Simplified for Information)
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: 999
Speaker’s audio: alternating talk spurts, silent periods. 64 kbps during talk spurt Pkt’s generated only during talk spurts 20 msec chunks at 8 Kbytes/sec:
receiver attempts to playout each chunk exactly q msecs after chunk was generated (received!). chunk has time stamp t: play out chunk at t+q chunk arrives after t+q : data arrives too late for playout: data “lost” tradeoff in choosing q : large q: less packet loss small q: better interactive experience
sender generates packets every 20 msec during talk spurt. first packet received at time r first playout schedule: begins at p second playout schedule: begins at p ’ Multimedia Networking 7 - 20
packets time packets generated packets received loss r p p' playout schedule p' - r playout schedule p - r P - r P’ - r
