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01introB - 01introB 18 Jan 2011 CSCD58S Computer Networks...

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01introB 18 Jan 2011 CSCD58S Computer Networks 1 01introB CSCD58S Computer Networks 1 CSCD58S CSCD58S Computer Networks Computer Networks Introduction, part B: network core, Internet structure, delay & loss, protocol layers, design principles, security
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01introB 18 Jan 2011 CSCD58S Computer Networks 2 01introB CSCD58S Computer Networks 2 Chapter 1: roadmap Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge Network access and physical media 1.3 Network core Internet structure and ISPs 1.4 Delay & loss in packet-switched networks 1.5 Protocol layers, design principles 1.6 Security issues 1.7 History
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01introB 18 Jan 2011 CSCD58S Computer Networks 3 01introB CSCD58S Computer Networks 3 The network core The network core boxshadowdwn mesh of interconnected routers boxshadowdwn the fundamental question: how is data transferred through net? circleshadowdwn circuit switching: dedicated circuit per call: e.g. telephone network circleshadowdwn packet-switching: data sent thru net in discrete “chunks”: e.g. Internet
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01introB 18 Jan 2011 CSCD58S Computer Networks 4 01introB CSCD58S Computer Networks 5 Network core: circuit switching Network core: circuit switching end-end resources reserved for “call” boxshadowdwn link bandwidth, switch capacity boxshadowdwn dedicated resources: no sharing boxshadowdwn the upside: circuit-like metered performance guarantees boxshadowdwn the downsides: call setup required and capacity/usage limits.
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01introB 18 Jan 2011 CSCD58S Computer Networks 5 01introB CSCD58S Computer Networks 6 Network core: circuit switching Network core: circuit switching network resources (e.g., bandwidth) divided into “slices” boxshadowdwn slices allocated to calls (connections, users) boxshadowdwn resource slice idle if not used by owning call (no sharing) boxshadowdwn dividing link bandwidth into “slices” circleshadowdwn frequency division circleshadowdwn time division FDMA frequency time TDMA frequency time 4 users Example:
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01introB 18 Jan 2011 CSCD58S Computer Networks 6 01introB CSCD58S Computer Networks 7 Network core: packet switching Network core: packet switching each end-end data stream divided into packets boxshadowdwn user A, B packets share network resources boxshadowdwn each packet uses full link bandwidth boxshadowdwn resources used as needed , resource contention: boxshadowdwn aggregate resource demand can exceed amount available boxshadowdwn congestion: packets queue, wait for link use boxshadowdwn store and forward: packets move one hop at a time xrhombus Node receives complete packet before forwarding to next link Bandwidth division into “pieces” Dedicated allocation Resource reservation
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01introB 18 Jan 2011 CSCD58S Computer Networks 7 01introB CSCD58S Computer Networks 8 Network core: packet switching Network core: packet switching boxshadowdwn Sequence of A & B packets does not have fixed pattern, bandwidth shared on demand barb4right statistical multiplexing boxshadowdwn In TDM each host gets same slot in revolving TDM frame A B C 10 Mb/s Ethernet 1.5 Mb/s 45 Mb/s D E statistical multiplexing queue of packets waiting for output link
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