lec05b - Network Core: Packet Switching each end-end data...

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Network Core: Packet Switching each end-end data stream divided into packets ! user A, B packets share network resources ! each packet uses full link bandwidth ! resources used as needed resource contention: ! aggregate resource demand can exceed amount available ! congestion: packets queue, wait for link use ! store and forward: packets move one hop at a time " node receives complete packet before forwarding Bandwidth division into l pieces z Dedicated allocation Resource reservation Introduction 1-6
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Packet Switching: Statistical Multiplexing ! sequence of A & B packets has no fixed timing pattern " bandwidth shared on demand: statistical multiplexing . ! TDM: each host gets same slot in revolving TDM frame. A B C 100 Mb/s Ethernet 1.5 Mb/s D E statistical multiplexing queue of packets waiting for output link Introduction 1-7
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Packet-switching: store-and-forward ! takes L/R seconds to transmit (push out) packet of L bits on to link at R bps ! store and forward: entire packet must arrive at router before it can be transmitted on next link ! delay = 3L/R (assuming zero propagation delay) Example: " L = 7.5 Mbits " R = 1.5 Mbps " transmission delay = 15 sec R R R L more on delay shortly … Introduction 1-8
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Packet switching versus circuit switching Example: ! 1 Mb/s link ! each user: • 100 kb/s when l active z • active 10% of time " circuit-switching: ! 10 users " packet switching: ! with 35 users, probability > 10 active at same time is less than .0004 Packet switching allows more users to use network! N users 1 Mbps link Introduction 1-9 Q: how did we get value 0.0004? Q: what happens if > 35 users ? ! ..
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Packet switching versus circuit switching ! great for bursty data " resource sharing " simpler, no call setup ! excessive congestion: packet delay and loss " protocols needed for reliable data transfer, congestion control ! Q: How to provide circuit-like behavior? " bandwidth guarantees needed for audio/video apps " still an unsolved problem (chapter 7) Is packet switching a l slam dunk winner? z Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)? Introduction 1-10
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Tier 2 Internet structure: network of networks Introduction 1-15 Tier 1 ISP Large Content Distributor (e.g., Google ) Large Content Distributor (e.g., Akamai ) IXP Tier 1 ISP Tier 2 ISP Tier 2 ISP Tier 2 ISP Tier 2 ISP Tier 2 ISP ISP ISP Tier 2 ISP !
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This note was uploaded on 02/28/2011 for the course CS 436 taught by Professor Dr.reidholmes during the Winter '11 term at Waterloo.

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lec05b - Network Core: Packet Switching each end-end data...

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