03-PreliminariesPriorities - Preliminaries, Protocols,...

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1 Preliminaries, Protocols, Preview Priorities, and Principles EE122 Fall 2011 Scott Shenker http://inst.eecs.berkeley.edu/~ee122/ Materials with thanks to Jennifer Rexford, Ion Stoica, Vern Paxson and other colleagues at Princeton and UC Berkeley
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2 Announcements • TAs gave me brutal feedback – Need to cover more of the basics – Goal today: fluency in packets, probability, terminology • Homework #1 Out – This is about learning, not evaluation – But please try to do it on your own first – Will entertain questions in office hours and in class • Today’s lecture will spill over into next week • There is a special place in hell reserved for the designer of Powerpoint’s animation package…. .
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Outline • Preliminaries – Life of a packet, types of delay, Little’s Law, etc. – Protocols – Client-server architectures • Preview of homework assignment – Clear up any misunderstanding • Design priorities (probably today) – Clark’s 1988 paper • Design Principles (I hope not today) – The good stuff…. . 3
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Preliminaries
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Nodes and Links • Link: transmission technology – Twisted pair, optical, radio, whatever • Node: computational devices on end of links – Host: general-purpose computer – Network node: switch or router 5 Node Node Link
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Properties of Links • Latency (delay) – Propagation time for data sent along the link – Corresponds to the “length” of the link • Bandwidth (capacity) – Amount of data sent (or received) per unit time – Corresponds to the “width” of the link • Bandwidth-delay product: (BDP) – Amount of data that can be “in flight” at any time – Propagation delay × bits/time = total bits in link 6 bandwidth latency delay x bandwidth
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Examples of Bandwidth-Delay • Same city over slow link: – B~100mbps – L~.1msec – BDP ~ 10000bits ~ 1.25MBytes • Cross-country over fast link: – B~10Gbps – L~10msec – BDP ~ 10 8 bits ~ 12.5GBytes • Another example where the Internet has to be prepared for a wide range of conditions! 7
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Examples of Transmission Times • 1500 byte packet over 14.4k modem: ~1 sec • 1500 byte packet over 10Gbps link: ~10 -6 sec 8
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Utilization • Fraction of time link is busy transmitting – Often denoted by ρ • Ratio of arrival rate to bandwidth – Arrival: A bits/sec on average – Utilization = A/B 9
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Packets • Payload (Body) – Data being transferred • Header – Instructions to the network for how to handle packet – Think of the header as an interface! 10
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The Lifecycle of Packets 11 Excess Packets Stored in Buffer Packet Arriving at Switch Packet Being Transmitted Packet Buffer Link Packet Currently Being Transmitted
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The Delays of Their Lives 12 Queueing Delay Transmission Delay Propagation Delay is how long it takes to reach the next switch after transmission Round-Trip Time (RTT) is the time it takes a packet to reach the destination and the response to return to the sender
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Review of Networking Delays • Propagation delay: latency
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03-PreliminariesPriorities - Preliminaries, Protocols,...

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