15-CongestionControl - Congestion Control EE122 Fall 2011...

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1 Congestion Control 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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Announcements • Get exams after class • No office hours on Thursday – See me tonight, or Wednesday 2
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3 TCP Refresher Same slides, more focus…. “Know This”
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4 TCP Header Source port Destination port Sequence number Acknowledgment Advertised window HdrLen Flags 0 Checksum Urgent pointer Options (variable) Data Starting sequence number (byte offset) of data carried in this segment This is the number of the first byte of data in packet!
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5 TCP Header Source port Destination port Sequence number Acknowledgment Advertised window HdrLen Flags 0 Checksum Urgent pointer Options (variable) Data Acknowledgment gives seq # just beyond highest seq. received in order . What s Next
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6 3-Way Handshaking Client (initiator) Server Active Open Passive Open connect() listen() accept()
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7 Sequence Numbers Host A Host B TCP Data TCP Data TCP HDR TCP HDR ISN (initial sequence number) Sequence number = 1 st byte ACK sequence number = next expected byte
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Data and ACK in same packet • The sequence number refers to data in packet – Packet from A carrying data to B • The ACK refers to received data in other direction – A acking data that it received from B 8
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9 TCP Header Source port Destination port Sequence number Acknowledgment Advertised window HdrLen Flags 0 Checksum Urgent pointer Options (variable) Data Buffer space available for receiving data. Used for TCP s sliding window . Interpreted as offset beyond Acknowledgment field s value.
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10 TCP Segment • IP packet – No bigger than Maximum Transmission Unit ( MTU ) – E.g., up to 1,500 bytes on an Ethernet • TCP packet – IP packet with a TCP header and data inside – TCP header 20 bytes long • TCP segment – No more than Maximum Segment Size (MSS) bytes – E.g., up to 1460 consecutive bytes from the stream – MSS = MTU – (IP header) – (TCP header) IP Hdr IP Data TCP Hdr TCP Data (segment)
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11 Congestion Control Overview Ask Questions!!!!!
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12 Flow Control vs Congestion Control Flow control keeps one fast sender from overwhelming a slow receiver Congestion control keeps a set of senders from overloading the network
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Huge Literature on Problem • In mid-80s Jacobson “saved” the Internet with CC • One of very few net topics where theory helps; many frustrated mathematicians in networking • Less of a focus now (bottlenecked access links?) • …but still far from academically settled – E.g. battle over “fairness” with Bob Briscoe… 13
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Because Internet traffic is bursty!
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This note was uploaded on 01/09/2012 for the course ELECTRICAL 122 taught by Professor Shenker during the Spring '11 term at University of California, Berkeley.

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15-CongestionControl - Congestion Control EE122 Fall 2011...

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