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CS536-2009-02-19

CS536-2009-02-19 - CS536 Transport Layer Charles Killian...

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CS536: Transport Layer Charles Killian Slides used from Kurose-Ross, Computer Networking, a Top Down Approach Transport Layer 1
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Announcements Programming assignment 1 (2/28, 11:59pm) Rescheduled class (April 21,23) Wednesday, April 15 th , 6-9pm, BRNG B222 Reading assignment TCP Vegas: Due 2/24 XCP: Due 3/3 Mid-term (Thursday, March 12 th , in class) Let me know if you must schedule a make-up. Transport Layer 2
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Recap Fast-retransmit 3-way handshaking Cumulative acks Byte ranges, not packet numbers Initial sequence numbers Delayed acking RTT estimation (and timeout computation) Transport Layer 3-3
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Transport Layer 3-4
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Transport Layer 3-5 TCP Connection Management (cont) TCP client lifecycle TCP server lifecycle
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Transport Layer 3-6
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Transport Layer 3-7 Chapter 3 outline 3.1 Transport-layer services 3.2 Multiplexing and demultiplexing 3.3 Connectionless transport: UDP 3.4 Principles of reliable data transfer 3.5 Connection-oriented transport: TCP segment structure reliable data transfer flow control connection management 3.6 Principles of congestion control 3.7 TCP congestion control
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Transport Layer 3-8 Principles of Congestion Control Congestion: informally: “too many sources sending too much data too fast for network to handle” different from flow control! manifestations: lost packets (buffer overflow at routers) long delays (queueing in router buffers) a top-10 problem!
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Transport Layer 3-9 Causes/costs of congestion: scenario 1 two senders, two receivers one router, infinite buffers no retransmission large delays when congested maximum achievable throughput unlimited shared output link buffers Host A λ in : original data Host B λ out
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Transport Layer 3-10 Causes/costs of congestion: scenario 2 one router, finite buffers sender retransmission of lost packet finite shared output link buffers Host A λ in : original data Host B λ out λ ' in : original data, plus retransmitted data
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Transport Layer 3-11 Causes/costs of congestion: scenario 2 always: (goodput) “perfect” retransmission only when loss: retransmission of delayed (not lost) packet makes larger (than perfect case) for same λ in λ out = λ in λ out > λ in λ out “costs” of congestion: more work (retrans) for given “goodput” unneeded retransmissions: link carries multiple copies of pkt R/2 R/2 λ in λ out b.
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