CS536-2009-02-17

CS536-2009-02-17 - 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) Written homework 1 (Due Now*) May turn in until Thursday (1:30pm, no penalty) Email to Me 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 Reliable Data Transport 1.0 Reliable link 2.0 Bit errors Fatal Flaw! 2.1 2.2 Nack-free protocol 3.0 errors and loss Transport Layer 3-3
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Recap (cont’d) Pipelining Go-back N Selective ack Selective ack problems? Transport Layer 3-4
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Transport Layer 3-5 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 3-6 TCP: Overview RFCs: 793, 1122, 1323, 2018, 2581 full duplex data: bi-directional data flow in same connection MSS: maximum segment size connection-oriented: handshaking (exchange of control msgs) init’s sender, receiver state before data exchange flow controlled: sender will not overwhelm receiver point-to-point: one sender, one receiver reliable, in-order byte steam: no “message boundaries” pipelined: TCP congestion and flow control set window size send & receive buffers
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Transport Layer 3-7 TCP segment structure source port # dest port # 32 bits application data (variable length) sequence number acknowledgement number Receive window Urg data pnter checksum F S R P A U head len not used Options (variable length) URG: urgent data (generally not used) ACK: ACK # valid PSH: push data now (generally not used) RST, SYN, FIN: connection estab (setup, teardown commands) # bytes rcvr willing to accept counting by bytes of data (not segments!) Internet checksum (as in UDP)
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Transport Layer 3-8 TCP seq. #’s and ACKs Seq. #’s: byte stream “number” of first byte in segment’s data ACKs: seq # of next byte expected from other side cumulative ACK Q: how receiver handles out-of-order segments A: TCP spec doesn’t say, - up to implementor Host A Host B Seq=42, ACK=79, data = ‘C’ Seq=79, ACK=43, data = ‘C’ Seq=43, ACK=80 User types ‘C’ host ACKs receipt of echoed ‘C’ host ACKs receipt of ‘C’, echoes back ‘C’ time simple telnet scenario
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CS536-2009-02-17 - CS536: Transport Layer Charles Killian...

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