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class4 - CSCI 233 Internet Protocols Class 4 David C...

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Unformatted text preview: CSCI 233 Internet Protocols Class 4 David C. Roberts Agenda • TCP Why Stream Delivery? • Packets may arrive out of order • Packet data may contain errors • Application program doesn’t want to know optimal packet size • Using stream delivery protocol frees the application from any concern about network delivery of data TCP—Reliable Stream Transport Service • Stream orientation—receiver gets the same sequence of octets sent by the sender • Virtual circuit connection—source and destination operate at the same time, interact during the transfer • Buffered transfer—large blocks can be transferred, fed to receiver as needed • Unstructured stream—no way to mark boundaries, applications must use a stream • Full duplex connection—communication can take place in both directions Reliable Delivery, Unreliable Transport • Ethernet is unreliable • IP is unreliable • But TCP, that runs over IP, is reliable • How? Reliability Positive acknowledgement with retransmission Error Behavior Delays A positive acknowledgement protocol introduces a number of delays because it delays sending a new packet until it receives an acknowledgement for the previous packet. Comer says that this effect wastes network bandwidth; if there is other traffic, it doesn’t waste bandwidth. But it does introduce delays. Sliding Windows To solve the problem, we use the sliding window approach to decouple transmissions from reception of acknowledgements. The sender transmits multiple packets before waiting for an acknowledgement. The number of packets is said to be the window size. Sliding Window Approach Sliding Window Example...
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This note was uploaded on 09/03/2010 for the course CS 233 taught by Professor Davidc.roberts during the Fall '10 term at GWU.

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class4 - CSCI 233 Internet Protocols Class 4 David C...

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