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Understanding TCP Features: Reliable End-to-End Communication

Learn about the features of Transmission Control Protocol (TCP), including connection-oriented setup, flow control, congestion control, and adaptive retransmission for reliable end-to-end communication over IP networks.

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Understanding TCP Features: Reliable End-to-End Communication

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  1. Transport Control Protocol (TCP) Features of TCP, packet loss and retransmission, adaptive retransmission, flow control, three way handshake, congestion control

  2. Reliable transport • IP is unreliable • Application programmers typically require reliability (although not always) • The Transmission Control Protocol (TCP) establishes a reliable end-to-end communication service on top of IP

  3. Seven major features of TCP 1. Connection oriented 2. Point to point 3. Complete reliability - delivered as sent 4. Full duplex communication 5. Stream interface 6. Reliable connection startup 7. Graceful connection shutdown

  4. End to end communication • TCP has no knowledge of the underlying Internet structure

  5. Fundamental reliability problems • Unreliable delivery by the communication system (IP) • Unreliable end hosts (e.g., crashes and reboots • TCP handles these through a variety of techniques

  6. Packet loss and retransmission • Sender sets a timer • Receiver sends a acknowledgement • Timeout results in retransmission

  7. Adaptive retransmission • Sensible timer values vary greatly on an Internet • TCP monitors the delay on a connection and adapts the timer • notes time taken to receive acknowledgements • computes weighted average and variance over many transmissions and uses these to set the timer

  8. Two different timeouts

  9. Flow control • TCP uses a window mechanism • Each end of the connection allocates a buffer and notifies the other end of its size • Receiver sends available window size in each acknowledgement (window advertisement) • Receiver sends window advertisement when the application consumes some data • Zero window advertisement tells the sender to stop transmitting until further notice

  10. Three way handshake • Uses special synchronisation (SYN) and finish (FIN) messages to open and close connections • Also confirms that all data has been received at both sides • Each end of each new connection randomly generates a 32 bit connection identifier

  11. Congestion control • TCP monitors congestion through message loss • first lost message, TCP backs right off and sends just one small message • if this is not lost, doubles data size and sends two • continues exponential growth until half receiver’s window size is reached then slows down rate of increase

  12. TCP segment format • TCP messages are called segments

  13. Example exam question: http://www.cs.nott.ac.uk/~mvr/3-ccn.doc

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