Transmission Control Protocol

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a Network Protocol used to establish a guaranteed, connection-oriented communication channel between communicating devices.
A bidirectional stream protocol that delivers arbitrarily long streams of bytes Sequence number in each direction to maintain packet order → Each connection maintains 2 sequence numbers SYN and ACK flag bits. 3 packets at beginning of TCP connection (3-way handshake) are SYN, SYN-ACK, ACK This handshake is the two sides exchanging randomly chosen sequence numbers to sychronize data going in both directions.

Exists in the Transport Layer Anything that wants a session with continuity uses TCP.

Stop and Wait Protocol

Send a packet. Await an acknowledgement before sending the next Packet. Repeat. Retransmission after timeout Because we might not get an ACK, we must buffer a packet a the sender and receiver. Use a monotonically increasing sequence number to keep track of ordering.

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Go Back N

Iterating upon Stop and Wait Protocol, we use our knowledge of Pipelines to speed things up! Send packets all at once. We need size buffers at the receiver and sender.

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Sliding Window Protocol

Sliding Window Protocol allows sending multiple Packets before receiving acknowledgments. The maroon packets can be sent in arbitrary order. Therein lies the optimization. See here

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Segment

Creates a PDU called a “segment” which includes a TCP Header consisting of connection state information known as a “TCP flag” Window size is size of sliding window The only place Professor Forsyth has even seen the urgent ptr actually be used is in Ctrl-C quit over SSH.

TCP Header

a 10-field, 20-byte header containing connection and payload delivery details for a segment. A TCP header is used to establish a three-way handshake for payload delivery.

3 Way Handshake

Client sends a packet iwth random sequence number and SYN flag Server recognizes the packet with a SYN as a request to initiate a stream. If it accepts, the it responds by

  • Putting the sequence number in the acknowledgement field
  • Setting the ACK bit
  • putting a different random sequence number in the packet
  • Setting the SYN bit before sending the packet to the client Client sends packet back with ACK field and populated data field When either are done transmitting, they send a packet with the FIN bit set, which causes the other side to no longer expect to receive packets from the stream

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