TCP/IP

TCP Protocol runs only in the end systems and not in the intermediate network elements, the intermediate network elements do not maintain TCP connection state. A TCP connection is also always point-to-point, between a single sender and a single receiver.

Three-way handshake connection-establishment procedure: the client first sends a special TCP segment, the server responds with a second special TCP segment, and finally the client responds again with a third special segment. The first two segments carry no payload, that is, no application data; the third of these segments may carry a payload.

TCP segment structures: 1) source port # 2) dest port # 3) sequence number 4) acknowledge number 5) receive window 6)checksum 7)Sign bits: ack urg, psh,rst,syn, fin8) header length 9)options 10)data 11)urgent data pointer

Sequence numbers: TCP views data as an unstructured, but ordered, stream of bytes. Sequence number for a segment is therefore the byte-stream number of the first byte in the segment.

Acknowledge numbers: The acknowledgment number that Host A puts in its segment is the sequence number of the next byte Host A is expecting from Host B. Because TCP only acknowledges bytes up to the first missing byte in the stream, TCP is said to provide cumulative acknowledgments.

TCP Congestion Control: TCP congestion-control mechanism has each side of a connection keep track of an additional variable, the congestion window, which imposes a constraint on the rate at which a TCP sender can send traffic into the network. 1) additive-increase, multiplicative-decrease 2) Slow start, the TCP sender begins by transmitting at a slow rate(hence the term slow start), but increases its sending rate exponentially. 3) reaction to timeout events. After a timeout event, a TCP sender enters a slow-start phase. TCP manages a variable called Threshold, which determines the window size at which slow start will end and congestion avoidance will begin. The canceling of the slow-start phase after a triple duplicate ACK is called fast recovery.