Instruction of TCP 2

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Each TCP segment contains the source and destination port number to identify the sending and receiving application.These two values, along with the source and destination IP addresses in the IP header, uniquely identify each connection.
The combination of an IP address and a port number is sometimes called a socket.
It is the socket pair (the 4-tuple consisting of the client IP address, client port number, server IP address, and server port number) that specifies the two end points that uniquely identifies each TCP connection in an internet.
The sequence number identifies the byte in the stream of data from the sending TCP to the receiving TCP that the first byte of data in this segment represents.If we consider the stream of bytes flowing in one direction between two applications, TCP numbers each byte with a sequence number. This sequence number is a 32-bit unsigned number that wraps back around to 0 after reaching 232 - 1.
When a new connection is being established, the SYN flag is turned on. The sequence number field contains the initial sequence number (ISN) chosen by this host for this connection. The sequence number of the first byte of data sent by this host will be the ISN plus one because the SYN flag consumes a sequence number.
Since every byte that is exchanged is numbered, the acknowledgment number contains the next sequence number that the sender of the acknowledgment expects to receive. This is therefore the sequence number plus 1 of the last successfully received byte of data. This field is valid only if the ACK flag (described below) is on.
TCP provides a full-duplex service to the application layer. This means that data can be flowing in each direction, independent of the other direction.
TCP can be described as a sliding-window protocol without selective or negative acknowledgments.
1:We say that TCP lacks selective acknowledgments because the acknowledgment number in the TCP header means that the sender has successfully received up through but not including that byte. There is currently no way to acknowledge selected pieces of the data stream.
2:There is no means for negatively acknowledging a segment.
The header length gives the length of the header in 32-bit words. This is required because the length of the options field is variable. With a 4-bit field, TCP is limited to a 60-byte header. Without options, however, the normal size is 20 bytes.
TCP's flow control is provided by each end advertising a window size. This is the number of bytes, starting with the one specified by the acknowledgment number field, that the receiver is willing to accept. This is a 16-bit field, limiting the window to 65535 bytes.
The checksum covers the TCP segment: the TCP header and the TCP data. This is a mandatory field that must be calculated and stored by the sender, and then verified by the receiver.
The most common option field is the maximum segment size option, called the MSS. Each end of a connection normally specifies this option on the first segment exchanged (the one with the SYN flag set to establish the connection). It specifies the maximum sized segment that the sender wants to receive.
The data portion of the TCP segment is optional.
TCP Connection Establishment and Termination
1:TCP is a connection-oriented protocol. Before either end can send data to the other, a connection must be established between them.
2:Output of connection establishment and termination:
1:        svr > bsd    SYN:141567    win 4096    mss 1024
2:        bsd > svr    SYN:234788    ACK:141568  win 4096    mss 1024
3:        svr > bsd    ACK:234789    win:4096
4:        svr > bsd    FIN:141568    ACK:234789  win 4096
5:        bsd > svr    ACK:141569    win 4096
6:        bsd > svr    FIN:234790    ACK:141569  win 4096
7:        svr > bsd    ACK:234791    win 4096
# 2009-09-21 22:1
               
               
               

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