TCP protocol operations may be divided into three phases. Connections must be properly established in a multi-step handshake process (connection establishment) before entering the data transfer phase. After data transmission is completed, the connection termination closes established virtual circuits and releases all allocated resources.
A TCP connection is managed by an operating system through a programming interface that represents the local end-point for communications, the Internet socket. During the lifetime of a TCP connection it undergoes a series of state changes:
1. LISTEN : In case of a server, waiting for a connection request from any remote client.
2. SYN-SENT : waiting for the remote peer to send back a TCP segment with the SYN and ACK flags set. (usually set by TCP clients)
3. SYN-RECEIVED : waiting for the remote peer to send back an acknowledgment after having sent back a connection acknowledgment to the remote peer. (usually set by TCP servers)
4. ESTABLISHED : the port is ready to receive/send data from/to the remote peer.
5. FIN-WAIT-1
6. FIN-WAIT-2
7. CLOSE-WAIT
8. CLOSING
9. LAST-ACK
10. TIME-WAIT : represents waiting for enough time to pass to be sure the remote peer received the acknowledgment of its connection termination request. According to RFC 793 a connection can stay in TIME-WAIT for a maximum of four minutes.
11. CLOSED
[edit] Connection establishment
To establish a connection, TCP uses a three-way handshake. Before a client attempts to connect with a server, the server must first bind to a port to open it up for connections: this is called a passive open. Once the passive open is established, a client may initiate an active open. To establish a connection, the three-way (or 3-step) handshake occurs:
1. The active open is performed by the client sending a SYN to the server. It sets the segment's sequence number to a random value.
2. In response, the server replies with a SYN-ACK. The acknowledgment number is set to one more than the received sequence number, and the sequence number is random.
3. Finally, the client sends an ACK back to the server. The sequence number is set to the received acknowledgement value, and the acknowledgement number is set to one more than the received sequence number.
At this point, both the client and server have received an acknowledgment of the connection.
[edit] Data transfer
There are a few key features that set TCP apart from User Datagram Protocol:
* Ordered data transfer - the destination host rearranges according to sequence number[2]
* Retransmission of lost packets - any cumulative stream not acknowledged will be retransmitted[2]
* Discarding duplicate packets
* Error-free data transfer
* Flow control - limits the rate a sender transfers data to guarantee reliable delivery. When the receiving host's buffer fills, the next acknowledgement contains a 0 in the window size, to stop transfer and allow the data in the buffer to be processed.[2]
* Congestion control - sliding window[2]
ajurNAstar
English Language
A TCP connection is managed by an operating system through a programming interface that represents the local end-point for communications, the Internet socket. During the lifetime of a TCP connection it undergoes a series of state changes:
1. LISTEN : In case of a server, waiting for a connection request from any remote client.
2. SYN-SENT : waiting for the remote peer to send back a TCP segment with the SYN and ACK flags set. (usually set by TCP clients)
3. SYN-RECEIVED : waiting for the remote peer to send back an acknowledgment after having sent back a connection acknowledgment to the remote peer. (usually set by TCP servers)
4. ESTABLISHED : the port is ready to receive/send data from/to the remote peer.
5. FIN-WAIT-1
6. FIN-WAIT-2
7. CLOSE-WAIT
8. CLOSING
9. LAST-ACK
10. TIME-WAIT : represents waiting for enough time to pass to be sure the remote peer received the acknowledgment of its connection termination request. According to RFC 793 a connection can stay in TIME-WAIT for a maximum of four minutes.
11. CLOSED
[edit] Connection establishment
To establish a connection, TCP uses a three-way handshake. Before a client attempts to connect with a server, the server must first bind to a port to open it up for connections: this is called a passive open. Once the passive open is established, a client may initiate an active open. To establish a connection, the three-way (or 3-step) handshake occurs:
1. The active open is performed by the client sending a SYN to the server. It sets the segment's sequence number to a random value.
2. In response, the server replies with a SYN-ACK. The acknowledgment number is set to one more than the received sequence number, and the sequence number is random.
3. Finally, the client sends an ACK back to the server. The sequence number is set to the received acknowledgement value, and the acknowledgement number is set to one more than the received sequence number.
At this point, both the client and server have received an acknowledgment of the connection.
[edit] Data transfer
There are a few key features that set TCP apart from User Datagram Protocol:
* Ordered data transfer - the destination host rearranges according to sequence number[2]
* Retransmission of lost packets - any cumulative stream not acknowledged will be retransmitted[2]
* Discarding duplicate packets
* Error-free data transfer
* Flow control - limits the rate a sender transfers data to guarantee reliable delivery. When the receiving host's buffer fills, the next acknowledgement contains a 0 in the window size, to stop transfer and allow the data in the buffer to be processed.[2]
* Congestion control - sliding window[2]
ajurNAstar