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Transmission Control Protocol
Transmission Control Protocol

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!!! Overview[1]
[{$pagename}] ([TCP]) is a core protocol of the [Internet protocol suite|Internet Protocol Suite].
[{$pagename}] originated in the initial network implementation in which it complemented the [Internet Protocol] ([IP]). Therefore, the entire suite is commonly referred to as [TCP-IP].
[{$pagename}] provides reliable, ordered, and error-checked delivery of a stream of octets between applications running on hosts communicating over an IP network. Major Internet applications such as the World Wide Web, email, remote administration and file transfer rely on [TCP].
Applications that do not require reliable [data] stream service may use the [User Datagram Protocol] ([UDP]), which provides a connectionless [datagram] service that emphasizes reduced [latency] over [reliability].
!! [{$pagename}] [Protocol] operation
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.
* data transfer
* termination closes established virtual circuits and releases all allocated resources.
A TCP connection is typically managed by an [Operating System] through a [Application Programing Interface|Application Programming Interface] ([API]) that represents the local [Endpoint] for [communications], the [Internet] [socket]. During the lifetime of a [TCP] [connection] the local end-point undergoes a series of [state] changes:
* [LISTEN] (server) represents waiting for a connection request from any remote TCP and port.
* [SYN-SENT] (client) represents waiting for a matching connection request after having sent a connection request.
* [SYN-RECEIVED] (server) represents waiting for a confirming connection request acknowledgment after having both received and sent a connection request.
* [ESTABLISHED] (both server and client) represents an open connection, data received can be delivered to the user. The normal state for the data transfer phase of the connection.
* [FIN-WAIT-1] (both server and client) represents waiting for a connection termination [request] from the remote [TCP], or an acknowledgment of the connection termination request previously sent.
* [FIN-WAIT-2] (both server and client) represents waiting for a connection termination [request] from the remote [TCP].
* [CLOSE-WAIT] (both server and client) represents waiting for a connection termination [request] from the local user.
* [CLOSING] (both server and client) represents waiting for a connection termination request [acknowledgment] from the remote TCP.
* [LAST-ACK] (both server and client) represents waiting for an acknowledgment of the connection termination request previously sent to the remote TCP (which includes an acknowledgment of its connection termination request).
* [TIME-WAIT] (either server or client) represents waiting for enough time to pass to be sure the remote TCP 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] known as two [MSL] (maximum segment lifetime).
* [CLOSED] (both server and client) represents no connection state at all.
!! 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 and listen at 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:
* [SYN-SENT]: The active open [Request] is performed by the [client] sending a [SYN-SENT]chronize to the server. The [client] sets the segment's sequence number to a random value A.
* [SYN-ACK]: In [response], the [server] replies with a [SYN-ACK] (Synchronize-Acknowledgement). The [Acknowledgement] number is set to one more than the received sequence number i.e. A+1, and the sequence number that the server chooses for the packet is another random number, B.
* [ACK]: Finally, the client sends an [ACK]nowledgement back to the [server]. The sequence number is set to the received acknowledgement value i.e. A+1, and the [Acknowledgement] number is set to one more than the received sequence number i.e. B+1.
At this point, both the [client] and [server] have received an [Acknowledgement] of the [connection]. The steps 1, 2 establish the connection parameter (sequence number) for one direction and it is acknowledged. The steps 2, 3 establish the connection parameter (sequence number) for the other direction and it is acknowledged. With these, a full-duplex [communication] is [ESTABLISHED].
!! More Information
There might be more information for this subject on one of the following:
[{ReferringPagesPlugin before='*' after='\n' }]
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* [#1] - [Transmission Control Protocol|Wikipedia:Transmission_Control_Protocol/|target='_blank'] - based on information obtained 2016-05-20-
This page (revision-1) was last changed on 29-Nov-2024 16:16 by UnknownAuthorTop