Transport Control Protocol

If a tree falls in a forest and no one is around to hear it, does it make a sound?

The transport control protocol (TCP) is what programmers around the world use to carry out point-to-point transmissions

We use it to establish a connection with another device ensuring that it exists, is willing and available to exchange data.

To make a connection, the essential thing is to have 2 end devices, usually called client and server.

The two ends use a combination of IP and port called a socket to establish the connection.

To make sure that the other end exists, is available and ready, a small dance is performed, this dance is called triple handshake( aka SYN-SYN/ACK-ACK) .

SYN -SYN/ACK -ACK

The specific sequence that makes up this dance is detailed below:

1. the client that wishes to establish the connection sends to the server a SYN type packet with a random sequence number that will serve to sort the packets at both ends
2. When the server receives this packet, it takes the sequence number, adds one to it and (if it is willing to establish the connection) it sends a SYN-ACK packet to the client attaching to it it's own sequence number
3. To end this dance the client sends an ACK packet to the server with the server's sequence number plus one. Establishing the connection and beginning to transmit the data flow

Controlled interruption

In addition to providing the framework to initiate connections, it also provides a framework to terminate them after the data stream was successfully transmitted.

1. the client that wishes to end the connection sends a FIN type packet with a random sequence number that will serve to sort the packets at both ends
2. When the server receives this packet, it takes the sequence number, adds one to it and it sends a ACK packet back, if the server has already finished sending his own data to the client it sends a FIN packet attaching to it it's own sequence number
3. To end this dance the client sends an ACK packet to the server with the server's sequence number plus one. Closing the connection and ending the data flow

Useful characteristics of the TCP protocol

• Establish neat ways to start and end communications
• Allows data to be formed into packets of varying length to be sent and received through Layer 3
• Allows devices to order the packets that are sent and received through layer 3
• allows data multiplexing (to send and receive multiple data streams at the same time)