3. TCP / IP

The protocol used for communicating over the internet is called TCP/IP, or "Transmission Control Protocol / Internet Protocol". It has two parts: TCP and IP.

TCP - Transmission Control Protocol

This protocol prepares messages for transmission and reassembles any received messages.

When sending data the TCP rules (protocol) include

• Dividing the message into packets
• Adding a sequence number to each packet so the message can be re-assembled
• Adding extra error-correction information, so errors can be spotted and fixed

When receiving data the TCP rules (protocol) include

• Examining each packet for errors by using the extra information that was added to it
• Fixing any errors (if possible) or requesting that the packet be re-sent
• Spotting missing packets and requesting them to be re-sent
• If all packets are present, using the sequence number of each packet to re-assemble the message

This TCP/IP process is shown in the diagram below.