TCP/IP Port

What is TCP/IP ?

• Short for Transmission Control Protocol/Internet Protocol, TCP/IP is a set of rules (protocols) governing communications among all computers on the Internet. 
• It dictates how information should be packaged (turned into bundles of information called packets), sent, and received, as well as how to get to its destination.

How does TCP/IP work?

• TCP/IP is a combination of two separate protocols. Transmission Control Protocol (TCP) and Internet Protocol (IP). 
• The Internet Protocol standard tells packets where to go and how to get there. 
• The Transmission Control Protocol is responsible for ensuring the reliable transmission of data across Internet-connected networks. TCP checks packets for errors and submits requests for re-transmissions if any are found.

Three of the most common TCP/IP protocols :

• HTTP : Used between a web client and a web server, for non-secure data transmissions. A web client (i.e. Internet browser on a computer) sends a request to a web server to view a web page. The web server receives that request and sends the web page information back to the web client.
• HTTPS : Used between a web client and a web server, for secure data transmissions. Often used for sending credit card transaction data or other private data from a web client (i.e. Internet browser on a computer) to a web server.
• FTP : Used between two or more computers. One computer sends data to or receives data from another computer directly.

TCP/IP Ports :

• On a TCP/IP network every device must have an IP address. The IP address identifies the device e.g. computer.
• However an IP address alone is not sufficient for running network applications, as a computer can run multiple applications and/or services just as the IP address identifies the computer, The network port identifies the application or service running on the computer.
• A port number uses 16 bits and so can therefore have a value from 0 to 65535.
• A connection between two computers uses a socket. Socket is the combination of IP address plus port.

• We have two browser windows open one looking at the Google website, and the other at the Yahoo website.
• The connection to Google would be, our PC – IP1+port 60200 —  Google IP2 +port 80 (standard port).
• The combination IP1+60200 = the socket on the client computer and IP2 + port 80 = destination socket on the Google server.
• The connection to Yahoo would be your PC – IP1+port 60401 — Yahoo IP3 +port 80 (standard port).
• The combination IP1+60401 = the socket on the client computer and IP3 + port 80 = destination socket on the Yahoo server.