PAT – port address translation
When you have multiple computers on the same local area network you need a way to tell one computer from another for incoming and outgoing data and messages. This is where the PAT comes in.
The computers are each assigned a different port address. When data or messages come in or go out the data or message is signed with that computer’s port address.
An example could be a company that has multiple computers on their system. They would all use the same router. That router would be assigned a public IP address. From the router each work station or computer would be assigned to a different port address.
This would allow the company to make use of a single internet access point instead of having to use multiple routers and modems to connect each computer to the internet.
In this example for each outgoing message the router would assign the data packet a port number if the message was going to an outside network or to the internet.
When a packet is received the packet would be read by the router and the router would then send the packet on to the computer or workstation that was assigned that port number.