Computer Science Principles The Internet - 03 Addressing and Routing Information - 07 Reliability and TCP

When hundreds or even thousands of packets are transmitted from one location to another, they can take different paths based on changing network conditions and other factors.

When they get to the destination, they are unorganized and sometimes not complete.

So the message needs to be audited and reviewed in order to put it together in the right way.

The Transmission Control Protocol or TCP does exactly that.

TCP uses a process where it looks at all the packets in a message and checks them.

Using the header information in each packet it knows how many there are, how large they should be, and in which order the packets should be in.

Using this checklist, it is able to rearrange the packets.

If it finds that a packet doesn't match the expected size or other characteristic, it is discarded and using the header information again, sends a request back to the sender for a specific packet to be resent.

After assembling the packets received, if TCP finds that packets are missing, it goes back to the sender and asks for the missing items to be resent.

After TCP has verified that all the packets are accounted for, are in the right order, and are free of any issues, it certifies the data and the packets are merged together to recreate the original file that was on the sender's device.

For most transmissions on the internet, the TCP method is used, which is why the IP and TCP protocols are referred to as a single item or TCP/IP.

TCP places reliability in a higher priority than speed or latency.

For instances where reliability isn't as important, but speed is, there is another protocol called UDP or User Datagram Protocol.

This protocol doesn't do the excessive reliability checks that TCP performs, but because of this it can send information at a faster rate.

TCP is the foundation of how a majority of data is transmitted over networks.

Using these protocols, every device has a unique address and data can be broken down into packets to send to any of these addresses.

When received, the packets of information can be verified and reconstituted back into the original form.