How Networks Send Data
Why Break the Data into Little Pieces?
Imagine that I have a 5 MB database file on the file server. I wish to copy the file to my workstation.
Q. Should the network put all of the 40,000,000 bits onto the network together, one after the other?
A. No. The network breaks the file into small pieces called packets and sends the packets one at a time. There are two reasons for this.
1. If the all 40,000,000 bits were sent in one go this would stop anyone else using the network for a while. If the file transfer took 15 seconds, then no one else could use the network for 15 seconds.
2. If an error occurred in the last few bits of the file, all of them would have to be transferred again.
Breaking the file up into pieces and sending one piece at a time solves both of these problems.
What is in a Packet?
The small pieces of data are called packets.
At the heart of each packet is the data to be transmitted. Extra bits are also added to the front and back of the packet as it passes down the layers of the OSI model. Every layer adds some extra bits to the data. See the attached diagram.
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