Sending the Bits a Packet (Package) at a Time

Sending the Bits a Packet (Package) at a Time

Although you've read about one example of a networking standard for the physical transmission of bits, many other standards are required before two computers can successfully communicate. For example, imagine that Wilma is successfully transmitting the contents of the file, but some of the data gets lost, as shown in Figure 3-2.

In normal operation, devices in a network send bits in groups, generally called packets. For instance, Wilma sends the first part of the file in the first packet, the next part of the file in the next packet, and so on. A packet is simply a group of bits that are combined for transmission in a network. You can think of a packet as a packageit holds some bits for you while they are being sent across the network.

Why do networks use packets? Well, it's sort of like if you worked at a company that sold widgets, and you needed to ship 1,000,000 widgets to a single customer. Would you put them all in one box? Probably not. You would put some in one box, and then another, until you had put all the widgets in several boxes. You would address the boxes to the same place, and you might even ship them all the same day, but it's easier to deliver the packages if the boxes are a more manageable size.

Similarly, rather than sending the entire contents of a filepossibly billions of bits long, all at oncecomputers send data in packets, making the delivery of the data a little more manageable. In fact, one of the reasons that networking standards call for the use of packets is for error recovery, which you learn about in the next section.