8 Chapter 1 ??? Unifi ed Communications
It is important to understand that while this conversation is occurring??”be it 30 seconds,
30 minutes, or 30 hours long??”it??™s always going to occur over the same circuit. In this scenario,
we are always going to be passing some sort of traffi c. It may be you speaking, the other person
speaking, or simply background noise. This type of communication is known as circuit switching.
With data networks, we do not use circuit switching. Instead, we use packet switching.
With packet switching, there is no need to pass traffi c over the same circuit for a potentially
endless period of time, much of which may be wasted time while no data is being passed.
With packet switching, we can break up a larger piece of data into smaller ???chunks??? and
distribute those chunks over an infi nite number of paths. At a high level, here is how packet
switching (Figure 1.6) works:
1. The fi rst device??”say, your laptop??”is attempting to send a fi le to a fi le server.
It breaks up that fi le into smaller packets (known as the payload ) and tacks on the
target system??™s address information.
2. Your laptop then sends that packet off to its gateway (which may be a switch, a
router, etc.), and assumes that the gateway knows how to deliver the packet. In turn,
the gateway may deliver the packet directly to the server (assuming it??™s on the same
network segment), or it will pass it off to the proper next ???hop.???
3. When the server receives the packet, it begins to restructure the fi le, much like a
jigsaw puzzle??”but with a specifi c set of instructions on assembly.
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