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Regular two-way telephone calls are relatively easy: the caller speaks to only one person,
so whatever he says is directed towards the other person. With three-way calling, things tend to
become more difficult. When the caller speaks, how will the other two people know if the
message is for one of them or both of them?
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Fig. 1
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Networks have this
problem as well (see Figure 1). When more than two computers are connected to a network, they are able to
communicate with each other through the transport layer, a combination of hardware and
software. Thing is, this layer is shared by all, not between individual pairs of computers. There
has to be a reliable way for one of the computers to send data to a specific computer and not all
of them. The computer may also want confirmation that its data was properly received.
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packets |
Computers send data through the transport layer using
packets, which isn't unlike regular mail messages. These packets contain not only the data, but
the sender's identification, the destination, and a little error-control information to make sure the
data was not damaged. (Derfler 88-89) (see Figure 2)
There are different ways these packets can be routed. In server-client networks, a server
could handle the messenging by processing it and sending it to its proper destination. When the
destination computer receives the message, it can return a message of confirmation to the
sender. This is a synchronous operation: the sender needs to have confirmation before it can
continue on its merry way. An asynchronous operation is where the sender continues on its task
whether or not it receives any confirmation. Here, the messenging
server can place the packets in a queue, where the other computers can look for it and pick it up,
like mail in a mailbox. (Burghart)
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Fig. 2: Packets
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continued...
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asynchronous oper...
