Section 17.2
Computers & Communication
17.3 Wide Area Networks
Both national and international networks are WANs.
There are usually many possible routes across a WAN.
17.3.1 Circuit Switching
A circuit switched network is one where switches are used to connect two
computer systems for a given length of time. The path does not change.
Advantages
- No waiting for messages to arrive.
Disadvantages
- There may not be a line avaliable.
17.3.2 Packet Switching
With packet switching the messages (or other data) are divided up into fixed
length blocks of data called 'Packets'.
These contain:
- a source and destination address
- a packet sequence number
- the data checksum
These packets can travel along different routes.
Advantages
- Communications channels are used more efficently because channels are
not 'tied up' when transmission is not in progress. Also, because data is
sent in packets, data compression can be used.
- More more resiliant to network failure.
- Data is more secure becuase packets are sent down various routes.
Disadvantages
- May be significantly slower.
