Information Technology Reference
In-Depth Information
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As the data rate is relatively low between central server and the node, a low-
specification twisted-pair cable can be used to connect the nodes to the server.
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A fault on one of the nodes will not affect the rest of the network. Typically, mainframe
computers use a central server with terminals connected to it.
The main disadvantage of this type of topology is that the network is highly dependent upon
the operation of the central server. If it were to slow significantly then the network becomes
slow. In addition, if it were to become unoperational then the complete network would shut
down.
25.2.2 Ring network
In a ring network, computers link together to form a ring. To allow an orderly access to the
ring, a single electronic token passes from one computer to the next around the ring, as illus-
trated in Figure 25.5. A computer can only transmit data when it captures the token. In a
manner similar to the star network, each link between nodes is a point-to-point link and al-
lows the usage of almost any type of transmission medium. Typically, twisted-pair cables to
allow a bit rate of up to 16 Mbps, but coaxial and fibre optic cables are normally used for
extra reliability and higher data rates.
A typical ring network is IBM Token Ring. The main advantage of token ring networks is
that all nodes on the network have an equal chance of transmitting data. Unfortunately it suf-
fers from several problems; the most severe is that if one of the nodes goes down then the
whole network may go down.
Electronic token
is passed from
node to node
Nodes can only
transmit data when
they capture
the token
Figure 25.5
Token passing ring network
25.2.3 Bus network
A bus network uses a multidrop transmission medium, as shown in Figure 25.6. All nodes on
the network share a common bus and all share communications. This allows only one device
to communicate at a time. A distributed medium access protocol determines which station is
to transmit. As with the ring network, data frames contain source and destination addresses,
where each station monitors the bus and copies frames addressed to itself.
Twisted-pair cables give data rates up to 100 Mbps, whereas, coaxial and fibre optic ca-
bles give higher bit rates and longer transmission distances. A bus network is a good com-
