Page 92 - DCAP104_EXPOSURE_TO_COMPUTER_DISCPLINES

Unit 5: Operations of Network

Bus Network Topology Notes
In local area networks where bus topology is used, each machine is connected to a single cable.
Each computer or server is connected to the single bus cable through some kind of connector.
A terminator is required at each end of the bus cable to prevent the signal from bouncing back
and forth on the bus cable. A signal from the source travels in both directions to all machines
connected on the bus cable until it finds the MAC address or IP address on the network that is the
intended recipient. If the machine address does not match the intended address for the data, the
machine ignores the data. Alternatively, if the data does match the machine address, the data is
accepted. Since the bus topology consists of only one wire, it is rather inexpensive to implement
when compared to other topologies. However, the low cost of implementing the technology is
offset by the high cost of managing the network. Additionally, since only one cable is utilized, it
can be the single point of failure. If the network cable breaks, the entire network will be down.

Figure 5.4: The Bus Topology

Backbone Cable
Terminator Terminator

Node

Linear Bus

The type of network topology in which all of the nodes of the network are connected to a
common transmission medium which has exactly two endpoints (this is the ‘bus’, which is
also commonly referred to as the backbone, or trunk) - all data that is transmitted between
nodes in the network is transmitted over this common transmission medium and is able to
be received by all nodes in the network virtually simultaneously (disregarding propagation
delays).
The two endpoints of the common transmission medium are normally
terminated with a device called a terminator that exhibits the characteristic
impedance of the transmission medium and which dissipates or absorbs the
energy that remains in the signal to prevent the signal from being reflected
or propagated back onto the transmission medium in the opposite direction,
which would cause interference with and degradation of the signals on the
transmission medium (See Electrical termination).
Distributed Bus

The type of network topology in which all of the nodes of the network are connected to
a common transmission medium which has more than two endpoints that are created by
adding branches to the main section of the transmission medium - the physical distributed
bus topology functions in exactly the same fashion as the physical linear bus topology (i.e.,
all nodes share a common transmission medium).

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