| The "topology" of a network refers to the actual physical layout of network
components, and how they are connected to each other.
There is now only
one basic type of topology infrastructure which is acceptable in schools
- a "star" topology (see picture below).
The name of this
infrastructure refers to the connection of network components to
one central point.
Previously, an infrastructure
known as "bus" topology was very common (see picture below), where components
were connected in a daisy-chain arrangement. With this daisy-chaining,
if one component failed, the whole network failed, much like the old
Christmas-tree lights.
A star arrangement
ensures that one faulty network connection on one computer will not
bring the whole network down (unless that connector is at the centre!)
Wireless networks
are also becoming an option. Wireless networks are an extension of the
"star" arrangement, but do not require electrical cable to join the
various components to each other.
In most cases, wireless
networks are still more expensive than equivalent wired networks, though
this will change as the various components become cheaper and more widely
available. Wireless networking is also slower than the faster wired
networks.
Wireless networking
may currently be an option where difficult terrain, or heritage buildings
are a factor.
- Bus Networking
- A "bus" network
involves connecting computers together in a daisy-chain fashion:
This type of networking
is how old administrative networks were originally installed in schools,
using black co-axial cable with silver "T" connectors at each computer
workstation. It often suffered the same fate as christmas-tree lights
- when one connection went down, so did the whole network!
Bus networking is
no longer considered suitable for new installations in a school environment.
Star
Networking- This is the preferred
model for school use. A star network connects each individual computer
to a central server, and to each other, via a "switching hub" (now simply called a switch):
In the example above,
each workstation has its own direct link to the central switch, which is also connected to a server.
Scaling this up a bit, the Server in most schools is usually more geographically remote from the workstations.
In the example below, the server is connected to a central switch (the campus distributor), which is connected directly to switches in other buildings, which in turn support the workstations in those buildings:
The planning considerations
of the above network revolve around the number of machines which each
switch can support, the speed of the switches (particularly the central CD switch),
the uplink bandwidth between the Campus Distributor and the Building Distributors, and the distances the cables have to run. Where copper cable which is
used for these uplinks, it is limited to runs of 90 metres or less, and
always internally.
Longer cable runs,
and any external connections, are made using fibre-optic cable.
It is now common
practice to install a "Gigabit" switch at the Campus
Distributor, and to install Building Distributors that support such a connection on at least one "uplink" port.
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