Network designs tend to follow one of two
general design strategies: mesh or hierarchical. In a mesh structure,
the network topology is flat; all routers perform essentially the same
functions, and there is usually no clear definition of where specific
functions are performed. Expansion of the network tends to proceed in
a haphazard, arbitrary manner. In a hierarchical structure the network
is organized in layers, each of which has one or more specific functions.
Benefits to using a hierarchical model
include the following:
- Scalability -- Networks that
follow the hierarchical model can grow much larger without
sacrificing control or manageability because functionality is
localized and potential problems can be recognized more easily. An
example of a very large-scale hierarchical network design is the
Public Switched Telephone Network.
- Ease of implementation -- A
hierarchical design assigns clear functionality to each layer,
thereby making network implementation easier.
- Ease of troubleshooting -- Because
the functions of the individual layers are well defined, the
isolation of problems in the network is less complicated.
Temporarily segmenting the network to reduce the scope of a
problem also is easier.
- Predictability -- The behavior
of a network using functional layers is fairly predictable, which
makes capacity planning for growth considerably easier; this
design approach also facilitates modeling of network performance
for analytical purposes.
- Protocol support -- The mixing
of current and future applications and protocols is much easier on
networks that follow the principles of hierarchical design because
the underlying infrastructure is already logically organized.
- Manageability -- All the
benefits listed here contribute to greater manageability of the
network.
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