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Unformatted text preview: e broken into two network segments with a
bridge interconnecting the two segments.
Routers operate at the network layer of the OSI model. Therefore, routers do not
care what topologies or access-level protocols the interconnected network
segments use. Since routers use the bottom three layers of the OSI model, they are
usually used to interconnect those networks that use the same high-level protocols
above the network layer. Note that the protocols of data-link and physical layers
are transparent to routers. Therefore, if two network segments use different
protocols at these two layers, a bridge must be used to connect them.
Unlike bridges, routers do not view an internetwork from end to end. That is,
bridges know the ultimate destination of a data, but routers only know which is the
next router for the data being transferred across the network. However, routers are
smarter than bridges in the sense that they not only copy a data from one network
segment to another, but they also choose the best route for the data by using
information in a routing table to make this decision. That is, managing traffic
congestion is a big plus of routers; they employ a flow control mechanism to direct
traffic on to alternative, less congested paths.
Routers are commonly used to interconnect those network segments of large
internetworks that use the same communication protocol. They are particularly
useful in controlling traffic flow by making intelligent routing decisions.
An internetwork often uses both bridges and routers to handle both routing and
multiprotocol issues. This requirement has resulted in the design of devices called
brouters, which are a kind of hybrid of bridges am routers. They provide many of
the advantages of both bridges and routers. They are complex, expensive, and
difficult to install, but for very complex heterogeneous internetworks in which the
network segments use the same high-level communication protocols, they often
provide the best internetworking solution.
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- Spring '14