Bicycles with moters
Data link addresses
Repeaters and bridges
Routers
Network addresses
So far, a LAN has been defined as being a community of devices such as PCs, printers, and servers coexisting on a common communications medium and following a comon protocol that regulates how they access the medium. But there is one last requirement: As in any community, each individual must be uniquely identifiable.
Attenuation, interference, and distortion prevent a signal from arriving in the same shape it was in when it left. Attenuation is a function of the resistance of the wire. A centain amount of signal energy must be spent"pushing past" the resistance. Interference is a function of outside influences noise which adds characteristics to the signal that should not be there. Distortion is a function of the wire impeding different frequency components of the signal in different ways.
Routers have been known by several names. Back in ancient times when what is now the Internet was called the ARPANET, routers were called IMPs, for interface message processors. More recently, routers were called gateways; remnants of this nomenclature can still be found in terms such as Border gateway protocol(BGP) and Interior Gateway Routing Protocol(IGRP). In the open system interconnection(OSI) world, routers are known as Intermediate Systems(IS)
The communication path between two devices sharing a common data link is a physical path, the communication path provided by routers between two devices on different network is a higher-level, logical path
The digital envelope used by routers is a packet
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