Hardware requirement of LAN

There are mainly 4 hardware devices which are required to establish linkage between geographically separated computers.  These are:

• Bridges
• Routers
• Gateways
• x.25 Standard Interface

Bridge-  These are used to connect two LANs that use the indentical protocols over a wide area.  The bridge acts as an address filters which picks up packets from one LAN that are intended for a destination on another LAN and passes these packets on the network. The amount of processing required at the bridge is minimal because all the devices use the same protocols.  In case the distance between two LANs is very large then the user is required to employ two identical bridges at either end of the communication link.

Routers-  It is special type of device that can be used to connect networks that may not be similar.  Such type of device provide connectivity between two LANs and two WANs over large geographical distances.  These device operate at the Network Layer of the OSI model.  These devices participate in a routing protocol to access the network topology, and on the basis  of this information routers compute the best route from a sender to the receiver.

Gateways-  These are used dsto connect two dissimilar LANs.  The terms Gateways and Routers are used interchangeably, though there is discriminating difference between the two.  A router  operates at the networklayer whereas a gateway operates on the application layer of the OSI model.  

x.25 Standard Interface-  X.25 is a protocol  for interfacing to a Public Packet Switched Network.  It is not a protocol used for immplementing a network.  Two systems that support X.25 can't necessarily be connected back-to-back.  They can only be connected through a DCE in a Public Packet Switched Inernational Telegraph and Telephone Consultative committee (ITTCC) developed X.25 as the standard interface between the Data Terminal Equipment (DTE)and Data Circuit Terminating Equipment (DCTE).  This recommendation has been widely accepted as the industry standard for public packet switched networks.