OSI model of a router This led to the development of the remote bridge which performed exactly the same functions as a local bridge, with the exception that it could now be used to build a single logical network, unrestricted Routers have the capability to transmit data packets over different by geography. Since this type of bridge had wide area interfaces the paths in an extended network depending on the network user's user typically had to have two identical bridges at either end of the priorities, such as the least costly, fastest, or most direct route. communications link. Thus, remote bridges were often referred to Because they operate at a higher layer in the OSI Model than as 'half bridges'. (See Figure 56.19.) bridges, routers have a greater level of 'understanding' of the data BRIDGE BRIDGE Figure 56.19 LAN interconncetion using remote bridges 56/14 Local and Wide Area Networking Router Router Router Router Figure 56.21 An example of an extended network using routers passing on the LAN. This allows routers to create a logically communicate. Such gateways may make use of common 'lower extended network comprised of separate subnetworks, in contrast to layer' network facilities such as X.25 packet networks. (See Figure the single logically unified network constructed by bridges. (See 56.22.) Operating at the Application Layer, gateways can enable Figure 56.21.) specific applications, such as different electronic mail systems to The extra processing required by routers to manipulate data communicate. packets, however, impacts upon throughput performance. Typically, Gateways were primarily designed for specific environment-to- conventional routers introduce longer delays in getting packets from environment connectivity and not particularly for the high speeds source node to destination node, resulting in slower response times common to LAN communications. Since they operate at the highest or require more processing power to provide the same response layers of the OSI Model, gateways are required to perform su