Physical Network Connection With Routers

The basic hardware component used to connect heterogeneous networks is a Router.Physically,routers resembles bridges that means each router is a special purpose hardware system dedicated to the task of interconnecting networks.Like a bridge,a contains a processor and memory as well as a separate I/O interface for each network to which it connects.The network treats a connection to a router, the same as the connection to any other computer.

The most important that you have to kept in your mind about router is that it is not only used to connect two similar technology,it can also be used to connect two different types of network technology. Router can connect two LAN's,a LAN and a WAN,or two WAN's.Furthermore,when a router connects two network in the same general category,the networks do not need to use the same technology.For ex:- A router can connect an Ethernet LAN to a frame relay network.Thus,each cloud represents an arbitrary network technology.On summarizing this whole,we can say that a router is a special purpose system dedicated to the task of interconnecting networks.A router can interconnect networks that use different technologies,including different media,physical addressing schemes or frame formats.

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Understanding Bridges

A bridge is an electronic device that is used to connects two LAN segments.Unlike a repeater,however a bridge is a digital device that uses the same network interface as a conventional computer and handles frames.The bridge listen to traffic on each segment in promiscuous mode.When it receives a frame from one segment,the bridge verifies that the frame arrived intact i.e there was no electrical interference on LAN during transmission and after that it forwards a copy of the frame to the other segment if necessary.Thus,two LAN segments behave connected by a bridge behave like a single LAN.A computer connected to either segment can send a frame to any of the other computers connected to the two segments.Because each segment supports standard network connections and uses the standard frame format that means computers do not know whether they are connected to a LAN or a bridged LAN.

When we compare bridges with LAN it is found that bridges are more useful and popular than repeaters because they help isolate problems.If two segments are connected by a repeater and lightning causes electrical interference on one of them,the repeater will propagate the interference to the other segment.In contrast if interference occurs on one of the two segments connected by a bridge,the bridge will receive an incorrectly formed frame,which the bridges simply discards the same way a conventional computer discards a frame that contains an error.Similarly,a bridge will not forward a collision from one segment to another.Thus,the bridge keeps problems on one segment from affecting the other.