Monday, 4 February 2013

Network Devices

Network Devices

In the previous post, we shared about network devices . this post will share to you about bridges,switches, and routers. happy reading..



Bridges improve network throughput and operate at a more intelligent level than do hubs.  A bridge is considered to be a store and forward device that uses unique hardware addresses to filter traffic that would otherwise travel from one segment to another.  A bridge performs the following functions:
         Reads data frame headers and records source address/port (segment) pairs
         Reads the destination address of incoming frames and uses recorded addresses to determine the appropriate outbound port for the frame.
         Uses memory buffers to store frames during periods of heavy transmission, and forwards them when the medium is ready.

Let’s take a look at an example.

The bridge divides this Ethernet LAN into two segments, each connecting to a hub and then to a bridge port.  Stations 123-125 are on segment 1 and stations 126-128 are on segment 2. 
When station 124 transmits to station 125, the frame goes into the hub (who repeats it and sends it out all connected ports) and then on to the bridge.  The bridge will not forward the frame because it recognizes that stations 124 and 125 are on the same segment.  Only traffic between segments passes through the bridge.  In this example, a data frame from station 123, 124, or 125 to any station on segment 2 would be forwarded, and so would a message from any station on segment 2 to stations on segment 1. 

When one station transmits, all other stations must wait until the line is silent again before transmitting. In Ethernet, only one station can transmit at a time, or data frames will collide with each other, corrupting the data in both frames. 

Bridges will listen to the network and keep track of who they are hearing.  For instance, the bridge in this example will know that system 127 is on Segment 2, and that 125 is on segment 1.  The bridge may even have a port (perhaps out to the Internet) where it will send all packets that it cannot identify a destination for.  network devices : bridge. to be continued...

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