Monday, 11 February 2013

Network Devices : Routers

Nework Devices

See previous post Network Devices. now we will share about Routers.



A router has two basic functions, path determination using a variety of metrics, and forwarding packets from one network to another.  Routing metrics can include load on the link between devices, delay, bandwidth, and reliability, or even hop count (i.e. the number of devices a packet must go through in order to reach its destination). 

In essence, routers will do all that bridges and switches will do, plus more.  Routers have the capability of looking deeper into the data frame and applying network services based on the destination IP address.  Destination and Source IP addresses are a part of the network header added to a packet encapsulation at the network layer.    


Summary Network Devices :

n  LANs are designed to operate within
a limited geographic area
n  Key LAN components are computers, NOS, NICs, hubs, and cables
n  Common LAN topologies include
bus, tree, star, and ring
n  Common LAN/WAN devices are hubs, bridges, switches, and routers

Friday, 8 February 2013

Network Devices : Switches

Network Devices

see previous post network devices. Now, we will share about Switches.



Switches use bridging technology to forward traffic between ports.  They provide full dedicated transmission rates between two stations that are directly connected to the switch ports.  Switches also build and maintain address tables just like bridges do.  These address tables are known as “content addressable memory.” Let’s look at an example.

Replacing the two hubs and the bridge with an Ethernet switch provides the users with dedicated bandwidth.  Each station has a full 10Mbps “pipe” to the switch.  With a switch at the center of the network, combined with the 100Mbps links, users have greater access to the network. 

Given the size of the files and applications on this network, additional bandwidth for access to the sever or to the corporate intranet is possible by using a switch that has both 10Mbps and 100Mbps Fast Ethernet ports.  The 10Mbps links could be used to support all the desktop devices, including the printer, while the 100Mbps switch ports would be used for higher bandwidth needs.

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...