Print Article for : Network Switches And Hubs

Your Online Guide » Guide to Technology » Guide to The Internet

[N143]Network Switches And Hubs

by M. Aslam, M.

Switch has replaced the bridge in the modern network, which is replacing routers in many instances as well. A switch is a box with multiple cable jacks in it that looks a lot like a hub. Some manufacturers have hubs and switches of various sizes that are all but identical in appearance. The difference between a hub and a switch is that while a hub forwards every incoming packet out via all ports, a switch forwards each incoming packet only to the port that offers access to the destination system.

Switches convert the LAN from a shared network medium to a dedicated one. If you have a small network that uses a switch instead of a hub, each packet takes a dedicated path from the source computer to the destination, forming a separate collision domain for those two computers. Switches forward broadcast
Messages to all ports, but not unicasts and multicasts. No systems receive packets destined for other systems, and no collisions occur during unicast transmissions. While a bridge reduces unnecessary traffic congestion
on the network, a switch all but eliminates it.

Another benefit of switching is that each pair of computers has the full bandwidth of the network dedicated to it. A standard Ethernet LAN using a hub have 20 or more computers sharing the same 10 Mbps of bandwidth. Replace the hub with a switch, and every pair of computers has its own dedicated 10 Mbps
channel. This improves the overall performance of the network without the need for any workstation modifications to it. Switches offer ports that operate in Full-duplex mode. Full-duplex operation can effectively double the throughput of a 10 Mbps network to 20 Mbps.

Even though switches and hubs are both used to link the computers together in a network; a switch is known to be more expensive and the network that is built with switches is typically said to be a bit faster than one that is rather built with hubs. The reason for this is because once a hub gets its data at one of the computer ports on the network, it will then transmit the chunk of data to all of the ports, before distributing it to all of the other computers on that network. If more than one computer on a single network tries to send a packet of data at the same time it will cause a collision and an error will occur.

When there is an error in the network all of the computers will have to go through a procedure in order to resolve the problem. It is quite a procedure as the entire process will have to be prescribed by the CSMA/CD (Ethernet Carrier Sense Multiple Access with Collision Detection). Every single Ethernet Adapter there is has their own transmitter and receiver, and if the adapters weren't required to listen using their receivers for collisions, then they would have been able to send the information while they are receiving it. But because they can only do one at a time, not more than one chunk of data can be sent out at once, which can slow the whole process down.

Due to the fact that they operate at only a half duplex, meaning that the data may only flow one way at a time, the hub broadcasts the data from one computer to all the others. Therefore the most bandwidth is 100 MHz, which is bandwidth that is to be shared by all of the computers that are connected within the network. Then, as a result of this, when someone making use of a PC on the hub wants to download a big file or more than one file from another PC, the network will then become crowded. With a 10 MHz 10 Base-T type of network, the effect here is to slow down the network to a crawl.

If you want to connect two computers, you can do so directly in an Ethernet using a crossover cable. With one of these crossover cables you will not have a problem with collision. What it does is it hardwires the transmitter of the Ethernet on the one PC to the receiver on the other PC. Most of the 100 Base-TX Ethernet adapters are able to detect when looking out for certain collisions that it is not necessary by using a system called the auto-negotiation, and it will run in a complete duplex manner when it's needed.

What this ends in is a crossover cable that doesn't have any delays that would be caused by collisions, and the data can be directed in both ways at the same time. The maximum bandwidth allowed is 200 Mbps, meaning 100 mbps either way.

Article Source : Pg. 3

About Author

Both M. Aslam & Derek Rogers are contributors for EditorialToday. The above articles have been edited for relevancy and timeliness. All write-ups, reviews, tips and guides published by EditorialToday.com and its partners or affiliates are for informational purposes only. They should not be used for any legal or any other type of advice. We do not endorse any author, contributor, writer or article posted by our team.

M. Aslam has sinced written about articles on various topics from Interview Questions, Personal Desktop and The Internet. . M. Aslam's top article generates over 27100 views. to your Favourites.

Derek Rogers has sinced written about articles on various topics from Leadership, Food and Drink and Computers and The Internet. Derek Rogers is a freelance writer who writes for a number of UK businesses. If your looking to , he recommends Prodec Networks.. Derek Rogers's top article generates over 74000 views. to your Favourites.