Ethernet : Computer Hardware Buyers’ Glossary

2007-12-14 by Roedy Green ©1997-2008 Canadian Mind Products
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Ethernet

aka IEEE 802.3, aka network adapter. You can connect computers together to let them share files, printers, or programs. Ideally you connect them in a star using 10-base T wiring, that looks like fat 8-conductor telephone wire with oversize clear plastic phone jack plugs. At the center of the star is a little box with indicator lights called a hub. The other technique is to snake a single coax cable (called ThinNet) through all the computers. Coax suffers from the same problem that cheap Christas tree lights do. If any link is not perfect, the whole system goes down. The advantage of coax is you need less wire altogether and you don’t need to poke around in the ceiling threading wire all the way back to the hub to add another workstation. Ordinary Ethernet can transmit 10 million bits per second, about 1/8 the speed you can access data off a good quality hard disk. There are various Ethernet variants that allow you to transmit 100 million bits per second. 100M Ethernet uses the same 10-base T cabling, though you will get better results with cat5 cable sometimes sold under the name Datatwist 350. If you mix slow and fast Ethernet on the same LAN, you need a switching hub. For heavy duty applications there are now Ethernets capable of a gigabit per second, i.e. ten times faster still at 1000 million bits per second. There is even a 10-gigabit per second Ethernet, which is 100 times faster than 100M. These are used primarily to link servers to the Internet.

The electronics to support Ethernet connections are sometimes part of the motherboard or sometimes on a separate PCI adapter card that Intel likes to call a desktop adapter. Intel reserves the term Ethernet controller for the master chip on that card. In a laptop, usually Ethernet is built-in, but sometimes you must buy an add-on PCMCIA card.

Long Distances

Ethernet via 10-Base T twisted pair won’t go further than 0.10 km (109.36 yards). There are several techniques to use to deal with LANs that are very spread out.

Use a good quality cable, and just deal with the losses from random errors. Watch out for ground loops if the remote site does not share a common ground.
Use wireless, perhaps with a directional antenna.
Use an active hub to act as a repeater. You read the remote site in two hops with the hub at the junction. The problem with this technique is you will need AC power for the hub, and it will have to be protected from weather if the other site is in another building. You also have to watch out for ground loops if the remote site does not share a common ground.
Use an optical link. This will let you go for 0.41 km (450.57 yards), but it is more expensive. Optical usually goes for kilometres, but Ethernet has the problem of collision detection which reduces the range. There are units that will extend up to 148 kilometres.

100M Optical Ethernet Extenders
firewall
Gigabit Optical Ethernet Extenders
IPsec
LAN
MAC address
MAC address: student project
router
wireless LAN

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