VINE SOFTWARE - TECHNICAL NOTES
VINE SOFTWARE - TECHNICAL NOTES
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This is not a comprehensive, or even 100% accurate, description of Ethernet. It is just an overview so the technical terms you might encounter can make some sort of sense.
Ethernet was designed as a way of communicating between computers using radio links. This did not catch on (until very recently) but it was employed to get computers connected by wires to communicate. However its wireless origins explain why things are done the way that they are.
The original Ethernets consisted of a single long wire to which all of the computers on the network connected. Modern networks do not look like this but, in essence, they work the same way.
When a computer wants to talk to another it sends a packet of information onto the network ("into the ether" from the old radio days). Every computer on the network looks at that packet and ignores it unless it is for it when it processes it. The network can only handle one packet at a time! If there is already a packet on the network this is a collision and the computer waits a random time and tries again. The effect of this is almost unnoticeable until the network gets so busy that there is a good chance that the retransmitted packet will also result in a collision. At that stage the network performance starts to drop off catastrophically.
Ethernets have got faster over the years. The speeds are expressed as a number and a name. They are:
10Base-T or "Ethernet". Runs at 10Mbs
This is old and
not used in modern equipment although it is still wide-spread.
100Base-T or "Fast Ethernet". Runs at 100Mbps
This is
the normal version used in modern equipment.
1000Base-T or "Gigabit Ethernet". Runs at 1000Mbps
This
is the new version and is just starting to become available at a
reasonable price.
So each of these is 10 times faster than the older version. Work is in progress for the next 10-fold speed increase.
The cable used for modern networks is known as CAT cable. The current common types are:
CAT5
Supports 10Base-T & 100Base-T
CAT5e
Supports 10Base-T, 100Base-T and 1000Base-T
CAT6
Not in common usage yet but will be required for
1000Base-T and faster.
Modern networks are formed by connecting all of the computers to a hub. This arranges things so that the system behaves the same as described above even though it is arranged as a star rather than a single string.
An alternative to a hub is a switch. This looks the same but it does not permanently connect every computer. Instead it looks at every packet and then switches on the connection between the sender and the recipient. In this way collisions are reduced because packets only go to their intended recipient and multiple packets may occur simultaneously on different parts of the network.
Switches obviously have to work very fast. It is thus an advantage to have a switch capable of running faster than you need initially (for example a 1000Base-T switch even though your computers have 100Base-T network cards) as they can operate faster and introduce fewer delays in the network.
Switches and hubs can be cascaded so you can have one plugged into another. In practice it is not a good idea to cascade hubs but switches can be cascaded a few times.
The wheel has turned full circle and wireless communication between computers has re-emerged. In general these are slower than wired connections. The common versions are:
802.11b. Runs at
11Mbps
This is the "normal" WiFi available
802.11a. Runs at
54Mbps
This is a new version and is not too widely available
802.11g. Runs at 108Mbps
full-duplex, although some devices are not full-duplex and thus run
at only 54Mbps
This is another new version (and probably explains
why 802.11a didn't take off!)
In practice you see performance nearer half the quoted speed as compared with a wired network.
There are a number of configurations for wireless networks. The two common ones are:
Ad-hoc, where all of the computers connect directly to each other
Managed, where all of the computers just connect to an Access Point in much the same way that in a wired network they connect to a hub.
Security is more of an issue than with a wired network as you do not need physical access to the network to tap into it. People might want to do that to gain access to the computers on the network or just to use the Internet connection to browse, send spam or whatever.
A properly configured wireless network needs a password to gain access to it which is normally sufficient to stop the person just wanting to use the network. Most networks can also be configured so only specific computers can use them.
The information passed around the network can also be spied on using special equipment. If that is an issue then the data itself can be encrypted making it very much more difficult to read the information.
So a properly configured wireless network using the standard encryption is probably more than secure enough for most offices. Like all networks it is not 100% secure but this should be safe against all but a determined attack .
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Wednesday, 25-Jul-2007 14:21:02 BST