Computer cables come in a huge variety of shapes, sizes, capabilities, advantages and drawbacks.

Each cable is made up of a few components - the fewer the better, to keep it simple, stupid. Each cable has one or two types of connector, at the end of the cable (der), and the transmission media, the actual wires or other way of passing a signal from one end of the cable to the other.

    The (now) most common type of computer cabling is RJ-45 connector Category 5 Unshielded Twisted Pair (aka CAT5 UTP or just CAT5). This has the RJ-45 connector, an eight-pin connector and simple copper wires as the transmission media. The term "twisted pair" refers to the connection pairing of transmit and receive channels at either end of the data channel.
    CAT5 is usually coated in a blue plastic cover (hence the laymans term "blue cable") and is cheap, plentiful and relatively hardy - no great restrictions for bending or stresses are placed upon it.
    The main drawback to it is that CAT5 can only transmit data or signals reliably up to 100m from the source. Good for local LANs but not for long distance communication.
    Variations include Shielded Twisted Pair (STP) which offers shielded and thus more reliable but shorter distance communication.

    The precursor to CAT5 was coaxial cable, "BNC". This uses standard, shielded coaxial cable, with a BNC steel ring and lock connector, to connect to a network card.
    Coaxial cable is connected in a serial connection type - i.e one PC after the other. This means that each cable must be one continuous line with PCs "dangling" off it. This leads to problems of severing the cable, and location of data hogging PCs. Being a single line, a T-connector was used to connect PCs or other data devices off the BNC cable. It also meant that you cannot have a central point for people to connect to - everything had to be joined to the one cable.
    Coax has the advantage of being able to stretch to a slightly longer distance (up to 250m was reported), and the ease of adding more connections by simply adding anothe T-connector and attaching a new PC. However, no central point can easily exist as in the Ethernet hub.

    Fibre optic cables allow the transmission of data over considerably longer distances than copper wires. Fibre optic cables are glass fibres, cylinders of glass stretched out, coated in (often orange) plastic. The average fibre, thickness of glass coating included, usually totals only 0.5mm in width. Thus you can get a large number of fibre bundled together to allow large numbers of connections in a small space. However, each fibre has to have a connector.
    Fibre optic as a transmission media is manufactured in a variety of specifications - Single Mode, Multi Mode, Long Haul, Long Haul Short Wavelength... etc etc etc. Each of these specifications affects the angle of incidence and wavelength of light allowed in the fibre, but it really just boils down to the maximum length of the fibre and the type of connector and media converter used.

    The connectors available to fibre optic cables are numerous. The most common and cheapest connector is the ST connector. The ST classification can be best described as a central core of the fiber, with a protective coating of either condensed plastic resin or aluminium, to form a stable central connector. The actual glass fiber extends further out of this central connector, in a "soft" resin plastic connector with a tiny, exactly manufactured central hole allowing physical transmission into the fiber.
    Surrounding the larger central connector is a spring-loaded R-shaped cable lock connector, similar to the sheath type used on BNC/coaxial cabling. This is used to hold the connections firmly in place, allowing reliable light transfer and thus reliable transmission of information.
    Advantages of the ST connector include the cheap cost to manufacture (being made of add-on materials rather than integrated components), and security of connections, since the locking connector hold the connector in place quite firmly and permanently.
    Diadvantages include the ease of damage to the central soft resin plastic connector with the physical end-point. The ends can very easily snap off IN the socket that it is connected to, rendering the both the socket AND the cable useless. Considering what you are connecting to, it is a pain to extract and can potentially permanently damage the socket.

    Another type of connector is the SC class connector. The SC classification can be best described as two (often joined) connectors with square, moulded plastic blocks with guides notched on the top to allow ease of connection. The sockets that SC connectors plug in to have appropriate guides as well, and clips to hold the square connector blocks gently in place. The square blocks also have very short soft resin cores (see ST-ST fibre optic cable) with the engineered entry hole to the pair of fibers.
    Advantages of the SC connector include the ease of connection (simple plug and go as opposed to locking in place of ST connectors), and the limited risk of damage since the soft resin connectors are much shorter and thus do not have much chance of snapping off.
    Diadvantages include the lack of security of the connector, since the connection from the socket is less firm than an ST connector, and the extra costs associated with SC connectors through the use of integrated plastic parts, unable to be changed once manufactured.

A standard Ethernet networking cable can be easily constructed inexpensively. If you want to create custom installations or wish to network your house, you will not want to use pre-made lengths, as you can create the exact lengths of wiring in the walls or raceways.

When assembling a network cable, only buy rolls of Category 5 (CAT5) cable. You can purchase a crimping tool and RJ-45 connectors inexpensively, and they make a good investment.

There are two types of cables to construct: the straight-through (normal) and the crossover (also known as a null modem Ethernet cable).

Industry standards in wiring construction have made it easier to make cables. You want to make sure that you construct the cable using pairs of wires inside the CAT5 cable. The pairs of wires are twisted together to reduce interference and crosstalk between wires.


Wire #       Colour of Wire

Wire 1       White with an Orange Stripe
Wire 2       Orange
Wire 3       White with a Green Stripe
Wire 4       Blue
Wire 5       White with a Blue Stripe
Wire 6       Green
Wire 7       White with a Brown Stripe
Wire 8       Brown



Straight-Through Construction:

Pin 1   ===>   Pin 1
Pin 2   ===>   Pin 2
Pin 3   ===>   Pin 3
Pin 6   ===>   Pin 6

Pins 1 and 2 (Transmit)   ===>   Pins 1 and 2 (Transmit)
Pins 3 and 6 (Receive)    ===>   Pins 3 and 6 (Receive)


Crossover Cable Construction:

Pin 1   ===>   Pin 3
Pin 2   ===>   Pin 6
Pin 3   ===>   Pin 1
Pin 6   ===>   Pin 2

Pins 1 and 2 (Transmit)   ===>   Pins 3 and 6 (Receive)
Pins 3 and 6 (Receive)    ===>   Pins 1 and 2 (Transmit)



       cables
        |  |
        |  |
        |  |
      __/  \__
     |   __   |
     |  |  |  |
     |  |  |<-|---Clip
     |  |__|  |
     |        |
     |        |
     |_||||||_|

       ^
     Pin 1

If you want to make a few bucks, you can construct custom cables for friends or for LAN parties.
Windows 2000 has a new feature where it detects whether a UTP cable is plugged in, and if it isn't, it disables the adaptor, rejecting outgoing packets instantly, rather than waiting for them to time out. This has the annoying drawback that yo can no longer access the local machine by its external interface, as apache will redirect clients to do. (For example, you can access the machine on 127.0.0.1, but not 192.168.0.1).

There is no way (that I know) to force win2k to enable the interface in software. However, if you have a plug, a crimp tool, and two wires, the following 'placebo network cable' will create a cross-over connection between the machine and itself, making it think there is a network present, and enable the interface1.

_________________________
|                        |
|- 1 -----\              |
|- 2 -----+-\    ______  |    
|- 3 -----/ |   |        |
|- 4        |   |  Clip  |
|- 5        |   |        |
|- 6 -------/   |______  |    
|- 7                     |
|- 8                     |
|________________________|
The connections are 1-3, 2-6. The wires can be as short as half an inch (ideally you don't want them poking out the end of the plug. These plugs will also activate the link and full duplex lights on a hub/switch.2



1 - I could have done with one of these last month... 'you simply click here, and ... D'oh! It worked back at the flat...'
2 - A hub might not be able to cope with every packet it sends being immediately bounced back...

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