Cabling 101

[Originally published 1996 |
Updated here 1999.06.28]

With telephones in more than 98% of Canadian households and cable TV in a large majority of homes, Canada is the most wired nation in the world. With telephone utilities rapidly replacing old copper wire with high-capacity fiberoptic connections, and as the use of intra-office E-mail and the Internet increase, there's a lot of discussion of ISDN, T1s, T3s, and other alphabet-soup monikers of telecommunications cabling. Here's a brief primer on the main varieties of cabling and what they can and can't do.

Twisted pair

This is the standard copper cable used in old-style telephone connections. Signals transmitted over the cabling are electrical and decay with distance, requiring repeaters to boost the signal over long distances. Though twisted-pair cables are an old technology, they're still viable for many uses, including:

• Voice telephones-- Most telephone wiring within a home and between a home and a utility pole is twisted-pair. Voices are typically transmitted as analogue data (i.e., sound waves). Confusingly, while it might seem that fax machines and computer modems work with data, not voice, you can use a fax machine or a computer modem over an analogue telephone line-- in fact, nearly every home-computer modem and home-office fax machine is analogue and works over analogue lines only.
• Data-- The same wires can handle digital data (zeroes and ones), assuming that the devices on both ends are themselves digital. Also confusingly, digital lines can carry voices if the voices are digitized. Many medium-sized and large offices use twisted-pair cabling with digital telephones and other digital equipment. Plugging, for example, an analogue fax machine into a digital line won't work.
• Integrated Services Digital Network, or ISDN-- A high-capacity digital signal consisting of two distinct channels of information, whether data or digitized voice. With the right hardware, you can use one channel for voice and the other for data, with both channels connecting to different points and everything taking place over a single outgoing ISDN line. All the equipment on an ISDN connection must be specifically ISDN-compatible; standard analogue or digital telephones, fax machines, and the like won't work unless you use a special adapter box.
• T1-- A T1 connection is equivalent in capacity to 24 regular digital telephone channels, whether data or voice (you can mix and match, but T1s are usually used exclusively for data). T1s are typically unswitched-- that is, they're linked more or less permanently to one specific point. A business, for example, might install a T1 connection between its office and an Internet service provider.

Fiberoptics

Fiberoptic connections are strands of highly refined glass through which digital data flow as beams of light. Signal loss is virtually nonexistent over the entire length of cable, so much higher data speeds are possible, and most fiberoptic connections are described as multiples of equivalent connections in other media. A typical use of a fiberoptic telecom connection is a T3, equivalent in capacity to 28 T1s. (Even faster connections, equivalent to 48 or even 192 T3s, are available but uncommon.) The T3 connection is the basic building block of inter-city communications.

Coaxial cable

Coaxial cable is mostly used for cable-TV signals in Canada. It consists of narrow thread-like strands of wire wrapped like a skein around a central thicker wire. Coaxial cable can easily handle 50 times the information contained in an analogue twisted-pair cable and an even greater proportion of digital data (in the latter case, a speed of up to 500 kilobits per second has been proposed as a typical cable-modem speed-- fast home-computer modems work at 56 kilobits per second). When cable-TV companies discuss using cable modems to connect homes to the Internet, the connections at issue take place via coaxial cable. A major downside of coaxial cable is that it is comparable to an old-style party line-- you and your neighbours are all on a single line, which has definite security implications for Internet service.

Sources: Harry van der Meer, Jack Basmadjian, and Paul Chalifour, Nordx/CDT, Inc., St. Laurent, Quebec and Chicago; Santoso Widjaja, CableTalk Systems Inc., Brampton, Ontario