Re: What determines bandwidth?

In it's simplest terms bandwidth is a determination of the amount of data which is traveling from one point to another, whether by wire or through the air.

There are several determining factors which may aid or decrease the amount of bandwidth. For example, RJ-45 jacks in a common household are most often a simple copper circuit between the house and the phone company with multi-plexers to allow lines to be shared. But the loop between the street and your house is a simple set of copper pairs, and this copper is not capable of transmitting analog signals greater than existing standards such as 33.6 or maybe 56K (provided there is only one digital to analog conversion in the downstream).

A household line can be used for faster communication if the line is converted to digital transmission, which essentially ISDN is -- a standard household copper line with a digital switch at the phone company to allow the user to send digital signals instead of the normal analog. Using digital communications, the copper line is capable of much higher speeds, better error correction, encryption/tamper resistance.

A T1 can be made of copper or more likely many copper wires together to serve as 1 line. Also, a T1 (or T3 for that matter) can be a fiber optic line. It depends on the locale and the phone company and its infrastructure. For example, in my old office in NYC, the building was wired with fiber from the street to the building, but within the building they used copper lines and multiplexers to attach individual offices to the street fiber line.

Wireless communications can be done using radio waves, microwaves, or infra-red, depending on the setup. Infra-red is really only good within a close poximity, so it is good for remote controls and wireless LAN's within an office space. Most wireless is done using radio waves or microwaves of varying frequencies. This is definitely the move of the future. In countries in Europe people use wireless more than wired communications. Cellular phones are the most relevant example of wireless communications. Wireless communications can be done at varying speeds depending on the equipment on both ends. In recent history, all cellular phones used analog communications (like the plain household copper, known as POTS (plain old telephone service)). But like houses going digital with services like ISDN, cellular phones are going digital as well. Digital offers many benefits such as security, privacy, call waiting, caller id, and much more that an analog transmission simply cannot handle.

Any other questions, please let me know,

Ben Saitz
bsaitz@cloud9.net