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Bandwidth
by Sharlee Plett

Bandwidth refers to the volume of packets that the lines and cables are able to carry. This governs how quickly the information can move through the line. Phone lines can only carry small numbers of packets so they are much, much slower than major backbones made of fiber optic cables which can carry massive numbers of packets.

Here are some examples of the various types of lines on the Internet and their speeds.

LINE	TYPE	DEFINITION	SPEED
OC-48	Fiber optic	backbone	2.49Gbps
DS3/T3	Fiber/copper	backbone	45Mbps or greater
DS1/T1	fiber optic	backbone	1.544Mbps
ISDN	Twisted pair	phone line	64Kbps or 128Kbps
56K	Copper	line	57,600bps
Standard phone line	Standard phone line	line	300 baud to 6Mbps

Gbps = billions of bits per second
Mbps = millions of bits per second
Kbps = thousands of bits per second

To put some meaning to transmission speeds, suppose you want to download a 16MB file. Here are the times you would wait for some of the line speeds described above:

LINE TYPE	SPEED	TRANSFER TIME
OC-48	2.49Gbps	<1 second
DS3/T3	45Mbps or greater	2.8 seconds
DS1/T1	1.544Mbps	1.3 minutes
ISDN	64Kbps or 128Kbps	33.3 minutes
56K	57,600bps	38 minutes
28.8K	28,800bps	1.25 hours

Bandwidth is only as good as the slowest line involved in the connection. If you have a DS1/T1 line, but the server that has the information you want is hooked to a 56K line, your top transfer rate is based on that 56K line, not your speedy DS1/T1.