Bandwidth—Measuring Capacity

In telecommunications, bandwidth refers to capacity. Bandwidth is expressed differently in analog and digital transmissions. The carrying capacity of analog media, such as coaxial cable, is referred to in hertz. Hertz is a way of measuring the capacity or frequency of analog services. For example, someone might say coaxial cable has a bandwidth of 400 MHz; 400 MHz means four hundred million cycles per second. The capacity of the cable can be stated as a frequency of 400 MHz. The bandwidth of an analog service is the difference between the highest and lowest frequency within which the medium carries traffic. Cabling that carries data between 200 MHz and 300 MHz has a bandwidth, or frequency, of 100 MHz. The greater the difference between the highest and lowest frequency, the greater the capacity or bandwidth.

On digital services such as ISDN, T-1, and ATM, speed is stated in bits per second. Simply put, it is the number of bits that can be transmitted in one second. T-1 has a bandwidth of 1.54 million bits per second. Bandwidth in terms of bits per second or hertz can be stated in many ways. Some of these include: