Bandwidth is the second concept important for transmission. This concept can be explained with the help of the traffic network mentioned earlier. If there is a two-way street, consisting of two single lanes, one in each direction, only one line of vehicles can travel in each direction. On a superhighway, however, there may be three or four lanes in each direction; cars may travel along these lanes, in parallel, each at its own rate of speed. We have a wider 'band' of highway which can accommodate more cars traveling in the same direction at the same time. In the same way, the width of the electronic path determines how many cycles or bits can travel along this given path at any given time; the more bandwidth is available, the more bits may be transmitted, and the better the quality of transmission. In a simple telephone conversation, we use a bandwidth of about 3000 bits per second or 3 KHz . Television needs more bandwidth to accommodate audio and visual signals, and uses approximately 4,500,000 Hz or 4.5 MHz.
Frequencies and bandwidth occur from low to very high along a continuous range of frequencies called the spectrum. To keep transmission from interfering with one another, each type (voice, radio, television, satellites, etc.) is allocated a bandwidth in this spectrum. Allocation is determined for any nation by its communications commission and internationally by the International Telecommunications Union (ITU) to avoid competition for the same bandwidths by different carriers and countries.
When bandwidths are allocated°, sufficient extra space is provided between frequencies to prevent electronic interference in so far as possible. This safety precaution might not always work, when we hear or see overlap among radio broadcasts or television programs.