1. Introduction to Baseband and Broadband
2. What's the Multiplexing used in Broadband
Baseband and Broadband
The two ways to allocate the capacity of transmission media are with baseband and broadband transmissions. Baseband devotes the entire capacity of the medium to one communication channel. Broadband enables two or more communication channels to share the bandwidth of the communications medium. Baseband is the most common mode of operation. Most LANs function in baseband mode, for example. Baseband signaling can be accomplished with both analog and digital signals. Although you might not realize it, you have a great deal of experience with broadband transmissions. Consider, for example, that the TV cable coming into your house from an antenna or a cable provider is a broadband medium. Many television signals can share the bandwidth of the cable because each signal is modulated using a separately assigned frequency. You can use the television tuner to choose the channel you want to watch by selecting its frequency. This technique of dividing bandwidth into frequency bands is called 'Frequency-division Multiplexing' (FDM) and works only with analog signals. Another technique, called 'Time-division Multiplexing' (TDM), supports digital signals.
Multiplexing
Multiplexing is a technique that enables broadband media to support multiple data channels. Multiplexing makes sense under a number of circumstances:
When media bandwidth is costly. A high-speed leased line, such as a T1 or T3, is expensive to lease. If the leased line has sufficient bandwidth, multiplexing can enable the same line to carry mainframe, LAN, voice, video conferencing, and various other data types.
When bandwidth is idle. Many organizations have installed fiber-optic cable that is used only to partial capacity. With the proper equipment, a single fiber can support hundreds of megabits -- or even a gigabit or more -- of data.
When large amounts of data must be transmitted through low-capacity channels. Multiplexing techniques can divide the original data stream into several lower-bandwidth channels, each of which can be transmitted through a lower-capacity medium. The signals then can be recombined at the
