When digital networks were introduced, the phone companies wanted to use them right away because they provided a more efficient means of transmitting signals all over the place. (Digital networks could carry data much faster than analog networks.) The phone companies were presented with a problem, how- ever: how to make existing analog phones work with a digital network.
The answer was to use a codec to convert the analog signal to digital. But where should the conversion take place? At the phone company’s facilities or at their customer’s location? In the early years of the digital revolution, the conversion took place at the phone company’s facilities, which allowed the phone company to utilize the existing wiring between their facilities and the customer’s location. This wiring between a phone company facility and a cus- tomer is often called a local loop.
Over the years, the codec has been pushed closer and closer to the cus- tomer, all in an effort to make the phone network as close to 100 percent digi- tal as possible. Most parts of the PSTN remain a combination of analog and digital. Customers pick up a phone, which converts audible sound into analog signals. These signals are carried over the local loop to the phone car- rier’s facilities, where they are converted to a digital signal. The signals are forwarded to the receiver’s end. After the signals are received by the last piece of carrier equipment (closest to the end customer), they are converted back to analog form. The analog signals go into the receiver side of the POTS telephone and are heard as a replica of the caller’s voice. Figure 2-1 illustrates how a phone call is transmitted over the PSTN. Today, a customer can have either an analog or a digital phone. Depending on customer location and end-user equipment, the POTS call can be 100 percent digital.
For more than a century, POTS remained the dominant form of two-way telecommunications. During that time, however, POTS-based telephone sys- tems changed dramatically in the number, length, diameter, and type of wire or cables used and in the types of telephone equipment both at the customer end and at the carrier’s facilities.
Over the years, the codec has been pushed closer and closer to the cus- tomer, all in an effort to make the phone network as close to 100 percent digi- tal as possible. Most parts of the PSTN remain a combination of analog and digital. Customers pick up a phone, which converts audible sound into analog signals. These signals are carried over the local loop to the phone car- rier’s facilities, where they are converted to a digital signal. The signals are forwarded to the receiver’s end. After the signals are received by the last piece of carrier equipment (closest to the end customer), they are converted back to analog form. The analog signals go into the receiver side of the POTS telephone and are heard as a replica of the caller’s voice. Figure 2-1 illustrates how a phone call is transmitted over the PSTN. Today, a customer can have either an analog or a digital phone. Depending on customer location and end-user equipment, the POTS call can be 100 percent digital.
For more than a century, POTS remained the dominant form of two-way telecommunications. During that time, however, POTS-based telephone sys- tems changed dramatically in the number, length, diameter, and type of wire or cables used and in the types of telephone equipment both at the customer end and at the carrier’s facilities.
No comments:
Post a Comment