<< Back to Networking Main Page      N E T W O R K I N G  W E E K  5 Telephone Digital Audio - Digital version of an analog audio signal. Diditization involves converting the analog signal to the digital form. Analog - to - digital converter (A to D converter) - AtoD takes a analog signal, takes a look at a peice of it at regular intervals (8000 times a second), and spits out a number representing the current voltage level of the signal. This produces a streem of numbers. Downside - The tradeoff is between accuracy and data size. A large range af integer values increases accuracy but is high in overhead, while the smaller range of integer values isnt very accurate but has a small overhead. The sweet spot seems to be 0 to 255. Pulse Code - Pulse code is the standard for digital encoding of audio used in telephone systems. PCM looks at a signal every .000125 seconds and changes each peice into an integer between 0 and 225. SONET Synchronous Optical NETwork - Phone companies have designed SONET a s a broad set of standards for digital transmission. SONET specifies details such as how data is framed, multiplexed, and syncronized. EXAMPLE:   Overhead Payload 9 Rows                         ...                                       ...                                       ...                                       ...                                       ...                                       ...                                       ...                                       ...                                       ...                 90 Columns   Jon's (classmate and friend*) Notes - "Although the SONET standard defines a technology that can be used to build a high-capacity ring network with multiple data circuits multiplexed across the fibers that constitute the ring, most data networks only use SONET to define framing and encoding on a leased circuit. Each frame is 810 octets long. Octets in the frame are divided into 9 rows with 90 columns in each row. An add/drop mux can be configured to accept additional data from a local circuit and add it to frames passing across the ring or extract data and deliver it to a local computer." ISDN ISDN Jon's Notes - "(Integrated Services Digital Network) offers digitized voice and data to subscribers over conventional local loop wiring. It is an expensive alternative to dialup modems now that techonology has increased." DSL DSL Jon's Notes - "(Digital Subscriber Line) - ADSL is a local loop technology that is optimized for typical users who receive much more information than they send. To accommodate such use, ASDL provides a higher bit rate downstream than upstream - from the subscriber to the provider. Web pages are displayed faster. The max downstream is 6.144 Mbps and the max upstream rate is 640 Kbps. The effective for a user upstream is 576 Kbps. It runs over the same local loop wiring. It can run simultaneously over the same wires as the standard phone service. It is adaptive. It uses an adaptive technology in which a pair of modems probe many frequencies on the line between them, and select frequencies and modulation techniques that give optimal results on that line."     *I would like to thank Jon Maddix for letting me use his notes while I was sick.