## Table of CCITT telephone modem characteristics

#### In Chapter 1, the influence of standards on digital communications systems design was discussed, and nowhere are standards more rigorously applied than for telephone dial-up modem systems.

#### In order to ensure interoperability of telephone modems, the International Telecommunications Union (ITU), formerly known as the International Telegraph and Telephone Consultative Committee (CCITT), oversees the standardization of modulation formats, coding schemes and so on for all telephone commercial modems. The table shown here lists most of the standard types, showing how the complexity and number of symbol states increase as the throughput increases. |

#### This table also provides an interesting insight into the development of modem technology. The early low speed modems used the very simple, but bandwidth and power inefficient, non-coherent FSK modulation format, while the most recent modems use the constellation space to the full and employ some of the most powerful DSP processors in the market-place to realize sophisticated equalization, convolutional coding, and so on.

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