Softmodem - Evolution and Technology

Evolution and Technology

As PSTN modem technology advanced, the modulation and encoding schemes became increasingly more complex, thus forcing the hardware used by the modems themselves to increase in complexity.

The first generations of modems (including acoustic couplers) and their protocols used relatively simple modulation techniques such as FSK or ASK at low speeds and with inefficient use of the telephone line's bandwidth. Under these conditions, modems could be built with the analog discrete component technology used during the late 70s and early 80s.

As more sophisticated transmission schemes were devised, the circuits grew in complexity, mixing analog with digital parts and eventually incorporating multiple ICs such as logical gates, PLLs and microcontrollers, while the techniques used in modern v34, v.90 and v.92 protocols (like 1024-QAM) are so complex that implementing a modem supporting them with discrete components or general purpose IC's would be very impractical, and a dedicated DSP or ASIC is used instead, effectively turning the modem into a special embedded system, a dedicated computer in its own right.

Furthermore, improved compression and error correction schemes were introduced in the newest protocols, requiring processing power by the modem itself. This made the construction of a mainly analog/discrete component modem impossible, especially when trying to achieve compatibility with older protocols using completely different modulation schemes.

Thus modems supporting those standards were becoming steadily more complex and expensive themselves, not to mention the fact that several conflicting standards in the early days of the various 33.6K (v34) and 56K protocols led to incompatibilities and the construction of modems with upgradeable firmware, which did all of the processing via a programmable DSP.

By offering (or claiming to offer) the same functionality as a hardware modem at a fraction of the price and (theoretically) a capacity for unlimited upgrades, the advantages of software-based modems became compelling. However, they would still require significant advances in home PCs' CPU power in order to compete with hardware modems in terms of performance and reliability.