V.pcm 56K modem standard nearly there, 62K planned

The International Telecommunications Union (ITU), is in the final stages of defining the 56kbps analogue modem standard. In a set of meetings starting September 7 in Sun River, Oregon, the last details are due to be decided.

The International Telecommunications Union (ITU), is in the final stages of defining the 56kbps analogue modem standard. In a set of meetings starting September 7 in Sun River, Oregon, the last details are due to be decided. The standard, provisionally called V.pcm but due to acquire a number shortly, is almost entirely complete although some decisions remain on technicalities, and there are also intellectual property rights issues to be concluded.

The technical details mostly concern data mapping, the method whereby transmitted data is encoded onto the sets of signals sent down the line. Two contenders are being considered, shell mapping and modulus conversion; while modulus conversion is simpler, shell mapping is already present in V.34 modems and would need much less development. Performance-wise, there is little to choose between the two.

Intellectual property rights are more complex: almost all of the techniques used in 56kbps modems are the subject of patents, and how these will be licensed to the adopters of the new standard is the subject of considerable horse trading. Normally, these issues would be enough to delay agreement but most industry players have unpleasant memories of V.34. That standard was delayed for over a year because of such issues: this time, the determination to push things through is probably enough to solve the problems by the end of the Sun River sessions.

Attention is already turning to the next generation of 56K modems, which will be the subject of a second version of the standard some time next year. This will probably provide more robust communication -- so the higher speeds are obtained more often over imperfect phone lines -- as well as a faster link between the user and the ISP. This is currently limited to 33.6kbps, but speeds of up to 45kbps using Lucent-designed technologies are being discussed.

After that, it seems the maximum speeds will be increased by a new method based on system identification, a mathematical method for analysing the performance of the telephone network. Speeds of 62Kbps in one direction and 45Kbps in the other are thought possible, although manufacturers are not prepared to discuss this. It is clearly going to be an important extension to the useful life of the analogue modem.