System types to be admitted a priori were identified

Written on 3:16 AM by ooe

The main intention was to identify the system types already deployed in significant numbers, since these cause the existing noise environment. ADSL was included because BT was already committed to mass deployment of it, although the actual deployment when the ANFP was started was small. As an aspiration for the future, the then yet-to-be-standardised technology called SDSL was also included, but only at rates that had minimal impact on the final masks. While the ANFP was being prepared, the masks in the SDSL draft standard were changed. Just this once the ANFP was reconstructed to match – this was the main change at issue 1.1 of the ANFP – but any future increase would disallow SDSL since the ANFP is now effectively fixed.

In addition, during the deliberations of the task group, another system type was identified by some of the members as being similar to already deployed systems but which would be unfairly excluded if only existing UK-deployed systems were admitted a priori. These systems were CAP-based HDSL systems (carrierless amplitude phase is a two-dimensional modulation scheme similar to QAM). Such systems are also operable at a variety of data rates and PSDs and the precise variants that were to be admitted a priori were the subject of some disagreements in the task group. Eventually an impasse had to be broken by a determination by the regulator who decided to sanction the admission of such systems operating at a rate of 1168 kbit/s sufficient to deliver 2 Mbit/s over 2 pairs [5].

This resulted in the following list of systems to be admitted a priori as basis of the ANFP masks:

• POTS

• ISDN basic access

• 2B1Q HDSL systems delivering 2 Mbit/s over 2 pairs

• CAP HDSL systems delivering 2 Mbit/s over 2 pairs

• 2B1Q HDSL systems delivering 2 Mbit/s over 3 pairs

• ADSL over POTS

• SDSL technology, but limited to those rates with minimal impact on the ANFP masks.