Telstra has announced that some 400,000 households and businesses may be able to gain access to ADSL services by the end of March, but not through the enabling of new exchanges.

The carrier claims to have 75 per cent of telephone services ADSL enabled, and that the new breakthrough could push this figure to about 90 per cent.

Telstra’s research laboratories have determined that the existing transmission limit placed on ADSL (3.5 km) may have underestimated the capacity of the technology.

After 12 months of “detailed testing”, Telstra said it had discovered it could increase this limit to 4km without affecting the quality of the service.

Previously, customers with telephone systems further than 3.5km (down the length of the phone line) from the nearest exchange could not qualify for Telstra’s ADSL services.

The transmission limit was implemented due to the effect that long distances can have on the quality of the voice and data traffic carried on a telephone line.