In the ADSL2 standards advanced technologies are implemented to improve the capacity/bit rate, to establishing QoS, and also to a lesser degree to improve the coverage. Furthermore, ADSL 2 standard introduces radical innovations when it comes to power consumption, monitoring etc. The extended possibilities for monitoring and control give the operators a tool to adjust the utilization of resources, so it becomes possible to deliver reliable capacity in spite of external degrading parameters like ‘Cross talk’ and noise. Furthermore, improvement of capacity is achieved by utilizing more efficient modulation technologies, reduction of overhead, deployment of efficient coding algorithms and a number of other techniques. Over short distances it is possible to achieve bit rates of about 12 Mbps downstream and 1.2 mbps upstream. Another way of achieving higher bit rates in ADSL2 is by bonding several lines. Here at the ends of the connection, multiplexing and de-multiplexing is deployed to split a connection to several parallel connections at one end and reassemble them at the other end.
ADSL2 enables the implementation of QoS by, for example, splitting the bandwidth into different channels with different characteristics, and reserving these channels for different applications. For example, it is possible to allocate a 64 Kbps of the bandwidth for the transmission of regular telephony. This makes it possible to establish a transparent communication path for the transmission of PSTN services (the so called CVoADSL) without IP conversion or conversion to other protocol. This is a technology that enables PSTN operators to deliver efficient voice and data services. This is, however, not in line with the general VoIP development, which requires interoperable technologies across different platforms.
In ADSL2+ the bit rate is increased by doubling the deployed frequency bandwidth, i.e. by including the frequency band between 1.1 to 2.2 MHz. As mentioned earlier, the high frequencies get strongly attenuated as function of distance, which implies that the increase in bandwidth is only valid for short distances of under 2.4 km. Doubling of capacity can be achieved for distances less than one km.
RE-ADSL2 (Reach Extended ADSL2) is designed to optimize the coverage by increasing the power used in the lower part of frequency spectrum in the upstream and downstream channels. Here it is possible to achieve coverage extension of about 900 meters, which increases the potential market for PSTN operators considerably. The coverage problem is however not solved totally, as there will still be areas where the PSTN operator cannot reach without changing of the current network.