DSL continues to advance in Upgrade and Evolution

The xDSL technology, represented by ADSL technology, has been on the "fast track" of development in recent years ". Along with the rapid development, ADSL evolved from the first generation of ADSL technology to the new generation of ADSL technology. With the continuous promotion of ADSL applications and the constant change of broadband business requirements, the ADSL Technology Based on G.992.1/G.992.2 has exposed some insurmountable weaknesses in business development and O & M. For example, the line diagnosis and detection capabilities supported by the first-generation ADSL technology are weak. As the number of users increases, how to achieve remote management of user terminals and automatic line testing has become a headache for operators. A single ATM Transmission Mode is difficult to adapt to the trend of network IP; low transmission rates are difficult to support high-bandwidth businesses, such as streaming media businesses.

In response to the above situation, ITU-T as early as two or three years ago through ADSL2 (G.992.3) and ADSL2 + (G.992.5) Two new generation of ADSL technology standards, to encourage global operators to better carry out the ADSL business and enjoy the ADSL business for users. ADSL2/2 + adds some new features on the basis of the first-generation ADSL and greatly improves the performance and functions. Its outstanding features and main improvements include: the coverage is extended and the data transmission rate is improved. In particular, ADSL2 + expands the spectrum range from 1.20.mhz to 2.208 MHz, greatly increasing the downlink rate (up to 25 Mbps, ADSL2/2 + has added the PTM (Group Transfer Mode), which can more efficiently transmit the increasing Ethernet and IP services. It also enhances the Line Fault Diagnosis and spectrum control capabilities, the dual-end test function is well supported, and some single-end test functions are supported. The speed adaptation capability is enhanced, and the speed can be dynamically adjusted to adapt to the changing line conditions without affecting the service; with the added energy-saving feature, both local and client devices can enter the low-power mode or sleep state when the business volume is small or there is no business. Multi-line rate bundling is supported, it can achieve a higher data rate. It is worth noting that although the new-generation ADSL technology has introduced the ADSL2 and ADSL2 + standards, the ADSL2 standard only paves the way for the final launch of the ADSL2 + standard, the new-generation ADSL technology will be promoted and applied in the form of ADSL2 + technology.

VDSL technology has always been a controversial technology. Its standard trend and its relationship with the booming ADSL technology have become a key factor that determines the vitality of VDSL technology. In terms of standards, neither the international four-band standard nor the domestic three-band standard has defined either the QAM or DMT modulation methods, as a result, there has been a long debate over the two standards, facing the choice of the two modulation methods. The QAM method is simple and easy to develop, and the DMT method is more complex.

Although with the development of ADSL2 + technology, many people have doubts about the application prospects of VDSL technology, on the other hand, VDSL technology has unparalleled advantages in bidirectional symmetry and high bandwidth within a short distance, so people may look forward to VDSL technology. It can be said that the choice of the two technologies is very contradictory. In the long run, Using DMT modulation is the only way to develop VDSL technology. The compatibility between VDSL2 and ADSL2 + gives the industry a clear idea of DSL technology development: prior to the maturity of the VDSL2 standard, you can prioritize the development of ADSL and ADSL2 + technologies. After the maturity of the VDSL2 standard and technology, the smooth transition to the VDSL2 solution avoids risks in the technical selection. It should be noted that, in long distance (greater than 1.5 km), due to the severe high-frequency attenuation, VDSL2 Transmission Performance is equivalent to ADSL2 +, but because the VDSL2 chip needs to process spectrum much higher than the AD-SL2 + chip, its cost is higher than the AD-SL2 +, VDSL2 technology has no advantage in long distance application environment. In short, ADSL2 + will be used for long-distance access. VDSL2 is mainly used for short-distance high-speed access. The two technologies will complement each other and will remain the mainstream Broadband Access Technology in the next few years.