ADSL2 Access Network Technology and Application Prospects

There are still many things worth learning about the ADSL2 access network. Here we will mainly introduce the ADSL2 access network technology and the future of application. Although the standards of ADSL2 and ADSL2 + have been formulated, the industry is still exploring these two ADSL upgrade technologies. In particular, the series of core technologies used by ADSL2/2 + have more advantages than ADSL, and thus bring about a series of new applications.

As a new technology developed on the basis of ADSL, ADSL2/2 + has many advantages over ADSL, which can help operators solve a series of problems encountered in ADSL Network operations, in particular, ADSL2/2 + has adopted a large number of new technologies in terms of transmission and encoding modulation. This also gives ADSL2 access networks a broader application prospect in the future market.

Significant improvement in Transmission Performance

Compare the maximum rate of ADSL8Mbit/s, and the maximum rate of ADSL2 access network can reach 12 Mbit/s. The downlink rate of the first generation of ADSL is at least 6 Mb/s, And the uplink rate is at least 640kb/s. The G.992.3 standard has stricter requirements on the rate of the ADSL2 access network, at least 8 Mb/s downstream and kb/s upstream speed should be supported. The ability of ADSL2 to adapt to poor line environments has been improved to a certain extent, especially when the distance is long, there are bridge connections, and the transmission performance is further improved due to RF interference. In this way, in the past, users who were unable to enjoy the ADSL service due to line quality reasons can also activate ADSL. Compared with ADSL, ADSL2 can get a speed increase of 50 kbps at the same transmission distance. With the same transmission rate, ADSL2 can extend the transmission distance by 183 meters. The improvement in Transmission Performance mainly relies on the following core technologies. Efficient modulation and demodulation technology is used to ensure a high transmission rate on a long transmission line under a low signal-to-noise ratio.

Reduces frame overhead. Compared with the ADSL technology, each frame uses a fixed 32 Kbps overhead, the ADSL2 access network uses a programmable frame header, so that each frame header can be flexibly adjusted from 4 Kbps to 32 Kbps as needed, this improves the efficiency of Net Information Load Transmission. The flexibility and programmability of the ADSL frame RS encoding structure are also greatly improved. The initialization mechanism established by the link is improved to ensure the speed and stability of the line. For example, the power control at both ends of the line can reduce crosstalk. the receiving end can easily select an appropriate channel based on the initialization information sent by the line status to avoid Channel Fading Caused by bridge connections or voice interference.

In addition to its own speed improvement, the ADSL2 access network standard also supports the InverseMultiplexingforATMIMA standard for ATM Forum. IMAsub-layer is added between the ATM layer and PHYlayer using the IMA standard, and IMAsub-layer is used for reuse and reuse ), the ADSL2 chip set can bind two or more copper wires to an ADSL link. With this bundle configuration, ADSL2 can flexibly obtain extremely high data rates. Compare G.992.3G in ADSL2. DMT. bis uses 1 MHz downstream bandwidth and G.992.4G. lite. bis uses a downstream bandwidth of 2.2 kHz, and ADSL2 + uses a downstream bandwidth of MHz. Therefore, its maximum rate is about 25 Mbit/s.

RE-ADSL2 loop distance further extended

In the original ADSL technology, the loop length is limited to less than 5km, so the application of ADSL is also limited. For example, in the United States, more than half of rural user residences are out of the service scope of ADSL. ADSLAnnexL, also known as ADSL2 attachment AnnexRE-ADSL2ReachExtendedADSL2, is intended to expand the scope of ADSL work. The RE-ADSL2 contains a mandatory downstream power spectral density mask PSDmask), an optional downstream power spectral density mask and two mandatory upstream power spectral density masks. By analyzing these PSD, we can see that the RE-ADSL2 is extended by using a narrow band and a stronger PSD. Because of the technical improvement of RE-ADSL2, the distance between the original ADSL technology loop can be expanded by about 2000 feet.

Dynamically adjusted power-saving mode

The power of the first-generation ADSL Transceiver is always the same regardless of whether it is in the data transmission status. The ADSL2 access network standard introduces two power management modes, while maintaining the ADSLalwayson characteristics, saves power consumption. The L2 low-power mode can quickly return to or exit the L0 full-power mode based on Internet traffic conditions, reducing the overall power loss. L3 low-power mode in a certain period of time when no traffic, ATU-C and ATU-R can enter sleep mode L3. ADSL2 + introduces two new L2 low-power mode and L3 low-power mode), enabling the transceiver to sleep when the data rate is low or there is no data transfer, which can greatly reduce the power consumption. For local devices, it can also reduce the heat dissipation requirements, which is of great significance for solving the problems that the local device consumes too much power due to long online or always online subscription.

For example, when a user downloads a large file, the ADSL2 access network works in L0 full-power mode to achieve the highest download rate. When Internet traffic decreases, if you are reading a long text page, the download speed will decrease, and the ADSL2 system will be transferred to the L2 low-power mode. Based on Traffic changes, the L2 ADSL2 system can quickly return to the L0 mode, or if there is no traffic within a certain period of time, the system will enter the L3 sleep mode. When a user re-online, it takes about 3 seconds for the system to reinitialize and enter a stable communication status.