Learn about ADSL2 and ADSL2 +

The development of networks is immeasurable. With the broadband access of ADSL, every household can access the Internet at high speed. Therefore, ADSL is constantly improved to achieve higher speed and wider bandwidth. Now let's take a look at the differences between ADSL2 and ADSL2 +.

Due to frame structure improvement and optimized RS encoding, ADSL2 can reach a maximum downlink rate of 12 Mb/s. because ADSL2 + uses a wider spectrum, there are more than 512 sub-carriers). When the distance is short, the downlink speed can reach up to 24 Mb/s. if g.992.32.16j is used, the maximum uplink rate between ADSL2 and ADSL2 + can be increased from 1.5 MB/s to about 2.3 Mb/s. ADSL2/ADSL2 + supports longer access distance. the first-generation ADSL transmission distance is less than 5 kilometers, while ADSL2/ADSL2 + supports applications with a distance close to 7km. The speed can reach kb/s downstream and kb/s upstream. higher speed and longer transmission distance are achieved through the following measures.

Improves modulation efficiency. the first-generation ADSL requires that the minimum data transmitted by each sub-channel is 2 bit. If the value is less than 2 bit, the sub-channel cannot be used to send data, the signal-to-noise ratio may be very low when the transmission distance is relatively long.) the data transmitted by most subchannels in the high-frequency segment may be less than 2bit. According to the requirements of the first-generation ADSL, these subchannels become unavailable. to maintain a high rate at a long distance, ADSL2 requires that each sub-channel can support 1 bit data to use many sub-channels with low signal-to-noise ratio and fail to carry 2 BIT data. in addition, ADSL2 and ADSL2 + require mandatory support for four-dimensional and 16 Status Codes (S = 1/2), which improves the modulation efficiency and enables the maximum downlink rate to reach 12 Mb/s. in the first-generation ADSL technology standard, the support for S = 1/2 is only an option, although some chip manufacturers support S = 1/2 in the first-generation ADSL technology, however, the connectivity of non-standard things fails to pass the connectivity test.

Supports more latency channels and bearer channels. the new-generation ADSL technology supports up to four bearer channels and four delay channels, while the first-generation ADSL supports up to three bearer channels and two delay channels ).

You can configure the frame structure latency and bit error rate (BER. the first generation of ADSL technology has fixed 10 error codes. because the BER is fixed, the line must maintain this BER indicator from start to end. Once the BER is greater than 10, the speed must be reduced to maintain the BER level, when the BER cannot be maintained even when the rate is reduced, it is difficult for both sides of the transceiver to train Training.) The ADSL service will be interrupted. the error rate of the next-generation ADSL technology can be configured in 10, 10, and 10. In this way, when the BER requirements are not high, you can choose to configure a high BER value to achieve a high rate and a longer transmission distance.

Reduces frame overhead. the overhead of the first-generation ADSL is fixed to 32 KB/s for any data rate. the frame overhead of the next-generation ADSL technology can be programmed between 432kb/s, so that the overhead can be set to 4kb/s for low-speed data services, allow more bits to be used for the transmission of net loads.

Optimized RS gain. ADSL2 and ADSL2 + enable the flexibility and programmability of constructing RS code fields. Therefore, ADSL2 and ADSL2 + can obtain higher encoding gain from RS code at low data rates. improved the initial state machine. ADSL2 and ADSL2 + have greatly improved the initial state machine, improving the data rate of ADSL2 and ADSL2 +.

Wider application scope. the first generation of ADSL mainly supports two business models: ADSLoverPOTS and ADSLoverISDN. in addition to the two modes, ADSL2/ADSL2 + also supports full digital business models and uses the bandwidth band of the narrowband voice business to transmit upstream data services. the first-generation ADSL technology only supports the synchronous transmission mode of STM) and the asynchronous transmission mode of ATM), while ADSL2 and ADSL2 + support both STM and ATM transmission modes, the PTM group transmission mode is also supported. Therefore, ADSL2 and ADSL2 + not only support ATM services, but also support groups such as Ethernet) services, making them more flexible in terms of service support.

More powerful line diagnosis capability. fault Locating is a very difficult problem in the application of the first-generation ADSL technology. ADSL2 and ADSL2 + have solved this problem well. the transceiver of ADSL2 and ADSL2 + greatly enhances the fault diagnosis capability. The embedded loop diagnosis function defined in the standard can measure the line conditions at both ends of the line in a timely manner without the need for maintenance personnel to use the test equipment. therefore, ADSL2/ADSL2 + supports the dual-end test function. The test results help to locate the fault location and cause. as long as the local terminal and the user side can perform the initialization sequence exchange process between the Training Board device and the user side device), even if the SHOWTIME stage cannot be performed, it refers to the data transmission phase after initialization and training ), you can also obtain the following line parameters through a special line test process by using the management interface to issue test commands by the network administrator: transmission Characteristics, background noise power spectrum, signal-to-noise ratio of each sub-channel, noise tolerance of each sub-channel, number of capable bits, and connection rate of the link.

Rate Adaptation capability. telephone lines are usually bundled with many pairs of cables. The bundled cables cause crosstalk and affect the performance of ADSL Services. for the first-generation ADSL technology, crosstalk, AM radio interference, temperature changes, and moisture in the wiring harness will lead to ADSL service disconnection. ADSL2 and ADSL2 + use real-time SRA seamless Rate Adaptation) technology to solve the problem of ADSL service disconnection, without service interruption or error codes, the data rate is changed in real time based on the line quality to meet the requirements of the line such as BER and noise capacity.

SRA is implemented based on the mechanism of separating the modulation layer and the frame layer in the ADSL2 and ADSL2 + systems, in this way, the data rate parameter of the modulation layer can be modified without changing any parameters of the frame layer. Because no parameters affect the frame layer, the user terminal keeps frame synchronization, the system will not be restarted or have an error code.

Energy-saving features. the first-generation ADSL Transceiver always works in the maximum power mode, even if there is no ADSL service on the line. the maximum power mode makes the ADSL device consume extremely much power, and the heat dissipation problem of the ADSL local device and ADSLModem is difficult to solve. Therefore, the energy-saving feature is particularly important for the wide application of ADSL. ADSL2 and ADSL2 + added two power management modes, L2 and L3, which can reduce the overall power consumption of the line while ensuring normal user services, it effectively solves the problem of local and user-side device heat dissipation. the power management functions of ADSL2 and ADSL2 + are mainly reflected in the following aspects.

In the new L2 low-power mode, when the business traffic on the line is reduced by an hour, the transmission power is reduced to exceed the required noise tolerance, reduces useless power consumption while ensuring stable business operation. the power consumption in the L2 state is about 30% of the maximum power consumption.

The new L3 low-power mode reduces the transmission power without transmitting user data, and only maintains the power consumption required for sending necessary management messages and synchronous signals, it can be quickly restored when the number of users passes in.

Both ADSL2 and ADSL2 + CO and CPE have the powercutback function, ranging from 0 ~ 40 dB, combined with L2 low-power status, can effectively reduce the sending power during normal operation, while the first generation of ADSL only has the powercutback function of CO, and the maximum range is only 12 dB.

Multi-line rate bundling. ADSL2 and ADSL2 + can bind multiple telephone lines to provide a higher data rate to meet the bandwidth requirements of different users. ADSL2 and ADSL2 + can bind two or more pairs of copper cables on an ADSL link by supporting the IMAATM used repeatedly in the ATM Forum, this provides a higher and more flexible downstream data rate.

Stronger interconnection capability. ADSL2 and ADSL2 + improve the intercommunication capability of different chip vendors and provide better performance when interworking through the following measures: by clarifying the initial state machine and adding some new features; ADSL2/ADSL2 + the ADSL Transceiver according to the function is divided into TPS-TC transmission protocol-related aggregation sub-layer), PMS-TC physical media-related aggregation sub-layer), PMD physical media-related sub-layer) and MPS-TC management protocol-related aggregation sub-layer, used for network management interface), and defines the message between the sub-layer, which helps different manufacturers of devices to achieve interoperability. in fact, the first-generation ADSL standard also includes these features, but does not define a clear hierarchy like ADSL2/ADSL2 +. when the ADSL2/ADSL2 + technology starts to use, it is estimated that it will also face interoperability issues. However, due to the above reasons, it is estimated that the problems will be much less. quick Start. the initialization time of the first generation of ADSL is greater than 10 seconds, while the fast initialization process supported by ADSL2 and ADSL2 + can make the initialization time less than 3 seconds.

In addition, ADSL2 and ADSL2 + have more stable operation and good spectrum compatibility. this is mainly reflected in the carrier sorting and pilot position determined by the receiver based on the channel analysis results, which can reflect the channel situation more realistically and select the best sub-carrier as the pilot, it is conducive to stable ADSL connection. in the training process, the process of disabling sub-carrier can let the receiver test rfi rf interference) distribution, and can control the transmit power of each sub-carrier through CO-MIB, avoids RFI and reduces interference with peripheral devices. OLR is reconfigured online.) This feature enhances dynamic adaptation to line parameter changes. short initialization is supported, can quickly restore connection synchronization from errors.