VDSL introduces innovations in ADSL Access Network Technology

The ADSL access network technology is constantly updated. Currently, VDSL has been born and will bring a new revolution to the access technology. There may be a lot of people who don't know VDSL. It doesn't matter. After reading this article, you will surely have a lot of GAINS. I hope this article will teach you more things. What is the most important thing about surfing the internet? Bandwidth! Choosing an appropriate access method is undoubtedly an important means to solve bandwidth problems. Currently, the most common broadband access methods for families or small and medium-sized enterprises include ISDN, ADSL, Cable Modem, set-top box, And ddnleased line. The most common methods are ISDN and ADSL. In particular, the latter has become the mainstream market. But what are the characteristics of ADSL? What are the defects? What is the next generation of ADSL Access Network Technology?

Do you understand ADSL Access Network Technology?
Among the many Broadband Access Technologies, DSL has become a main competitor in the market for its advantages such as easy installation, satisfying various application requirements, and no need to transform network devices. ADSL has become the killer of China Telecom.

The full name of ADSL is asypolicric Digital Subscriber Line. The Chinese meaning is "Asymmetric Digital user Line", that is, the uplink/downlink rate provided by ADSL on Copper Twisted Pair wires is Asymmetric. The Communication Standards Department of ITU-T International Telecommunication Union (ITU) proposed two standards for ADSL: G.992.1G. dmt) is the ADSL standard with full speed. The downstream speed of this ADSL separator is at least 6 Mb/s, the uplink speed is at least kb/s, and the transmission distance reaches M ~ 4500 m; G.992.2 is the sub-rate ADSL standard G. Lite), without separator Splitter), its downlink rate is only 1.544 Mb/s. The use of ADSL is very simple. You can use the high-bandwidth service provided by the ADSL Access Network Technology by installing the ADSL access network technical equipment on both ends of the line such as a telephone line, which is one hundred times faster than the ordinary MODEM. At the same time, another major benefit of the ADSL access network technology is that SOHO (working at home) becomes possible.

Another advantage of the ADSL access network technology is that it can coexist with a common phone on a telephone line. As long as a separator is installed at both ends of the line, the Internet connection and the answer and the call do not affect each other, supports 24 hours online. This is because ADSL is used to access the Internet, and data signals are not sent through the telephone switch device, which reduces the load on the telephone switch and does not require dialing. This is a physical connection method, the bandwidth used by the user can be fully guaranteed. This also means that you do not have to pay additional phone fees when using ADSL to access the Internet.

The next generation of ADSL Access Network Technology
Although ADSL has many advantages, all technologies have its own limitations. ADSL has some problems in terms of technology, engineering implementation, comprehensive benefits and promotion methods. We can see two ways to solve these problems:

ADSL2
ITU-T is working on the second generation of ADSL, and actively develop relevant technical standards. ITU-T G.992.3ADSL2) recommended second generation ADSL should support at least 8 Mb/s downstream, upstream kb/s net Data rate, support Data + POTS, Data + ISDN, Voice over Data three application environments, with Multi-delay channels and multi-carrier channels, fast initialization, seamless rate adaptation, and other capabilities.

Among them, Voice over Data is particularly worth noting, that is, providing Voice services through Data channels. In this case, the Voice Gateway needs to complete the conversion from voice to group data. This function enables end users of ADSL to make and receive calls without having to install traditional phones. It reflects the convergence of the data network and the telephone network on the network edge.

ADSL +
The standard of this technology is in ADSL2G. 992.3) based on the improvements, mainly including two changes: wider spectrum Expansion using 1.1 M-2.208 MHz); the number of sub-carriers increased from 252 to 512. ADSL + includes four application modes: Data + POTS, Data + ISDN, full digital ADSL compatible with POTS, and full digital ADSL compatible with ISDN. Some chip manufacturers now support this technology, such as ti and GlobespanVirata, and are expected to get the downlink speed of 16 Mb/s and the uplink speed of 1 Mb/s.

The "ultimate" of DSL-VDSL
The next trend of DSL system development is to further increase the downstream bandwidth of the system, that is, to evolve into a so-called high-speed digital user line VDSL system. VDSL technology is a direction for the development of copper access networks to higher bandwidth. As its technology continues to develop and mature, it is very competitive in the last mile-"last mile" technology. Some people even say that VDSL is the "ultimate" Technology of DSL.

VDSL uses frequency division multiplexing to transmit upstream and downstream signals of POTS, ISDN, and VDSL in different frequency bands. POTS businesses use a frequency band of less than 4 kHz in the copper spectrum. ADSL and HDSL high-speed digital user lines are also an important member of the DSL family, VDSL uses a bandwidth of up to 12 MHz.

The rate of asymmetric downlink data provided by VDSL on a pair of twisted pair telephone cables is Mbps ~ 52 Mbps, the uplink data rate is 0.8M ~ 6.4 Mbps. It can also support symmetric uplink/downlink speeds. The rate of symmetric data is Mbps to Mbps ~ To 26 Mbps, the transmission distance is about M ~ 1500 m. However, it is worth noting that the transmission rate of VDSL technology depends on the length of the transmission line. Therefore, the above data is relative. If the transmission distance is shortened, the interference between codes is greatly reduced, and the digital signal processing requirements are greatly simplified. The cost of the transceiver is expected to be reduced by 50% compared with that of ADSL. Therefore, if the quality of the wiring or introduced cables is acceptable, the combination of FTTC and VDSL technology can provide the optimal balance between the optical fiber laying cost, the electronic equipment cost, and the bandwidth capability, it is an ideal broadband hybrid access solution.

Development of VDSL
Different implementation schemes of VDSL have their own supporters. There are two main camps in the selection of line encoding schemes: one Party supports the QAM/CAP orthogonal bilateral modulation technology/non-carrier amplitude modulation and Phase Encoding) scheme, including Broadcom, Infinion, and other companies in the United States; the other side supports DMT discrete multi-tone modulation technology), including Alcatel, TI, GlobespanVirata and other companies. They have successively launched VDSL chipsets and systems that support their respective solutions. Several domestic communication manufacturers and companies have begun to develop and manufacture VDSL devices. The China Thiel lab and other network access testing departments under the Telecommunications transmission Research Institute of the Ministry of Information Industry are also doing research on the Detection Technology of VDSL equipment, it is expected that the inbound detection of VDSL equipment will be carried out in a timely manner after the official release of China's VDSL industry standards.

Application of VDSL
VDSL technology can provide all common services that traditional xDSL can provide. In addition, VDSL can simultaneously deliver a variety of broadband services, such as high-definition TV HDTV), high-definition image communication, and visual computing. Many foreign phone companies are currently conducting video service tests through VDSL. The video service provided on VDSL will be a direct challenger to cable TV, and may even be replaced. The reason users are willing to switch to VDSL is that the cost is relatively low. In addition, cable TV companies may experience slow infrastructure transformation outside the urban area. Instead, they can use VDSL to get digital TV in advance.

Integration of VDSL and ADSL
At present, VDSL technology and Ethernet technology are widely combined, so that users can enjoy the advantages of both technologies at the same time, but also to avoid their respective shortcomings. Because VDSL technology is developed from the ADSL access network technology, there must be a technical connection between the two. From the table, we can see the technical differences between VDSL and ADSL access networks. The latest development direction is to integrate VDSL and ADSL access network technologies, that is, local devices support both VDSL and ADSL technologies, and combine the advantages of both technologies, allow users to select the DSL technology that suits them.

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