Research on emerging technologies of Broadband Access Networks

At present, China's broadband access network has developed very mature and many new technologies have emerged. Here we introduce the development status of VDSL and analyze some of its problems, I would like to share it with you here and hope it will be useful to you.

1. Technical Standards of VDSL

VDSL currently has two major incompatible technical standards: one is DMT discrete multi-audio modulation, and the other is CAP and QAM without carrier amplitude modulation/modulation and orthogonal amplitude modulation ). DMT divides the signal into 247 independent channels. The bandwidth of each channel is 4 K, and the bandwidth of 247 4 K lines in parallel can be obtained at the same time. Each channel is monitored at any time, and the entire system constantly switches the signal to the channel with the best performance. In addition, channels that are regarded as low-level channels starting from 8 K will be used for two-way channels to monitor and pick out information in two-way channels in a timely manner, to ensure synchronization with all 247 channels, this makes the DMT method more complex than other bearer technologies, but also provides better adaptability to different line quality. Another VDSL technology CAP divides the signals on telephone lines into three different frequency bands. Voice calls accounted for O ~ 4 K bandwidth, upstream channels use 25-K bandwidth, and downstream channels use K ~ Mbps bandwidth band. The interference between channels on one circuit and different lines is minimized. QAM is a modulation technology that can efficiently transmit three to four times of information in one line.

In terms of technical performance and application flexibility, the DMT technology is more attractive among the three modulation modes of QAM, CAP and DMT, but its flexibility and high performance are in exchange for device complexity. In terms of cost, DMT technology is still relatively expensive.

2. VDSL Application Prospect Analysis

The domestic broadband market is taking off, and the main broadband access methods are ADSL and Ethernet technologies. Although China Telecom decided to shift the market focus to ADSL last year, Ethernet broadband access network users still have a large market share.

From the perspective of technological development, Ethernet is already a mature network technology. More importantly, the cost of each interface only accounts for 1/3 of ADSL, which is in line with China's national conditions. However, the most widely laid telephone lines in users and homes are still not widely used. It takes time to re-build an Ethernet line. If you can use an existing telephone line to transmit Ethernet data, it will greatly save the operator's time and money. Therefore, EthernetOverVDSL, which is based on telephone lines, has an opportunity for development. EthernetOver VDSL has the following development advantages:

1) Extend the Ethernet transmission distance. The difficulty in Ethernet development lies in the receipt distance limit, which can only be transferred to 50-meters. When VDSL is used, the distance will reach 300 ~ 1000 meters. Therefore, this technical solution can greatly extend the transmission distance of Ethernet.

2) reduce costs. Since Ethernet is not as popular as telephone lines, the biggest problem for operators is that Ethernet needs to be rewired from scratch. Due to the architecture of EthernetOverVDSL over telephone lines, the telephone lines in the home are almost ready-made, which can save a lot of money and be cost-effective for development. At present, the open rate of Ethernet broadband access network is still very low in the domestic market, which increases the investment and operation risks of service providers. The cost-effectiveness brought by EthernetOver VDSL will be a good solution for operators.

Currently, the overall network environment in China also provides development conditions for EthernetOverVDSL. First, because VDSL is expensive, many vendors prefer ADSL. However, the price of VDSL has now dropped below several hundred RMB, which is the same as that of ADSL. Therefore, many integrators have begun to consider using VDSL solutions. Second, the backend of the optical network architecture must consider the high speed of VDSL. In general, it seems that the optical network environment currently being constructed in China is enough to make EthernetOver VDSL develop steadily. In the future, Ethernet Over VDSL needs will be greatly improved, and there will be a very bright prospect.

3. Problems faced by VDSL technology

Although VDSL technical standards have not yet been finalized, their good availability, technical compatibility, and competitive prices have attracted device manufacturers and operators to look forward to this market. standards are not the main problem. However, from the perspective of practical application, the provision of VDSL services still needs to solve the following three problems:

◆ There are many factors affecting the frequency of VDSL operations, such as serial telephone connections and antenna radiation. In addition, the VDSL frequency band is close to the frequency range of amateur radio, which implies the possibility of mutual interference, these are problems related to signal strength or transmission distance.

◆ QoS Assurance: if the core network technology of Ethernet rather than ATM is used, how can we ensure the user's expected bandwidth?

◆ To solve the problem of transmission distance, an ONU must be set up and the fee must be borne by the user. This problem does not exist in ADSL.

4. Conclusion

In terms of technology and market, VDSL has great development potential. In terms of technology, VDSL has become the first choice for all-round broadband access network technology with its high bandwidth and configuration flexibility, and can be combined with Ethernet technology. VDSL represents the development direction of the broadband access network technology "full IP". In terms of the market, Asia countries, especially China, Japan and South Korea, are opening DSL services on a large scale, as the first and cheapest DSL technology, VDSL plays an important role. It can be said that it is only a matter of time for VDSL to become a new force in the broadband access network market. As the living standard of Chinese people continues to improve, many of the broadband services it brings will make a qualitative leap in people's quality of life.

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