Hotspot perspective of optical switching in all optical networks

Asymmetric Digital Subscriber Line System (ADSL) is a digital subscriber line system using the DMT line code. Its downlink single channel rate can be as high as 8. 192MBIT/S, the actual rate depends on the line diameter and transmission distance. ADSL supports the main business is the internet and telephone. The biggest feature is the ability to provide broadband services without altering existing copper network facilities. In the past five years, due to the gradual maturation of technology, the production of a large increase in the market price of ADSL dropped more than 80%, coupled with the rapid development of cable modem pressure, ADSL has begun to enter a major stage of development.

However, the cost of the traditional full-speed ADSL system is high, and the actual opening of 1. 5MBIT/S speed above the user line is usually only 35% or so; the installation of the user side equipment CPE should be sent to install, so not only the installation of high cost, but also time-consuming and cumbersome, not suitable for large-scale business promotion and development. The ADSL standard g of a portable type without a shunt. 992. 2 came out quickly, some people called UADSL. The basic idea has two points: the first is to lower the downward rate to 1. 5MBIT/S or so, the second is in the user's place without telephone tap. The former makes the UADSL band only half of the ADSL, thus making the complexity and power consumption only half, and 1. The transmission distance of the 5mbit/s downlink rate is up to 5. 4km, the latter can be exempted from sending people to the user to carry out CPE installation test trouble and the corresponding additional high cost, suitable for large-scale application. This UADSL system has one of the biggest benefits is the high degree of standardization, easy to achieve the different manufacturers at the end of the user side equipment and the compatibility of CPE, conducive to large-scale promotion.

At present, the interoperability test of major UADSLCPE in the world has entered the final stage, and it is expected to realize the interoperability between arbitrary CPE and any local end, which not only greatly increases the user's choice, but also can greatly promote the decline of UADSL price and the large-scale expansion of the business. Its user side modem will be like today's analog modem, as the computer card, and the performance price is better, the line conditions are not high, it is likely to become the next 5 years, one of the leading broadband access technology.

On the other hand, ADSL technology is also continuing to improve and develop, especially without tap ADSL. This way, just install a tiny micro-filter in front of each phone. At this point, no tap ADSL also has UADSL need not send people to install CPE important advantages, but has the original full speed ADSL has all the advantages, such as high speed, network upgradeable, support future images and interactive online games and other new business and VODSL applications, But it remains to be seen whether it has no effect on all other businesses. Another new development trend of ADSL is VOICEOVERADSL (VODSL), the basic idea is that the original analog voice business is unchanged, and then provide 4~20 digital voice channel, but also provide Ethernet interface and even set-top box interface. The advent of this technology has greatly improved the bandwidth utilization and business revenue of the subscriber line, and strengthened the performance price ratio advantage of ADSL for small and medium sized enterprises. For ADSL, in order to reduce the cost of laying, to facilitate large-scale promotion, in addition to improving equipment technology, but also must pay close attention to reduce the installation of operating costs related to the operation.

In general, ADSL has entered a big stage of development, if there are any obstacles, it is the telecommunications operators own business strategy considerations, that is, 2MBIT/S and ISDN business coordination issues. It would be a painful and forced decision. In addition, it is also largely related to control policies. Open markets, especially the opening of user lines (unbound user loops) will undoubtedly greatly accelerate the development of ADSL. It is reported that in the next few years, several local telephone companies in North America have planned to lay out 30 million-line systems, the number of unbound subscriber rings has exceeded 5%, and the UK and Germany are planning 6 million and 1.5 million-line systems respectively, while South Korea has installed 2.2 million lines to become the world's fastest-growing ADSL. China has begun to conduct tens of thousands of-line trial business, the initial reflection is good, this year plans to develop 900,000 line users. ADSL is the main disadvantage of the line to the harsh requirements, affecting the transmission rate or transmission distance, this aspect depends on the combination with fiber-DLC will be a good way to avoid weaknesses. According to the US SBC analysis, in the above DLC environment can be at least 80% of the user line to provide 1. 5MBIT/SDSL business, 60% of which can provide at least 6mbit/s business, greatly expanding the scope of DSL services. In addition, whether the equipment or business prices are still high, not conducive to large-scale promotion.

VDSL System

Another trend in the development of ADSL systems is to further improve the downlink bandwidth of the system, i.e. to evolve into the so-called very high speed Digital subscriber line (VDSL) system. This technique can be extended to (26~52) mbit/s on twisted-pair lines, thus accommodating 6 to 12 4mbit/smpeg-2 signals, and the transmission distances are reduced to 1000 or 300 meters respectively. Due to the reduction of transmission distance, the interference between the code is greatly reduced, the digital signal processing requirements for simplification, transceiver cost is expected to be reduced by half than ADSL. Therefore, if the wiring or the quality of the introduction line, at this time will be FTTC, especially apon and VDSL technology combined to provide optical fiber laying costs, electronic equipment costs and the provision of bandwidth capabilities of the best balance, is a more realistic and ideal broadband hybrid access scheme. At present, VDSL is still in the field test stage, its standard work is still underway, its spectrum arrangement has not reached the agreement, the line code type is also in dispute, its performance and cost are competitive still need to practice test.