Development of access network technology-XDSL and hybrid Access Technology

Overview of technical development requirements for access networks

With the advancement of society and technology, the general trend of information technology development is the integration of three technologies, telephone, computer, and television, industry, and even network ". It is manifested in the Cross-penetration of the business layer, the application layer uses a unified communication protocol, the network layer is interconnected, and the technology tends to be consistent. Under the impetus of this tide, the telecom information industry is restructuring, and various related systems and regulations have also undergone corresponding changes. This brings both opportunities and challenges to the telecom industry. It puts forward a new requirement on the telecom network: that is, the current telecom network must be transformed to make it suitable for data transmission and image transmission. The following two access network technologies are introduced:

Access Network Technology-XDSL

Making full use of the existing huge twisted pair copper cable network to open up broadband business is the main competition strategy of telephone companies, asymmetric digital user lineADSLThe system is an ideal Broadband Access Technology for twisted pair copper cables. The downlink ticket channel speed can be 2.048 Mb/s, 4.096 Mb/S, and 6. 144 Mb/s, 8. 192 Mb/S. optional dual-MIIT channels can be set to 0 kb/S, 160kb/S, 384kb/S, 544kb/s, and 576kb/s. 6 Mbit/S signal is sent on a 5-core twisted pair wire. 6km far. The main services supported by ADSL are Internet and telephone, followed by on-demand TV. Its biggest feature is that it can provide broadband services without having to change the existing cable network facilities.

At present, the trial and commercial use of a certain scale has been started, and the development momentum is good. Its main drawback is the strict requirements on the line, and the domestic twisted pair can open ADSL with less than 10% of the lines. In addition, the price is still high.

Although the asymmetry inherent in the ADSL technology has been able to adapt well to Internet services, the cost is still high, and the installation of user-side equipment is still troublesome. At present, a lightweight and non-sharded ADSL is developed. The basic idea is to reduce the speed to around 1.5 Mb/s, and to avoid telephone sharding for users, in this way, the price may decrease and the installation is more convenient. However, the interference problem, especially the interference problem with the conversation, needs to be properly solved. The development of lightweight ADSL has been supported by all walks of life, and its application prospects are very promising. It is possible to develop into a major Broadband Access Solution for telecom operators in the near future.

The second trend in the development of the ADSL system is to further increase the downlink bandwidth of the system, that is, to become a so-called high-speed digital user line VDSL system. This technology can expand the uplink/downlink transmission rate of the twisted pair to 25 ~ 52 Mb/s, which can accommodate 6 ~ 12 4 Mbit/S MPEG-2 signals and 1.5 Mbit/S uplink rate are allowed, and the transmission distance is shortened to about Mbit/S. Interestingly, due to the short transmission distance, the inter-code interference is greatly reduced, and the digital signal processing requirements are greatly simplified. The cost of the transceiver is expected to be halved than that of ADSL.

CDSLConsumer DSL) is a registered trademark version of DSL. It is slower than the speed of ADSL. the downlink speed is 1 Mb/S, And the uplink line may be less ). However, it also has its own advantages. It does not need to install the "shard" on the client ".

G. lite or DSL Lite access technology is also called non-shard ADSL or general ADSI. It is a slow ADSL and does not require line separation on the user end, instead, the telephone company's remote user line. Officially referred to as ITU-T standard G a 992.2G. Lite provides 1.544 ~ 6 Mb/s downstream rate, 128 ~ The uplink rate of 384kb/s. G. Lite is expected to become the most widely deployed DSL technology.

IDSLISDN-DSL access) technology is a bit inappropriate because its speed is closer to the data rate and service of KB/8 of ISDN, and is far different from that of ADSL with a higher speed.

In the RADSL rate adaptive DSL access technology, the software can determine the transmission rate of the signal on a specific customer's telephone line and adjust the transmission rate accordingly. The Wested FlexCapZ system uses RADSL to provide the range from 640kb/s ~ The downlink rate of 22 Mb/s, and from 272kb/s ~ The uplink speed of 1.088 Mb/s.

UDSL one-way DSL access) is a recommendation made by a European company. It is a one-way version of HDSL.

Access Network Technology-hybrid Access Technology

HFCsFiber-optic coaxial hybrid network) technology enables telephone companies to quickly provide broadband services. In a coverage area of around 500 optical nodes, the service can provide 60 analog radio and television channels, at least two telephones per household, and data services with a rate of at least 10 Mbps. Use its MHz ~ The 200 MHz band also provides at least MPEG-2 of on-demand TV services and other two-way telecommunications services.

An important trend in the development of Wired Access networks is the integration of FTTC and HFCs, which leads to the development of FTTC. Recently, the access network has proposed a new networking solution: FTTC + HFC. The FTTC + hfc-trunk system transmits digital bidirectional data using optical fiber cables) and analog signals respectively. After the two types of information are restored from the optical network units on the roadside to their respective baseband signals, voice signals are sent to users through twisted pair wires, while digital and analog video signals are sent to users through coaxial cables.

In the long run, the entire business network FSN is provided by the HFC network plan. That is, various types of simulation and digital services are provided by a single network. The number of users can be reduced from 500 to 25, enabling optical fiber to the roadside. The number of end users is expected to be reduced to 1, achieving fiber-optic home. The Application of Optical Fiber provides a new channel for broadband communication, but the interference problem of the return channel still needs to be properly solved.

At present, there are a variety of solutions available to solve the back-return interference. The more thorough solution is the small Optical Node solution, which uses independent optical fiber to transmit bidirectional services, and small optical nodes adopt low-cost lasers. Small optical nodes are close to the user, so the coaxial network is divided into passive networks, and the return channel is arranged at the high-frequency end, which completely avoids interference of the return channel.

The second better solution is to use the Synchronous Code Division Multiple Access S-CDMA technology. At this time, the signal processing gain can reach ZI. sdB greatly reduces interference, and the system can work in the negative signal-to-noise ratio condition, which is expected to better solve the noise and Interference Problems of the return channel.

The Latest Development Trend of HFCs is to combine with DWDM to fully utilize the price reduction trend of DWDM to simplify the second hub station, move routers and servers to the front end, and eliminate the process of one-RF and One-optical conversion, this simplifies the system and further reduces the cost. For more analysis on the technical development of access networks, please read:

Technology Development of access networks-optical fiber access technology

Access Network Technology-Wireless Access and large network access