Access Network, (AN) is made by the international community in recent years (2006), a new concept, which includes subscriber line transmission system, MUX, but also including digital cross-connect equipment, and user / network interface device. In the ITU-T Study Group No. 13, the latest recommendations G.963, the access network is defined as the local exchange (LE) and customer premise equipment (TE) between the implementation of the system with the aim of considering the local exchange, the user ring Road and terminal equipment, through the standardization of interfaces will be limited demand for a variety of user access nodes. Access to the communications network of the introduction of new changes in the structure of the entire communications network, fundamental changes have taken place.
Due to transmission loss, such as transmission bandwidth and noise restrictions and the impact of the existing copper access network has become increasingly difficult to meet the telecommunications needs of new business development and gradually become the broadband integrated services digital network where bottlenecks. Exchange between the Bureau and the user terminals connecting link, the number of access networks, broadband and naturally it would be on the agenda, the development of telecommunications network has become one of the focal points.
Recently, as technology costs decline, the increasingly open telecommunications market and IP data services as represented by the explosive growth in network bandwidth and capacity once again become a hot topic and a shortage of goods. Represented by the United States, developed countries are high-speed backbone network and the direction of the development of large capacity, up to 160Gbps (16 × 10Gbps) of WDM systems have been put into application. At the same time, in order to adapt to this new situation, the access network of a broadband access technology is also a new momentum of development.
Access to new technologies
copper for HDSL, ADSL, we have been more familiar with technology, focusing on the following several other copper access technology.
VDSL (Very high bit-rate Digital Subscriber Line) technology
using DMT line code, line up and down in the twisted-pair transmission rate can be extended to 25M ~ 52Mbps, which can accommodate 6 to 12 4 Mbps for MPEG-2 signal, at the same time , the allowed uplink rate of 1.5Mbps, the transmission distance is about 300 to 1000 meters.
CDSL (user DSL access) technology
CDSL (Consumer DSL) is a registered trademark of versions of DSL, ADSL than slower (downlink rate of 1Mbps, a number of uplink may be less). However, it also has its own advantages, it does not need to install the client “splitter.”
FreeDSL (free DSL access) technology
not so much this is a technology, we might as well say that this is a service. FreeDSL refers to companies providing free ADSL hardware and installation, and do not charge a monthly service charge.
G. Lite or DSL Lite Access Technologies
G. Lite (also known as DSL Lite, free ADSL splitter or universal ADSL) is a slower ADSL, it does not require the client to carry out the separation line, but telephone company long-distance line splitter for users. The official name for the ITU-T standard G-992.2 provides the G. Lite from 1.544M ~ 6Mbps downlink rate, and from 128 k ~ 384kbps uplink speed. G. Lite is expected to become the most widely deployed DSL technology.
IDSL (ISDN-DSL access) technology
IDSL (ISDN-DSL) called some of this wrong, because its rate of 128kbps with ISDN data rates and services closer to, but the difference between the speed of ADSL far higher.
RADSL (Rate Adaptive DSL access) technology
in the technology, the software can decide in a particular customer telephone lines and signal transmission speed and can adjust the transmission rate accordingly. Westell’s FlexCap2 system uses the existing line RADSL submitted from 640k ~ 22Mbps downlink rate, as well as from the 272kbps uplink speeds to 1.088Mbps.
UDSL (one-way access DSL) technology
in Europe, a company UDSL a proposal, which is one-way version of HDSL.
Wireless access technology
is the wireless access nodes to the user from the exchange of some or all of terminals means the use of wireless access technology. Wireless access technologies and mobile access can be divided into two major categories of fixed access. Mobile wireless access network, including cellular mobile telephone network zone, wireless paging network, wireless telephone network, telephone network clusters, satellite mobile communication network until the global personal communications networks, today’s communications industry, one of the most active areas. Wireless Subscriber Loop (WLL) is currently moving from analog systems to digital systems development.
Wireless access and mobile access can be divided into two types of fixed access. Which can be divided into high-speed mobile access and low-speed two. Generally available high-speed mobile access cellular system, satellite mobile communications systems, cluster systems. PGN available low-speed access system of micro-and nanotechnology area districts, such as CDMA-WILL, PACS, PHS, etc.. Fixed access nodes from the exchange of user terminals using the fixed wireless access, it is PSTN / ISDN network, a wireless extension. The goal is to provide users with transparent PSTN / ISDN services, fixed wireless access system does not contain or contain only the terminal mobility is limited. Microwave access point has multiple access, cellular areas of the fixed-mobile access applications, wireless DSL and satellite VSAT network. Fixed wireless access system to provide narrow-band-based business is basically telephone service.
Mainly fixed wireless access technology has three categories, namely, has been put into use the multi-channel Multipoint Distribution Service (MMDS) systems and direct broadcast satellite (DBS), and are doing field tests of the Local Multipoint Distribution Service (LMDS). The first two have been well-known, and the rise of LMDS is just recently become a hot spot gradually emerging broadband wireless access technology.
Overall, broadband fixed wireless access technology on behalf of the broadband access technology, a new trend of development can not be ignored, not only to open fast, simple maintenance, the user more closely at low cost, and changed the tradition of the local telecommunications business concepts, the most suitable for the new local network competition with traditional telecommunications companies and cable companies to compete effectively, but also can serve as a telecommunications company as an important complement to wired access and the development it deserves.
Optical fiber access technology
users is the central office network with the user completely to optical transmission media as the access network. Fiber-optic network of users, many programs have fiber to the curb (FTTC), fiber-to-cell (FTTZ), fiber to the office (FTTO), fiber-to-floor (FTTF), fiber-to-home (FTTH). But no matter what kind of applications, the realization of optical fiber to the home must be high-speed broadband services to meet the two-way broadband services, as well as an objective need.
The main fiber-optic network technology users is light transmission technology. At present, the development of optical multiplexing transmission quite rapidly, the majority have been in practical use. Reuse has the largest number of used time-division multiplexing (TDM), wavelength division multiplexing (WDM), frequency division multiplexing (FDM), code division multiplexing (CDM) and so on.
Hybrid access technology
of the access network in China is still the traditional copper-based subscriber line, a small number of urban areas using a fiber-optic access equipment. Access networks in urban areas of the vast majority of network topology is star or bus-type main transmission medium for telephone cable, twisted pair dominated. Thus, the focus on Hybrid Fiber Coax (HFC) access network in China to achieve the fiber of the transition process has very important practical significance.
HFC (Hybrid Fiber Coax) technology enables telephone companies to provide broadband services quickly. HFC around 500 in a coverage area of the node can provide 60-channel analog radio and television, each at least 2-way phones, the rate of at least up to 10Mbps data services. Future use of its 550MHz ~ 750MHz spectrum can also provide at least 200 the way of on-demand MPEG-2 television business, as well as other two-way telecommunications services. Cable Access Network an important trend is the integration FTTC and HFC, FTTC and then to the development. Recently, the access network and a network of new programs: FTTC + HFC. FTTC + HFC backbone fiber-optic cable system uses the method of total transmission, respectively, the number of (two-way) and the analog signal, two types of information from the settings on the side of the road were the restoration of optical network units into their base-band signal, the speech signal by the twisted pair to the user , and digital and analog video signals sent by the user of copper cable axis.