Access networks are divided into several categories according to the different transmission media used.

is divided into 4 categories: 1. Copper wire access network, which is the general name for the lines that connect users’ phones to the telephone office; 2. Fiber optic access network, which uses optical fiber as the transmission medium and uses light waves as light Access network for carrier transmission signals; 3. Hybrid fiber coaxial cable (HFC) access network is a network that uses optical fiber as the transmission backbone, uses analog transmission technology, and transmits analog and digital information through frequency division multiplexing; 4 , Wireless access network, consisting of a series of transmission entities between service node interfaces and related user network interfaces, is a wireless implementation system that provides the required transmission carrying capacity for the transmission of telecommunications services.

The operating environment of this tutorial: Windows 7 system, Dell G3 computer.

With the rapid development of communication technology, telecom services are developing in the direction of comprehensive, digital, intelligent, broadband and personalization. People's demand for diversified telecom services is also increasing. At the same time, due to the SDH, The increasing maturity and use of ATM, Passive Optical Network (PON) and DWDM technologies has laid the foundation for the realization of "three lines in one, one line to the home" of voice, data and images. How to make full use of existing network resources to increase service types and improve service quality has become a subject of increasing research attention by telecom experts and operators. The "last mile" solution is the focus of everyone's greatest concern. Therefore, access network has become a hot spot in network application and construction.

The so-called access network refers to all the equipment between the backbone network and user terminals. Its length is generally a few hundred meters to several kilometers, so it is vividly called the "last mile". Since the backbone network generally adopts optical fiber structure and has high transmission speed, the access network has become the bottleneck of the entire network system. Access network access methods include copper wire (ordinary telephone line) access, optical fiber access, optical fiber coaxial cable (cable TV cable) hybrid access, and wireless access.

Copper cable access network

The copper cable access network is also called the traditional twisted pair user loop, which is the line that connects user phones to the telephone office. General term. It is widely distributed and numerous and is an important part of the telecommunications network. The network is generally a tree structure, consisting of trunk cables, distribution cables and user lead wires

The trunk cable connects the telephone exchange to the user centralized wiring area (handover box) Feeder cables generally use audio symmetrical cables with a large number of core wires; distribution cables are feeder cables that connect transfer boxes and distribution boxes, and usually use audio symmetrical cables with a small number of core wires; user introduction lines are connected to branch lines The lines between the boxes and user telephones; the transfer boxes and distribution boxes are called wiring equipment, which complete the distribution and connection functions of trunk cables, distribution cables and user lead-in lines.

According to statistics, in the city's user line network, the length of the backbone cable is usually several kilometers, rarely exceeding 10km; the length of the distribution cable is generally several hundred meters; and the user lead-in line is generally only tens of meters long. It can be seen that the main length of user lines is the length of the trunk cable. The length of user lines has a great impact on the applicable technology, thus directly affecting the development and evolution of the network.

Optical fiber access network

Optical fiber access refers to the end user connecting to the central office equipment through optical fiber. Depending on the degree of fiber penetration into users, fiber access can be divided into FTTB (Fiber To The Building), FTTP/FTTH (extending optical cables to homes or businesses), FTTO, FTTC, etc. Optical fiber is the most ideal among various transmission media in broadband networks. It is characterized by large transmission capacity, good transmission quality, low loss, and long relay distance.

Optical fiber access network is an access network that uses optical fiber as the transmission medium and uses light waves as optical carriers to transmit signals. The biggest features of optical fiber access technology are high transmission rate and high capacity. As the cost of optical fiber decreases, the price of optical cable is comparable to that of copper cable. Coupled with its inherent broadband advantages, it can be predicted that the fiber-optic access network will be the ultimate solution to the "bottleneck" problem at the user end.

Optical fiber access network refers to a network environment that uses optical fiber as the transmission medium. Optical fiber access networks can be technically divided into two categories: active optical network (AON, Active Optical Network) and passive optical network (PON, Passive Optical Network). Active optical networks can be divided into SDH-based AON and PDH-based AON; passive optical networks can be divided into narrowband PON and broadband PON.

Since the transmission medium used by the optical fiber access network is optical fiber, the optical fiber access network can be divided into FTTC (fiber to the roadside), FTTZ (fiber to the community), according to the degree of penetration of the optical fiber into the user group. FTTB (Fiber to the Building), FTTO (Fiber to the Office) and FTTH (Fibre to the Home) are collectively referred to as FTTx. FTTx is not a specific access technology, but the advancement or usage strategy of optical fiber in the access network.

Hybrid Access Network

Hybrid fiber coaxial cable (HFC) access technology is the first to mature and enter the market among broadband access technologies, with huge bandwidth And its relative economy makes it very attractive to cable TV companies and newly established telecommunications companies, especially in countries and regions with complete coaxial cable networks. It has broad application prospects.

HFC access network is a network that uses optical fiber as the transmission backbone, adopts analog transmission technology, and transmits analog and digital information through frequency division multiplexing.

HFC access network is a highly distributed access network that comprehensively applies analog and digital technology, coaxial cable and optical cable technology, and radio frequency technology. It is the product of the combination of telecommunications network and CATV network. It actually transforms the existing one-way analog CATV network composed of mixed optical fiber/coaxial cable into a two-way network. In addition to providing the original analog radio and television services, it uses frequency division multiplexing technology and a dedicated cable demodulator to realize voice Access and application of broadband two-way services such as , data and interactive video.

Wireless access network

Wireless access refers to the use of wireless means partially or completely from the switching node to the user terminal. A typical wireless access system mainly consists of several parts such as a controller, an operation and maintenance center, a base station, a fixed user unit, and a mobile terminal.

Wireless access network means that all or part of fixed users access the switch wirelessly.

The wireless access network is composed of a series of transmission entities between service node (for switches) interfaces and related user network interfaces. It is a wireless implementation system that provides the required transmission carrying capacity for the transmission of telecommunications services.

Wireless access network (WAN) actually uses wireless communication technology to replace traditional subscriber lines. Therefore, wireless access network is also called wireless local loop (WWL) or wireless subscriber system (WSS).

Characteristics of wireless access network:

Wireless access network refers to a communication network where some or all of the access network uses wireless transmission media to connect the originating office to users. As an effective supplement to the wired access network, the wireless access network has technical features such as large system capacity, the same voice quality as wired, wide coverage, simple system planning, easy expansion, and the ability to add encryption or use CDMA to enhance confidentiality. It can solve Communication problems in remote areas and areas where wiring is difficult are currently one of the fastest growing access networks.

Wireless access networks can be divided into many categories according to their technologies from mobile communications, cordless phones, trunked phones, cellular mobile communications, microwave communications or satellite communications, corresponding to different frequency bands, capacity, business bandwidth and coverage. Different.

The main working mode of wireless access is point-to-multipoint. Uplink technologies to solve multi-user contention include FDMA (frequency division multiple access), TDMA (time division multiple access) and CDMA (code division multiple access). , CDMA is the best in terms of spectrum efficiency, followed by TDMA. Among them, CDMA can include spread spectrum (DS), frequency hopping (FH) and synchronization (S-CDMA).

At present, wireless access technology has been widely used in rural areas and towns, and has also been used to a certain extent in private networks such as water conservancy, electric power, industry and mining.

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