Comprehensive Analysis of Access Network Technology

There are many areas worth learning about the access network technology. Here we mainly introduce the power of the development of the access network technology, including the social needs, fiber-optic access network technology and so on. Hope to help you. The last two decades of the 20th century are the most brilliant period for the rapid development of telecommunication networks. The exchange network and transmission network in the telecom network have successively completed the transition from analog to digital. The information highway from the exchange node to the exchange node can be said to have been basically built. However, user terminals and switching nodes are still connected by traditional user loops. These user loops are the peripheral nerves of the entire telecommunication network. They are like the "goat's intestines", which greatly limit the information transmission rate between the user terminal and the exchange node and become the "bottleneck" of the entire telecommunication network ". To build an information highway from a user to a user, you must broaden the "goat's intestines" between the user terminal and the exchange node, and break through the "bottleneck" in the telecom network ".

In recent years, the project that breaks the "bottleneck" of telecom networks has suddenly emerged, and the traditional user loop has begun to evolve to the access network technology, copper wire access, optical fiber access, wireless access, and other access methods form a competitive situation, making the access network technology another hot spot in telecom network construction. At present, the ITU-T has made suggestions on the V5 interface standard and VB5 interface standard between the access network technology and the switch, which further promotes the formation and development of this hot spot.

Social Needs -- Access Network came into being
As we all know, an important feature of the information society is the dominant position of the information economy. There is a growing demand for information and a growing demand for different types of information. The telecom business began to shift from traditional telephone business to non-voice business, and a variety of new businesses emerged, such as data, visual text, e-commerce, e-mail, videophone and conference and television. The transmission of these new services is not a traditional user loop. In order to meet the needs of a variety of telecom services that can be quickly and reliably transmitted between user terminals and business nodes, the construction of access networks has become an urgent need of the society.

The access network technology is developed under the impetus of social needs. The core of the access network technology is digitalization, broadband and integration. These technologies allow the access network to be flexible, reliable, resource-sharing, and easy to manage, so as to provide users with a variety of access services. Currently, access network technology supports the following access services: voice, data, and multimedia services.

Technology push-driving force of Access Network Technology Development
In addition to social needs, the development of access network technology must be driven by advanced technologies. Currently, with the impetus of many new technologies, multiple access modes are available in the access network technology, such as copper wire access, optical fiber access, wireless access, and hybrid access.

I. Copper access
Copper wires are connected to transmission media including Copper Twisted Pair wires and coaxial cables. The traditional copper wire user loop is an important infrastructure with a large proportion of investment in the telecom network. Currently, it is mainly used to transmit analog telephone services. The adoption of new technologies enables it to undertake the task of transmitting broadband services, and continues to play an important role in the modern telecommunication network, bringing vitality and creating benefits, it is undoubtedly the most economical, effective, and simple means of access network technology construction. The digital technology of user loop is the core of all new technologies. This includes digital duplex technology, digital multiplexing technology, and digital collection technology designed to improve the efficiency of line use; there are also digital coding technology, digital modulation and demodulation technology and digital adaptive balancing technology to improve the efficiency and transmission performance of lines. Due to these breakthroughs, multiple systems such as xDSL and CATV have emerged in the copper access network technology.

ADSL is an asymmetric digital user loop. It is a digital user loop with different downlink signal rates on a pair of Copper Twisted Pair wires. The ADSL system is designed for residential users. In addition to providing original telephone services to users, it can also provide users with a medium speed of up to 576 kbit/s) duplex Data Channel and a high-speed up to 6 Mbit/s) single-line downlink data channel. In this way, it can provide users with a variety of broadband services. The key technologies of the ADSL system mainly include spectrum structure design, efficient modulation and demodulation, high sensitivity reception, and anti-residential noise.

HDSL is a high-speed digital user loop. It uses two or three pairs of Copper Twisted Pair wires to provide users with a PDH one-time group rate T1 or E1) Duplex Digital connection. The HDSL system is mainly designed for users of enterprises and institutions. It can be used as a universal platform for copper dual-line access services, providing users with various broadband services such as voice, data, and images. Key HDSL systems include line encoding, Echo offset, and adaptive balancing. VDSL (VADSL ). It is a high-speed ADSL, and some people call it a broadband digital user loop BDSL ). The VDSL system is generally used for the last entry-to-entry connection in the fiber-optic access network technology. The transmission distance is only Mbit/s )~ 1km13Mbit/s ). The downlink transmission rate can reach 13 Mbit/s, 26 Mbit/s, 52 Mbit/s, or even 155 Mbit/s. The modulation technology is generally DMT or 16CAP; the uplink transmission rate is 1.5 ~ 2 Mbit/s, the modulation technology used is generally DMT, PSK or 4CAP. The combination of VDSL and FTTC provides users with various broadband access services.

CATV is a cable TV. It has been widely used in urban and rural areas in China, and its system bandwidth has gradually increased from 450 MHz to 550 MHz, 630 MHz, MHz, or even 1 GHz. The CATV system has a coaxial cable as a broadband transmission medium, which provides a congenital condition for introducing broadband telecommunication services. The existing CATV system can be used to deliver broadcast TV programs to users and provide users with various broadband telecommunication services. In this way, the CATV system will become a new broadband access technology that distinguishes the telecommunication network from the audio cable access technology. At present, due to market needs and technological development, the CATV system is evolving in two aspects: one is dual-oriented; the other is introducing the optical fiber transmission technology. Its key technology is efficient modulation and demodulation technology that achieves multiplexing of signals.

Ii. Optical Fiber Access Network Technology
The optical fiber transfer media is optical fiber. Because the optical fiber has the outstanding advantages of transmission band width and available bandwidth of 50THz1THz = Hz), the minimum transmission attenuation of single-mode optical fiber with low transmission attenuation at 1550nm wavelength can reach 0.2dB/km, therefore, it has become the main means of long-distance trunk line transmission and inter-Bureau Relay Transmission in modern communication networks. The continuous development of optical fiber transmission will inevitably extend to the access network. In recent years, with the maturity and development of optical communication technology, the network design and construction technologies of various devices and components used in the access network have reached the practical level, it provides powerful technical support for the engineering implementation of the optical fiber access network. Currently, fiber-to-road FTTC (optical fiber to building FTTB), fiber-to-Office FTTO), and fiber-to-home FTTH (optical fiber to home FTTH) systems are available in the optical fiber access network. However, the development speed is not very fast. The main factor limiting the development of optical fiber access networks is economic affordability, rather than technical problems. With the continuous development of social economy, the optical fiber access network will continue to expand.

Compared with copper access, the introduction of optical fiber access network can bring two obvious advantages: first, the transmission distance of the access line is greatly extended, thus expanding the coverage of the access network. In this way, the number of nodes in the entire telecom network can be reduced, making the telecom network structure simpler. Second, it can meet users' various broadband business needs and improve service quality. This fundamentally solves the "bottleneck" problem of traditional copper access networks and provides necessary conditions for the implementation of information highways. Therefore, the optical fiber access network should be the main battlefield for the construction of the Wired Access Network.

Iii. Wireless Access
The transmission media for wireless access is radio waves. In addition to providing users with fixed access, it can also provide users with mobile access. Compared with wired access, including copper access and optical fiber access, wireless access has greater flexibility and strong Disaster Tolerance and changes, so it is the most active in the development of access networks. Currently, the wireless access network mainly has the following systems: wireless local loop, includes microwave point-to-point systems, microwave point-to-point systems, fixed cellular systems, fixed cordless systems, and local broadband CDMA dedicated wireless loops that support Internet access and ATM access;

Mobile cellular systems, including the first generation of analog systems using FDMA), the second generation of digital systems using TDMA and CDMA) and the upcoming third generation of mobile system IMT-2000 ). Third-generation systems provide global coverage, including satellites, and achieve seamless connection between wired and wireless networks and services between different wireless networks, provides access rates from 9.6 kbit/s to 2.048 Mbit/s to meet multimedia business needs. Cordless systems have evolved from the first generation of simulation systems to the second generation of digital systems, it is also developing along personal communications; paging systems; fixed satellite systems, I .e. synchronous satellite systems); mobile satellite systems, such as the "Iridium" Satellite System ).

Compared with coaxial and optical fiber access, wireless access bandwidth is narrower. Therefore, the main services currently supported are voice and low-speed data. However, wireless access is also evolving towards broadband. The fourth-generation mobile system being studied is a system that supports broadband ATM access. Many key technologies are involved in wireless access systems. The most important technologies are coding and modulation and demodulation technologies that increase the spectrum efficiency and power efficiency.

Iv. Hybrid access
Hybrid access refers to the hybrid use of copper, optical fiber, and wireless access. For example, fiber optic/coaxial Hybrid System (HFCs) can extend FTTB and FTTC to office and home respectively.

Outlook -- Development of access network technology to broadband
Looking at the development status of telecommunication networks, it is not difficult to find that modern telecommunication networks are characterized by connection orientation, circuit switching, and time division multiplexing, it is transitioning to a future telecom network with "no connection, Packet Exchange, and statistical multiplexing" as its basic features. Due to the impact of Internet), "convergence" has become a new trend in the development of telecom networks: telephone networks, data networks, and video network will be "three in one "; the telephone lines, data lines, and video lines are "three in one ". The "three-in-one" of telecom networks will inevitably lead to "three-in-one" of access networks ".

The "three-in-one" architecture of the access network technology does not cause problems for coaxial and fiber-optic access. However, it is difficult for Copper Twisted Pair wires and wireless access. Because the optical fiber has the characteristics of low bandwidth consumption, fiber access becomes the best solution to expand the coverage of the access network and completely solve the "bottleneck" of the access network. Therefore, optical fiber access represents the development direction of the wired access network technology. Wireless Access is also mobile, so its development is not only very active, but will remain a hot spot in the future. It is not hard to see that in the future, the access network will be in the form of optical fiber access, supplemented by a hybrid access network with wireless access and copper access. It supports INTRENET access and ATM access as the main form of broadband access, providing users with multimedia-based businesses.

1. Comprehensive comparison of Broadband Access Technology
2. Development Direction of Remote Access Network
3. Comprehensive comparison of two common broadband access network Modes
4. ADSL Access Network is the most suitable access method for Internet cafes
5. Introduction to Integrated Access Network