Full explanation of Access Network Technology

Currently, the access network technology is widely used. Many people may not understand the technical features and practical applications of the access network. It does not matter. After reading this article, you will certainly have a lot of GAINS. I hope this article will teach you more. Computer network technology is one of the most popular technologies in the industry and contains a wide range of contents. For example, the routing technology, network interconnection technology, data exchange technology, network management technology, network security technology, and integrated wiring engineering are all under the scope of Network Technology discussion. Currently, the network technology discussed in the industry is mainly physical network technology, which corresponds to the physical layer, data link layer, and network layer in the OSI network architecture, and implements data transmission between physical devices in the network. From this point of view, we can divide the network into LAN and WAN by region. The geographical coverage of a LAN is relatively small, usually a building or a limited geographical area. The Wan runs beyond the geographical range of the LAN, it uses data exchange networks of telecom operators to achieve connections in larger regions.

The broadband network we usually call is generally used for wide area networks. The broadband network can be divided into two parts: the broadband backbone network and the access network. The data rate of the early broadband backbone network is above 2 m, and the data rate of the access network is above kbps, the data rate of the current broadband backbone network is about several hundred M-1G, the data rate of the access network is about dozens of megabytes, the data rate of the future broadband backbone network is about 10 Gb, the data rate of the access network is about Mbps. The backbone network, also known as the core network, is shared by all users and is responsible for transmitting backbone data streams. Generally, the backbone network is based on optical fiber, which can transmit data streams in the geographic area. These networks usually use high-speed transmission networks such as SONET/SDH) to transmit data, and high-speed packet switching devices such as ATM and IP-based switching) provide network routing. We mainly introduce the broadband access network, so the broadband technology of the backbone network is not much involved.

Broadband access network technology provides the last kilometer of connection, that is, the connection between the user and the backbone network. With the large-scale investment in network infrastructure by major telecom operators, it can be said that the backbone of the network is ready to carry various broadband services. According to the different transmission media used, the access network technology can be divided into two types: Wired Access Network and Wireless Access Network. Wired Access Technology includes copper wire access, optical fiber access network technology and hybrid access technology. wireless access technology includes fixed access and mobile access network technology, such as microwave and satellite single-receiving stations as fixed access; mobile phone and paging are mobile access. Next we will introduce several access technologies using a wide range of Wired copper access networks as an example.

In our country, telephones have become very popular. traditional telephone users, copper wire access networks, constitute an important part of the entire communication. They are widely distributed and account for a large proportion, how to make good use of these resources to develop new broadband services is an important task for the development of access networks. In view of the current situation and the National Day, copper access network technology is the most widely used technology in China, and it makes full use of the original copper telephone user line) this resource, various High-Speed Modulation and coding technologies are used to achieve broadband access.

Currently, xDSL is the most popular copper access technology. DSL is short for "Digital Subscriber Line", the so-called Digital user loop. DSL technology is a broadband access network technology based on a common telephone Line. It transmits data and voice signals separately on the same copper Line, data signals do not use telephone switch devices, which reduces the load on the telephone switch. They do not need to be dialed and are always online. This means that xDSL does not have to be used to access the Internet. The "x" in xDSL represents various digital user loop technologies, including HDSL, SDSL, ADSL, RADSL, and VDSL. The following describes the DSL technologies.

1. HDSL high-speed digital user line)

HDSL is a symmetric DSL technology with the same uplink and downlink speeds. HDSL uses two pairs of existing telephone user lines to provide full-duplex 1.544 Mbps (T1) or 2.048 Mbps (E1) signal transmission. Transmission distance up to 3 ~ 5 kilometers. HDSL/SDSL features bidirectional symmetry and high speed, making full use of existing cables for resizing. The disadvantage is that it requires two pairs of cables, which are difficult for residential users to use. In addition, at present, the information above kbps cannot be transmitted, and the transmission distance is limited to 6 ~ Within 10 kilometers, the cost is relatively high. HDSL is mainly used by enterprises and institutions, including conference and television lines, LAN interconnection, and PBX Programmable switch interconnection. It can also meet the needs of a small number of users to transmit kbps and kbps of broadband signals.

2. SDSL single-line digital user loop)

There is also an HDSL product that transmits T1/E1 signals on a pair of twisted pair wires, often called SDSL, a single-line digital user loop.

3. ADSL Asymmetric Digital user line)

ADSL is an asymmetric broadband access network technology, that is, the uplink and downlink speeds of user lines are different. As you know, most Internet users use multimedia services, such as VOD, multimedia information retrieval, and other interactive services. The uplink speed is low, the downstream speed requirement is relatively high. Therefore, ADSL is developed to solve this problem. As a new technology that expands the transmission capacity of twisted pair copper wires after HDSL, ADSL has been hailed as "express trains on modern information highways" by developed countries such as Europe and America. ADSL not only inherits the technical achievements of HDSL, but also adopts more advanced technologies in signal modulation and coding, phase balancing, and echo cancellation, with better performance. The typical uplink rate of ADSL is 1.544-8.192 kbps, the downlink rate is 6 km-Mbps, and the transmission distance is 3. The advantage of ADSL is that it can make full use of existing copper resources and share copper wires with common telephone services, with less investment in the system. The disadvantage is that there is a problem of line selection rate and low bandwidth rate. Due to the characteristics of ADSL, ADSL is mainly used for Internet access, home shopping, and remote medical care.

4. RADSL rate adaptive Asymmetric Digital user loop)

RADSL is a self-adaptive rate ADSL technology. It can dynamically submit kbps ~ based on the quality of twisted pair wires and transmission distance ~ The downlink rate of 22 Mbps and the uplink rate from 272Kbps to 1.088Mbps.

5. VDSL high-speed digital user loop)

VDSL high-speed digital user loop) technology is developed in view of the limited bandwidth and high economic cost of the existing ADSL technology in providing image services. VDSL is the fastest in xDSL technology. On a pair of copper twisted pair telephone lines, the downlink speed is 13 Mbps ~ 52 Mbps, the uplink speed is 1. 5 Mbps ~ 2.3 Mbps. However, the transmission distance of VDSL is shorter, generally within several hundred meters. Because the average residential area in China is less than 1km, if VDSL technology is used, the common residential area can centrally manage all the access network technical equipment in one or two centers, it is of great significance for network management and equipment maintenance. In addition, because VDSL covers a wide range of fields, it can cover enough Initial users, with a small initial investment. It also facilitates centralized device management and system expansion. Therefore, the solution using VDSL technology is a broadband access network technology solution suitable for the actual situation in China.

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