Technical analysis of broadband access network

What we usually call broadband, generally refers to the broadband Internet, that is, to enable users to achieve transmission rate of more than 1M, 24-hour connection of the network infrastructure and the existence of the service. Broadband Internet can be divided into two parts: Broadband backbone network and access network, so the two key technologies to build broadband network are backbone network technology and accessing net technology.

The backbone is also called the core network, which is shared by all users and is responsible for transmitting the backbone data stream. Backbone networks are usually based on fiber optics and can deliver data across a wide range of cities and between countries. These networks typically 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. Industry in the broadband backbone of the transmission rate of the conventional definition is to be at least 2Gbps.

This time we mainly introduce the Broadband Access Network section, so the backbone of the broadband technology is not too much involved.

The Broadband access network provides the usually-said last-kilometer connection-the connection between the user and the backbone network.

In the access network, the current international mainstream and more mature technology, including xDSL technology, HOMEPNA technology, optical fiber access technology, cable technology and wireless Broadband access network technology. These technologies are based on a different hardware environment, their performance characteristics are also significantly different, described below.

1, xDSL Technology

DSL (Digital subscriber Line Digital Subscriber Loop) technology is a broadband access technology based on ordinary telephone lines, it transmits data and voice signals separately on the same copper wire, and the data signal does not reduce the load of the telephone switch by means of the telephone switch device; and does not need to dial, always online, 　　It is a special line, which means that using XDSL to surf the internet does not require payment of additional telephone charges. Because of historical reasons, the traditional telephone subscriber wire access network constitutes an important part of the whole communication, it distributes widely, occupies a large proportion, its investment occupies 70%-80% of total transmission line investment, how to make full use of this part of valuable resources to develop new broadband business is an important task for the development of the recent access network. And xDSL is an effective broadband access technology to make full use of copper wire.

The "X" in xDSL represents a variety of digital subscriber loop technologies, including ADSL, RADSL, HDSL and VDSL, among others.

ADSL Technology

ADSL (Asymmetric digital subscriber line loop) by Europe and the United States and other developed countries as the "modern information superhighway on the Express", because of the downlink rate of high, frequency bandwidth, performance and excellent characteristics of the user's favorite, become a modem, ISDN after a new faster, more efficient way of access.

ADSL is an asymmetric DSL technology, the so-called asymmetric refers to the user line uplink rate and downlink rate is different, uplink rate is low, downlink rate is high, especially suitable for transmission of multimedia information services, such as video-on-demand (VOD), multimedia information retrieval and other interactive services. ADSL supports uplink rate 512kbps~1mbps on a pair of copper wire, downlink rate 1mbps~8mbps, effective transmission distance within 3~5 kilometer range.

Now the more mature ADSL standard has two kinds of--g.dmt and g.lite. G.DMT is a full speed ADSL standard, support 8mbps/1.5mbps high speed downlink/uplink rate, but G.DMT require the client to install pots separator, more complex and expensive; G.lite standard rate is low, downlink/uplink rate is 1.5mbps/ 512Kbps, but eliminates the complex pots separator, the cost is low and easy to install. As far as the applicable area is concerned, the G.DMT comparison applies to small or home offices (SOHO), while G.lite is more applicable to ordinary home users.

ADSL is a more mature one in many DSL technologies at present, its large bandwidth, simple connection, small investment, so the rapid development of the current domestic Guangzhou, Shenzhen, Shanghai, Beijing, Chengdu and other telecommunications departments have launched ADSL broadband access services, and regional applications are rapid development, but from a technical point of view, ADSL can only be used as a transitional method for broadband services.

HDSL Technology

HDSL (High-speed digital subscriber loop) is a symmetric DSL technology that provides full duplex 1.544Mbps (T1) or 2.048Mbps (E1) digital connectivity with a two-pair or triple-pair UTP in the existing telephone line copper subscriber line, with a distance of up to 3~5 km.

The advantage of HDSL is to make full use of existing cable to achieve the expansion, and can solve the requirement of small number of users to transmit 384Kbps and 2048Kbps wideband signal. The disadvantage is that it is not currently able to transmit more than 2048Kbps of information, transmission distance limited to 6~10 kilometers.

RADSL Technology

RADSL (Rate Adaptive Asymmetric Digital subscriber Loop) is an adaptive rate ADSL technology that can dynamically submit 640kbps~22mbps downlink rate and uplink rate from 272Kbps to 1.088Mbps according to the quality and transmission distance of twisted pair.