On ADSL broadband network access technology

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On ADSL broadband access technology

Abstract: This paper briefly introduces the characteristics and application of ADSL broadband access technology, and points out that it is a practical broadband access scheme for residential areas

key words: broadband access broadband ADSL HFC Untitled Document as we all know, the Internet is infiltrating into our daily work, life and study with an irresistible trend. Users' demand for bandwidth is also getting higher and higher, so a number of broadband access technologies came into being. This paper briefly introduces the ADSL access scheme with high degree of standardization and commercialization and mature technology. 1 definition of ADSL in terms of dependency, ADSL is a kind of xDSL family. The full English name of DSL is digital subscriber li ne, which means digital subscriber line. It is a transmission technology using copper core twisted pair as the transmission medium. ADSL (asymmetric digital subscriber line) means asymmetric digital subscriber line. The high-speed video, audio and data signals are transmitted by ordinary lines, which enables ordinary fixed users to realize home office, multimedia communication, video on demand, fast access to the Internet and many other services with a small investment. 1.1 why can ADSL achieve high-speed transmission speed on ordinary lines? Theoretically, the line has about 2MHz bandwidth, while ordinary voice communication only occupies 0~4khz frequency band, and the line bandwidth is not fully utilized. ADSL adopts frequency division multiplexing technology to transmit data online in the frequency band above 4kHz. The research shows that the working frequency band of ADSL is 25k~1104khz. It is precisely because the working frequency band of ADSL signal and voice service () do not overlap each other, and ADSL data flow does not pass through the program-controlled switch. Therefore, through one line, users can achieve high speed while playing. 1.2 what is asymmetry? We say that ADSL asymmetry refers to the asymmetry of its uplink rate (up to 640kbps) and downlink rate (up to 8mbps)

1.3 ADSL includes some interesting resin system structures. The ADSL system is mainly composed of ADSL local end equipment (ADSL Access Multiplexer) DSLAM installed on the network side and user end equipment atr-u (ADSL modem) installed on the user side. In addition, pots signal separator (ADSL filter) shall be installed on both sides of the line. On the network side, the pots separator places the signal and ADSL signal No. 2 sub-1] into the box, occupying the smooth channel separation, and sends them to the program-controlled switch and ATM switch (or core router) respectively. On the user side, the pots separator is responsible for separating the mixed signals in the downlink direction from analog signals and digital signals, and sending them to the user computer and ADSL modem respectively. In the uplink direction, it is also responsible for multiplexing the analog signals from the slave computer and the digital signals from the ADSL modem on the same pair of twisted pairs

3adsl technical standards there are two ADSL technical standards: one is the full rate ADSL standard - t, which supports a high-speed uplink/downlink rate of 640kbps/8mbps; The other is a simplified ADSL technical standard, te. The maximum uplink rate is reduced to 512Kbps and the maximum downlink rate is reduced to 1.5mbps. In addition, pots signal separator is cancelled on the user side. We say that ADSL has a high degree of standardization, which has two meanings: first, there are only two ADSL technical standards (HFC broadband has four technical standards); The second is that the two technical standards are not completely different. Te is only a simplified version of T. In fact, this leaves a great deal of room for engineers and technicians to maneuver. Different schemes can be adopted according to the actual situation of the project: first, as for high-end communities and small offices, there are high requirements for intelligence. We might as well adopt a high configuration scheme and use the full rate ADSL broadband access technology. Second, for ordinary home users, it is suitable to promote the simplified ADSL technical solution te. Although the speed is reduced, the user end eliminates the POTS signal separator, reduces the equipment purchase cost and installation cost, and has a certain advantage in cost performance. Third, generally speaking, in order to expand the market to the largest extent and seize the huge ordinary consumer groups, the telecom bureau should speed limit ADSL broadband (generally provide 512Kbps access rate) to reduce user fees. Under this background, te has a better market prospect

4adsl features 4.1.adsl advantages compared with the hybrid fiber coax (HFC) pilot projects in some places, ADSL has the following advantages: ① the technical standards are relatively unified. As mentioned earlier, ADSL has two technical standards - t and Te, and the latter is only a simplification of the former. At present, there are four different standards for cable modem: MCNS in North America and IEEE 802.14 working group, dvb/david in Europe and ITU-T. The disunity of standards limits the development of HFC to some extent. ② ADSL does not need to reconstruct the existing lines. At present, the common antenna system (CATV) in residential areas in China belongs to the unidirectional CATV network. When HFC broadband access technology is adopted, the existing lines must be transformed, the original coaxial cables must be replaced, and the original unidirectional amplifiers of the lines must be replaced with bidirectional amplifiers, so the investment on the lines is large. ③ ADSL users have exclusive bandwidth. From the perspective of network topology, ADSL provides each user with a separate line, which is equivalent to a star topology, and its bandwidth is exclusive to each user. The HFC Access Scheme with bandwidth advantage adopts a hierarchical tree structure, which is essentially a rough bus topology, which means that users will share bandwidth with neighboring users. When the number of people on the same line increases at the same time, the network speed will obviously change. The manufacturing industry has always been the basic factor in building the American middle class, and its bandwidth advantage will be greatly reduced. And the poor security of the bus network is its inherent defect. Compared with ordinary dial-up modem and ISDN, ADSL has a much higher rate, and the rates of the latter two are 56kbps/128kbps respectively. In addition, the ADSL data signal does not pass through the switch, so there is no need to dial, and there is no need to pay fees on the dedicated line. 4.2.adsl defects of course, ADSL also has its disadvantages: ADSL has high requirements for lines. As mentioned earlier, ADSL is based on copper core twisted pair

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