ADSL (Asymmetric Digital Subscriber Line) stands for asymmetric digital subscriber line, is called a non-symmetric, is due to the realization rate is up less than 1Mbps, down less than 7Mbps. It is a home or small business can make use of the existing telephone network with high-frequency digital compression for network service providers ISP for broadband access technology. This access method so it is a non-symmetrical manner, from ISP-ended client (downlink) requires large bandwidth to support, but from the client to the ISP side (upstream) bandwidth of only a small amount can be.
ADSL principle introduced
ADSL modem and ISDN and traditional as well as the transmission medium using the telephone network. When the two ends of a pair of telephone lines were in place an ADSL device, the use of modern frequency modulation and coding, this phone line will be able to create three information channels: a high-speed downlink channel (1.5 1.8Mbps), one is the speed duplex channel, one is the ordinary telephone channel, and these three channels can work simultaneously. That is, it can get the most out of existing telephone line data transmission capacity, so users can access a telephone line not only fast-track "Surf", you can call to send a fax, call or reduced without affecting the effect of Internet . Specific work flow is: ADSL Modem encoded by the signal transmitted through the telephone line telephone office and then by a signal recognition / separator, if it is transmitted voice signal on the telephone switch, if the digital signal to access Internet.
See Figure 1, ADSL service is composed mainly of the following:
Figure 1 ADSL diagram
* ATM Backbone (ATM backbone): is the ISP to provide broadband services to the core backbone network, is the intersection of all data. Not only provides high bandwidth, and because ATM has its own advantages, making use of the channel and data exchange more efficient.
* DSLAM (DSL ATM multiplexer): This is the central office equipment to provide ADSL services. Central Office on a similar program-controlled switches.
* Telephone lines to provide services: the current ADSL services provided through the normal analog telephone line that carries voice and data services. People were asked whether the ISDN line will be converted into ADSL line, in fact, provide ISDN is a digital transmission, and ADSL must rely on analog circuit implementation.
* Voice, data separation / integrator: This is an important part of the output in the central office DSLAM ADSL central office line and voice line when the device is integrated through a transmission line. To the client and then separated by a similar device to form a data line, a voice line.
* ADSL CPE equipment (ADSL customer premises equipment): This is a user-purchase or lease of equipment to the central office. Usually ADSL Modem or ADSL Router.
Some of the problems on the ADSL
* ADSL in the end be able to provide much speed? See from Figure 2, ADSL lines using a frequency higher than the Mandarin audio line (4400kHz), up to 1MHz. Therefore, to provide 8Mbps maximum bandwidth.
Figure 2 ADSL lines over the frequency of use of 4400Hz
* ADSL there are no weaknesses? It is susceptible to interference, high requirements for the line, with the cable length increases the quality of subsequent deterioration of data transmission.
* ADSL is not an outdated technology?
In fact, the application of each technique has its surface, just as Bluetooth technology is the same as 10 meters for communication, and wireless local area network suitable for a wider range communication. I believe that, ADSL as an ordinary telephone line can transfer the technology itself has very good flexibility, that is, each ADSL phone users are directly applicable. Also for home users and small and medium enterprises do not need a guarantee by buying bandwidth of 10M FTTB access the Internet, as 10M itself is virtual, if it is the commitment rate, then ISP, ISP to guarantee the export of the Internet bandwidth, this cost is not generally Users can affordable.
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