Category: Computer/Network >> Internet
Problem description:
What is the full English name of ADSL?
Analysis:
ADSL
abbr.
=Asymmetric Digital Subscriber Line Computer asynchronous digital subscriber line
The main features and access methods of ADSL
DSL (Digital Subscriber Line) is a combination of transmission technologies using copper telephone lines as the transmission medium. It includes HDSL, SDSL, VDSL, ADSL and RADSL, etc., generally called xDSL. Their main differences are reflected in the difference in signal transmission speed and distance and the difference in the symmetry of the uplink rate and downlink rate.
HDSL and SDSL support symmetrical T1/E1 (1.544Mbps/2.048Mbps) transmission. The effective transmission distance of HDSL is 3-4 kilometers and requires two to four pairs of copper twisted pair telephone lines; the maximum effective transmission distance of SDSL is 3 kilometers and only one pair of copper wires are needed. Comparatively speaking, symmetrical DSL is more suitable for enterprise point-to-point connection applications, such as file transfer, video conferencing and other tasks that require a roughly corresponding amount of data to be sent and received. Compared with asymmetric DSL, the market for symmetric DSL is much smaller.
VDSL, ADSL and RADSL are asymmetric transmissions. VDSL technology is the fastest among xDSL technologies. On a pair of copper twisted pair telephone lines, the uplink data rate is 13 to 52 Mbps, and the downlink data rate is 1.5 to 2.3 Mbps. However, the transmission distance of VDSL is only Within a few hundred meters, VDSL can become a cost-effective alternative to optical fiber to the home. Currently, VOD (Video on demand) in Shenzhen is implemented using this access technology; ADSL supports uplink rates of 640Kbps to 640Kbps on a pair of copper wires. 1Mbps, the downlink rate is 1Mbps to 8Mbps, and the effective transmission distance is within 3-5 kilometers; the speed range that RADSL can provide is basically the same as ADSL, but it can be dynamically adjusted according to the quality of the twisted pair copper wire and the distance of the transmission distance. User access speed. It is these characteristics of RADSL that make RADSL an ideal technology for high-speed Internet surfing, video on demand (IAV), and remote local area network (LAN) access, because in these applications users often download more information than they upload (send commands) Much more.
The fact that ADSL access services can achieve a higher performance-price ratio is inseparable from the fact that ADSL access technology has its unique technical advantages compared with other access technologies. Let's take a look at the comparison between ADSL and other access services:
Comparison between ADSL and Cable Modem:
Compared with Cable Mode, ADSL technology has considerable advantages. Cable Modem's HFC access solution adopts a hierarchical tree structure. Its advantage is relatively high bandwidth (10M), but this technology itself is a rough bus network, which means that users have to share limited bandwidth with neighboring users. Bandwidth, when there is a surge in users on a line, its speed will slow down. Furthermore, relevant information shows that in most cases, HFC solutions must take into account existing cable TV programs and occupy part of the bandwidth, leaving only part for transmitting other data signals. Therefore, the theoretical transmission rate of Cable Modem can only reach A little less than half. Experiments by foreign companies show that the rate is reduced to 1M-2Mbps, and more commonly 400K-500Kbps. Taken together, even under ideal conditions, HFC is only equivalent to a 10Mbps shared bus Ethernet, while the ADSL access solution is more advanced in network topology because each user has a separate line Connected to the ADSL central office, its structure can be regarded as a star structure, and its data transmission bandwidth is exclusive to each user.
Comparison between ADSL and ordinary dial-up Modem and N-ISDN:
A) Compared with the maximum 56K rate of ordinary dial-up Modem and the 128K rate of N-ISDN, ADSL has the speed advantage It's self-evident.
B) Compared with ordinary dial-up Modem or ISDN, ADSL is more attractive: it transmits data and voice signals separately on the same copper wire. The data signal does not pass through the telephone switch equipment, which reduces the load on the telephone exchange. This means that there is no need to pay additional phone bills when using ADSL to access the Internet.
ADSL access type:
Dedicated line access method:
Users have a fixed static IP address and are online 24 hours a day.
Virtual dial-up network access method:
It is not a real phone dial-up, but the user enters the account number and password, and obtains a dynamic IP address through identity verification, which allows the user to take the initiative to access the Internet. sex.
Applications and Prospects of ADSL
Applications of ADSL
Since ADSL was designed specifically for on-demand video programs in the early stages of development, it has asymmetry. and high-speed downlink channels. With the rapid development of the Internet, ADSL, as a high-speed access to the Internet technology, is more vital. It makes it possible to provide multimedia services on the existing Internet.
At present, Zhanjiang ADSL mainly provides Internet high-speed broadband access services. Users can enjoy a variety of broadband multimedia services for free as long as they access through ADSL and visit the corresponding sites.
With the further promotion and application of ADSL technology, ADSL access will also be able to provide point-to-point telemedicine, distance teaching, remote video conferencing and other services.
The Prospect of ADSL
Many experts in the industry firmly believe that xDSL technology, mainly ADSL, will eventually become the winner on copper twisted pairs. Currently, ordinary dial-up Modem and N-ISDN are used Users with technical access will gradually transition to broadband access methods such as ADSL, and eventually realize optical fiber access.