Easy to understand: let you understand the advantages of ADSL Technical Principles

Easy to understand: it helps you understand the advantages of ADSL technology principles and introduce the principles of ADSL technology. Many people may not understand the principles of ADSL technology, after reading this article, you must have gained a lot. I hope this article will teach you more things.

What is the technical principle of ADSL?

The principle of ADSL technology is an asymmetric digital user line technology for broadband access to the Internet. As a transmission layer technology, ADSL technology makes full use of existing copper wire resources, on a pair of twisted pair wires, the uplink bandwidth is 640kbps down 8 Mbps, which overcomes the "bottleneck" of traditional users in the "Last Mile" and achieves real broadband access.

ADSL technical principles:

Traditional telephone systems use the low-frequency section of copper wires at frequencies below 4 kHz ). The ADSL technology uses the DMT discrete multiple audio) technology to divide the original telephone line 0Hz to 1 MHz into 256 sub-bands with a bandwidth of kHz. Among them, the frequency band below 4 kHz is still used to transmit the traditional telephone service of POTS), the frequency band from 20 kHz to kHz is used to transmit upstream signals, and the frequency band from kHz to MHz is used to transmit downstream signals.

DMT technology can adjust the number of BITs modulated on each channel according to the line conditions, so as to make full use of the line. Generally, the higher the signal-to-noise ratio of a sub-channel, the more bits are modulated on the channel. If the signal-to-noise ratio of a sub-channel is poor, discard it.

Currently, the technical principle of ADSL can reach the data transmission rate of up to 640 kbps and down to 8 Mbps. We can see that the original telephone signal still uses the original frequency band, while the business based on the principles of ADSL technology uses a bandwidth other than voice. Therefore, the original telephone service is not affected.

Basic Principles of ADSL:

With the rapid and healthy development of the Internet, the application of e-commerce and the Internet are fast, efficient, and convenient, and have already become an essential part of people's life, interNet applications have also developed rapidly. Users can access the Internet in multiple ways. digitalization, broadband, and FTTH are inevitable directions for future access.

Due to the high cost of Fiber-to-the-home, most users will continue to use the existing transitional Broadband Access Technology in the next few years, including the principles of N-ISDN, Cable Modem, And ADSL, the principle of ADSL technology is asymmetric digital user loop, which is the most promising and competitive. It will take a dominant position in the next decade or even decades.

Advantages of ADSL technical principles:

DSL Digital user Line (Digital Subscriber Line) is a combination of transmission technologies using copper telephone lines as transmission media. It includes HDSL, SDSL, VDSL, ADSL technical principles, and RADSL. It is generally called xDSL. The main difference between them is the differences in signal transmission speed and distance, and the differences in Uplink speed and downlink speed symmetry.

HDSL and SDSL support symmetric T1/E11.544Mbps/2.048 Mbps) transmission. The valid transmission distance of HDSL is 3-4 kilometers, and two to four pairs of copper twisted pair telephone lines are required. The maximum valid transmission distance of SDSL is 3 kilometers, and only one pair of copper wire is required. In comparison, symmetric DSL is more suitable for enterprise point-to-point connection applications, such as file transmission, video conferencing, and other processes that send and receive data volumes. Compared with asymmetric DSL, the market for symmetric DSL is much smaller.

The technical principles of VDSL and ADSL and RADSL are asymmetric transmission. Among them, VDSL is the fastest xDSL technology. On a copper pair of twisted pair telephone lines, the uplink data speed is 13 to 52 Mbps, And the downlink data speed is 1.5 to 2.3 Mbps, however, the transmission distance of VDSL is only several hundred meters. VDSL can be a cost-effective alternative to fiber-to-home. Currently, VODVideo on demand in Shenzhen) this access technology is used;

The principle of ADSL technology supports the uplink speed of Kbps to 1 Mbps on a copper line, the downlink speed is 1 Mbps to 8 Mbps, and the valid transmission distance is within 3-5 km; the speed range provided by RADSL is basically the same as that provided by ADSL, but it can dynamically adjust the user access speed based on the quality of twisted pair copper wires and the distance between transmission.

These characteristics make RADSL an ideal technology for high-speed surfing, on-demand video IAV, and remote LAN access, because in these applications, the user downloads much more information than the uploaded information sending command.

Comparison of ADSL technical principles with Cable Modem:

Compared with Cable Mode, the principles of ADSL technology have considerable advantages. Cable Modem uses a hierarchical tree structure to connect to the HFCs. The advantage is that the bandwidth is relatively high (10 Mbps). However, this technology itself is a rough bus network, this means that users need to share limited bandwidth with neighboring users. When users on a line surge, the speed will slow down.

In addition, the relevant information indicates that, in most cases, the HPC solution must take into account the existing cable TV programs, while occupying part of the bandwidth, only part of the remaining part can be used to transmit other data signals, therefore, the theoretical transmission rate of the Cable Modem can only reach half of that. Foreign Companies' experiments show that the speed is reduced to 1 Mbit/s, and the more common is 400K-500Kbps.

In general, even in an ideal situation, HFC is only equivalent to a 10 Mbps shared-bus Ethernet, while the ADSL technology principle access solution is more advanced in the network topology structure, because each user has a separate line connected to the ADSL local terminal, its structure can be viewed as a star structure, and its data transmission bandwidth is exclusive to each user.

Comparison between ADSL and common dial Modem and N-ISDN:

◆ Compared with ordinary dial Modem up to 56 K rate, and N-ISDN K rate, ADSL speed advantage is self-evident.

◆ Compared with common dial-up Modem or ISDN, the principle of ADSL technology is more attractive: it transmits data and voice signals separately on the same copper line, and the data signals are not transmitted through telephone switch equipment, this reduces the load on telephone switches and keeps online without dialing. This means that you do not have to pay additional phone fees when using ADSL to access the Internet.