This is the amount of information that we receive per unit of time. And the time at modern man worth its weight in gold. We are constantly nervous in lines, traffic jams, and slow Internet makes the picture even more aggravated, brings us to a boil. Can we influence the connection speed? When choosing a provider and equipment, you need to understand whether the Internet speed depends on the modem, or whether a slow connection to the World Wide Web is caused by some other reason.

Of course, the speed of the Internet is determined by many factors:

• type of network connection (fiber-optic or telephone line, 3G, satellite communications);
• technical capabilities of the provider (availability of a sufficient amount of equipment, its modernity, quality of communication lines, frequency of coverage);
• tariff plan(provider can artificially limit access speed);
• software on the computer, the correct settings for working on the network, the presence of viruses, software errors, etc.;
• the parameters of the sites themselves that you visit (there may be server problems, congestion, etc.);
• weather conditions (rain, hurricane, snow, thunderstorms can create trouble on the line, equipment failure, lack of communication with towers and servers).

To figure out if the modem affects the speed of the Internet, let's analyze different types connections.

Connection via fiber optic line

The fiber optic cable has a high bandwidth and provides the fastest data exchange. It often happens that the fiber is simply brought to the building, and then a twisted pair goes through the premises (apartments), which significantly limits the speed (up to 100 Mbps). In this case, a modem is not required - the cable can be connected directly to the computer's network card, but a router may be required. This is a more complex device that allows you to create local and WiFi networks indoors, connect various mobile and stationary devices to them. The maximum speed in such a network is determined by the capabilities of the router.

If the provider offers to bring a fiber optic cable directly into the apartment (or office space), then you will need a special modem. As a rule, the operator provides it himself and includes a fee for it in the tariff plan. In this case, the Internet speed depends on the modem and, perhaps, the company will offer you different options for cost and functionality.

At the time of the advent of the Internet, access was made through the telephone network using Dial-up technology with a very low connection quality (up to 56 Kbps). At the same time, while working on the network, the telephone line was busy. Now this outdated communication method has been replaced by ADSL technology, which allows you to simultaneously use the Internet and telephone. However, in this case, the connection speed technically cannot be higher than 24 Mbps. In practice, due to the poor condition of the lines, the figure is much lower, and this is precisely the determining factor. But with the right ADSL modem settings, connection speed can be increased.

At the same time, the modem model affects the speed of the Internet - on the same line, a more modern, expensive device will achieve better performance. The difference can reach up to 2-3 times. In addition, slowness is due to frequent freezing, communication instability.

To improve internet speed, please note the following:

• Do not allow the device to overheat, provide adequate ventilation, and do not stack things on top. Overheating causes braking in work, freezing, failures.
• Contact your ISP for advice on setting up hardware and software. Some operators offer a file with parameters for a particular model.
• Update the device firmware. Outdated software may limit communications.

Connectivity via 3G/LTE /4G network

3G/LTE/4G connectivity is gaining popularity because it allows you to literally carry the Internet with you. A small device that looks like a USB flash drive, fits easily in your pocket, allows you to connect a laptop to world wide web anywhere you work mobile operator. It is for this type of connection that there is no doubt whether an increase in the speed of an Internet connection depends on right choice modem models.

First of all, the communication standard itself determines the speed of data exchange. 3G gives up to 2 Mbps, LTE already up to 299.6 Mbps, and 4G can theoretically reach 1 Gbps. Naturally, the higher the technical capabilities, the more expensive the equipment.

Besides technical parameters, there are still factors of how the Internet speed depends on the modem:

• If the network is busy, i.e. many users download or upload large amounts of information, the modem switches to a lower communication standard, which affects the speed of operation.
• Overheating of the device can lead to slowdowns, this is a problem for budget models.
• Poor quality of the receiving antenna. Even if the operator has provided good network performance, the device is simply not able to fully capture the connection.
• Incorrect device settings, as well as operating system and software.

There are several ways to slightly increase the speed of your network:

Thus, it is impossible to say that the speed of the Internet depends on the modem and only on it. Many factors affect the acceleration of work, they are often interdependent. Nevertheless, you can solve the problem of slow internet, well, or at least significantly improve the situation, with the help of the right choice and configuration of the modem.

One of the most popular and available ways connection to the World Wide Web today is an ADSL connection. The abbreviation ADSL stands for "Asymmetric Digital Subscriber Line" - an asymmetric digital subscriber line. Despite its simplicity and almost 100% availability, the mobile connection is significantly inferior to the ADSL connection in terms of its capabilities: the data transfer rate is lower, the range of services is less, and the connection cost is much higher. Connection using ETTH technology (“Ethernet to every home”), GPON and FTTH (using fiber optic cable) is currently available only for residents of the multi-apartment sector in large settlements, as it is economically justified with mass connections. Therefore, today ADSL connection is relevant for most users, especially in small towns.

ADSL connection problems

Despite its mass availability and fairly decent technical characteristics:

1. Practical access speed: up to 24 Mbps;
2. Subscriber line length for satisfactory operation: up to 7.5 km;
3. Service availability triple play- simultaneous transmission of voice, video and data.

This technology uses in its work a telephone subscriber line with all the ensuing problems.

Consider a typical subscriber connection scheme using ADSL technology:

The practice of operating this technology shows that the most common problems that lead to the fact that the user installs slow speed on adsl connection, or no Internet access at all, are:

1. Telephone line failure;
2. Access equipment port failure (DSLAM) on the provider side;
3. Incorrect connection on the user's side.

Telephone Line Trouble

This is the most common type of damage that occurs in the "Subscriber-Provider" chain. Unfortunately, the telephone line is far from perfect. While it "gets" from the Internet provider to the user, it can go through quite a lot of different sections: trunk, cable, distribution cables, cables between cabinets and even the so-called air ducts - wires that go from the cabinet to the subscriber by air. Each of these sections, in addition to attenuation of the useful signal, can also introduce various interferences, leading both to a general decrease in speed and to the fact that the subscriber has frequent disconnections during adsl connection.

Of course, in order to measure the physical parameters of a telephone line in order to obtain its qualitative characteristics, it is necessary to have special devices and the ability to use them. But an ordinary user can also easily assess its condition in order to understand why certain access problems arise. To do this, you need to connect to an ADSL modem and view the ADSL connection statistics.

Not only problems with the communication line or with the provider's equipment lead to problems in working with the Internet. Asking the question - “How to increase the speed with an adsl connection?”, The user sometimes forgets that incorrectly working equipment or an incorrect connection on his side can also cause failures and low speed. Therefore, before calling the service technical support, you need to check if the telephone line, modem and telephone are connected correctly.

First of all, you should start with splitter- a special device that is designed to ensure that high-frequency noise from the modem does not interfere with telephone conversations. In fact, it is a special filter for separating the operating frequency bands of the modem and the telephone.

Consider the correct scheme for connecting user devices:

It should be remembered that telephone sets and any other telephone devices must not be connected before the splitter! All phones must be strictly connected to the PHONE jack! Otherwise, the connection will be unstable, and usually slow. Adsl connection breaks will be almost permanent in this case.

Connecting an adsl modem without a splitter will lead to noise during a telephone conversation and, as in the first case, to a poor connection quality. However, if you are not using a telephone set, then the modem can be connected to a telephone line without this device.

Excessively long telephone extension cords should be avoided. If you really can’t do without it, you need to choose those that use not four, but two conductors. This will reduce the level of interference and improve the quality of the connection.

Unfortunately, the adsl modem is also not immune from damage. Moreover, there are obvious damages, that is, when it simply does not work or does not work correctly, but there are hidden ones associated with damage to its linear part. Especially often, such malfunctions quite often occur after a thunderstorm. At the same time, the modem itself is working and can even establish a connection with the provider's equipment, but it is unstable, or the connection is at low speed. The first impression that arises is that the telephone line is malfunctioning, since the “symptoms” are very similar. In this case, you should take readings of the main characteristics of the connection from its menu in the "Statistics" section, and check it at the provider's stand, asking you to take the same data. If the readings are similar, most likely, the linear part of the modem is “burned out” and needs to be repaired.

1. If the speed of Internet access is periodically reduced, start the test by examining the stability of the established connection - the “link”. (The English version of the word is Link). Follow the indicator with the same name. On some models it is called ADSL. During operation, if the adsl connection is stable and established, it should just be on. If it blinks periodically, the connection with the provider is unstable, a check of the communication line is required.
2. Watch outgoing (upstream) speed in the line. Practice shows that the lower it is, the lower the quality of the connection. Ideally, it should be equal to or close to 1 Mbps (unless specifically limited by the tariff).
3. With constant disconnections, you can try to turn off the splitter and phone, turning on the modem for a while, directly into the line. This eliminates the possible influence of other devices on the connection. If in this case everything works stably, then you can, turning on the devices in turn, find out which one has an impact.
4. Always check the quality of the contact in the connectors. The modern RJ11 telephone jack is not a very high quality product, its contacts are often oxidized. Remove and reinsert it two or three times.

ADSL is understood as an asymmetric method of access to the global information network Internet. This is the so-called asymmetric system, which allows you to work with connections at speeds up to eight Mbps. So, ADSL, through which the data transfer rate is calculated up to one Mbit per second, operates at a distance of more than five kilometers.

So let's look at what kind of connection it is and how it actually works.
So, before touching on the very concept of ADSL, let's plunge into history a little. It is today that high-speed connections are not surprising, but are perceived as something ordinary and supposed to be a privileged property of modernity. But in order for the end user to be able to use this resource, the developers had to work hard and create the perfect version.

For the first time, the idea of ​​creating high-speed connections, as such, appeared precisely in the eighties, when no one even thought about the Internet. A high-speed connection was required to improve and speed up data transmission over copper wires in telephony.

After some time, the people were faced with familiarity with computer technology, the concept of the Internet. This is where the development of a resource was required for the rapid transfer of information electronic units between various interactive services, video game products, as well as for access to other network local systems.

Modern ADSL technology is a network that is based on a digital subscriber line, through which a connection to an Internet resource is made through telephone channels. Since these telephone lines use an analog signal in their work to be able to transmit voice messages, ADSL transforms it into a digital format and transfers it directly to a computer.

If the previously used Dial-up modems blocked the telephone line, then it is timely ADSL that allows you to simultaneously use both an analog signal and a digital signal at the same time.

So, the whole point of the new generation of ADSL lies in the fact that the user of computer technology has the ability to download a very large amount of information and save it on a hard disk, or simply view it and transmit a minimum of information in the form of requests. In other words, maximum traffic - minimum downstream traffic - this is the principle of modern ADSL technology.

Naturally, incoming traffic is video files, media products, software applications, and graphic elements. Downstream traffic includes only technically important information at the level of commands and various requests, emails, and some other minor components of working with the Internet.

So, the asymmetry in question implies the connection speed of the subscriber is much higher than the speed of traffic from the user himself. Asymmetric system high speed connection today is the most budgetary and economical. In operation, this system uses the same copper telephone wires. The only thing that has changed compared to the first samples is the number of twisted pairs in them, this fact did not require any actions in the direction of upgrading the switches and measures for their reconstruction.

Modern ADLS-ka connects very quickly, it is perceived by all types of modern modems. But still, for the optimal connection of this system, special types of modem devices are used. This list includes modems connected via USB ports, devices similar to the Ethernet interface, as well as routers and routers with the Ethernet scheme itself, profile modems, routers for Wi-Fi are also suitable.

Often additional elements are also used in the form of splitters and microfilters, they are selected for the type of telephone cable. Splitters are used when a cable outlet is made in order to separate the modem channel and the phone itself. In other cases, microfilters are suitable for installation; one such element is installed on each telephone in the room.

The use of splitters allows you to prevent interference in the operation of the phone and modem, which seem to work in the same bundle, but one device receives voice calls, the other makes it possible to connect to the Internet.

Splitter devices are compact and do not interfere with their presence at all. This is a miniature box with three light weight connectors.
ADLS technology in modern times is recommended to be used by every second Internet provider. Naturally, the types and tariffs of connection to the global information network are classified depending on the regional predisposition of PC users. Yes, coverage is important.

When building a network, it is inappropriate to buy everything today - a modem, a router, a router, and splitters. The network provider offers to rent all the necessary equipment today, this list also includes an ADSL modem. If the contract for the services provided is terminated, then all equipment is returned to the provider intact and safe.

This is the cheapest way to use the Internet as such. The user pays only for the connection itself, without incurring the cost of purchasing all the necessary equipment for connection.

So, we are convinced that ADLS is nothing but the fastest, highest quality and cheapest method of connecting to the Internet. Each user using this type of connection must have his own account, which is assigned to him by the provider himself. It is activated within twelve days after registration. If the region has normal uninterrupted coverage, then this procedure does not exceed two hours.
Before using DDLS technology, the provider must check the phone for the presence of already used elements of the same DDLS. If the coverage is not effective, then it is unlikely that you will ever need to use a high-speed network connection at all.

To use this very ADLS connection, you must first connect and configure all the elements correctly. So, a modem, splitters, microfilters are connected to the phone, drivers are installed on a computer storage medium, the network parameters of the modem are set in the browser used to use browsing sites located in the Internet environment.

Now let's touch on the question of the advantages of modern high-speed technology for connecting to the global information network, which makes using the Internet many times effective and elementary simple.

So, the most important advantages of ADLS-ki include the high speed of information electronic data transfer. In order to send or receive the necessary file, you do not need to wait a long time for the connection, it happens instantly.

This type of technology is constantly evolving and more and more connection speeds are offered to the consumer.
The second advantage of modern ADLS-ki is the fact that the phone works as a phone, and the modem as a modem, the work of these devices is not interrupted by each other. The use of ADLS-ki does not require installation of overall equipment, cable laying to the subscriber. Interference on the telephone line is absent in principle.

ADLS is a reliable stable system that does not fail, which does not require reconnection, the user with such a connection can sit in the Internet space around the clock. This is the most efficient method of connecting to the Internet, which has no alternatives.
The minimum prices for connecting ADLS-ki, installing a modem with a router spare the family budget. Despite these advantages, this technology still has its modern disadvantages.

None of the users of such a connection is protected from cross connections to the network and other Internet users. If dozens and hundreds of subscribers are connected to such a network, there is no need to talk about high speed. Naturally, the more consumers eat, the lower.
The disadvantages also include low speed file transfer. Receiving and quickly viewing information is good, but sending is not very convenient. So keep in mind, if you want to use the high-speed connection model, that it is not aimed at sending data, but at constantly receiving it in large volume.

The speed of such a perfect system as ADLS depends in most cases not on its perfection, but on many side factors. And this is the main prerequisite for the network to be laid by a specialist who will evaluate the effectiveness of the coverage, correctly connect all the elements and achieve a high-quality result.

The quality of communication is affected by the condition of the subscriber line. That is, we are talking about the presence of cable outlets, their serviceability, wire diameter and length, which can reach several kilometers. If the signal goes astray, this indicates that the subscriber line is too long, this defect can be eliminated with a large wire diameter.

A well-functioning ADLS-ka has a length of five kilometers. This is the fastest system, as mentioned above. It allows you to transfer data at a speed of 2048 Mbps.

If the length of the wire does not go off scale, then the user is practically not limited in anything - neither in speed, nor in the number of other connected subscribers, as well as mobile phones, tablets and other modern gadgets.

Developers say that ADLS has not yet fully exhausted its resource and there are long-term plans for its development in the future.
So we figured out what modern Internet connection technology is - ADLS, what are its advantages and disadvantages, why many today focus on this type of network creation.

If you decide to connect your computer device to the network, do not look for a better way, it does not exist today. A lot of personal computer users are convinced of this. This method is used not only by individuals, but also large companies who have to work with a large amount of information on a daily basis.

Trust the suggestions of specialists, try this method in practice, and you will see that this is the limit of perfection today in terms of achieving connection speed and connecting subscribers to the virtual space.

We hope that the information presented in this article was clear to you, and you have drawn the right conclusions for yourself. In modern times, you need to use the most advanced high-quality communication systems, one of which, just the same, is the above-mentioned ADLS technology.

V last years The development of the telecommunications services market has led to a shortage of bandwidth for access channels to existing provider networks. If at the corporate level this problem is removed by leasing high-speed data transmission channels, then what alternative can be offered to subscribers on existing lines, instead of a dial-up connection, in the residential sector and the small business sector?

Today, the main way for end users to interact with private and public networks is access using a telephone line and modems, devices that provide digital information transmission over subscriber analog telephone lines - the so-called Dialup connection. The speed of such a connection is low, the maximum speed can reach 56 Kbps. This is still enough to access the Internet, however, the pages are saturated with graphics and videos, large volumes Email and documents, the possibility of users exchanging multimedia information, set the task of increasing the capacity of the existing subscriber line. The solution to this issue was the development of ADSL technology.

ADSL technology (Asymmetric Digital Subscriber Line - asymmetric digital subscriber line) is the most promising at present, at this stage of development of subscriber lines. It is included in the general group of high-speed data transfer technologies, united by the general term DSL (Digital Subscriber Line - digital subscriber line).

The main advantage of this technology is that there is no need to lay a cable to the subscriber. Already laid telephone cables are used, on which splitters are installed to separate the signal into "telephone" and "modem". Different channels are used for receiving and transmitting data: the receiving one has a significantly higher bandwidth.

The common name of DSL technologies originated in 1989, when the idea first appeared to use analog-to-digital conversion at the subscriber's end of the line, which would improve the technology of data transmission over twisted-pair copper telephone wires. ADSL technology was developed to provide high-speed (one might even say megabit) access to interactive video services (video on demand, video games, etc.) and equally fast data transfer (Internet access, dial-up LAN and other networks). To date, DSL technologies are represented by:

• ADSL (Asymmetric Digital Subscriber Line - asymmetric digital subscriber line)

This technology is asymmetric, that is, the data transfer rate from the network to the user is much higher than the data transfer rate from the user to the network. This asymmetry, combined with the "always connected" state (which eliminates the need to dial a phone number each time and wait for a connection to be established), makes ADSL technology ideal for organizing access to the Internet, access to local area networks (LANs), etc. When organizing such connections, users usually receive much more information than they transmit. ADSL technology provides downstream data rates ranging from 1.5Mbps to 8Mbps and upstream data rates from 640Kbps to 1.5Mbps. ADSL allows you to transfer data at a speed of 1.54 Mbps over a distance of up to 5.5 km over a single twisted pair of wires. The transfer rate of the order of 6-8 Mbps can be achieved when transmitting data over a distance of no more than 3.5 km over wires with a diameter of 0.5 mm.

• R-ADSL (Rate-Adaptive Digital Subscriber Line)

R-ADSL technology provides the same data transfer rate as ADSL technology, but at the same time allows you to adapt the transfer rate to the length and condition of the twisted pair wires used. When using R-ADSL technology, the connection on different telephone lines will have different speed data transmission. The baud rate can be selected at line synchronization, during connection, or by a signal coming from the station

• G. Lite (ADSL.Lite)

It is a cheaper and easier-to-install version of ADSL technology that provides downstream data rates up to 1.5Mbps and upstream data rates up to 512Kbps or 256Kbps in both directions.

• HDSL (High Bit-Rate Digital Subscriber Line)

HDSL technology provides for the organization of a symmetrical data transmission line, that is, the data transfer rates from the user to the network and from the network to the user are equal. With transmission speeds of 1.544 Mbps over two pairs of wires and 2.048 Mbps over three pairs of wires, telecommunications companies are using HDSL technology as an alternative to T1/E1 lines. (T1 lines are used in North America and provide a data rate of 1.544 Mbps, and E1 lines are used in Europe and provide a data rate of 2.048 Mbps.) Although the distance over which the HDSL system transmits data (which is about 3.5 - 4.5 km), less than with ADSL technology, for inexpensive, but effective, extension of the HDSL line length, telephone companies can install special repeaters. The use of two or three twisted pairs of telephone wires to organize an HDSL line makes this system an ideal solution for connecting remote PBX nodes, Internet servers, local networks, etc.

• SDSL (Single Line Digital Subscriber Line)

Like HDSL technology, SDSL technology provides symmetrical data transmission at rates corresponding to T1/E1 line rates, but SDSL technology has two important differences. Firstly, only one twisted pair of wires is used, and secondly, the maximum transmission distance is limited to 3km. Within this distance, SDSL technology provides, for example, the operation of a video conferencing system when it is required to maintain the same data transfer flows in both directions.

• SHDSL (Symmetric High Speed ​​Digital Subscriber Line - symmetrical high-speed digital subscriber line

The most modern type of DSL technology is aimed primarily at providing a guaranteed quality of service, that is, at a given speed and range of data transmission, to ensure an error level of at least 10 -7 even in the most adverse noise conditions.

This standard is an evolution of HDSL as it allows the transmission of a digital stream over a single pair. SHDSL technology has several important advantages over HDSL. First of all, these are better performance (in terms of the maximum line length and noise margin) due to the use of a more efficient code, a precoding mechanism, more advanced correction methods and improved interface parameters. This technology is also spectrally compatible with other DSL technologies. Because the new system uses a more efficient line code than HDSL, at any rate, the SHDSL signal occupies a narrower bandwidth than the corresponding HDSL signal at the same rate. Therefore, the interference from the SHDSL system to other DSL systems is less powerful than the interference from HDSL. The spectral density of the SHDSL signal is shaped so that it is spectrally compatible with ADSL signals. As a result, compared to single-pair HDSL, SHDSL allows a 35-45% increase in transmission speed at the same range, or a 15-20% increase in range at the same speed.

• IDSL (ISDN Digital Subscriber Line - IDSN digital subscriber line)

IDSL technology provides full duplex data transmission at speeds up to 144 Kbps. Unlike ADSL, IDSL is limited to data transmission only. Although IDSL, like ISDN, uses 2B1Q modulation, there are a number of differences between the two. Unlike ISDN, the IDSL line is a non-switched line that does not increase the load on the provider's switching equipment. Also, an IDSL line is "always on" (like any DSL line), while ISDN requires a connection.

• VDSL (Very High Bit-Rate Digital Subscriber Line)

VDSL technology is the "fastest" xDSL technology. It provides downstream data transfer rates ranging from 13 to 52 Mbps, and upstream data transfer rates from 1.5 to 2.3 Mbps, with one twisted pair of telephone wires. In symmetrical mode, speeds up to 26Mbps are supported. VDSL technology can be seen as a cost effective alternative to running fiber optic cable to the end user. However, the maximum transmission distance for this technology is between 300 meters and 1300 meters. That is, either the length of the subscriber line should not exceed given value, or the fiber optic cable must be brought closer to the user (for example, brought into a building in which there are many potential users). VDSL technology can be used for the same purposes as ADSL; in addition, it can be used to transmit high-definition television (HDTV) signals, video-on-demand, and the like. The technology is not standardized, different equipment manufacturers have different speeds.

So what exactly is ADSL? First of all, ADSL is a technology that allows you to turn a twisted pair of telephone wires into a high-speed data transmission path. The ADSL line connects the provider side DSLAM (DSL Access Multiplexor) access equipment and the client modem, which are connected to each end of the twisted pair telephone cable (see Figure 1). In this case, three information channels are organized - "downstream data transfer," upstream "data transfer and a regular telephone communication channel (POTS) (see Figure 2). telephone set.This scheme allows you to talk on the phone simultaneously with the transfer of information and use telephone communications in the event of a malfunction of ADSL equipment.Constructively, the telephone splitter is a frequency filter that can be either integrated into an ADSL modem or be an independent device.

Rice. one


Rice. 2

ADSL is an asymmetric technology - the rate of the "downstream" data stream (ie the data that is transmitted towards the end user) is higher than the rate of the "upstream" data stream (in turn transmitted from the user to the network side). It should immediately be said that one should not look for a cause for concern here. The data transfer rate from the user (the "slower" data transfer direction) is still significantly higher than when using an analog modem. Such asymmetry is introduced artificially, the modern range of network services implies a very low transmission speed from the subscriber. For example, MPEG-1 movies require 1.5 Mbps of bandwidth. For service information transmitted from the subscriber (command exchange, service traffic), 64-128 Kbps is quite enough. According to statistics, incoming traffic is several times, and sometimes an order of magnitude, higher than outgoing. This ratio of speeds ensures optimal performance.

ADSL technology uses digital signal processing and specially designed algorithms, advanced analog filters and analog-to-digital converters to compress the large amount of information transmitted over twisted-pair telephone wires. Long distance telephone lines can attenuate a transmitted high frequency signal (for example, at 1MHz, which is the normal transmission rate for ADSL) by up to 90dB. This forces the analog ADSL modem systems to work with a large enough load to have a large dynamic range and low noise. At first glance, the ADSL system is quite simple - high-speed data transmission channels are created over a regular telephone cable. But, if you understand in detail the work of ADSL, you can understand that this system belongs to the achievements modern technology.

ADSL technology uses a method of dividing the bandwidth of a copper telephone line into multiple frequency bands (also called carriers). This allows multiple signals to be transmitted simultaneously on a single line. Exactly the same principle underlies cable television, when each user has a special converter that decodes the signal and allows you to see a football match or an exciting movie on the TV screen. With ADSL, different carriers simultaneously carry different parts of the transmitted data. This process is known as frequency division multiplexing (FDM) (see Figure 3).

Rice. 3

With FDM, one band is allocated for the transmission of "upstream" data, and the other band for the "downstream" data stream. Information "downward" flow is divided into several information channels - DMT (Discrete Multi-Tone), each of which is transmitted on its own carrier frequency using QAM. QAM is a modulation method - Quadrature Amplitude Modulation, called Quadrature Amplitude Modulation (QAM). It is used to transmit digital signals and provides for a discrete change in the state of the carrier segment simultaneously in phase and amplitude. Typically, DMT splits the 4 kHz to 1.1 MHz band into 256 channels, each 4 kHz wide. This method, by definition, solves the problem of dividing the band between voice and data (it simply does not use the voice part), but is more difficult to implement than CAP (Carrierless Amplitude and Phase Modulation) - amplitude-phase modulation without carrier transmission. DMT is approved in the ANSI T1.413 standard and is also recommended as the basis for the Universal ADSL specification. In addition, Echo Cancellation technology can be used, in which the upstream and downstream ranges overlap (see Figure 3) and are separated by local echo cancellation.

This is how ADSL can provide, for example, simultaneous high-speed data transmission, video signal transmission and fax transmission. And all this without interrupting the usual telephone connection, for which the same telephone line is used. The technology provides for the reservation of a certain frequency band for ordinary telephone communication (or POTS-Plain Old Telephone Service). It's amazing how fast telephone communications turned not only into "simple" (Plain), but also into "old" (Old); it turned out something like "the good old telephone connection". However, one should pay tribute to the developers of new technologies, who still left telephone subscribers with a narrow band of frequencies for live communication. Wherein telephone conversation can be driven simultaneously with high-speed data transmission, rather than choosing one of the two. Moreover, even if your electricity is turned off, the usual "good old" telephone service will still work and you will not have any problems with calling an electrician. Making this possible was part of the original ADSL development plan.

One of the main advantages of ADSL over other high-speed data transmission technologies is the use of the most common twisted pairs. copper wires telephone cables. It is quite obvious that there are much more such pairs of wires (and this is still an understatement) than, for example, cables laid specifically for cable modems. ADSL forms, so to speak, an "overlay network".

ADSL is a high speed data transfer technology, but how fast? Given that the letter "A" in the ADSL name means "asymmetric" (asymmetric), we can conclude that data transfer in one direction is faster than in the other. Therefore, there are two data rates to consider: "downstream" (transferring data from the network to your computer) and "upstream" (transferring data from your computer to the network).

The maximum reception speed - DS (down stream) and transmission - US (up stream) depends on many factors, the dependence on which we will try to consider later. In the classic version, ideally, the reception and transmission speed depends and is determined by DMT (Discrete Multi-Tone) by dividing the bandwidth from 4 kHz to 1.1 MHz into 256 channels, each 4 kHz wide. These channels, in turn, represent 8 digital streams T1, E1. For down stream transmission, 4 T1,E1 streams are used, the total maximum throughput which is 6.144Mbps - in the case of T1 or 8.192Mbps in the case of E1. For upstream transmission, one T1 stream is 1.536 Mbps. The maximum speed limits are indicated without taking into account overhead costs, in the case of classic ADSL. Each stream is provided with an error correction code (ECC) by introducing an extra bit.

Now let's look at how the real data transfer takes place in the following example. Informational IP packets generated as in local networks clients, and personal computers, directly connected to the Internet, will come to the ADSL modem input framed by the Ethernet 802.3 standard. The subscriber modem splits and "stacks" the content of Ethernet 802.3 frames into ATM cells, supplies the latter with a destination address and transmits them to the output of the ADSL modem. The latter, in accordance with the T1.413 standard, "encapsulates" the ATM cells in the digital stream E1, T1, and then the traffic over the telephone line goes to the DSLAM. Station concentrator DSL multiplexor - DSLAM, carries out the procedure of "restoring" ATM cells from the T1.413 packet format and sends them via the ATM Forum PVC (Permanent Virtual Circuit) protocol to the backbone access subsystem (ATM network), which delivers the ATM cells at the address indicated in them, i.e. to one of the centers for the provision of services. When implementing the Internet access service, the cells arrive at the router of the Internet provider, which performs the function of a terminal device in a permanent virtual channel (PVC) between the subscriber terminal and the node of the Internet provider. The router performs the reverse (with respect to the user terminal) transformation: it collects incoming ATM cells and restores the original Ethernet 802.3 frame. When traffic is transmitted from the service center to the subscriber, completely similar transformations are carried out, only in the reverse order. In other words, a "transparent" Ethernet 802.3 local area network is created between the Ethernet port of the subscriber terminal and the virtual port of the router, and all computers connected to the subscriber terminal perceive the router of the Internet provider as one of the devices of the local network.

The common denominator in the provision of Internet access services is the IP network layer protocol. Therefore, the chain of protocol transformations carried out in the network broadband access, can be represented as follows: client application - IP packet - Ethernet frame (IEEE 802.3) - ATM cells (RFC 1483) - ADSL modulated signal (T1.413) - ATM cells (RFC 1483) - Ethernet frame (IEEE 802.3) - packet IP is an application on a resource on the Internet.

As mentioned above, the declared speeds are possible only in the ideal version and without taking into account overhead costs. So in the E1 stream, when transmitting data, one channel (depending on the protocol used) is used to synchronize the stream. And as a result, the maximum speed, taking into account overhead costs, will be Down stream - 7936Kbps. There are other factors that have a significant impact on the speed and stability of the connection. These factors include: the length of the line (the bandwidth of the DSL line is inversely proportional to the length of the subscriber line) and the cross section of the wire. The characteristics of the line deteriorate with an increase in its length and a decrease in the cross section of the wire. Also, the data transfer rate is affected by the general condition of the subscriber line, the presence of twists, cable outlets. The most "harmful" factors that directly affect the possibility of establishing an ADSL connection are the presence of Pupin coils on the subscriber line, as well as a large number of taps. None of the DSL technologies can be used on lines with Load Coils. When checking the line, it is ideal not only to determine the presence of load coils, but also to find the exact place of their installation (you still have to look for coils and remove them from the line). The load coil used in analog telephone systems is a 66 or 88 mH inductor. Historically, Pupin coils were used as a structural element of a long (more than 5.5 km) subscriber line, which made it possible to improve the quality of transmitted audio signals. A cable outlet is usually understood as a cable section that is connected to the subscriber line, but is not included in the direct connection of the subscriber to the telephone exchange. The cable outlet is usually connected to the main cable and forms a "Y" shaped branch. It often happens that the cable outlet goes to the subscriber, and the main cable goes further (in this case, this pair of cables must be open at the end). However, the suitability of a particular subscriber line for the use of DSL technology is affected not so much by the fact that there is a connection, but by the length of the cable outlet itself. Up to a certain length (about 400 meters), cable outlets do not significantly affect xDSL. In addition, cable taps affect different xDSL technologies differently. For example, HDSL technology allows cable outlets up to 1800 meters. As for ADSL, cable outlets do not prevent the very fact of organizing high-speed data transmission over a copper subscriber line, but they can narrow the line bandwidth and, accordingly, reduce the transmission speed.

The advantages of a high-frequency signal, which makes it possible to digitally transmit data, are its own disadvantages, namely, exposure to external factors (various pickups from third-party electromagnetic devices), as well as physical phenomena that occur in the line during transmission. Increasing the capacitive characteristics of the channel, the occurrence of standing waves and reflections, the isolation characteristics of the line. All these factors lead to the appearance of extraneous noise on the line, and faster signal attenuation and, as a result, to a decrease in the data transfer rate and a decrease in the length of the line suitable for data transmission. Some values ​​of the characteristics of the ADSL line, by which you can directly judge the quality of the telephone line, can be given by the ADSL modem itself. Almost all models of modern ADSL modems contain information about the quality of the connection. Most often, the Status-> Modem Status tab. The approximate content (may vary depending on the model and manufacturer of the modem) is as follows:

modem status

Connection Status Connected
Us Rate (Kbps) 511
Ds Rate (Kbps) 2042
US Margin 26
DS Margin 31
Trained Modulation ADSL_2plus
LOS Errors 0
DS Line Attenuation 30
US Line Attenuation 19
Peak Cell Rate 1205 cells per sec
CRC Rx Fast 0
CRC Tx Fast 0
CRC Rx Interleaved 0
CRC Tx Interleaved 0
Path Mode Interleaved
DSL Statistics

Near End F4 Loop Back Count 0
Near End F5 Loop Back Count 0

Let's explain some of them:

Connection Status Connected - connection status
Us Rate (Kbps) 511 - Up Stream speed
Ds Rate (Kbps) 2042 - Down Stream rate
US Margin 26 - Outgoing connection noise level in db
DS Margin 31 - Downlink noise level in db
LOS Errors 0 -
DS Line Attenuation 30 - Downstream signal attenuation in db
US Line Attenuation 19 - Signal attenuation in the outgoing connection in db
CRC Rx Fast 0 - number of uncorrected errors. There are also FEC (corrected) and HEC - errors
CRC Tx Fast 0 - number of uncorrected errors. There are also FEC (corrected) and HEC - errors
CRC Rx Interleaved 0 - number of uncorrected errors. There are also FEC (corrected) and HEC - errors
CRC Tx Interleaved 0 - number of uncorrected errors. There are also FEC (corrected) and HEC - errors
Path Mode Interleaved - Error correction mode enabled (Path mode Fast - disabled)

By these values, you can judge, as well as control yourself, the state of the line. Values:

Margin - SN Margin (Signal to Noise Margin or Signal to Noise Ratio). The level of interference noise depends on many different factors - wetting, the number and length of taps, the synchronism of the line, the "spread-out" of the cable, the presence of twists, the quality of the physical connections. In this case, the signal of the outgoing ADSL stream (Upstream) decreases until it is completely absent and, as a result, the ADSL modem loses synchronization

Line Attenuation - attenuation value (the greater the distance from the DSLAMa, the greater the attenuation value. The greater the signal frequency, and hence the connection speed, the greater the attenuation value).

ADSL2 and ADSL2+ Technologies and Standards

ADSL2 and ADSL2+ technologies enabling true solutions. New video applications such as IPTV and VoD require high data rates (over 10 Mbps) towards the user, and ADSL2+ technology can provide them. Transmission speeds over ADSL2+ reach 24 Mbps.

Advantages

ADSL2+ technology also has a number of new features and benefits over older ADSL. The most important features, such as increased range and transmission speed, line diagnostics, transmission power control, fast connection establishment and improved interoperability, are already with initial stage integrated on new subscription cards of BAN, mBAN and ipBAN nodes. ADSL2+ technology is also well suited to replace VDSL in home subscriber environments with more demanding access requirements. With ADSL2+, video service providers will be able to offer users even 3 simultaneous video programs on a single broadband port.

Key Features and Benefits

Improved transmission speed and distance parameters

ADSL2 and ADSL2+ use enhanced modulation to reduce framing overhead, increase coding gain, and provide improved initialization mechanisms and signal processing algorithms. ADSL2 allows you to increase the data transfer rate in the direction to the user to more than 12 Mbps, compared to about 8 Mbps in the case of ADSL. ADSL2 allows you to increase the length of the loop by about 200 m, or increase the data rate by about 50 kbps at the same distance for long distance subscriber lines.

The ADSL2+ standard doubles the maximum frequency used for data transmission towards the user - 2.2 MHz instead of 1.1 MHz. This allows the maximum downstream transmission rate to be increased to 25 Mbps on telephone lines up to 1500 m in length.

Diagnostics and automatic adjustment

Real-time monitoring functions provide real-time information about line quality and noise at both ends of the line. Service providers can use this data to monitor the quality of an ADSL connection and prevent service degradations. In addition, providers can use this data to determine if a particular user can be provided with higher bit rate services. SELT (line test without remote end connection) and DELT (line test with remote end connection) provide the ability to determine the length of the line, presence of shorted and open circuits, wire size and expected capacity before operation. In case of changing conditions in the channel, it is used new opportunity, which is called seamless rate adaptation (SRA). This feature allows the ADSL2 system to change the data rate of the connection without service interruption or bit error.

Advanced power management options

With two power management modes, you can reduce power consumption while maintaining the always-on ADSL connection for users. The L2 power mode is for a low bit rate mode that does not require full bandwidth, and the L3 power mode is for a standby or "sleep" mode. This feature allows you to reduce energy consumption by more than 50% for each line.

Quick Start

Quick start mode reduces initialization time from approximately 10 seconds to less than 3 seconds.

Full digital mode

This additional option allocates the "telephone" frequency band for data transmission. In this case, the upstream data rate (user to network) increases by 256 kbps, which may be an attractive solution for enterprises that have voice services on different telephone lines and for which the possibility of increasing the upstream data rate is special interest. This capability may also be of interest to service providers who can lease subscriber lines from telecommunications companies on a subscriber line sharing (LLU) basis.

Improved hardware interoperability

New modem initialization procedures address hardware compatibility issues and provide better performance when connecting ADSL transceivers from different chip vendors.

Other functions and features

channeling

ADSL2's channelization capabilities provide support for the transport of voice channels formed in this way over DSL lines (CVoDSL), a method for transparently transporting TDM voice traffic over DSL lines. CVoDSL carries voice traffic at the physical layer, allowing analog telephone "lines" to be placed on a DSL channel and carried in parallel with data traffic, supporting both the analog telephone network (POTS) and high-speed Internet access.

Combining multiple lines for more high speeds transmission

The new standards support Inverse Multiplexing for ATM (IMA), developed by the ATM Forum for networks with traditional ATM architecture. Thanks to IMA, ADSL2 integrated circuits can combine multiple copper pairs into a single ADSL link. The result is a data transfer rate over existing copper lines that is comparable to fiber optic lines.

Support for packet network services

Packet network services (such as Ethernet) can be carried over ADSL2 as an addition to ATM.