DSL technologies. What is ADSL - where and how the technology is used
ADSL stands for Asymmetric Digital Subscriber Line in English. There are several types of DSL connections: ADSL, HDSL and VDSL. All three options are based there is a telephone line.
What is ADSL
DSL technology was developed at a time when telephone lines became popular and became available to every citizen of the country. In the late 80s and early 90s, the first version of the ADSL protocol appeared. She supported incoming traffic speed up to 1 Mbit/s, and outgoing – up to 8 Mbit/s.
ADSL was born thanks to the company Bellcore, which in the mid-eighties was looking for methods to create interactive TV. Next, the technology was adopted by providers of access services to the World Wide Web. Thus, the first devices that transmitted and received signals appeared - ADSL modems.
Today asymmetrical line used in remote settlements, where it is impossible to use other wired technology or wireless communication via 3/4G USB modems
ADSL technology - operating principle
The first word in the name - asymmetrical - implies that it is used uneven distribution telephone line between receiving and sending data.
In this case, incoming traffic has a wider bandwidth compared to outgoing traffic. Earlier we mentioned approximate figures - the difference in speed can reach eight times.
The use of a telephone line as a means of data transmission implies that ADSL uses another frequency in cables. This fact allows you to use the phone and the Internet simultaneously without interfering with each other.
Sometimes situations arise in which the use of a telephone core for two directions leads to certain interference, but such cases are rare and are associated with improper cable shielding.
The signal comes from the provider and reaches the end user on special equipment - a modem. It translates the incoming data stream into a digital value.
Equipment used
As with any technology, ADSL also uses special equipment and components. Let's take a closer look at the example diagram below.
The signal coming from the telephone socket is initially sent to a special device - splitter. He divides it into telephone and high frequency. The first goes directly to the communication device, and the second to the translator. In turn, the network device processes the incoming analog stream into a digital one. After this operation, the data can be processed by the operating system of the user's finished device: for example, a workstation or tablet.
ADSL modem
The network device is the entry point for the analog data stream. He can convert the signal in both directions simultaneously, allowing you to use bandwidth more efficiently.
Pure ADSL modems are almost no longer produced, since there are more modern network equipment - routers. They will be discussed below.
ADSL cable
The cable is a wire with an RJ-12 connector. It is used to connect the telephone line to the modem.
Contains four cores, through which an analog signal is transmitted to the input and output.
Routers
Improved version of the modem. It is equipment capable of not only receive and transmit signal to the end user, but also route traffic within the local network.
Using an ADSL router, a user can connect several devices to gain access to the World Wide Web.
Today, most ADSL routers have a built-in WiFi module, which allows you to connect mobile devices to the Internet.
Splitters and microfilters
To separate the signal coming through the telephone line for the modem and telephone, a special filter is used - a splitter.
The operating principle is as follows. One incoming signal – several outgoing ones. The simplest example of a splitter is shown in the screenshot above. It can split a maximum of 16 signals.
Microfilters needed to create two parallel signals. This allows you to use ADSL Internet and telephone simultaneously, without creating interference on the line.
Other equipment
There are other devices used to create a connection to the World Wide Web based on ADSL technology.
For example, a user only has an ADSL modem, but wants to use wireless communication at home. He will have to purchase additional router withWi— Fimodule. It connects via an Ethernet port to the modem.
The second common option. There is an office space in which access to the global network is organized using ADSL technology. To provide Internet in each room you must purchase switches and router. The first ones are installed separately in each office, and the router will carry out the correct routing of data within the local network.
Basic connection steps
The first step is to connect the telephone cable going into the room through a splitter. Next from connector Phone we bring out the wire to the phone, and from ADSL– to network equipment.
The next step is to connect the ADSL device to the power supply network and connect it to the workstation via an Ethernet cable.
At the last stage, the user conducts setting up network equipment in accordance with the instructions provided by the provider.
Maximum ADSL speed
The data transfer speed when using ADSL depends on the standard used by the provider. The last option is ADSL2++. The data can be summarized in one table.
The information presented above is theoretical, i.e. the specified values are achieved under ideal conditions. In fact, 13-15% of the speed is lost when the signal passes from the provider to the endpoint. This fact is due to the technical characteristics of the equipment used.
Also, do not forget about other subscribers. The signal comes from a single point of exit from the service provider. Many other clients are connected to it, so the total speed value begins to be divided into equal parts.
Advantages and disadvantages of technology
Advantages of using ADSL technology:
- Subscribers receive high frequency access service to the World Wide Web without laying additional cables indoors.
- Organize a global network it is possible almost anywhere where there is a telephone line.
- Initial financial costs to connect below some other methods.
- High download speed files for the end client.
- Using modern network equipment, the client can organize a wireless network.
Flaws:
- Exists more modern solutions Internet connections that provide high download speeds.
- Technology gives away most of the channel for incoming traffic, and outgoing is several times lower. Accordingly, sending larger files to another subscriber will take a long time.
- Signal quality and stability depends on the telephone line, which is not designed for high-frequency signals.
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The acronym ADSL stands for Asymmetric Digital Subscriber Line. ADSL is translated as “Asymmetric Digital Subscriber Line”. This is one of the high-speed data transmission technologies related to DSL (Digital Subscriber Line) technology, also referred to as xDSL.
The group of DSL technologies also includes:
- High speed digital subscriber line. HDSL – High data rate Digital Subscriber Line;
- Ultra-high-speed digital subscriber line. VDSL – Very high data rate Digital Subscriber Line;
- ETTH("Ethernet...");
- GPON;
- FTTH.
What is ADSL technology?
As you already understand, ADSL technology is a technology for connecting to the Internet via wired networks, in particular telephone wires such as twisted pair. The essence of the technology is the ability to carry out high-speed data transmission over twisted pair telephone wires.
To implement this technology, an ADSL line is created that connects two ADSL modems. A twisted pair telephone cable is used to connect ADSL line modems. Each modem is connected to a telephone cable via an RJ-11 connector.
The technology creates 3 channels of information transmission:
- Downdraft;
- Updraft;
- POTS telephone channel.
In this case, the telephone channel is allocated by filters and does not depend on the ADSL connection.
Features of ADSL technology
Firstly, ADSL technology is asymmetrical. This means that the speed of data transfer towards the end user is higher than the speed of data transfer from the user to the network. That is, the speed of the downward flow is higher than the speed of the upward flow.
Secondly. Information transmitted over telephone wires using ADSL technology is compressed. For compression, digital signal processing is used using specially created algorithms, advanced analog filters and analog-to-digital converters.
Thirdly. ADSL technology uses a method of dividing the bandwidth of a copper telephone cable into several carrier frequency bands. This separation allows several signals to be transmitted simultaneously over one line.
In this case, different carrier bands simultaneously transmit different parts of the transmitted data. This process is called Frequency Division Multiplexing (FDM), which means frequency division multiplexing of the communication line.
FDM allows you to allocate one band for the upstream data stream, and a second band for the downstream stream. In this case, the downstream range is divided into high-speed channels and low-speed data channels. The upstream is also divided into low-speed data links.
It is possible to overlap the upstream and downstream ranges with Echo Cancellation technology.
Fourthly. ADSL technology allows you to reserve a narrow band of bandwidth for the transmission of regular telephone service (POTS) signals. POTS is Plain Old Telephone Service. When using ADSL, telephone communication will not be disrupted, even during a power outage.
ADSL Advantage
Despite all the shortcomings, ADSL technology allows you to use already laid telephone wires to connect to the Internet. This globally expands Internet connectivity. This does not require expensive upgrading of switching equipment, as for ISDN technology.
Flaws
The main disadvantage of ADSL is the weakening of the signal on long-distance telephone lines. For example, at a standard speed of 1 MHz, signal loss can be up to 90 dB.
ADSL speed
The first letter in the name ADSL means asymmetric. That is, the transfer of data from the network to the computer (downstream) and the transfer of data from the computer to the network (upstream) will occur at different speeds.
The transmission speed depends on the condition of the line, cable cross-section, and the presence of taps. In fact, the limit for an ADSL subscriber line is a length of 3500 - 5500 meters with a cable cross-section of 0.5 mm 2.
In practice, ADSL will provide speeds to the computer of 1.5 - 8 Mbit/s, and speeds from the computer from 640 to 1.5 Mbit/s.
ADSL and Internet
If you want to connect to the Internet via ADSL, you need to understand that you do not need to dial telephone numbers to communicate. ADSL technology immediately creates a broadband channel for data transmission over an existing telephone line.
Immediately after installing the ADSL modem, you will receive a constant high-speed Internet connection. At the same time, only 1% of the bandwidth is left for telephone communications (low frequency up to 4 kHz). 99% goes to ensuring high-speed data transfer. In this case, different frequency bands are used for different functions.
Testing Methodology for ADSL
The testing methodology is intended to evaluate and visually display test results when problems arise when working on the Internet.
You can read how to take a “screenshot”
.
We draw your attention to some features of working on the Internet:
1) When the Subscriber connects to its Data Network, the Provider is not responsible for the quality of communication outside the subscriber's terminal device (if any) connected to the Provider's equipment.
The provider guarantees Internet access speed only under the condition of a direct connection, i.e. The Provider's cable connects directly to a laptop or personal computer. You can read more about the Procedure for the provision of services.
2) You can familiarize yourself with the division of areas of responsibility between the Provider and the Subscriber.
3) When using ADSL technology, the data transfer speed is always less than the connection speed by at least 13-15%. This is a technological limitation, which we will discuss in more detail later. It does not depend on the provider or the modem used.
Under ideal conditions, with a connection speed of 12 Mbit/s, you can expect a maximum real speed of ~ 10 Mbit/s.
Note!
You can find out more about the factors affecting the data transfer speed when using ADSL technology.
Attention! If you use Wi-Fi wireless networks to surf the Internet, it will be useful for you to read the information below.
1. Sources of interference affecting the operation of wireless Wi-Fi networks may be the following:
- material of walls and partitions in your apartment or office;
- location of your neighbors' Wi-Fi points. For example, if your neighbor’s point is located near the wall adjacent to your apartment, and your point, in turn, is located near this wall, then the signals from both points will interrupt each other;
- Wi-Fi module in your PC or other mobile device. A mobile device may not have the most modern module installed, which has a maximum speed limit;
- simultaneous downloading from different devices, both inside your apartment and at neighboring points outside your apartment;
- Bluetooth devices operating within the coverage area of your Wi-Fi device;
- various household appliances that use the 2.4 GHz frequency range when operating within the coverage area of your Wi-Fi device.
You can find out more about possible sources of interference affecting the operation of wireless Wi-Fi networks.
2. To speed up your work on the Internet and make it more stable, you need to:
- configure the router to work with mobile devices. How to do this on a TP-Link router, see;
- choose a freer channel;
- select the optimal location of the Wi-Fi point;
- purchase an external Wi-Fi adapter;
- use a two-antenna wireless access point operating in the 2.4 GHz band;
- use a wireless access point operating in the 5 GHz band;
- work via Ethernet cable.
You can learn more about ways to increase your Wi-Fi connection speed and bandwidth.
- We measure Internet speed.
A) Let's go by link and press the button "Begin Test". We are waiting for the test to complete.When the test is completed, you will be presented with a window similar to this. Let's make it " screenshot” and attach it to the results.
b) Download the file (size about 75 MB) from here: http://www.apple.com/itunes/download/
We start downloading by clicking on the button "Download Now".
During the download process we do "screenshot"
Attention! To display the download speed in the browser, you need to go to the Downloads section by pressing the key combination Ctrl+J.With) Download a large file (about 2.3 GB) from here:
ftp://ftp.freebsd.org/pub/FreeBSD. During the download process we do "screenshot" Your download manager or browser and attach it to the testing results.
Attention! There is no need to download the entire file! It’s enough to wait a minute or two until a stable speed is established, then do 2-3 “ screenshot"with an interval of 20-30 seconds and stop the download.d) Download the file using a torrent client. For correct speed testing, it is necessary to exclude local retrackers. You can see how to do this.
Attention! It is necessary to test the connection speed when downloading 3-4 files at the same time, for which the number of uploaders is more than 100. During the download process, do “ screenshot» Your torrent client and attach it to the test results. - We measure speed from internal resources. For this Minsk subscribers come in next link .
On the website click on "Change Server".
In the search bar we write "Atlant Telecom" and select it as a server.
Then press the button "GO".
We are waiting for testing to be completed.As a result, a window with the results should appear.
We take a screenshot and attach it to the overall results.
Regional subscribers go to the following links and download the file:
- link for Brest;
- link for Vitebsk;
- link for Grodno;
- link for Gomel;
- link for Mogilev.
During the download process, we take a “screenshot” of your download manager or browser (except Internet Explorer) and attach it to the testing results. - Download the program and install it (for D-link brand modems - program).
Zyxmon- a free Windows program for managing and monitoring the status of Zyxel routers.
Unpack the zip folder using some archiver. For example, WinRAR or WinZIP. Run the executable file " ZyxMon" A program window will open. Click on the button " Settings"(circled in red).
The following window will appear. Filling out the fields Router IP And Router password. Click " OK».
- After pressing " OK"we will return to the Main window of the program. We activate the connection with the modem. To do this, press the button " Telnet Router Connections" (circled in pink), while the indicators " Telnet connection status" And " PPPoE session status"will have to change color from red to green.
Description of bookmarks:
Telnet: Modem connection status and PPPoE status.
Log: Modem text log;
SyslogD: Messages received from the Syslg Daemon modem;
SNMP: RealTime channel filling statistics;
DynDNS: Dynamic DNS status (not used);
Line: Data required for testing the line: noise margin , attenuation . To receive data you need to press the “ Get ”.Let's do " screenshot” of the obtained result and attach it to the test results.
Testing methodology
Attention! If you are connected through additional equipment or use wireless Wi-Fi networks, you must first connect the Internet cable directly to your laptop or personal computer without additional devices, and then perform the speed testing procedure.
To obtain adequate results during each of the test points, NO work on the Internet should be carried out!
For Windows OS
Download the archive. Unpack it to any folder on your computer. The file should appear in the same folder TEST.bat. We launch it and wait from 10 to 20 minutes (depending on the quality of the DSL connection).
Attention! For Windows 7 and Windows 8, you must run the file as an administrator (right-click on TEST.bat and select “Run as Administrator”). When the BAT file has completed all the actions, you will see the following window.
Press any key on the keyboard and the window will close. After that we go to Drive C and find text files there PING.txt, PATHPING.txt And CONFIG.txt . We attach these files to the results.
For Mac OS X
Download the archive. Unpack it to any folder on your computer. After unpacking, a file should appear in the same folder Test.app. We launch it and wait from 10 to 20 minutes. After completing the test, press any key on the keyboard - the window will close.
Once testing is complete, three text files will appear on your desktop - CONFIG, PING, TRACEROUTE. We attach these files to the results.
We check at what speed the modem receives/sends data.
a) telnet.
Let's go to the command line: Start -> Run -> cmd -> Ok
. In the window that appears, write the command telnet
From the main menu of the modem, go to the menu 24.1 - System Maintenance - Status
. To do this, press on the keyboard 24 - “Enter”, 1- “Enter”.
Let's take screenshots of this window:
Explanations for the fields of interest to us in this menu:
Tx B/s
- transfer speed in Bytes per second;
Rx B/s
[Reception speed, Bytes/s] - reception speed in Bytes in seconds;
Up Time
[Connection time] - duration of connection between the modem and the provider;
My WAN IP (from ISP)
[my IP address on the global network (from the provider)] - the IP address received by the modem from the provider;
Line Status
[Line status] - current xDSL line status: Up - up, Down - not up;
Upstream Speed
[Outgoing speed] - transmission speed of outgoing traffic in Kbps;
Downstream Speed
[Incoming speed] - transmission speed of incoming traffic in Kbit/s;
CPU Load
[CPU load] - percentage of modem CPU load.
b) For modems ZyXel 660R, ZyXel 660R-T1, ZyXel 660RU-T1, ZyXel 660HT1, ZyXel 660HW-T1 via WEB interface.
192.168.1.1
and press the key "Enter".
1234
and press the button "Login".
"Ignore"
In the main menu of the modem, select "System Status".
In the window that opens, find the button "Show Statistics"
and press it. Let's do " screenshots» last window:
- first: during downloading from the Internet;
- second: during downloading from internal resources.
We name the files accordingly and attach them to the results.
c) For modems ZyXel 660R-T2, ZyXel 660RU-T2, ZyXel 660HT-2, ZyXel 660HW-T2.
Type in the address bar of your Internet browser (Chrome, Mozilla Firefox, etc.) the address 192.168.1.1
and press the key "Enter".
Next, a window will appear asking for a password. We register 1234
and press the button "Login".
A window will appear in which you are advised to change the password for logging into the modem. Press the button "Ignore"
In the main menu of the modem, click "Status",
and in the window that opens, click the link "Packet Statistics".
As a result, a statistics window will open, do it “ screenshot»:
- first: during downloading from the Internet;
- second: during downloading from internal resources.
We name the files accordingly and attach them to the results.
d) For D-Link 2500/2540/2600/2640U v.2 modems
Type 192.168.1.1 in the address bar of your Internet browser (Chrome, Mozilla Firefox, etc.) and press the " Enter
" Next, a window will appear asking for a user and password. We register the user - admin
and password - admin
, press the button " Ok
».
Next we go to the menu Device Info -> Statistics -> WAN
As a result, a window will open, do it “ screenshot»:
- first: during downloading from the Internet;
- second: during downloading from internal resources.
We diagnose the DSL channel connection.
To do this we go: Start -> Run -> cmd -> Ok.
In the window that appears, write the commands one by one (after each press the key "Enter"
):
netsh("Enter")
ras("Enter")
set tracing ppp enable("Enter")
exit("Enter")
Next, go to the Windows folder (usually c: Windows) and create a folder there tracing
. If it writes to you that such a folder already exists, do not be alarmed. We go into it (example path: c:Windowstracing) and copy the ppp.txt file from there with the results of the commands we entered earlier. We attach this file to the results of the method.
Analyzing the DSL channel on the modem.
a) For modems ZyXel 660R, ZyXel 660RT1, ZyXel 660RU1, ZyXel 660HT1, ZyXel 660HW-T1
We go to the modem configurator, as shown in step 6-a, go to the menu
- modem command line. We write the commands one by one (after each press the key "Enter"
):
wan adsl chandata ("Enter")
wan adsl opmode (“Enter”)
wan adsl linedata far (“Enter”)
wan adsl linedata near (“Enter”)
wan adsl perf (“Enter”)
wan hwsar disp (“Enter”)
Let's do " screenshots» the results obtained. First of all, the state of the 1st (physical) level is analyzed. This information is retrieved using the commands “xdsl state”, “wan adsl linedata far”, “wan adsl linedata near”. Link for information: http://zyxel.ru/kb/1543.
The main parameters for monitoring are “SNR margin value”, “Loop attenuation” for 782 and 791, and “noise margin downstream”, “attenuation downstream” - for 642, 650, 650, 660. Both values are measured on the receiving channel of the transceiver. The first universally characterizes the noise immunity margin of the line. A level of 6 db roughly corresponds to an error rate of 10E-6 and is the threshold for reliable communication. This parameter clearly depends on the speed, i.e. the higher the speed, the smaller the margin. It is also worth noting that the measured values at each line end device may differ. This indicates that the source of interference is located closer to one end of the line.
Attenuation downstream is the attenuation of the signal in the line and clearly depends on the active resistance of the wire. The effect of noise on communication quality and maximum speed is higher than that of attenuation. You need to do this several times at different times of the day. The results should be attached to the results of the method.
b) For modems ZyXel 660RT2, ZyXel 660RU2, ZyXel 660HT2, ZyXel 660HW-T2, ZyXel 660RT3, ZyXel 660RU3, ZyXel 660HT3
When entering the modem settings via telnet
(as shown in point 6-a), you will immediately be taken to the modem command line, where you need to enter the commands indicated above.
c) For ZyXel 700 series modems (782 and 791)
In a similar way, go to the modem configurator (see point 6-a) and go to the menu 24.8 - Command Interpreter Mode.
We write the commands one by one (after each press the key "Enter"
):
xdsl cnt disp ("Enter")
wan hwsar disp (“Enter”)
xdsl state ("Enter")
Let's do " screenshots» obtained results and attach them to the test results.
d) For D-Link 2500/2540/2600/2640U v.2 modems
We go to the modem configurator, as shown in point 6-d, go to the menu Device Info -> Statistics -> ADSL
.
We take a screenshot and attach it to the results.
We save all the results of the testing methodology in one archive and send them to the technical support email address [email protected] indicating client data (personal account number/organization name, contact phone number/email address) for feedback.
There are several ways to access the Internet using a regular telephone cable, and ADSL technology is one of them. The purpose of this article is to tell the reader, what is an ADSL modem how data is exchanged, and what is the advantage of this method of organizing information transfer.
What is ADSL and how does it work
Digital subscriber line, or DSL (Digital Subscriber Line) for short, is a way of organizing data exchange by creating a high-speed connection for transferring it between two or more computers. To connect computers into a local area network or to access the Internet, special DSL modems are used on the client side and switches on the provider side.
The technology appeared back in the late 80s of the last century and combines several technologies under the general name xDSL:
- ADSL - asymmetric digital subscriber line or Asymmetric DSL. The data transfer speed reaches 8 Mbit/s for receiving, and up to 1 Mbit/s for sending data from the subscriber;
- HDSL - high-speed digital subscriber line or High Data Rate DSL, where the transmission speed is up to 2 Mbit/s in two directions;
- VDSL - ultra-high-speed digital subscriber line or Very High Data Rate DSL, when the highest speed of 52 Mbit/s is achieved.
When used by private subscribers, the technology of asymmetric data transmission has become the most popular. This allows you to use one phone line for accessing the Internet and for regular calls. High connection speed is achieved by using a higher frequency than that used by a conventional dial-up modem.
The principle of asynchronous data transfer is quite simple:
- Frequencies up to 4 kHz are used directly for telephone communication or fax transmission.
- When creating a connection between the client modem and the provider modem, frequencies from 4 to 140 kHz are used. At these frequencies, data is transmitted from the client to the Internet provider. Because Since relatively little data is sent from the client, there is no need to use higher frequencies and, accordingly, higher speed. Speeds rarely exceed 1 Mbps.
- Frequencies from 1.1 to 4.4 MHz are used for incoming traffic. The connection speed here reaches 8 Mbit/s.
What is an ADSL modem
By connecting to the Internet via an ADSL line, the user does not need to perform any additional actions, for example, making a call to the provider, as in a dial-up connection. The modem will do all the necessary work for the client. So, what is an adsl modem? This is a high-tech device that is designed to convert an incoming or outgoing signal from analog to digital and vice versa. The modem creates a permanent broadband connection and monitors its stability.
Constantly improving ADSL technology has undergone several evolutionary transitions, which is reflected in the ADSL modems offered for purchase, which are now of the following types:
- internal modem for connecting to a PCI connector;
- external version with USB or Ethernet connectors;
- external routers with Ethernet ports;
- external routers with a built-in WiFi access point.
Now that it's a little clearer how it works adsl modem what is it and about technology in general, we can draw a conclusion about the advantages and disadvantages of using the described technology to access the Internet.
Advantages and disadvantages of ADSL connection
The most obvious advantages of ADSL technology are very high data transfer speeds and connection stability. But there are several more important points that speak in favor of ADSL:
- constant connection and access to the Internet;
- there is no need to lay additional cables, because the telephone line is already installed in almost every apartment, office or house;
- using both the telephone and the Internet simultaneously on one telephone line;
- relatively low price for equipment and provider services.
The disadvantages of this type of connection mainly include the low quality of telephone lines, which can significantly reduce the data transfer speed and the rather low speed of outgoing traffic. But technology is developing and these problems should be solved in the near future.