Internet connection using adsl technology. What is an ADSL modem. Data transfer rate
ADSL is a technology for asymmetric Internet access. Its structure is an asymmetric system and allows you to work with connections at speeds up to 8 Mbit/s. ADSL technology, the transmission speed of which is calculated to be up to 1 Mbit/s, operates on average at a distance of more than 5 km. Today we will look at what this type of connection is and how it works.
History of appearance
Before answering the question: “ADSL - what is it?”, we bring to your attention some historical data. They first started talking about its creation in the late 80s, when even the Internet in its modern guise was only its main task in 1989 was to improve and modernize the technology for transmitting data over copper telephone wires. Analog-to-digital conversion was created mainly for the rapid transfer of information between various interactive services, video games, video files, as well as for instant remote access to a LAN and other network systems.
Modern ADSL technology: operating principle
The network operates on the subscriber's digital line, which provides access to the Internet through telephone channels. But telephone lines use an analog signal to transmit voice messages. An ADSL connection is designed to convert an analog signal into a digital one and transmit it directly to a computer. At the same time, unlike already outdated Dial-up modems, ADSL-based devices do not block the telephone line and allow you to use digital and analog signals simultaneously.
The essence of the technology (asymmetry) is that the subscriber receives a huge amount of data - incoming traffic, and transmits a minimum of information from himself - downward traffic. Input refers to various types of content: video and media files, applications, objects. The downstream sends only important technical information - various commands and requests, emails and other minor elements. The asymmetry is that the speed from the network to the subscriber is several times higher than the speed from the user.
The most important advantage of ADSL technology is its cost-effectiveness and cost-effectiveness. The fact is that the same copper ones are used to operate the system. The quantity in them, of course, significantly exceeds the number of similar elements in cable modems. But at the same time, no modernization of switching equipment or complex reconstruction is necessary. ADSL connects quickly, and modern types of modems are intuitive to manage and configure.
What equipment is used for this connection?
In order for the technology to work, special types of modems are used, differing in their structure, design, and connection type:
- PCI modems (internal computer devices).
- External modems with USB connection type.
- Devices with an Ethernet type interface.
- with Ethernet circuit.
- Profile types of modems (for security companies, private telephone lines).
- Router with internal Wi-Fi access points.
Additional equipment: splitters and microfilters
We must not forget that to connect a gadget such as an ADSL modem, you will need splitters and microfilters. Devices are selected in accordance with the design of the telephone cable. In a situation where a cable outlet has been made (or can be done) to separate the modem and telephone channels, a splitter is used. In another case, it is necessary to purchase a microfilter, which is installed on each telephone present in the room.
The main task of the splitter is to separate frequencies - voice (0.3-3.4 KHz) and those used directly by the modem itself (25 KHz-1.5 MHz). It is in this way that the simultaneous operation of the modem and telephone is ensured, which do not interfere with each other and do not create interference. Splitters are compact and will not cause unnecessary inconvenience. The miniature box is equipped with three connectors and is lightweight.
ADSL - what is it? Stages of connecting high-speed Internet
- Choosing a provider. Every provider currently offers to use this technology. Different types and tariffs depend on the region, as well as on the technical capabilities of the company, whose coverage area may be limited.
- Purchase of equipment. Currently, it is not at all necessary to buy a modem, splitters and microfilters. When signing a connection agreement, the provider offers to rent the necessary equipment, including an ADSL modem. In the future, when the document is terminated, the equipment is returned back. The client pays exclusively for the Internet connection. Modern Internet ADSL - what is it? This is a fast, cheap and high-quality connection method.
- Account activation. The provider reserves an account for each client, activation of which may take up to 12 days. However, in most cases, with normal network coverage, the procedure does not require more than a few hours. The provider first checks the phone number for ADSL connectivity. If the access zone of the technology is not enough, then high-speed Internet will not be possible.
- Equipment setup. At this stage, devices are connected to the telephone line, splitters and microfilters are installed, modem drivers are installed on the computer, and the modem’s network parameters are set in the Internet browser.
pros
What are the advantages of ADSL technology? Here are a few of them:
- High ADSL allows you to easily transfer files of any size without long waits. The technology is constantly being improved, and speeds are increasing, significantly expanding the subscriber's capabilities.
- Wireless connection. To use an ADSL system, you do not need to extend the cable to the subscriber and install a large amount of equipment. The reliability, quality and functionality of the network increases.
- No interference on the telephone line. The ADSL router operates in independent mode and does not create any problems for the phone. You can make calls and travel around the virtual space completely freely.
- Constant Internet access ADSL. What it is? This means that the network will not fail during operation. The technology does not require reconnection. The user gets access to the Internet constantly and can be online around the clock.
- Reliability and stability. Today ADSL is the most reliable type of Internet connection.
- Profitability. The cost of connecting ADSL and installing a modem with a router is minimal and will not hit the family budget.
Flaws
- No crosstalk protection. If several dozen clients are connected to one channel, you won’t have to count on high speed. The more subscribers on one ADSL, the lower the quality of data transmission.
- Although ADSL technology has disadvantages, they are few. This also includes the minimum speed from the subscriber. ADSL asymmetry has an obvious disadvantage - file transfer from the subscriber will be long and inconvenient. But the technology is intended, first of all, for quick access to the Internet and surfing. In addition, the information transmitted from the subscriber takes up minimal space and does not require a large resource.
Speed and factors influencing it
ADSL is a high-speed Internet technology, but there is no universal meaning or formula. For each individual subscriber, the speed is individual and is determined by a whole set of factors. Some of them may affect the reliability and quality of the equipment. Therefore, it is best for professionals to install modems and routers.
The main reason for low ADSL connection speed is the quality of the subscriber line. We are talking about the presence of cable outlets, their condition, wire diameter and length. Signal attenuation is a direct consequence of increasing the length of the subscriber line, and interference can be reduced by expanding the diameter of the wire. The standard length of an ADSL channel does not exceed 5 km - the optimal range for high-speed data transfer.
Speed characteristics
When compared to other Internet connection technologies, ADSL is significantly superior in speed. An analog modem will give a maximum of up to 56 Kbit/s, while ADSL at the dawn of its appearance already made it possible to transmit information at speeds of up to 144 Kbit/s.
ADSL technology, the maximum speed of which is also determined by the characteristics of the modem and can reach 2048 Mbit/s, optimizes the process of information transfer. Digital lines significantly increase the user's capabilities, taking him beyond the limitations of even multiple connected computers, mobile phones, tablets and other gadgets.
Technology Outlook
The capabilities and resources of ADSL technology are far from being exhausted. Even the ADSL2 and ADSL2+ standards, introduced back in the mid-2000s, still retain their relevance and capabilities. This is, in fact, the only technology that can provide broad Internet access without interruptions and software problems, and therefore is a competitor to many other methods of connecting to the Internet.
The minimum technical equipment is complemented by modern types of modems. Manufacturers annually release new devices designed for continuous operation without the need for maintenance and servicing. In addition, ADSL speed is constantly increasing and is not limited to megabits. Connection becomes relevant both for the home and for an entire office company with several dozen computer clients.
Conclusion
So, we found out what ADSL technology is, what its essence is and how it works. As you can see, this is one of those technologies that practically does not fail during operation (even if several dozen users are connected to the network). At the same time, it does not require constant reconnections and speed restrictions.
In recent years, the development of the telecommunications services market has led to a shortage of capacity for access channels to existing provider networks. If at the corporate level this problem is solved by providing high-speed data transmission channels for rent, then what alternative can be offered to subscribers on existing lines, instead of a dial-up connection, in the residential and small business sectors?
Today, the main way end users 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 communication is low, the maximum speed can reach 56 Kbps. This is still enough for Internet access, but the saturation of pages with graphics and video, large volumes of email and documents, and the ability for users to exchange multimedia information have raised the challenge of increasing the throughput 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 part of a general group of high-speed data transmission technologies, united by the general term DSL (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 to receive and transmit data: the receiving channel has significantly greater throughput.
The general name for DSL technologies arose in 1989, when the idea first appeared to use analog-to-digital conversion at the subscriber 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, remote access to LANs and other networks). Today DSL technologies are presented:
- 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 on” state (which eliminates the need to dial a phone number each time and wait for the connection to be established), makes ADSL technology ideal for organizing Internet access, local area network (LAN) access, etc. When organizing such connections, users usually receive much more information than they transmit. ADSL technology provides downstream data rates ranging from 1.5 Mbit/s to 8 Mbit/s and upstream data rates from 640 Kbit/s to 1.5 Mbit/s. ADSL allows you to transmit data at a speed of 1.54 Mbit/s over a distance of up to 5.5 km over one twisted pair of wires. Transmission speeds of the order of 6-8 Mbit/s can be achieved when transmitting data over a distance of no more than 3.5 km via wires with a diameter of 0.5 mm.
- R-ADSL (Rate-Adaptive Digital Subscriber Line)
R-ADSL technology provides the same data transfer speed as ADSL technology, but at the same time allows you to adapt the transfer speed 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 data transfer rates. The data rate can be selected by line synchronization, during connection or by signal coming from the station
- G. Lite (ADSL.Lite)
It is a cheaper and easier to install version of ADSL technology, providing downstream data speeds of up to 1.5 Mbit/s and upstream data speeds of up to 512 Kbit/s or 256 Kbit/s 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 transmission speeds 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 transfer rate of 1.544 Mbps, and E1 lines are used in Europe and provide a data transfer 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 using ADSL technology, telephone companies can install special repeaters to inexpensively but effectively increase the length of an HDSL line. 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)
Just like HDSL technology, SDSL technology provides symmetrical data transmission at speeds corresponding to the speeds of the T1/E1 line, 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 necessary to maintain the same data 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 ensuring guaranteed quality of service, that is, at a given speed and data transmission range, ensuring an error level of no worse than 10 -7 even in the most unfavorable noise conditions.
This standard is a development of HDSL, since 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 characteristics (in terms of maximum line length and noise margin) due to the use of more efficient code, a pre-coding 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 speed the SHDSL signal occupies a narrower bandwidth than the corresponding HDSL signal at the same speed. Therefore, the interference generated by the SHDSL system to other DSL systems is less powerful than the interference from HDSL. The spectral density of the SHDSL signal is shaped in such a way that it is spectrally compatible with ADSL signals. As a result, compared to the single-pair version of HDSL, SHDSL allows you to increase the transmission speed by 35-45% at the same range or increase the range by 15-20% 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's capabilities are limited to data transmission only. Despite the fact that IDSL, like ISDN, uses 2B1Q modulation, there are a number of differences between them. 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 line organized using DSL technology), while ISDN requires a connection to be established.
- VDSL (Very High Bit-Rate Digital Subscriber Line - ultra-high-speed digital subscriber line)
VDSL technology is the "fastest" xDSL technology. It provides downstream data transfer rates ranging from 13 to 52 Mbit/s, and upstream data transfer rates ranging from 1.5 to 2.3 Mbit/s, over one twisted pair of telephone wires. In symmetric mode, speeds up to 26Mbps are supported. VDSL technology can be seen as a cost-effective alternative to laying fiber optic cable to the end user. However, the maximum data transmission distance for this technology is from 300 meters to 1300 meters. That is, either the length of the subscriber line should not exceed this value, or the fiber-optic cable should 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), video on demand, etc. signals. The technology is not standardized; different equipment manufacturers have different speed values.
So what is ADSL? First of all, ADSL is a technology that allows you to turn twisted pair telephone wires into a high-speed data transmission path. The ADSL line connects the provider's DSLAM (DSL Access Multiplexor) access equipment and the customer's modem, which are connected to each end of the twisted pair telephone cable (see Figure 1). In this case, three information channels are organized - the "downstream" data stream, the "upstream" data stream and the regular telephone service (POTS) channel (see Figure 2). The telephone communication channel is allocated using a frequency splitter filter, and directs it to the normal telephone set. This scheme allows you to talk on the phone simultaneously with the transfer of information and use telephone communication in the event of a malfunction of the ADSL equipment. Structurally, the telephone splitter is a frequency filter, which can be either integrated into the ADSL modem or be an independent device.
Rice. 1
Rice. 2
ADSL is an asymmetric technology - the speed of the “downstream” data flow (that is, the data that is transmitted towards the end user) is higher than the speed of the “upstream” data flow (in turn, transmitted from the user to the network). It should be said right away that there is no cause for concern here. The data transfer rate from the user (the "slower" direction of data transfer) is still significantly higher than using an analog modem. This asymmetry is introduced artificially; the modern range of network services requires a very low transmission speed from the subscriber. For example, to receive videos in MPEG-1 format, a bandwidth of 1.5 Mbit/s is required. For service information transmitted from the subscriber (command exchange, service traffic), 64-128 Kbit/s is quite sufficient. According to statistics, incoming traffic is several times, and sometimes even an order of magnitude, higher than outgoing traffic. This speed ratio ensures optimal performance.
To compress large amounts of information transmitted over twisted pair telephone wires, ADSL technology uses digital signal processing and specially created algorithms, advanced analog filters and analog-to-digital converters. Long-distance telephone lines can attenuate the transmitted high-frequency signal (for example, at 1 MHz, which is the typical transmission rate for ADSL) by up to 90 dB. This forces analog ADSL modem systems to operate under a fairly heavy load to allow for high dynamic range and low noise levels. 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 how ADSL works, you can understand that this system belongs to the achievements of modern technology.
ADSL technology uses a method of dividing the bandwidth of a copper telephone line into several frequency bands (also called carriers). This allows multiple signals to be transmitted simultaneously on one line. Exactly the same principle underlies cable television, when each user has a special converter that decodes the signal and allows them to see a football match or an exciting film on the TV screen. When using 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
In FDM, one band is allocated for the upstream data stream and another band for the downstream data stream. The downstream information stream 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 discrete changes in the state of a 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 bandwidth between voice and data (it simply does not use the voice part), but is more complex 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 of 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 transmission and fax transmission. And all this without interrupting regular telephone communication, for which the same telephone line is used. The technology involves reserving a certain frequency band for regular telephone communications (or POTS - Plain Old Telephone Service). It's amazing how quickly telephone communication turned not only into "simple" (Plain), but also into "old" (Old); it turned out something like “good old telephone communication”. However, we should pay tribute to the developers of new technologies, who still left telephone subscribers a narrow band of frequencies for live communication. In this case, a telephone conversation can be carried out simultaneously with high-speed data transfer, rather than choosing one of the two. Moreover, even if your electricity is cut off, the usual “good old” telephone connection will still work and you will not have any problems calling an electrician. Providing this capability 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 ordinary twisted pair copper telephone cables. It is quite obvious that there are much more such pairs of wires (and this is 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 technology, but how high-speed? Considering that the letter "A" in the name ADSL stands for "asymmetric", we can conclude that data transfer in one direction is faster than in the other. Therefore, there are two data transfer 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 speed - 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 on and is determined by DMT (Discrete Multi-Tone) 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 of which is 6.144 Mbit/s - in the case of T1 or 8.192 Mbit/s in the case of E1. For up stream transmission, one T1 stream is 1.536 Mbit/s. 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 additional bit.
Now let's look at how real data transfer occurs using the following example. IP information packets generated both in clients’ local networks and by personal computers directly connected to the Internet will be sent to the input of the ADSL modem framed by the Ethernet 802.3 standard. The subscriber modem splits and “packs” the contents 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. In accordance with the T1.413 standard, it “encapsulates” ATM cells into the digital stream E1, T1, and then the traffic over the telephone line goes to the DSLAM. The DSL multiplexor station concentrator - 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 service delivery centers. When implementing Internet access services, cells arrive at the Internet provider's router, which performs the function of a terminal device in a permanent virtual channel (PVC) between the subscriber terminal and the Internet provider's node. The router performs the opposite (in relation to the subscriber terminal) transformation: it collects incoming ATM cells and restores the original Ethernet 802.3 format frame. When transmitting traffic from the service delivery center to the subscriber, completely similar transformations are carried out, only in the reverse order. In other words, a “transparent” local network of the Ethernet 802.3 protocol 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 Internet provider’s router as one of the local network devices.
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 a broadband access network can be represented as follows: client application - IP packet - Ethernet frame (IEEE 802.3) - ATM cells (RFC 1483) - modulated ADSL signal (T1.413) - ATM cells (RFC 1483 ) - Ethernet frame (IEEE 802.3) - IP packet - application on a resource on the Internet.
As mentioned above, the stated speeds are only possible ideally 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 - 7936 Kbps. There are other factors that have a significant impact on the speed and stability of the connection. These factors include: line length (the throughput of a DSL line is inversely proportional to the length of the subscriber line) and wire cross-section. The characteristics of the line deteriorate as its length increases and the wire cross-section decreases. The data transfer speed is also affected by the general condition of the subscriber line, the presence of twists, and cable outlets. The most “harmful” factors that directly affect the ability to establish an ADSL connection are the presence of Pupinov coils on the subscriber line, as well as a large number of taps. None of the DSL technologies can be used on lines with Pupin coils. When checking a line, it is ideal not only to determine the presence of Pupin coils, but also to find the exact location of their installation (you will still have to look for the coils and remove them from the line). The Pupin 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 section of cable 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 using DSL technology is influenced not so much by the fact of the connection itself, but by the length of the cable outlet itself. Up to a certain length (about 400 meters), cable outlets do not have a significant impact on xDSL. Additionally, cable outlets affect different xDSL technologies differently. For example, HDSL technology allows for a cable outlet of up to 1800 meters. As for ADSL, cable outlets do not interfere with 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 disadvantages, namely susceptibility to external factors (various interference from third-party electromagnetic devices), as well as physical phenomena that arise in the line during transmission. An increase in the capacitive characteristics of the channel, the occurrence of standing waves and reflections, and the insulation characteristics of the line. All these factors lead to the appearance of extraneous noise on the line, and faster attenuation of the signal and, as a consequence, to a decrease in the data transmission speed and a decrease in the length of the line suitable for data transmission. The ADSL modem itself can provide some values of the characteristics of the ADSL line, by which one can directly judge the quality of the telephone line. Almost all models of modern ADSL modems contain information about the quality of the connection. Most often, the Status->Modem Status tab. Approximate contents (may vary depending on the model and manufacturer of the modem) are 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 speed
US Margin 26 - Outgoing connection noise level in db
DS Margin 31 - Downlink noise level in db
LOS Errors 0 -
DS Line Attenuation 30 - Downlink 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 is enabled (Path mode Fast - disabled)
Based on these values, you can judge, and also control yourself, the state of the line. Values:
Margin - SN Margin (Signal to Noise Margin or Signal to Noise Ratio). The noise level of interference depends on many different factors - getting wet, the number and length of branches, line synchronicity, cable “breakage”, the presence of twists, the quality of physical connections. In this case, the signal of the outgoing ADSL stream (Upstream) decreases until it is completely absent and, as a consequence, the ADSL modem loses synchronization
Line Attenuation - the attenuation value (the greater the distance from DSLAMa, the greater the attenuation value. The higher the signal frequency, and therefore the connection speed, the greater the attenuation value).
ADSL(Asymmetric Digital Subscriber Line) is one of the high-speed data transmission technologies known as DSL (Digital Subscriber Line) technologies, collectively referred to as xDSL. Other DSL technologies include HDSL (High data rate Digital Subscriber Line), VDSL (Very high data rate Digital Subscriber Line) and others.
The general name for DSL technologies arose in 1989, when the idea of using analog-to-digital conversion at the subscriber end of the line first appeared, 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, remote LAN access and other networks).
ADSL technology - so what is it?
First of all, ADSL is a technology that allows you to turn twisted pair telephone wires into a high-speed data transmission path. ADSL line connects two ADSL modem, which are connected to each end of the twisted pair telephone cable (see Figure 1). In this case, three information channels are organized - a “downstream” data stream, an “upstream” data stream and a regular telephone service (POTS) channel (see Figure 2). The telephone communication channel is allocated using filters, which ensures that your phone will work even if the ADSL connection fails.
Picture 1
Figure 2
ADSL is an asymmetric technology - the speed of the “downstream” data flow (that is, the data that is transmitted towards the end user) is higher than the speed of the “upstream” data flow (in turn, transmitted from the user to the network). It should be said right away that there is no cause for concern here. The data transfer rate from the user (the "slower" direction of data transfer) is still significantly higher than using an analog modem. In fact, it is also significantly higher than ISDN (Integrated Services Digital Network).
To compress large amounts of information transmitted over twisted pair telephone wires, ADSL technology uses digital signal processing and specially created algorithms, advanced analog filters and analog-to-digital converters. Long distance telephone lines can attenuate the transmitted high frequency signal (for example, at 1 MHz, which is the typical transmission rate for ADSL) by up to 90 dB. This forces analog ADSL modem systems to operate under a fairly heavy load to allow for high dynamic range and low noise levels. 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 how ADSL works, you can understand that this system belongs to the achievements of modern technology.
ADSL technology uses a method of dividing the bandwidth of a copper telephone line into several frequency bands (also called carriers). This allows multiple signals to be transmitted simultaneously on one line. Exactly the same principle underlies cable television, when each user has a special converter that decodes the signal and allows them to see a football match or an exciting film on the TV screen. When using ADSL, different carriers simultaneously carry different parts of the transmitted data. This process is known as Frequency Division Multiplexing (FDM) (see Figure 3). In FDM, one band is allocated for the upstream data stream and another band for the downstream data stream. The downstream range is in turn divided into one or more high-speed channels and one or more low-speed data channels. The upstream range is also divided into one or more low-speed data links. In addition, echo cancellation technology can be used, in which the ranges of the “upstream” and “downstream” streams overlap (see Figure 3) and are separated by means of local echo cancellation.
Figure 3
This is how ADSL can provide, for example, simultaneous high-speed data transmission, video transmission and fax transmission. And all this without interrupting regular telephone communication, which uses the same telephone line. The technology involves reserving a certain frequency band for regular telephone communications (or POTS - Plain Old Telephone Service). It's amazing how quickly telephone communication turned not only into “simple” (Plain), but also into “old” (Old); it turned out something like “good old telephone communication”. However, we should pay tribute to the developers of new technologies, who still left telephone subscribers a narrow band of frequencies for live communication. In this case, a telephone conversation can be carried out simultaneously with high-speed data transfer, rather than choosing one of the two. Moreover, even if your electricity is cut off, the usual “good old” telephone connection will still work and you will not have any problems calling an electrician. Providing this capability was part of the original ADSL development plan. This feature alone gives ADSL a significant advantage over ISDN.
One of the main advantages of ADSL over other high-speed data transmission technologies is the use of ordinary twisted pair copper telephone cables. It is quite obvious that there are much more such pairs of wires (and this is an understatement) than, for example, cables laid specifically for cable modems. ADSL forms, so to speak, an “overlay network”. At the same time, expensive and time-consuming upgrades of switching equipment (as is necessary for ISDN) are not required.
ADSL connection speed
ADSL is a high-speed data technology, but how high-speed? Considering that the letter “A” in the name ADSL stands for “asymmetric”, we can conclude that data transfer in one direction is faster than in the other. Therefore, there are two data transfer rates to consider: "downstream" (transferring data from the network to your computer) and "upstream" (transferring data from your computer to the network).
Factors affecting the data transfer speed are the condition of the subscriber line (i.e., the diameter of the wires, the presence of cable outlets, etc.) and its length. Signal attenuation in a line increases with increasing line length and increasing signal frequency, and decreases with increasing wire diameter. In fact, the functional limit for ADSL is a subscriber line 3.5 - 5.5 km long with a wire thickness of 0.5 mm. Currently, ADSL provides downstream speeds ranging from 1.5 Mbit/s to 8 Mbit/s and upstream speeds from 640 Kbit/s to 1.5 Mbit/s. The general development trend of this technology promises an increase in data transfer speeds in the future, especially in the “downstream” direction.
In order to evaluate the data transfer speed provided by ADSL technology, it is necessary to compare it with the speed that may be available to users using other technologies. Analog modems allow you to transfer data at speeds from 14.4 to 56 Kbps. ISDN provides a data rate of 64 Kbps per channel (typically the user has access to two channels, for a total of 128 Kbps). Various DSL technologies give the user the opportunity to transmit data at speeds of 144 Kbps (IDSL), 1.544 and 2.048 Mbps (HDSL), downstream 1.5 - 8 Mbps and upstream 640 - 1500 Kbps s (ADSL), “downstream” stream 13 - 52 Mbit/s and “upstream” stream 1.5 - 2.3 Mbit/s (VDSL). Cable modems have data transfer speeds from 500 Kbps to 10 Mbps (note that the bandwidth of cable modems is divided among all users simultaneously accessing a given line, so the number of concurrent users has a significant impact on the actual speed data transmission of each of them). Digital lines E1 and E3 have data transfer rates of 2.048 Mbit/s and 34 Mbit/s, respectively.
When using ADSL technology, the bandwidth of the line through which the end user is connected to the backbone network always belongs to that user entirely. Do you need an ADSL line? It's up to you, but to help you make the right decision, let's look at some of the benefits of ADSL.
First of all, the data transfer speed. The numbers were stated two paragraphs above. Moreover, these numbers are not the limit. The new ADSL 2 standard implements speeds of 10 Mbit/s “downstream” and 1 Mbit/s “upstream” with a range of up to 3 km, and ADSL 2+ technology, the standard of which should be approved in 2003, includes “downstream” speeds. streams of 20, 30 and 40 Mbit/s (on 2,3 and 4 pairs, respectively).
Internet via ADSL
In order to connect to Internet via ADSL, no need to dial the phone number. ADSL creates a broadband data link using an existing telephone line. After installing ADSL modems, you get a permanent connection. A high-speed data link is always ready to go – whenever you need it.
The line bandwidth belongs entirely to the user. Unlike cable modems, which allow the bandwidth to be shared among all users (which greatly affects the data transfer speed), ADSL technology allows only one user to use the line.
ADSL connection technology allows you to fully use line resources. Typical telephone communications use about one hundredth of the telephone line's bandwidth. ADSL technology eliminates this "disadvantage" and uses the remaining 99% for high-speed data transmission. In this case, different frequency bands are used for different functions. For telephone (voice) communications, the lowest frequency region of the entire line bandwidth is used (up to approximately 4 kHz), and the entire remaining band is used for high-speed data transmission.
The versatility of this system is not the least argument in its favor. Since different frequency channels of the subscriber line bandwidth are allocated for the operation of different functions, ADSL allows you to simultaneously transfer data and talk on the phone. You can make and answer calls, send and receive faxes, while at the same time being on the Internet or receiving data from the corporate LAN. All this over the same telephone line.
ADSL opens up completely new possibilities in those areas where it is necessary to transmit high-quality video signals in real time. These include, for example, video conferencing, distance learning and video on demand. ADSL technology allows providers to provide their users with services that are more than 100 times faster than the current fastest analog modem (56 Kbps) and more than 70 times faster than ISDN (128 Kbps) ).
ADSL technology allows telecommunications companies to provide a private, secure channel to facilitate the exchange of information between the user and the provider.
Internet connection via ADSL
We should not forget about costs. The technology for connecting to the Internet via ADSL is effective from an economic point of view, if only because it does not require the installation of special cables, but uses already existing two-wire copper telephone lines. That is, if you have a connected telephone at home or in the office, you do not need to lay additional wires to use ADSL. (Although there is a fly in the ointment. The company that provides you with regular telephone service must also provide ADSL service.)
Not much equipment is needed to make an ADSL line work. ADSL modems are installed at both ends of the line: one on the user side (at home or in the office), and the other on the network side (at the Internet provider or at the telephone exchange). Moreover, the user does not have to buy his own modem, but it is enough to rent it from the provider. In addition, in order for the ADSL modem to work, the user must have a computer and an interface card, for example, Ethernet 10baseT.
As telephone companies gradually enter the untapped field of delivering video and multimedia data to the end user, ADSL technology continues to play a large role. Of course, after some time, the broadband cable network will cover all potential users. But the success of these new systems will depend on how many users will be involved in the process of using new technologies now. By bringing movies and television, video catalogs and the Internet into homes and offices, ADSL makes the market viable and profitable for telephone companies and other service providers in a variety of industries.
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