Network connection technology. Dial-up Internet access: types and types of connection, equipment setup, pros and cons. Twisted pair and optical cable

Dial-up access.. Broadband xDSL access.. Leased line connection.. Cable TV network access.. Local area network connection.. Wi-Fi wireless technology.. Mobile technology access.. Radio Internet.. Satellite Internet access. .. Asymmetric ADSL standard.. High-speed VDSL standard.. Dedicated Ethernet line.. Wireless high-speed standard 802.11n.. Data transfer rate.. 3G/4G technologies.. High-speed mobile Internet.. 3G/4G network coverage area..

How to connect to the Internet? Which connection method to choose and what are these methods in general? Such questions inevitably arise when the first computer (smartphone, tablet) appears in the family. I don't think that Internet-savvy users will find anything new for themselves. This article is for those who are faced with solving such issues for the first time. I hope that they will find answers to their questions here.

Everyone knows about the unlimited possibilities of the Internet in terms of communication, entertainment, searching for the necessary information. Today, the answer to any question is easier and faster to find on the Internet than in any reference books or encyclopedias.
Currently There are many ways to connect to the Internet. The most used technologies for accessing the Network are divided into the following types:

Dial-up access;
access via broadband xDSL network;
access via leased lines;
access via local network;
access via cable television network;
wireless access Wi-Fi;
mobile technology access;
satellite Internet access;
radio internet

Dial-up access.

Historically connected to the Internet began with the connection of the subscriber and the provider via a regular telephone line using a modem. It is also called dial-up access or dial-up. It has many disadvantages: a modest information transfer rate (up to 56 kbps), a strong dependence on quality telephone communication and modem, busy telephone line during a modem connection, high cost of traffic. However, dial-up access is often the only choice available to many rural or remote areas where broadband access is not possible due to low population density.

Broadband xDSL access

With the advent of the xDSL family of technologies (Digital Subscriber Line) through the existing cable infrastructure of telephone networks, it became possible to transfer data at speeds up to 50 Mbps. These technologies support voice, high-speed data and video transmissions, creating significant benefits for subscribers and providers. Existing types of xDSL technologies differ mainly in the form of modulation used and the data rate.

Of the most used and well-known xDSL standards, the following can be noted:

IDSL (Digital Subscriber Line ISDN) : Inexpensive and proven technology that provides subscriber access at speeds up to 128 Kbps.
ADSL (Asymmetric Digital Subscriber Line) : A widely used DSL variant that allows data to be transmitted to the user at up to 8 Mbps, and from the user at up to 768 Kbps.
VDSL (Very High Speed ​​Digital Subscriber Line) : A promising DSL technology that provides data transfer rates up to 52 Mbps to the user.

Asymmetric ADSL Operation takes into account the main feature of the Internet, according to which the information flow from the network to the user significantly exceeds the information flow from the user to the network.

Speed ​​standard VDSL can work not only in asymmetric, like ADSL, but also in symmetrical mode. When operating VDSL in asymmetric mode, the data transfer rate is from 13 to 52 Mbps in the direction from the network to the user and up to
1.5 Mbps from user to network.
In symmetrical mode, the maximum throughput of a VDSL line is approximately 26 Mbps in each direction. Symmetric mode can be used, for example, in corporate data networks - video conferences, seminars, etc.

Leased line access

Internet access via leased lines (analog and digital) - this is a way to connect to the Network when the user's computer is connected to the provider's server using a cable (twisted pair) and this connection is permanent, i.e. unswitched and this is the main difference from conventional telephone communication. Data transfer rate up to 100 Mbps. In this case, a special network cable"twisted pair". The length of this cable determines the main cost of this type connections.
If we talk about the quality of transmission over a leased line, then it can be put next to ADSL technology.

LAN connection

Internet access via local network (Fast Ethernet) is carried out using a network card (10/100 Mbps) with a data transfer rate of up to 100 Mbps for the end user. But keep in mind that the cable modem bandwidth is shared among all users connected to the line, and therefore depends on how many users work at the same time. Therefore, the data transfer rate when using a cable modem in some cases may even be lower than when using ADSL.
To connect the user's computer to the Internet, a separate cable (twisted pair) is connected to the apartment, while the telephone line is always free. Access over a local area network with Fast Ethernet architecture provides the user with access to both the resources of the global Internet network and the resources of the local network.

Access via cable TV network

Cable TV (KTV) can be a good medium for transferring digital information. This idea is at the heart of cable modem technology. Cable television users can use their own cable television network to access the Internet, while the data reception rate is from 2 to 56 Mb / s. A cable modem is used to connect to a cable television network.
There are two connection methods:
cable modem is installed separately in each user's apartment;
a cable modem is installed in a house where several users of Internet services live at once.
To connect users to a common cable modem, a local network is used and common Ethernet equipment is installed for all. The advantages of accessing the Internet via cable TV are obvious: the subscriber receives a high-quality service from one source, which is convenient for him, because. Reduced time spent paying bills. But there are limitations - you can use inexpensive, affordable Internet access only in cases where a similar network has already been laid in the area and the building is connected to it.

WiFi access

Wi-Fi wireless technology (Wireless Fidelity) is a specific type wireless connection. Now almost every more or less modern phone and laptop has a receiver for this technology. Connection is made to "access points" with a range of up to 100 meters. There are few providers for this technology. most often this technology is used for private distribution of the Internet in public places, cafes, airports as an additional free service. Also, you can arrange Wi-Fi in your apartment to share the Internet with a neighbor and walk around the apartment with an Internet-connected laptop. The technology itself is quite fast, but public hotspots are often slow, because. overwhelmed by lovers of free internet.

The most common and modern today are, respectively, 802.11g and 802.11n technologies. The speed of equipment operating according to the 802.11g standard is quite enough for working on the Internet - most of the offered tariff plans does not exceed 25 Mbps. However, when transferring large amounts of information over internal local networks, the loss in speed of a cable connection can reach four or more times.

The way out in this situation is the 802.11n standard that is used in newer models WiFi routers and adapters. The main benefits of 802.11n are increased coverage and improved performance. In terms of performance: under favorable circumstances, data transfer rates of up to 100 Mbps can be obtained, which is close to the data transfer rate over a cable. In the conditions of the infrastructure of the house, the signal is attenuated, and real speed turns out to be lower.
The new 802.11n standard is compatible with any equipment that operates on 802.11b/g versions, but keep in mind that having devices of both versions on the same local network reduces network performance as a whole.

Mobile Connectivity


Mobile Internet. This includes connections from a mobile phone that supports one of the wireless technology standards, or from a computer using a wireless modem. Now almost any mobile phone has access to the Internet and at the same time can act as an Internet modem for a computer with the appropriate settings.

Old phone models connect to the Internet using slow and expensive GPRS technology, and new ones use faster ones: CDMA, UMTS (2G), HSDPA (3G), HSPA, LTE (4G), WiMAX. Their speed is often good, but the signal quality can be very different depending on the operator.

Networks of high-speed standards of the third and fourth generations is stationary and mobile connection and high speed mobile internet. To use the Mobile Internet service using these technologies, you must have a phone (smartphone, tablet) with a built-in 3G (4G) modem or a corresponding modem and a computer.

3G networks operate in the range of about 2 GHz, transmitting data to the subscriber at a speed of up to 14 Mbps and up to 6 Mbps from the subscriber. At this speed, almost any kind of content becomes available to you, including watching streaming video.

Finally, fourth generation technologies (for example, LTE) provide an average data transfer rate of up to 173 Mbps for reception and 58 Mbps for transmission, which makes it possible to provide the entire range of services - from high-speed Internet access to organizing videotelephony and receiving mobile high-definition television. Obviously, advertised data rates are possible under ideal conditions.
In practice, real speed wireless internet will, of course, be less. Coverage of 3G/4G networks even in large Russian cities leaves much to be desired. The coverage area is very uneven and depends on many factors: the remoteness of the cell tower, the presence of natural barriers (trees, tall houses), the height of the USB modem, etc.

Satellite internet access

satellite access it is practically not used in home networks due to the high cost of equipment, but it allows you to connect to the World Wide Web where there are no other Internet providers. Most often, a one-way connection option is used, in which the "dish" serves only as a receiver of incoming traffic, and data transmission (outgoing traffic) must be carried out via another, alternative channel - for example, via mobile phone with built-in 3G modem, via telephone (DSL) or cable (Ethernet) line.

Prices for satellite traffic very low, the speed depends on the provider and the tariff plan. Satellite Internet providers offer a very wide range of tariff plans, including unlimited ones.
The cost of satellite Internet will consist of two parts. The first is the provision of alternative access, such as modem access, the cost of which can vary widely. The second part will require more serious expenses and more complex work - you need to purchase and install a satellite dish, lay special cables, install a DVB-card in a computer, and perform configuration software. As a result, the total costs will amount to a tidy sum.

The task is simplified if you have satellite TV . In this case, you do not need to buy equipment specifically for satellite Internet, since the leading satellite TV providers also provide access to satellite Internet (for a fee).

Radio Internet

Radio Internet - technology of broadband access to the Network using a special antenna, provides a data transfer rate of 1 to 11 Mbps, which is shared among all active users.
This type of connection is used if the provider, for some reason, cannot extend the cable to the desired place to use the Internet, but can provide a wireless access point. For operation, direct visibility between the antennas of subscriber points is required. Range up to 30 km.

A special antenna is installed, the antenna horn is directed directly to the access point, the antenna is connected by cable to the computer's radio card and the Internet connection is configured. The quality and speed of data transfer will be acceptable, however, may depend on weather conditions. Of course, you will have to spend money on equipment, since it is quite expensive. The subscription fee is also quite high.

Continued in the article

If five years ago, not every owner of a home computer could boast of a modem, but today the modem has become the same integral attribute of a computer as a sound card or printer. Indeed, it is difficult to imagine a modern computer not equipped with a modem, because it is modems that allow connections between different computers within the World Wide Web. Not without reason, for all modern laptops, the presence of a built-in modem (as well as the presence of a network card) has become the de facto standard.

The ability to connect a computer to the global network gives it completely new qualities. However, it is unlikely that anyone will dare to dispute the advantages of joining this World Wide Web. You can talk about them for a long time, but it is better to see once than hear a hundred times. Therefore, let's follow step by step the path of a novice user, which leads him to his cherished dream - access to the Internet.

First of all, we note that although at present users are given relative freedom to choose how to connect to the Internet (we are talking about satellite Internet and cable modems with leased lines), however, connection via dial-up communication lines using analog modems is the most common (and sometimes and the only possible) option for home users. All other solutions have not yet received a sufficiently wide distribution not only in the regions, but also in large cities, and primarily because of unreasonably high prices. And therefore, high-speed methods of accessing the Internet (connection via dial-up lines does not apply to them) are currently available exclusively to corporative clients and not to ordinary users.

Therefore, in the future we will consider in detail exactly the connection to the Internet via dial-up communication lines using an analog modem.

In addition to being able to connect to the Internet (currently given function modem can be recognized as the main one), usually a modem allows you to connect two remote computers. This allows the user to copy necessary information from one computer to another, such as a desired program or document, or play a favorite game with a friend. Of course, all this can be done with the help of the Internet, but sometimes, at the most necessary moment, access to the Internet is temporarily blocked.

Another function of modems is to send and receive faxes. If you have a modem, there is no need to purchase a fax machine - the possibilities are the same, but it is cheaper.

In addition, many modern modem models are endowed with additional features and capabilities. For example, using a modem, you can determine the number of the calling phone (AON function), block calls from certain phone numbers, configure an answering machine, and perform many other actions.

Step 1. Choose a modem

So, to connect to the Internet, we first of all need (in addition to a computer, of course) the actual modem and a free telephone socket.

Choosing a modem is perhaps the most important step, so let's dwell on it in more detail. Unfortunately, there is no universal method for choosing a modem. The problem is that the quality of communication (and, consequently, the stability of the connection and the speed of the connection) is 90% determined by the characteristics of the switched communication line itself and only 10% depends on the type of modem used. As a result, if you are lucky and you have a “good” communication line, then almost any modem will suit you, providing you with a completely acceptable connection speed (48,000 bps or even 52,000 bps using the V.90 protocol). If the communication line is “unsatisfactory” (of which there are still many in the vastness of our Motherland), then in order to obtain a stable connection and an acceptable connection speed, you will not get by with the first cheap noname modem that comes across.

How to determine which line you have, which means which modem you need? If you live in Moscow (for other large cities, unfortunately, we do not have information), then you can safely buy literally any inexpensive modem. Almost all residents of Moscow can afford confident access to the Internet using the V.90 or V.34 protocol at a speed of 33,600 bps.

The fact is that in order to obtain a “good” communication line (by “good” we mean a line that allows communication using the high-speed V.90 protocol), three problems must be solved: organizing digital access from the subscriber to the switching center, upgrading the switch itself to ATS and creation of a digital transport network (a network of connecting lines between ATSs).

Back in 2001, Moscow completed the modernization of the unified digital transport network, which since then has been providing subscribers with digital access to the network using ADSL technology. As a result, even subscribers included in the analog station have improved communication quality when using digital access technology.

The only remark in this case is the following. If your modem cannot connect using V.90, then it is better to manually disable the connection using this protocol, since not all modems can switch from one protocol to another on their own, but all modems by default try to connect using the V.90 protocol. However, we will return to the features of setting up modems and connection protocols, but for now we will find out what to do for those who cannot boast of a “good” communication line. Naturally, we cannot give an error-free recipe for choosing a modem (and no one can), so we will limit ourselves to only general recommendations that will allow you to avoid many mistakes.

First of all, you should decide which modem to buy. Structurally, modems can be divided into two types: internal and external.

As a rule, external modems are more expensive than similar internal ones and have both certain advantages and some disadvantages. The undoubted advantage of external modems is the simplicity of their physical connection to a computer. To install an external modem, you do not need to open the computer case, the modem can be easily disconnected from one computer and connected to another. In addition, each external modem has a so-called indicator panel, which can be used to visually diagnose its operation. (In fairness, we note that many internal modems allow you to programmatically emulate a similar panel with indicators that can be displayed on the monitor screen.)

Another advantage of many models of external modems is the ability to manually adjust the sound volume. To do this, of course, you need the modem to have a built-in speaker. The sound played by the modem allows you to work with it in the mode of a regular phone - modems can do that too. But the main thing for which this sound is required is the diagnosis of the connection establishment process. Those who have ever accessed the Internet, that is, established a connection with a remote computer using a modem, know that after a connection is established, the modem starts making sounds similar to hissing. These sounds are nothing more than a conversation between two modems. Literally translated from English, such negotiations are called "handshake". During the handshake, modems determine the quality of the communication line, negotiate the speed of information transfer between them, and many other details.

Of course, internal modems also allow you to adjust the sound. However, you have to do this either programmatically, which is not always convenient, or by connecting the modem to the sound card and using the sound control on the speakers. In any case, the problem is solved, but the easiest way to do this is with an external modem with sound control.

Along with the listed advantages, external modems also have some disadvantages. First of all, the modem requires additional space on desktop which is constantly in short supply. In addition, any external modem will have to be plugged into the network using a special adapter - which means you will need another outlet. And the last thing: all external modems have a power button, and, of course, you will constantly forget to turn off your modem.

Internal modems, as the name implies, are installed inside the computer in one of the free slots on the motherboard. There are several types of slots on the motherboard: PCI, AGP, AMR and CNR (you can already forget about the ISA slot). Most modems currently produced are designed to be installed in a PCI slot.

Many modems with a PCI interface are called Soft or Win modems. Soft-modems are classic modems truncated in hardware. However, do not take the word "stripped down" as poor quality or unfinished. It's just that some of the functions that a modem usually performs are shifted to the central processor in Soft modems. Naturally, they do not get worse from this, but cheaper - no doubt. Not only Soft-modems can be truncated, but also other internal modems with a PCI interface, the so-called controller less. The difference between such modems and soft modems lies in the degree of their "cutback". Controllerless modems are less stripped down than soft modems, and in this respect they are more like regular modems. Therefore, having bought such a modem and installed it in your computer, you may never know what kind of modem you have: regular or controllerless. In any case, you won’t find out from the documentation, and the sellers in the store are unlikely to tell. There is an opinion that the use of controllerless and soft modems requires the use of a powerful processor, since these modems load it too much. However, the experience of repeated testing of such modems shows that this is not the case and there is no need to worry about the limitations on processor performance. The situation is more serious with the possibility of such a modem running various operating systems. As a rule, they all work under Windows 98, Windows Me and Windows XP, but can they work with another operating system- another question. Therefore, if you prefer to work in Windows 2000, then first of all you need to find out if this modem supports this operating system.

At the same time, it is controllerless and soft modems that allow a simple firmware update. The process of updating the modem's firmware is called "flashing". This is due to the fact that the firmware that controls the operation of a conventional classic modem is located in its ROM (Read Only Memory). They say that the firmware is “hardwired” into the ROM, and in order to change it, the ROM is “flashed”. However, the term "firmware" is only correct for regular modems that actually have ROM. For controllerless and modems, as a rule, there is no ROM (for Soft modems it is always missing). The control firmware itself is located in the computer's RAM and is loaded there every time the modem is initialized. Accordingly, there is no need to “reflash” such modems, and the process of updating the firmware itself consists in a simple procedure for installing new drivers.

The second important point that you should pay attention to when buying a modem is the way it is connected to a computer. As already noted, internal modems are inserted into a free slot on the motherboard, but external modems are connected to the computer using a special modem cable. The modem cable is usually sold with the modem. The vast majority of external modems connect to a computer through a serial interface called RS-232C. To do this, connect the cable to the serial port (COM port) of the computer. Most modern computers have two serial ports that have 9-pin connectors. Each such pin is called a pin, so these serial ports are also called 9-pin. In addition to 9-pin, there are also 25-pin serial connectors, so if you have this connector installed, you will need the appropriate cable. Nowadays, computers with 25-pin serial ports are no longer being manufactured, but if your computer is not new, then this is worth looking into.

On the modem side, the connector can also be different - either 25- or 9-pin. In this case, both pin connectors and connectors with holes into which pins are stuck are possible.

Some external modems can connect to the computer not via a serial interface, but via a USB port. The only advantage that such a connection gives is the absence of a power cable (and even then not for all models), since power is supplied to the modem via a USB port. Otherwise, such modems are absolutely no different from those that connect to a serial port.

The next important point that you should pay attention to when choosing a modem is the possibility of connecting it in parallel to a telephone set. Many models of both internal and external modems have two jacks: one, called LINE (line), is designed to connect the modem to the telephone line, and the other is used to connect the telephone to the modem. This method of connecting the phone is preferable, since in this case the modem blocks the telephone set using a relay during operation. Of course, the modem and telephone can be connected in parallel to each other using a special telephone socket for this, but guarantee good quality communication in this case is difficult. The problem is that the telephone set has a certain resistance, which can adversely affect the operation of the modem.

So, the first important tip: choose a modem with the ability to connect a telephone to it.

In addition to sockets for connecting a telephone set and connecting the modem itself to a telephone line (these sockets are called RJ 11), modems can have outputs for connecting a microphone and an external speaker. Such modems are called voice (Voice Modem). You can also use the connector for connecting an external speaker to connect the modem to the computer's sound card, so as not to connect additional speakers. Well, if you connect an external microphone to such a modem, then you can work with it in the same way as with a regular phone.

In addition to the described functions, almost all modern modems are able to work as a fax machine. With the help of a special program supplied with the modem or purchased separately, you can not only send faxes (text documents or pictures), but also receive them. Therefore, the full name of a modern modem may sound like Voice Fax Modem.

However, when choosing a modem, one must take into account the fact that the additional functions performed by modems are far from the most important thing. If you have to use the modem in voice mode and in fax mode, it is extremely rare if you have to. In 99% of cases, you will use the modem directly to transmit or receive data, that is, in the mode for which it is primarily intended. Therefore, too serious attitude to the additional functions of the modem is hardly justified.

The next thing to consider when choosing a modem is the supported protocols. Protocols are a specific set of rules for interaction between modems. Exists a large number of modem protocols, but two protocols are currently predominantly used: V.34/V.34+ and V.90. In this case, if the modem supports the V.90 protocol, then it automatically supports the V.34 protocol as well. The most important difference between protocols, from the user's point of view, is the maximum transfer rate possible. Data transfer rate is usually measured in the number of bits transmitted per second (bps). Such units of measurement are sometimes called bps, which in translation from English just means “bits per second” (bit per second). In the V.34+ protocol, the maximum transmit and receive data rate is set to 33,600 bps, while in the V.90 protocol, the data rate is limited to 56,000 bps and the data rate cannot exceed 33,600 bps. Thus, the V.90 protocol is asymmetric in terms of transmission and reception rates. But the most interesting feature of this protocol is that the ability to use it does not depend on the modem, but on the connection established between you and the Internet provider. Therefore, you can buy a very expensive modem that supports the V.90 protocol and not get the desired connection speed. V.90 requires at least (but not sufficient) your local telephone exchange to be digital. Otherwise, connection via this protocol will be impossible and purchasing a modem with support for this particular protocol will lose its meaning. You can find out what type your local telephone exchange (PBX) is, either by contacting the PBX directly, or by asking neighbors in the microdistrict who have already encountered a similar problem.

In addition to the above transmission protocols, there are other protocols - protocols for data compression and error correction. All modern modems support the protocols necessary for normal operation, so you should not worry about this.

Step 2 Installing the modem

After we have considered the basic rules for choosing a modem, you can proceed to the next step - installing the modem in your computer.

As a rule, detailed installation instructions are attached to all modems, but in most cases these instructions are written in English, which is not for everyone. Therefore, we present here detailed instructions modem settings, especially since all modems are installed almost the same way.

Regardless of the type of modem you have, the first thing you should do is turn off your computer. If you have an internal modem, then, depending on the type, it must be installed in the appropriate slot on the computer's motherboard. If your modem is external, then using the appropriate cable, you need to connect it either to the serial port or, depending on the type of modem, to the computer's USB port. After that, using a telephone cable (usually included in the kit), you need to connect the modem to the telephone socket, and the telephone to the modem. In order not to be mistaken, carefully study the marking of the sockets on the modem itself. Most often, the jack for connecting the modem to the telephone line is marked "LINE" or "JACK".

In the case of an external modem, after connecting to a computer, the modem must be connected to a power source and turned on. After that, you can turn on the computer.

Since all modern modems support Plug-and-Play technology, that is, they are self-configuring (the era of internal ISA modems, for which it was necessary to configure interrupt lines and addresses with jumpers on the board, is gone forever), when you boot your computer will detect a new device and try to install either independently or under your direction.

Unlike other devices, the modem does not require a driver (although many people mistakenly think so). Any modem works with a universal COM port driver built into the operating system. However, for the modem to work correctly, you must install the so-called inf-file (configuration file), which contains all the modem settings. These inf-files are attached to the modem on CDs. Actually, if the operating system has detected and correctly identified the modem, then this means that the required inf file is already included in the operating system and that the disk with the proposed configuration file is not needed. If you use the Windows XP operating system, then there are quite a few modems that this system does not know, since since the release of this OS, modem manufacturers have not yet had time to update their lineups. Exceptions are, perhaps, only new modems from ZyXeL. In this case, the operating system will launch the "Installation Wizard", which will ask you to specify the path to the directory with the necessary files. However, even if the OS installs the modem on its own, it often becomes necessary to change the version of the modem's inf file to a more recent one.

We will perform this operation together with you using the example of a 3Com Courier V.Everything (3453) modem with the Windows XP Professional SP1 operating system installed on the computer (the modem is installed in other operating systems in the same way).

To do this, from the Control Panel, launch the Phone and Modem Options object, and in the dialog box that appears on the Modems tab, click the Properties... button. The dialog box that opens (Fig. 1) with the name of the modem model will allow you to make all the necessary settings and update the inf file. In particular, to reinstall the modem driver, you need to go to the "Driver" tab and click on the "Update Driver ..." button. The "Installation Wizard" launched at the same time will allow you to install the desired inf-file from the specified directory.

After the modem or a new driver is installed, it is necessary to diagnose the modem's performance. To do this, in the previous dialog box, go to the "Diagnostics" tab and click on the "Query Modem" button. This starts the modem health test, the result of which will be displayed in a few seconds (Fig. 2).

Trying to understand the information displayed in the first stages is not worth it. What you will see is the modem's response to so-called AT commands. If the modem responds to the input commands, then everything is in order - it is correctly installed and working.

After the diagnostics, you can proceed to setting up the modem.

Step 3. Setting up the modem

The modem is configured in the already mentioned “Phone and Modem Options” dialog box. The first tab in this window, "Dialing Rules", allows you to set the necessary dialing parameters. To do this, click on the "Edit ..." button and in the dialog box that opens, set the "Pulse" switch, that is, specify the pulse dialing number (Fig. 3).

AT various countries telephones and modems may dial differently. In Russia, the so-called pulse dialing is adopted, and in the USA - tone dialing. Some modems can independently determine in which mode to dial a number; more precisely, if the tone dialing fails, then they repeat the dialing in a pulsed mode. However, most modems are not capable of this, and it is better to immediately set the pulse dialing mode. In addition, in the text field "Country / Region" ("Location"), you need to select "Russia" from the drop-down list (if this was not done during the installation of the OS), and in the text field "Area code" enter the telephone code of the city (for Moscow - 095). The modem will not use this information, but it is better not to leave these fields free. The rest of the options in this dialog box refer to the local PBX call mode and the long distance PBX call mode. Naturally, you should not set any parameters when calling from home.

After setting the dialing options, you can configure the modem itself. To do this, go to the already discussed dialog box with the name of the modem model and select the “Modem” tab. This tab (Fig. 4) allows you to programmatically set the volume of the modem speaker (if the modem supports it) and change the so-called maximum speed of the Com-port (Maximum speed). It is important that the maximum speed of the Com-port is not less than the maximum speed at which your modem is capable of operating. Usually, this speed is made as large as possible, for example, it is set equal to 115,200 bps.

The next tab - "Advanced" - allows you to fine-tune the modem. In the "Extra initialization commands" text field, you can enter the so-called initialization string, which consists of a set of AT commands. The modem initialization line (“Extra Settings”) is used to enter modem commands (AT commands) and allows you to effectively control the modem and adjust it to lines of various quality. It is recommended to prescribe the initialization string only after a thorough study of the modem documentation. The main problem is that different modems have a different set of commands, so you can set the optimal modem settings using these commands only by trial and error. However, the result may exceed all expectations. Due to the introduction of one command, an unstable and often interrupted connection can turn into a stable and high-speed connection.

On the same tab there is a button "Change Default Preferences ...", which allows you to open a dialog box that sets the parameters of asynchronous transmission, as well as set the number of data bits (Data bits), the number of stop bits (Stop bits) and parity (Parity). You should not change these settings, although even if you change them, nothing will change, because modems operate in asynchronous-synchronous mode and remove stop bits and parity bits from the sequence of incoming bits. In addition, the same dialog box allows you to change important options such as data compression and data flow control (Fig. 5).

The “Compression” data compression control option allows you to enable the modem data compression protocol during transmission. In this case, the transmitted data is automatically compressed - in the same way as it happens when they are archived. In many cases, enabling this option will increase the usable data rate, but this will not affect the precompressed data rate in any way.

Another parameter related to the transfer of data from a computer to a modem is flow control. Since the state of the telephone line can change unpredictably over time, the modem must be able to control the flow of data coming from the computer, that is, slow it down and enable it again. There are two methods of flow control - software (software) and hardware (hardware).

The first method, also called "XON / XOFF", is based on the fact that the modem sends one of two service characters to the computer at the right time: "XOFF", indicating that data transfer should be suspended, or "XON", allowing resume transmission. These service characters are transmitted over the same channel as the data.

The hardware method, also called "CTS/RTS", uses two separate control channels for the modem to communicate with the computer instead of two special characters. In the case of an external modem, these are two wires in the cable connecting the modem to the computer, and in the case of an internal modem, these are two pins on the modem board. If the modem is ready to receive a data stream from the computer, then it sends a CTS (Clear To Send) signal over the appropriate channel, and when the computer is ready to transmit this data, it issues an RTS (Ready To Send) signal.

The advantage of the hardware method of data flow control is that in this case no time is wasted sending special signals, which noticeably speeds up the transmission process. Therefore, for modern modems, this flow control method is preferred.

Step 4. Working with the terminal program

so, your modem is installed and configured, but this is not enough to establish a connection to the Internet. Before proceeding to the connection settings with the Internet provider, we recommend that you try out your modem in the terminal program mode. Such a program is part of the operating system and is called Hyper Terminal for Windows families. The terminal program is designed to control the computer's serial port. Since your modem either physically or virtually (if it is internal or connected via USB) interacts with the computer via a COM port, you can take full control over the modem using a terminal program. For this, so-called AT commands are used, which are accepted by the modem.

Working with a terminal program will also be very useful for those users who are not satisfied with the quality and speed of the connection provided by the default modem settings. In fact, the terminal program is the only tool for fine-tuning the modem for a specific line. The terminal program allows (if, of course, your modem supports it) to diagnose the line and, using the results of this diagnosis, try out various modem settings (you can always check the result).

In addition, a terminal program is used when you simply need to establish a connection to a remote modem to transfer files without using the Internet.

Thus, to begin with, launch the Hyper Terminal program (Programs/Accessories/Communications/Hyper Terminal) and in the New Connection window that opens, click the Cancel button. In the "File" menu on the toolbar, select the "Properties" item, which will allow you to configure the connection parameters in the corresponding dialog box (Fig. 6).

The only thing you need to do is to check that the connection is made through your modem (Connect using). You don't have to enter phone numbers, as you can do it from the command line as well.

After that, your program is ready to interact with the modem.

All commands (except commands "A/", "A>" and "+++") sent to the modem must begin with the prefix "AT" (Attention - "attention"), and they are executed by pressing the Enter key. Commands after the prefix are entered either with or without a space; however, multiple commands with the same prefix are allowed. There is no space between commands. The case of the letters used for the set of commands does not matter, but we (for beauty) will use capital letters in the future. If the modem correctly responded to the entered command, it will answer "OK". Try typing on the keyboard (use only the English layout) the prefix "AT". If at the same time nothing is displayed on the screen, then you need to turn on the echo. The "E1" command is intended for this (the "E0" command turns off the echo). So, by typing the command "ATE1", press Enter. After that, the modem's response - "OK" will appear on the screen, and all commands entered from the keyboard should be displayed.

Unfortunately, various models modems (depending on the controller and firmware) use different sets of commands. Therefore, it is simply impossible to describe all the possible commands. To do this, refer to the instructions that came with the modem. We will describe here only the basic set of commands (which is present in any modem model) and general principles their use on the example of the Courier V.Everything modem.

So, the first useful command that will come in handy is dialing. To do this, after the prefix "AT" the command "D" ("Dial") is entered and after the space the phone number is indicated. However, your modem will most likely start dialing in tone mode. To indicate to the modem that the number should be dialed in pulse mode, after the dialing command, you must enter the “P” (“Pulse”) pulse dialing command. As a phone number, you can choose the number of any provider (the main thing is that this number should have an answering modem, and not annoying neighbors). We will use the number 9951060 as an example (this is the phone number of a real Internet provider). Thus, the complete command format will look like this: AT DP 9951060.

Type this command from the keyboard and press Enter. After that, your modem will start dialing in pulse mode. If the provider's answering modem is not busy, then the modems will begin the process of establishing a connection, which can be understood by the characteristic sounds, reminiscent of whistling and hissing. When the connection process is completed, your modem will be able to display the set connection speed (in our example 48,000 bps) and the registration screen (if you use a different number, the screen content will also be different) (Fig. 7).

There are situations when dialing has to be done not in pulse, but in tone mode. For example, this situation is realized if the modem is connected to an internal office PBX, which understands only tone dialing. In this case, after the dialing command “D”, you must enter the tone dialing command “T” (“Tone”), that is: AT DT 9951060.

Another frequently used command when dialing a number is the "A>" or ">" repeat command. This command is intended to redial any command, but it is most commonly used to automatically redial a number. For example, if you know that the modem you are accessing is often busy, include the ">" command in the dial string, as in the following example: AT > DP 9951060.

In this case, the modem dials the number and, if the answering modem is busy, hangs up. After a 2-second pause, the dialing is repeated. This continues until the modem can dial out or until the number of retries reaches 10.

In some situations, dialing a number may not be as easy as it seems. For example, if you call from the office, then in addition to tone dialing, you will have to use an additional number to access the city line. For such cases, when dialing a number, additional commands are used: "," and "W":

• "," (comma) - defines a 2-second pause before continuing dialing. For example, when you enter the command AT DT 99.95101060, the modem dials 99 in tone mode, pauses for 2 seconds, and then continues dialing;
• "W" - this command is used in cases where it is necessary to wait for the second answer of the station (beep) before continuing to dial the number. For example, when you enter the command AT DT 99W95101060, the modem dials 99 in tone mode, pauses until a carrier signal (beep on the line) is detected, and then continues dialing.

So, you have learned how to dial the number of the Internet provider. However, as noted, a terminal program can be used by you to establish a connection to any remote modem, for example, to exchange files with your buddy without using the Internet. To do this, one of the modems must be in call mode (the one that dials the number), and the second modem must be in answer mode. In the case of an ISP, the modem you are connecting to is always in answer mode. If it becomes necessary to put your modem into answer mode (that is, it is assumed that they are calling you), then the “A” (“Answer”) command is used. This command puts the modem into forced answer mode, regardless of whether the modem has received an incoming call or not. Type the command "ATA" from the keyboard and press Enter. In response, you will hear the characteristic sounds emitted by your modem against the background of the carrier signal - this is your modem trying to establish a connection (it does not know that there is no one to negotiate with yet) and sends signals to the line. You need to use the “A” command as follows: wait for the prearranged call and enter the “ATA” command from the keyboard. Your modem and the calling modem will then begin the connection establishment process.

Speaking about the auto-answer mode, one cannot fail to mention such a command as setting the S0 modem register. Although registers are not AT commands, they allow you to effectively control the modem. In fact, the modem is configured precisely through registers, and entering any command leads to a change in the values ​​of certain registers. Many AT commands can also be executed by accessing the modem's registers, but working with AT commands is easier than working with registers.

The register is set using the ATS command r=n, where r is the register number and n is its value.

The S0 register determines the number of rings before the modem starts answering in auto answer mode. When S0=0, auto answer is disabled, and when S0=1, the answer occurs after the first ring.

To enable auto answer mode after the first call, enter the ATS0=1 command. To verify that the register is set correctly, issue the command ATS0? and press "Enter". In response, the screen should display the value 001, meaning that S0=1.

The following commonly used commands are the H0 and H1 line control commands. The "H0" (go on hook) command causes the modem to hang up, that is, to break the connection. The command "H1" ("Go off hook"), on the contrary, causes the modem to hang up.

Type the command "ATH1" from the keyboard and press Enter. In response, you will hear a line signal as in a regular phone - this is your modem picked up the phone. Enter the command "ATH0" next, and by doing so you will terminate the connection - your modem will hang up.

Also often used when working with a modem are speaker control commands - “Ln” and “Mn”.

The "Ln" command allows you to set the volume of the built-in speaker signal (some models of modems may not have this command). There are several options for the command: "L0", "L1", "L2" and "L3", differing in the level of the set volume.

The "Mn" command controls the state of the speaker, that is, turns it on or off.

With the "M0" syntax, the speaker is always OFF.

With the syntax "M1" (default value), the speaker is on until the modem detects a carrier, that is, until you hear your modem dialing and establishing a connection (negotiating with another modem).

The "M2" syntax sets the speaker to ON during dialing and during data transmission. Such a constant mode of turning on the speaker can be useful in order to determine by ear the moments of occurrence of retrains (renegotiations between modems) during data transfer.

Last possible variant this command - "M3". In this mode, the speaker turns on as soon as the last digit is dialed and remains on until the carrier is detected.

Well, the last basic command that we will focus on here is the “In” command. This command (depending on the number n) displays information about the modem on the screen, and in some models of modems, connection statistics. For example, the "I0" command displays information about the product code, the "I1" command displays the checksum stored in the ROM, and so on. Enter the command AT I1I2I3I4I5I6I7I8I9I10I11 from the keyboard, and you will see which of these commands are supported by your modem and which are not (in the latter case, the modem will display an error message on the screen - "ERROR").

And now, having finished reviewing the syntax of the main commands, we can proceed to the stage of setting up the modem for a specific communication line. At the same time, we emphasize once again that we have described only a small part of all supported commands, however, we did it intentionally, since the supported commands and their syntax differ for different modem models.

To take advantage of the possibility of entering commands during the connection process, a special control sequence “+++”, called the Escape sequence, allows. This command is entered without the AT prefix and switches the modem from data mode to command mode. To enter the Escape sequence, you must type +++ on the keyboard and wait 1 second. You do not need to press the Enter key - the modem will execute the command itself and respond: “OK”. After that, you can enter commands. In order to switch back to the data transfer mode, the "AT On" command is used. Thus, if you were in command mode, then executing the “ATO0” or “ATO1” command switches the modem to data transfer mode, in which it does not respond to input commands (the only exception is the Escape sequence). In this case, the "ATO0" command leads to a standard return to the data transfer state (zero can be omitted, that is, the "ATO" command is equivalent to the "ATO0" command). The “ATO1” command, in addition to returning to the data transfer mode, initiates the retrain procedure (the procedure for reconfiguring modems).

Enter the command to dial the provider's number from the keyboard and after the connection is established, enter the Escape sequence to exit the command mode:

We deliberately switched our modem to command mode, since the next logical step is to register a user (entering Login and password), but in this case this is not necessary. Since the connection with the provider's modem has already been established, you can use special commands to assess the quality of the connection, for which you need to put the modem into command mode.

Unfortunately, line diagnostics using a modem depends on the specific modem model. Command syntax for different modems is different; moreover, not all modems allow diagnosing the line. Modems Courier, ZyXeL, Inpro and some others have this property. We will describe the diagnostic process for the Courier V.Everything modem.

After entering the command mode, type the command "ATI6", which will allow you to display the diagnostic information of the block exchange in the communication session (Fig. 8).

These statistics represent the parameters of the V.34 protocol. The first value corresponds to receiving data, and the second - to transmitting. In the given characteristics Special attention it is worth paying attention to only a few characteristics and values: Modulation, Carrier Freq., Symbol Rate, Recv / Xmit Level, Near Echo Loss and Far Echo Loss:

• Modulation (modulation type) - the protocol on which the connection was established for receiving (V.90 for receiving and V.34+ for transmitting);
• Carrier Freq. - carrier frequency in hertz. For the V.90 protocol, this value is meaningless (NONE), and for data transmission, the frequency is 1829 Hz;
• Symbol Rate - symbol rate. When transmitting data, a symbol rate of 3200 CPS is selected, and for receiving data using the V.90 protocol this value is 8000 samples per second (this value is standard in the V.90 protocol, but completely different modulation methods are used than in the V.90 protocol. 34);
• Recv/Xmit Level (-dB) - received/transmitted signal levels. Varies when transmitting (Xmit) from 0 to -20 dB and from -8 to -50 dB when receiving (Recv);
• SNR (dB) (Signal to Noise Ratio) - signal to noise ratio. The larger this value, the better. Determining parameter for the modem to select the transmit/receive rate;
• Near Echo Loss (dB) and Far Echo Loss (dB) - Near and far echo loss levels. When the modem line is negotiated with the local PBX and with the remote one, a reflected signal, called an echo, inevitably occurs. This signal is returned back to the modem, but as noise. The higher the loss of the near and far echo, the weaker the reflected signal and, accordingly, the better.

Well, the last important command (unfortunately, most modems do not know how to do this) the “ATI16” command. This command graphically displays the frequency response of the communication line (Fig. 10).

Knowing the connection statistics, you can try to adjust the modem settings for specific conditions. Of course, the statistics obtained in our particular case indicate only one thing: no additional settings are required, since all the characteristics of the line are simply excellent. In general, if the modem establishes a connection using the V.90 protocol, then it hardly makes sense to try to improve something.

If the situation is not as encouraging as in the above example, then you can try to adjust the modem settings. The most common use in this case is to limit the connection speed. Although it may seem paradoxical, it is the limitation of the connection speed that often leads to an increase in the real (physical) data transfer rate and to a more stable connection. The fact is that many modems do not always correctly determine the quality of the line and sometimes overestimate their capabilities, establishing a connection at a higher speed than necessary. As a result, frequent disconnections and repeated retracements can be observed, leading (if they are correctly handled) to a decrease in the connection speed. In addition, since "broken" data packets are transmitted under such conditions, retransmission requests are initiated from the receiving modem. As a result, the transfer rate useful information decreases as the modem starts to repeat. So, the first step is to adjust the connection speed. Look in the modem documentation for a command that allows you to limit the maximum possible connection speed. At the same time, options are possible when setting a possible range of speeds is allowed (that is, limiting the connection speed "from below" and "from above". The main thing is not to set a hard connection speed. For example, in Courier V.Everything, the "& Nn" command, depending on the value of n causes the modem to connect at a fixed rate, but if "&Un&Nn" is used instead, it sets the range of possible connection speeds ("&Un" sets the lower speed limit, and "&Nn" the upper one).

Although the method we have described for adjusting the modem settings is not the only one, it is the most effective.

Another way to tune the modem is to adjust the symbol rate. Here it is necessary to make a small digression to explain what symbol rate is and why it is so important.

As you know, analog modems use various types of modulation (in particular, amplitude-phase modulation is used in the V.34 protocol) to encode useful information. In this case, the carrier frequency of the signal undergoes a change in amplitude and phase of the signal at a certain rate, called the modulation rate. Each discrete state of the signal corresponds to a certain value of the phase and amplitude, and taking into account the fact that there are several possible values ​​of the phase and amplitude of the signal, several information bits can be encoded in one discrete state (one symbol). For example, if the protocol provides for 4 different signal phases and 4 different amplitudes, then there are 16 different combinations of phases and amplitudes in total. This allows a sequence of 4 bits to be encoded in one state. Thus, in the considered example, the information or bit rate will be greater than the transmission rate of individual symbols. Therefore, in addition to the bit rate, the concept of a symbol rate is introduced, which coincides with the signal modulation rate.

The V.34 protocol provides for several possible symbol rates. Symbol rate is measured in characters per second, or, according to the English abbreviation, CPS (Characters per Second). The protocol provides six possible symbol rates (Symbol Rate): 2400, 2743, 2800, 3000, 3200 and 3429 CPS. Note that the symbol rate determines the width of the spectrum of the transmitted signal and, from this point of view, could also be measured in hertz.

The carrier frequency of a sinusoidal signal can also have several different values: 1600 Hz, 1646, 1680, 1800, 1829, 1867, 1920, 1959 Hz. Naturally, there is a strict relationship between the symbol rate and the carrier frequency, and each symbol rate, except for the highest one, corresponds to two different frequencies of the carrier harmonic (Table 1).

The position of the spectrum of a signal located symmetrically about the carrier frequency is determined by both the symbol rate and the carrier frequency. The symbol rate determines the bandwidth of the spectrum, and the carrier frequency determines the minimum and maximum frequency of the signal. The minimum signal frequency is less than the carrier frequency by half the symbol rate, and the maximum frequency, on the contrary, is more than the carrier frequency by half the symbol rate. For example, if the symbol rate is 3000 CPS, then at a carrier frequency of 1800 Hz, the signal spectrum ranges from 1800 - (3000/2) = 300 Hz to 1800 + (3000/2) = 3300 Hz. At the same symbol rate, but at a carrier frequency of 2000 Hz, the signal spectrum lies in the range from 500 to 3500 Hz.

The use of not one, but two carrier signal frequencies makes it possible to shift the signal spectrum towards higher or lower frequencies within the bandwidth of the communication channel. This feature allows you to avoid dangerous sections of the bandwidth of the communication channel, where, for example, noise or excessive signal attenuation can be observed.

Some modem models allow you to adjust the symbol rate selection, thus providing the ability to shift the signal spectrum within the bandwidth of the communication channel. To determine if symbol rate adjustment is needed, look at the frequency response of the link. Ideally, the shape of the frequency response should not contain blockages at the edges of the passband. If such blockages are present, for example, in the high-frequency region, then it is better to immediately prohibit the use of higher symbol rates in order to narrow the signal spectrum. In addition (which, again, not all modems can do), it is desirable to be able to select a carrier, that is, set a priority for choosing a higher or lower carrier frequency.

The Courier V.Everything modem adjusts the symbol rate using the S54 register. This register is bit-settable and has two possible syntaxes, so we need to elaborate on that. The first option for setting a bit-settable register has the syntax ATSr.n=x, where Sr is the register to be set, n is the bit of that register, and x is the value of the bit (0 or 1). Each register is assigned 8 bits (from 0 to 7). For example, if we want to enable the fifth, fourth and third bits in the S54 register, then the command must have the following syntax: ATS54.5=1S54.4=1S54.3=1.

The second possible syntax for setting bitwise registers is to assign some decimal number to the register, which, when converted to binary, represents the enabled bits as "1" and the disabled bits as "0". In the example above, the sequence of bits on and off would be written as: 00011100. If we consider this sequence as a representation of a number in binary code, then when we switch to decimal code, we get the number 56. Therefore, the syntax of the command will look like this: ATS54=56.

Each bit in the S54 register (there are 6 such bits in total) corresponds to one or another symbol rate. When a bit is enabled (set to one), its corresponding symbol rate is disabled for use. The correspondence table between register bits and symbol rates is shown below (Table 2).

Thus, if there are cutoffs in the frequency response of the line in the high-frequency or low-frequency region, try to disable the use of the highest symbol rate of 3429 CPS (ATS54=32) or the speed of 3429 CPS and 3200 CPS (ATS54=48).

If your modem additionally supports the choice of carrier frequency (the Courier modem cannot do this), then you can also try to shift the modem's signal spectrum towards less frequency response distortion.

We have described the two most effective ways to tune the modem to a specific communication line. Of course, there are other methods, but, as a rule, they do not bring tangible results, although in some cases they may be useful. Such methods include the following:

• changing the power level of the signal transmitted by your modem;
• changing the modem sensitivity threshold;
• prohibition of full and fast retrains;
• selection of the filter "Pre-correction" (Pre-emphasis);
• choice of trellis decoder.

A change in the power level of the transmitted signal can indirectly affect the level of the so-called far echo (reflected signal), which, from the point of view of the modem, is noise. Therefore, you need to carefully increase the signal level so that the modem does not “choke” on its own echo.

It has been experimentally established that modems are very critical of the ratio of the received signal level and the near echo level, therefore it is highly desirable that the Recv level exceed or at least be equal to the Near Echo level. In the example above (see Figure 9), the received signal level is -28.6 dBm and the transmitted signal level is -17.3 dBm. Given that the near echo loss is 13 dB, we get the near echo level: -17.3 - 13 = -20.3 dBm, that is, slightly higher than the received signal. In this case, to reduce the level of the near echo, you can try to slightly reduce the level of the transmitted signal, but this may adversely affect the receiving modem: the received signal may be too weak for it. Therefore, the optimal solution is a kind of golden mean between the conditions in which your modem and the remote modem are located.

Changing the modem sensitivity threshold (which can be implemented by additionally amplifying the received signal) also has a negative side: along with the useful signal, the noise level is also amplified, therefore, from the point of view of the signal-to-noise ratio (the most important characteristic of the line quality), this possibility does not lead to to a positive result.

It is advisable to use the prohibition of retrains when your experience suggests that the characteristics of the line do not change over time, which means that renegotiation of the connection parameters does not make sense.

Regarding the last two possibilities - the choice of the pre-correction filter and the choice of the type of trellis encoder - the following remark can be made. The ability to manually set the pre-emphasis selection is extremely rare (it is implemented in some versions of ZyXEL modems) and is used only if it seems to you that the modem itself selects this filter incorrectly. Here, of course, we need to make a little clarification regarding the pre-correction filters and the V.34 protocol.

Precorrection as a way to improve noise immunity is defined in the V.34 protocol. Precorrection is a special way of introducing distortion into the transmitted signal. The fact is that almost any telephone channel distorts the amplitude-frequency characteristic of the signal to one degree or another, as a result of which some frequencies are attenuated, while others are amplified. This leads to the fact that on certain transitions between symbols the signal is amplified, while on others it is attenuated. As a result, the characters can shift and slightly “call in” on each other (inter-symbol interference). In order for such symbols to be correctly perceived at the receiving end, it is necessary to compensate for these distortions. Compensation on the receiving side is possible with a frequency equalizer. However, this solution has a serious drawback: the equalizer is able to amplify some frequencies and attenuate others, but along with the amplification and attenuation of useful signals, noise also undergoes a similar transformation. A more preferable solution is when the amplification of some frequencies and the attenuation of others occurs not on the receiving, but on the transmitting side. Thus, when transmitting a signal, pre-distortions are specially introduced into it, which compensate for transmission distortions. Therefore, precorrection is pre-emphasis introduced into the transmission path based on one of the fixed frequency patterns. There are 11 such templates (masks) in total, and each of them has its own index. These patterns suggest a rise in the high-frequency components of the spectrum, which should compensate for the distortion introduced by subscriber and trunk lines.

To more accurately equalize the frequency response, modems also use another type of pre-distortion - precoding. Unlike pre-correction, which is performed according to one of the fixed patterns, pre-coding implies a way to adjust the frequency filter on the transmitting side. The modem receiver calculates the optimal signal correction coefficients and returns them back to the transmitter, which builds the desired transmission filter based on them. While some modems (notably the Courier V.Everything modem) allow you to disable precoding using a certain case, you should not do this.

Another important difference in the V.34 protocol is its implementation of a special trellis modulation (TCM) technique. In all other protocols using TCM modulation, in order to improve noise immunity, one extra trellis bit is added to the sequence of bits per symbol. A trellis bit is formed by performing a convolution operation (convolutional coding) on ​​a part of the bits in a group and allows, using special decoding algorithms, to detect and correct transmission errors. The signal constellation structure formed in this case (the distribution of possible signal states in phase and amplitude), or, in other words, the signal-code structure (SCC), is called two-dimensional (2D). In the V.34 protocol, one trellis bit is added per two consecutive symbols, and the TCM modulation is called four-dimensional and is denoted as 4D. To calculate the trellis bit, coding schemes for 16, 32, and 64 states of the convolutional code are used. So, if 4D-64S appears in the connection statistics given by many modem models, this means that a four-dimensional CCM with a 64-position convolutional encoder is used.

Some modem models allow you to select the type of encoder to use by setting a special register bit by bit. So, in the Courier V.Everything modem, register S55 is intended for this. However, it is not necessary to expect that the communication quality will change when choosing a different encoder than the modem itself installed. The fact is that for your modem the received information is much more important, and the encoder can only be changed to transmit.

By learning how to use a terminal program and mastering the rules for using AT commands, you can adjust the modem to a specific communication line by finding the necessary sequence of AT commands. Further, this sequence of commands (excluding the dialing command) must be written to the modem's initialization line. In this case, each time before establishing a connection, the modem will execute a given sequence of AT commands.

In order to assign an initialization string to the modem from the “Control Panel”, launch the “Phone and Modem Options” object and in the dialog box that appears on the “Modems” tab, click the “Properties…” button. In the dialog box that opens, go to the "Advanced" tab (Fig. 11). In the corresponding text field, you can enter the desired sequence of commands.

Step 5: Set up a network connection

The terminal program itself only allows you to establish a connection to a remote modem, but our ultimate goal is to set up the modem to surf the Internet.

The Internet is a global computer network, where there are their own laws of communication between computers. In order for the data sent by your computer to the network to be correctly understood by other computers, it must be provided with certain service information.

In order to supply the sent data with service information and be able to correctly interpret the received information, it is necessary to establish the so-called network protocols by associating them with the modem. The network protocol breaks the sent sequence of bits into blocks of a certain length, called frames. Service information is added to each frame, containing the addresses of the sender and recipient, and much more. When receiving such frames, the computer, guided by the rules defined in the network protocol, collects individual frames together, removing (after appropriate analysis) service information from them. For the user, the service information added to the frames is uninformative and useless, but without this important information, computers simply cannot understand each other. The amount of service information depends on the operations performed and can be 15-20% of the transmitted useful information. By the way, this is one of the reasons that when copying compressed files, it is never possible to achieve a speed that would be equal to the maximum speed of the protocol.

The Windows XP operating system independently installs all the necessary protocols to establish communication with providers via a modem. However, the user must independently specify all the settings that will be used to communicate with the provider. To do this, from the "Control Panel" run the "Network Connections" utility and create a "New connection" ("Create a new connection"). This will launch the New Connection Wizard and open the New Connection Wizard dialog box (Fig. 12).

By clicking on the "Next" button, go to the next dialog box and select "Connect to the Internet". After that, go to the next dialog box (using the "Next" button) and select the "Set up my connection manually" item.

In the next dialog box (again using the "Next" button), select "Connect using a dial-up modem" (Create a connection using a modem).

In the next window, in the text field, you must specify the name of the connection to be created. This can be, for example, the Internet or the name of your provider (Fig. 13).

In the next window, you must specify the provider's phone number: all seven digits are entered in a row, that is, without spaces and dashes (Fig. 14).

In the last window, the most important information is entered: login and password (Fig. 15). If you are already registered, then enter your login and password in the appropriate fields, and if not, then follow the instructions received from the provider. For example, when connecting using an Internet card, you must specify a guest name and password that will allow you to enter the provider's website for further registration.

In the same dialog box, there are three more important items:

• "Use this account name and password when anyone connects to the Internet from this computer" (use an account for all users);
• "Make this the default Internet connection" (use the default connection);
• "Turn of Internet Connection Firewall for this connection" (activation of the Firewall for this connection).

The choice of the first item is relevant if several users are registered on the computer and you do not want the connection you created to be available to all users.

The second item indicates that the connection being created will be used by default when connecting to the Internet, and the choice of the third item activates the Firewall built into the operating system. For those who are unfamiliar with this concept, let's explain that Firewall is the simplest (in this case) means of protection against attacks on your computer via the Internet.

After a new connection is created, double-click on it, after which a dialog box will open that allows you to establish a connection with the provider at the specified phone number (Fig. 16).

Before pressing the Dial button, which causes the modem to start dialing, double check that the connection is set to pulse dialing. To do this, click the "Properties ..." button and in the dialog box that opens, check the checkbox next to the "Use dialing rules" item (Fig. 17).

If the checkbox is checked, then the "Dialing rules" button will be activated. Click it and in the new window select the "Edit" mode (button Edit). In the next dialog box, check that pulse dialing is installed (the “Pulse” item is checked).

If everything was done correctly, then after pressing the Dial button, the modem will start dialing the number and establish a connection with the provider (the corresponding window will be displayed on the screen, in which you can monitor the connection with the provider).

If the negotiation stage ended with a positive result (the modems agreed on everything), then the line “Verifying user name and password…” will appear in the window (Checking the user name and password). After the username and password are verified, the network will be logged on. After completing the registration process on the network, the window displaying the connection process will close, and an icon will appear in the lower right corner of the monitor, indicating that the computer is working on the network. If you double-click on this icon with the left mouse button, a window will appear in which the current connection speed will be displayed, or rather, the speed with which your computer can receive data from the Network (Fig. 18).

In our example, the connection speed is 52,000 bps (bits per second - bits per second), which indicates a very good link.

Topic 2.3. Global network Internet

Topic 2.4. Browsers - Web browsers

Topic 2.5. Email. Mail applications

Topic 2.6. FrontPage 2003 program

Topic 2.7. Creating a Web Page

Topic 2.8. Website creation

Topic 2.9. Business on the Internet

Topic 2.10. Internet resources

Global Network Technologies

2.3. Global networks Internet

2.3.2. Ways to access or connect to the Internet

Currently, there are many ways to connect to the Internet from connecting a computer via an analog modem to connecting using high-speed technologies.

The method of connecting a computer to the Internet depends on the level of services used by the user, which he wants to receive from the provider (service provider), on the speed and quality of data transfer. The services provided by the Internet include: E-mail, WWW, FTP, Usenet, IP-telephony, streaming video, etc.

Ways to connect to the Internet can be classified into the following types:

• dial-up access;
• access via leased lines;
• broadband network access (DSL - Digital Subscriber Line);
• Internet access via local network;
• satellite Internet access;
• Internet access using cable TV channels;
• wireless technologies.

Dial-up access typically uses an analog modem and an analog telephone line, but dial-up access over the ISDN (Integrated Services Digital Telephone Network) is also used. An ISDN adapter is used to connect a PC to a digital network with integrated ISDN services. In addition, dial-up access to the Internet can be carried out using wireless technologies: mobile GPRS - Internet and mobile CDMA - Internet.

Access via dedicated communication channels implies a permanent communication channel from the premises with a computer to the switch owned by the ISP (provider). This access method ensures that the computer is connected all 24 hours a day. There are several connection options: via leased lines with speeds of 2400 bps - 1.544 Mbps. and via permanent virtual frame switching channels with speeds of 56 Kbps - 45 Mbps. For large organizations, this method of connecting a local network to the Internet is the most efficient.

A promising method of connecting to the Internet, both for individuals, and for companies is a DSL broadband network. Digital Subscriber Line - a family of digital subscriber lines designed to organize access over an analog telephone network using a DSL / cable modem. This method provides data transfer up to 50 Mbps.

Access to the Internet over a local area network with Fast Ethernet architecture provides the user with access to the resources of the global Internet network and the resources of the local network. The connection is made using a network card (10/100 Mbit/s) with a data transfer rate of up to 1 Gbit/s on trunk sections and 100 Mbit/s for the end user.

Satellite Internet access (DirecPC, Europe Online) is popular for users in remote areas. Max speed data reception up to 52.5 Mbps (real average speed up to 3 Mbps).

Cable TV users can use cable TV network channels to connect to the Internet, while the data reception rate is from 2 to 56 Mb / s. A cable modem is used to connect to a cable television network.

Recently, wireless methods of connecting to the Internet have become more and more popular.

Last mile wireless technologies include:

• WiFi;
• WiMax;
• Radio Ethernet;
• MMDS;
• LMDS;
• mobile GPRS - Internet;
• mobile CDMA - Internet.

For more information on how to connect to the Internet, see the page

    The history of the Internet began in 1969, when the first network node called ARPANet was created at the University of California, USA. Gradually, the network grew, developed, improved, and by the middle of the 80s, separate local networks (later called the Internet) began to connect to it. A set of protocols has been developed for data exchange. TCP/IP(Transmission Control Protocol / Internet Protocol), which replaced the protocol originally used in ARPANet NCP(Network Communication Protocol). Protocols of the TCP / IP family made it possible to work both in local networks (LAN- Local Area Network), and global ( WAN- Wide Area Network).
    In 1986, on the basis of the already existing ARPANet network (with a data transfer rate of up to 56 kbps), the creation of a new high-speed network of 13 nodes was started, each of which was represented by a local network of high-performance IBM computers, the main purpose of which was packet routing . Moreover, when a node failed, the network continued to function, due to the fact that the functions of the failed node took over the remaining nodes. Within a few years, thousands of individual networks and computers were connected to this network. And then millions.

    The simplest and most widespread access to the Internet for a long time was access via analog telephone lines, characterized by low speed and reliable connection. Today, this access method has been almost completely superseded by leased-line connection technologies, which allow:

• get high speed and reliability of data transfer.
• through various IP-based application solutions to achieve
reduction of expenses for other types of communication (IP-telephony, various conferences, etc.).
• have a constant round-the-clock connection to the Internet without occupying a telephone line.
• ensure the placement of WWW, FTP, PROXY servers, etc. inside the office.
• improve document flow with territorially remote divisions of the company.
• build a unified system of access control and information security.

    The Internet is a worldwide global network that unites a huge number of individual computers and computer networks. Such a network cannot exist without unified rules for the construction and functioning of its individual elements.

    According to the TCP/IP specification, each computer on a network is assigned a unique 32-bit address (IP address). For convenience of perception, such addresses are written as four decimal numbers from 0 to 255, separated by dots - 192.168.12.2. Their distribution is handled by a special Internet Organizing Committee (IANA).
Part of the address space is allocated for use only in local networks (private network address) So, for example, the address range 192.168.0.0 - 192.168.255.255 (And also IP addresses from the ranges 0.0.0.0/8, 14.0.0.0/8, 169.254. 0.0/16, 192.0.2.0/24, 192.88.99.0/24, 198.18.0.0/15, 224.0.0.0/4 are reserved for use in private networks, see RFC 3330.) That is, there are no computers with such addresses on the global Internet (and never will be), and this range is used only in local networks.

    Since it is difficult for an ordinary person to remember sets of numbers that have no meaning, a special Internet name system is used - Domain Name System (DNS), thanks to which it is possible to assign a so-called domain name to each IP address, for example - yandex.ru. Domain names are registered special organizations and services.

    When your computer (or a group of computers with a single point of connection) connects to the Internet, it becomes the same element of the global network as others already included in it. It obtains an IP address and access to the DNS service using the technical and software resources of an organization specialized in providing Internet access services - Internet Service Provider or simply provider.

In small local networks, the most commonly used address range is 192.168.0.0 - 192.168.0.255. (class C network) . The first address is used as the address of the whole network (network number), and the last one is used as the broadcast address, when the sent packet is received by all computers.

    The exchange between computers on the network is carried out in blocks called packets, and each packet includes the IP address of the receiving computer and the IP address of the transmitting one. And if, for example, 192.168.0.0 is used as the address of the receiving computer, no one will receive such a packet, and if 192.168.0.255, then everyone will receive such a packet.

In addition to the address, the network mask is set in the TCP/IP protocol settings of the computer. It is a way to indicate to TCP/IP protocol tools the starting and ending IP addresses of a network. The mask is structured like an address with high bits set to 1 and low bits set to 0. (255 in hexadecimal = FF).

The AND operation of the IP address and mask determines the network address:
192.168.0.1 & 255.255.255.0 = 192.168.0.0
The OR operation of an IP address and an inverted mask specifies a broadcast address:
192.168.0.1 + 0.0.0.255 = 192.168.0.255

Broadcast transmission is used in cases where it is necessary to transmit a data packet to all computers on the network, for example, to control the distribution of IP addresses and bind them to specific network cards.

    If necessary, establish a connection with a computer outside our network, ie. having an IP address that is not in the range specified by the network address and mask (for the purposes of this topic, let it be a computer with, for example, an IP address of 212.248.0.3) is used routing- a way to send packets between computers belonging to different networks.
To implement routing, a special device must be present in the network - router(router). Simplified, the router can be represented as a specialized computer with two (at least) network interfaces, one of which is connected to our network, and the other to the network in which the computer is located, for example, with the address 212.248.0.3.

    Upon receipt of each next data packet, the router analyzes the destination address and determines through which of the network interfaces to forward it. If the destination node is reachable locally, direct transmission to the addressee is performed (direct delivery - Direct Delivery), if not, then the router determines which of the neighboring router nodes known to it is closer to the recipient and sends the packet to it through the appropriate network interface (indirect indirect delivery). delivery).

The next router follows exactly the same algorithm. And, sooner or later, according to the "from node to node" (Hop-By-Hop) principle, the data will be delivered to the addressee by the last router in the chain. To successfully complete a network route lookup, routers generate, store, and update special routing tables.

Thus, the procedure for connecting to the Internet is reduced to obtaining a reachable IP address for a host and the address of the router closest to it. In other words, the whole problem of connecting any computer to any Internet site is to obtain a data transmission channel (preferably inexpensive and high-speed) to the router on the Internet access site of the selected provider. How can such a channel be organized? Today there are several options:

• Using fiber optic communication line. It is characterized by the highest throughput and noise immunity. High price.


• Using satellite channels. The option is also quite expensive and can be used to connect geographically remote subscribers when laying a physical line is impossible or economically unprofitable.
• Using access by radio channels. Wireless Internet access is developing quite rapidly, and it is possible that it will soon become one of the most common. In particular, in the United States, a part of the territory with a poorly developed infrastructure is planned to be covered with a new 4G wireless network (WiMax)


• Using physical (dedicated) communication line. Allows you to get acceptable data transfer rates at minimal cost, but requires the availability of urban telecommunications and a limited distance to the provider's access node.

    When connecting to the Internet via a leased line, an ordinary telephone pair of wires is most often used as a data transmission medium, and there are technologies that allow the same pair to be used in parallel for both Internet access and a regular phone. There are other options, less common, when a cable television network or even an alternating current network is used as a data transmission medium.

    To implement a connection using a telephone pair, you need to rent private line from one of the local telephone operators. This line is leased to the client and connects the equipment of the subscriber (your) with the equipment of the provider, bypassing the switching equipment of the telephone exchange. All work on organizing a private line is carried out by specialists from the technical service of the provider and the local telephone exchange.
As channel-forming equipment, special modems are used to organize a digital channel. The selected channel type determines the modem type. Most modern modems have an Ethernet output and can connect directly to your local network.




• Channel Access frame relay- An ordinary copper telephone pair is used for connection. Simultaneous use of a pair for telephony and channel organization is excluded.
• Channel Access ISDN- "digital network with integrated services" (Integrated Services Digital Network). ISDN services are not only Internet access, but also a set of other services (digital telephony, voice mail, etc.) that can be received by a client when connected to this network. You can find out the possible set of services and their cost from a specific provider and specify when concluding an agreement. ISDN is a long-established standardized technology. The connection is made via ordinary copper telephone lines and provides digital signal transmission throughout the connection.
• Access via digital channels using technology xDSL- the possibility of obtaining high speeds data transmission at a relatively low cost of equipment using a conventional telephone network. The data transmission medium is ordinary telephone cables, and the transmission speed depends only on the quality and length of the line connecting the user and the provider.
    In the xDSL acronym, "x" is used to represent the first character in a particular technology name, and DSL stands for DSL Digital Subscriber Line ( Digital Subscriber Line). xDSL technology allows you to transfer data at speeds that are significantly higher than those available even to the best analog modems. Moreover, many xDSL technologies make it possible to combine high-speed data transmission and voice transmission over the same conventional copper pair. The existing types of xDSL technologies differ mainly in the form of modulation used and the data rate, which can reach 52 Mbps for VDSL technology (on a good link and distance up to 1.5 km). At present, the most popular technology ADSL(Asymmetric Digital Subscriber Line - Asymmetric digital subscriber line). ADSL is a technology that allows you to turn an ordinary pair of telephone wires into a high-speed data transmission path. ADSL line connects subscriber ADSL modem, with the provider's equipment installed at the local telephone exchange (the provider's DSL or DSLAM hubs). In this case, three information channels are organized - a "downward" data transfer stream ( downstream) with an exchange rate of 1.5 Mbps. up to 8 Mbps, "upstream" data transfer ( upstream) with an exchange rate of 0.64Mbps. up to 1.5 Mbps. and a conventional telephone channel ( POTS- Plain Old Telephone Service). Moreover, the telephone channel is allocated using filters, which guarantees the operation of your phone even if the ADSL connection fails. . As a result, you get round-the-clock access to the Internet while maintaining the normal operation of a regular phone.

    More detailed information about xDSL technologies you can get on the site xDSL technologies.

As an example of a connection diagram using the above technology, I took a diagram from the website of the Moscow provider "Comstar"



As you can see from the diagram, the incoming telephone pair of your existing telephone number is switched to the input of a special device - splitter. The splitter does not require a power source and has 2 outputs - the first one for connecting a telephone set (instead of which the splitter was turned on) and the second one for connecting an ADSL modem.
The connection is made through ordinary telephone jacks. An ADSL modem (in this connection option CISCO 827-4V is used) actually performs not only the functions of a modem, but also a router with network address translation (NAT) and is something like a specialized computer based on a RISC processor with its own operating system (Cisco IOS). This device provides not only digital channel Internet access, but also provides hardware-based voice compression and its transmission over IP (VoIP technology).




Cisco 827 on the rear wall has several connectors. One of them (ADSL port) connects the device to the second output of the splitter either directly or using wiring through the telephone socket




Another connector is used to connect to the network (Ethernet port) either through the Hub / Switch, or to network card directly. The “Console port” connector is technological and is used to connect console equipment when setting up the software. A separate group of connectors (Telephone ports) is used to connect up to 4 regular telephones, which are provided with an ADSL connection.

An article about Internet access using ADSL technology.

AT modern world There are a large number of possible ways to access the Internet. We invite you to talk about the traditional (even slightly outdated for many), which, meanwhile, stands out for its reliability and prevalence. We are talking about dial-up Internet access. In the article, we will reveal the features of such a connection, its advantages, necessary components and other important characteristics.

What's this?

Dial-up Internet access is sometimes referred to as dial-up access. Another name is dial up. From English literally - "dialing", "dialing".

Dial-up Internet access is:

• One of the ways to connect to the Internet, where a dial-up telephone line is used for communication between modems. A simple, acceptable solution for both legal entities and individuals who do not need constant access to the Internet.
• A service that allows a computer, using only the public telephone network and a modem, to connect to an access server or another computer to initiate data exchange sessions. For example, to access the same Internet.
• Internet access on your home computer.
• Modem remote access to corporate network using a special point-to-point PPP protocol.

Required Equipment

Thus the list necessary equipment for dial-up Internet access is simple:

• Personal computer or laptop.
• Modem.
• Telephone line.

Access Benefits

Switched Internet access is the following indisputable advantages:

• Possibility of using the telephone line already installed in the apartment for Internet access.
• Represents access to the Internet wherever there are telephone lines for wired devices.
• Low cost of both the connection itself and the equipment. In other words, the user in this case practically does not bear any costs. The cost of modems is acceptable. It should be noted that they are already built in by the manufacturer in some models of modern laptops.
• Ease of connection.
• Ease of payment. Some providers offer subscribers to buy special cards. To activate the payment, it is enough to indicate the series, the number of such an acquisition. In other cases, the service is provided on credit. The bill for it comes in receipts for the use of a wired telephone.
• In the developed countries of the world, dial-up remote access is already provided to subscribers absolutely free of charge! This is a great opportunity for people with a modest budget to enjoy pastime in the Global Network.
• In many remote rural settlements dial-up access to the Web remains to this day the only way to access the Internet.

Access Disadvantages

Dial-up access using dial up technology is still an outdated method of communication, relatively long ago replaced by more functional and high-speed ones. Let's pay attention to its annoying shortcomings:

• Limited data transfer rate. The most "sick" point. If modern networks are capable of providing information transfer rates at the level of 100 Mbps - 1 Gbps, then this is impossible for dial-up access. Maximum Opportunities modern models- 56 Kbps However, most devices operate at 30 Kbps. Moreover, the network performance is also affected by the following parameters: modem functionality, presence/absence of interference in the telephone network itself.
• Payment is charged by the operator according to the time that the user spent on the network. In this case, the amount of transmitted/received data (traffic) is not taken into account.
• The provider sets a specific place for a communication session. After this period, the user is disconnected. For the next connection, you need to make a call. This (depending on the provider, the location of the user himself) can take from a few seconds to an hour.
• While using the Internet with this access method, it is not possible to talk on a wired telephone.

Varieties of access

Dial-up access types can be divided according to the data compression protocol used:

• V.42, V.42bis, V.44 standards. They allow you to transfer compressed files at a speed of 160 Kbps, text - up to 320 Kbps.
• ISP. The working bandwidth is about 350 Kbps. Maximum - up to 1000 Kbps. The main disadvantage of the protocol is the loss of quality of transmitted data. It is not uncommon for providers to refer to this type of dial-up access as "high-speed dial-up".

Connection Availability

Dial-up access (dial up, "daylap", slang - "dialup") - one of the most affordable ways to connect to the Internet. In fact, a modem connection does not require any additional infrastructure other than the telephone network.

As we have already noted, such a connection (via a telephone line and a modem) remains the only one available today for many rural settlements both in our country and in other countries of the world. Conducting broadband access there is impossible because of the low population density, and because of the inconsistency of many factors with the requirements of such a network.

Dial-up analog access is sometimes the only way for people with limited financial resources to use the Internet. He is distinguished low prices for using the service. More and more global telecom operators offer their subscribers the opportunity to "day-lap" for free.

Reasons for the lack of demand for the service

However, despite the technological and financial accessibility, dial-up access is losing its positions every year, becoming unclaimed by the population. The reasons are in the shortcomings we have identified. For example: a relatively large time for dialing, determining the cost of a service by the time spent on the network (and not by the amount of traffic).

The biggest dissatisfaction, based on user feedback, is that dial-up access, in fact, is a non-permanent, temporary connection that can be broken at any time. If you work on the Web, play games on the server, then the need to reconnect, the sudden disconnection of the connection negatively affects your productivity.

Performance

And one more important characteristic of access. As we already mentioned, the highest theoretical speed of modern modems today is 56 Kbps. But in fact it does not exceed 40-50 Kbps. Average indicators are even lower - 30 Kbps.

The following also affects the data transfer rate: the quality of the device itself - the modem, the noise level of the telephone line. Under the action of negative factors, it can drop to a completely frivolous 15 Kbps.

And one more negative moment. Dial-up access also features high response latency (up to 400 milliseconds). And such a characteristic makes it impossible, for example, to conduct video conferences, online games. However, according to user reviews, many managed to play Sims, Star Wars Galaxy, Warcraft, and so on using a modem.

Broadband Replacement

Already at the beginning of the 2000s, the usual Internet access via a modem began to be replaced everywhere by a more functional broadband software. DSL technologies. The minimum data transfer rate here was 128 Kbps. dial-up preference broadband internet became ubiquitous and because of the prices for services.

Moreover, many sites today offer such voluminous data (three-dimensional images, audio, video files) that old modems cannot handle. But, I must say, dial-up access has not yet lost its positions everywhere. It is still relevant in areas where high-speed data transfer is not required.

You also need to remember that it is not economically profitable or simply impossible to conduct broadband networks somewhere. Despite the fact that wireless technologies have long declared themselves, it is very difficult to organize such an infrastructure in practice. The reason is low profitability, high implementation cost, poor communication quality.

Operators are also increasing the attractiveness of the once-popular dialup economically. For example, in Russia, if you only wish to view email, read text files on the Internet, communicate in instant messengers, pay about 150 rubles a month for a daylap.

Dial-up access to the global network today, unfortunately, is already considered something outdated. At least in some regions of the globe, it remains the only way to the Internet. Many users today stop at it because of the low price of such a service.