Advantages.

S Do not take up additional space

S Do not push the nearby connection to the electrical circuit

S Much cheaper than foreign ones S Do not borrow standard

subsequent ports of the computer

S It is important to install a modem on your computer without your permission

The underdogs.

The number of days the LED indicator is not

allows you to quickly remove

Information about the modem

To install the modem you need

Uncover the system unit

Frequently arising conflicts with others

possess, for example, s

video adapter or mouse

Management including programs,

and with a guilty mercy for her

susunennya, it might happen

plug in the entire computer

The modem is always turned on, if not

computer __________________

External modems.

Advantages.

It is extremely simple to connect a modem to

computer

LED indication allows

quickly find out about the modem

The ability to quickly transfer the modem

one computer to another

If you ask for help, you can just stick it out

life to the modem, not to interfere with the computer

The modem can be connected practically up to

whatever the computer _____________

The underdogs.

Occupies additional space on the desktop

Requires additional connection to the electrical circuit.

There are two types of telephone lines.

a) Switched lines- this is, in fact, the primary telephone line. Koristuvach will cooperate. The connection is established through the GTS. The transmission speed does not exceed, say, 28800 baud.

b) Visible lines- to ensure a permanent connection with the network, especially for which purpose

koristuvacha.

The replacement of visible lines is even expensive, so the cost of connections is as stable as possible

The transmission of such lines is very high, and the distribution rate is low.

The phone lines are buzzing with disgusting rage. This is to ensure consistency with the information that is being transmitted. Sometimes one solution may reveal all the information. See:

1) Non-intelligent modems- remove the modulation and demodulation functions.

2) Intelligent modems- based on microprocessors, complex functions are created: control and correction of errors that occur during data transmission, compression and encryption of data, etc.

One of the most important characteristics of a modem is transmission speed. Vaughn is dying in beats - how many beats per second. Most current modems can operate at speeds of 14,400 baud or higher

After the liquidity of the trace, the respect of the pharmaceutical company was gained. More than half of the commercial modems in our country use US Robotics modems. The following companies also produce excellent modems: Motorola (they are expensive), ZyXEL, GVC, MultiTech, INPRO (which produces IDC modems).

4. Mist divide the measure into parts that transfer information from one part to another, only in the case where such transfer is effectively necessary, since the computer addresses are intended to belong to another part of the measure. Thus, the place isolates the traffic of one side from the traffic of others, so that:

1) greater productivity of data transmission at the edge

2) reduces the possibility of unauthorized access to data, so that the data remains without the need to leave its premises.

Well, modems and modulation-demodulation...

The term modem is short for the common computer term modulator-demodulator. A modem is a device that converts digital data that comes from a computer and analog signals that can be transmitted over a telephone line. Everything on the right is called modulation. The analogue signals are then converted back into digital data. The one on the right is called demodulation.

The scheme is very simple. The modem from the central processor of the computer receives digital information in the form of zeros and ones. The modem analyzes this information and converts it into analog signals that are transmitted through the telephone line. Another modem receives these signals, converts them into digital data and sends this data to the central processor of a remote computer.

Modulation type which allows you to select frequency and pulse modulation. Pulse modulation is used throughout the entire territory of Russia.

Analog and digital signals

Telephone calls are made through analogue (sound) signals. An analog signal identifies the information that is transmitted continuously, while a digital signal identifies the data specified at a specific stage of transmission. The transition of analogue information to digital information means that there is a continuous flow of information.

On the other hand, digital data shows less noise and scratching. On computers, data is stored in individual bits, the essence of which is 1 (start) or O (finish).

As you can see graphically on the right, analog signals are sinusoidal waveforms, while digital signals are represented as straight-wave waveforms. For example, the sound is an analog signal, so the sound changes from time to time. Thus, during the process of sending information over the telephone line, the modem takes digital data from the computer and converts it into an analog signal. Another modem, located at the other end of the line, converts these analog signals to output digital data.

Interface

You can use the modem on your computer using one of two interfaces. Nimi:

MNP-5 Serial RS-232 interface.

MNP-5 Chotirikontaktny telephone cable RJ-11.

For example, the external modem is connected to the computer via an additional RS-232 cable, and to the telephone line via an additional RJ11 cable.

Squeezed tributes

The transmission process requires a speed greater than 600 bits per second (bps chi bits per second). This is due to the fact that modems are responsible for collecting this information and transmitting it further through a folding analog signal (a very clever circuit). The process of such transfer itself allows for the transfer of large amounts of data simultaneously. It is understood that computers are more sensitive to the information that is transmitted, and therefore receive it more widely, even below the modem. This arrangement creates additional time for the modem, which indicates that these data bits need to be grouped and compressed to them by other compression algorithms. So two so-called press protocols appeared:

MNP-5 (transmission protocol with compression level 2:1).

V.42bis (transmission protocol with compression level 4:1).

The MNP-5 protocol tends to slow down during the transmission of both small and large files, while the V.42bis protocol is limited to compressed files, which may speed up the transfer of such data itself.

It is necessary to say that when transferring files, since the V.42bis protocol is no longer available, it is better to enable the MNP-5 protocol.

Correction of pardons

Correction of data transfers is a method, using any modem, to test the information that is being transferred, for the presence of any defects in it that have occurred during transmission. The modem breaks this information into small packets called frames. The modem that transmits carries the so-called check sum to each of these frames. The modem then checks whether the control sum of the sent information confirms. If not, then the frame is overpowered again.

The frame is one of the key terms of transmission. Under the frame, understand the basic block of data with a header, information and data attached to this header, which complete the frame itself. The added information includes the frame number, data on the size of the block being transmitted, synchronizing symbols, station address, error correction code, data on the changeable volume and the name of the indicator Start of transmission (start bit)/End of transmission (stop bit). This means that the frame is a packet of information that is transmitted as one whole.

For example, in Windows 98, the settings for setting up the modem have an option Stop bits (Stop bits), which allows you to set the number of stop beats. These stop beats are one of the different types of so-called boundary service beats. The table bit indicates the end of the cycle for asynchronous transmission (the hour interval between the characters that are transmitted varies) of data in a short-hour cycle.

Protocols MNP2-4 and V.42

Regardless of the fact that correction of data can improve data transmission on noisy lines, this method will ensure reliable communication. Protocols MNP2-4 and V.42 are protocols for correction of errors. These protocols indicate how modems verify data.

Like data compression protocols, data correction protocols are required by both transmitting and receiving modems.

Flow control or Flow Control

During the transmission process, one modem can re-send the data, while another modem can receive the data. Thus, this method of flow control allows you to inform the modem that it is receiving information about those, so that the modem at any time slows down the reception of data. Flow control can be implemented both at the software level (XON/XOFF - Start signal/Stop signal) and at the hardware level (RTS/CTS). Flow control on the software level is effected through the transfer of the song sign. After terminating the signal, another character is transmitted.

For example, in Windows 98, the settings for setting up the modem have an option Data bits which allows you to set data bits that are detected by the system for the selected serial port. The standard computer character set consists of 256 elements (8 bits). Therefore, the option is 8. If your modem does not support pseudographics (more than 128 characters), please select option 7.

There, in Windows 98, the modem parameters have the option Use flow control

which allows you to determine the method of implementing data exchange. Here you can correct possible errors that occur during the transfer of data from the computer to the modem. Accepted installation XON/XOFF means that the processing of the data stream is carried out using software methods through standard ASCII characters, which is used to send a command to the modem downgrade/upgrade transfer.

Carrying out the flow on the software level is only possible if the serial cable is installed. Flow control components at the software level regulate the transfer process, such as the transfer of certain characters that may fail and cause the session to end. It is explained that other line noise can generate an absolutely similar signal.

For example, when streaming on a software level, binary files cannot be transferred, and some similar files may contain kernel characters.

Through flow control at the RTS/CTS hardware level, information is provided more quickly and securely than through flow control at the software level.

FIFO buffer and microcircuits of the universal asynchronous interface UART

The FIFO buffer is similar to a transshipment base: while data is received by the modem, part of it is sent to the buffer capacity, which gives the first win when switching from one task to another.

For example, the Windows 98 operating system supports only 16550 series Universal Asynchronous Receiver Transmitter (UART) chips and allows servicing with a FIFO buffer. For further assistance the ensign Use FIFO buffers requres 16550 compatible UART (Vikorystuvati FIFO buffers) You can lock (prevent the system from accumulating data from the buffer capacity) or unlock (prevent the system from accumulating data from the buffer capacity) the FIFO buffer. By pressing the button Advanced, you are eager for dialogue Advanced Connection Settings Options that allow you to configure the connection to your modem.

S-registry

The S-registry is located in the middle of the modem itself. These registers themselves store settings that, in this or other ways, can influence the behavior of the modem. The modem has a lot of registers, and only the first 12 of them are respected by standard registers. S-registries are installed in such a way that you force the command to the modem ATSN=xx, where N indicates the register number that is being installed, and xx indicates the register itself. For example, through the SO register you can set the number of calls for dialing.

Interchange IRQ

Peripheral devices communicate with the computer processor through IRQ. Interruption with signals that interfere with the processor, slow down the other operation and transfer the data to the so-called collector, interrupt. When the central processor detects an interruption, it simply terminates the process and passes the interruption to a middleware called the Interrupt Handler. Everything on the right works regardless of whether there was a problem in the work of either process or not.

Information port link or just COM port

The serial port is very easy to identify. You can profit by simply marveling at the roses. The COM port is a 25-pin connector with two rows of contacts, one of which is connected to the others. In this case, practically all subsequent cables are connected with 25-pin connectors on both sides (in other cases, a special adapter is required).

COM port (serial port) is the port through which the computer communicates with devices, such as a modem or Misha. Standard personal computers have several ports.

Ports COM 1 and COM 2 are defined as external ports by the computer. After all the subsequent ports, there are two IRQ interruptions:

COM 1 bindings to IRQ 4 (3F8-3FF).

COM 2 bindings to IRQ 3 (2F8-2FF).

COM 3 bindings up to IRQ 4 (3E8-3FF).

COM 4 bindings up to IRQ 3 (2E8-2EF).

Here, conflicts may arise from external ports of other input-output devices 1/0 or controllers may suffer from the same IRQ interruptions.

Therefore, having assigned the modem a COM port or IRQ, you must check other devices to see if they have

the same successive ports and interrupt.

It is necessary to say that connections to the telephone line in parallel with the modem and the device (especially Caller ID) can even reduce the power of your modem. It is therefore recommended to connect phones through the designated socket in the modem. Only in this case we switch them off from the line during operation.

Flash memory of your modem

Flash memory is permanent memory or PROM (permanent memory device that reprograms a memory device), which can be erased and reprogrammed.

Reprogramming is supported by all modems, in which there is a row “V. Everything”. In addition, "Courier V.34 dual standard" modems support software upgrades at any time. Options The input to the ATI7 command has the V.FC protocol. Since the modem has a German protocol, upgrading in Courier V. Everything is carried out by replacing the daughter board.

There are two modifications of Courier V. Everything modems - with the so-called supervisor frequency of 20.16 MHz and 25 MHz. Until each time, you need to check your firmware versions, and they are interchangeable, then. The firmware for the 20.16 MHz model is not suitable for the 25 MHz model, as well.

NVRAM memory programmed by koristuvach

All settings for the modem are carried out until the values ​​of the NVRAM registers are set correctly. NVRAM - a memory programmed by the computer that saves data during active use. NVRAM is used in modems to save configurations that will be transferred to RAM when turned on. NVRAM programming can be done in any terminal program using additional AT commands. A new transfer of commands can be either extracted from the documentation of the modem, or extracted from the commands in the terminal program AT$ AT&$ ATS$ AT%$. Write factory settings to NVRAM with hardware data control - AT&F1 command, then make adjustments to the modem setup together with a specific telephone line and write them to NVRAM with the command AT&W. Further initialization of the modem must be carried out through the command ATZ.4.

Application software for data transfer

Data transfer programs allow you to connect to other computers, BBS, Internet, Intranet and other information services. Your manager may have a large selection of similar programs. For example, in Windows 98 you can use the very nasty Hyper Terminal terminal client.

If you are experiencing problems related to connections to other modems

From the very beginning it is necessary to evaluate the nature of the line of connection. For which, after a successful session, before restarting the modem, enter commands ATI6- diagnosis of ligament, ATI11- connection statistics, ATY16- Amplitude-frequency response. When removing the data, you need to write it to a file. After analyzing the captured data, it is necessary to change the current configuration and then write it to NVRAM behind the command AT&W5.

Russian telephone lines and imported modems

The choice of modems today is great, and the difference in their performance is even significant. Transmission speed above 28800 bps on Russian telephone lines is unattainable. More than 16,900 bps can be obtained only because the Internet service provider runs the same PBX lines before your phone connects. In other cases, working on the Internet is extremely tiring, and the gaps at the typical (and not soon to be achieved) speed of 9600 bps will be transformed into a major problem. Therefore, for stable data transmission during phone line recodes, you need a high-quality modem that costs at least 400 US dollars.

Which modem is better - internal or external?

The internal modem is installed in an open expansion slot on the computer’s motherboard and connected to the built-in housing unit, and the external modem is a stand-alone device connected to the computer via a standard serial port.

The design of the skin has its advantages and disadvantages. The internal modem occupies the system bus slot (and it, as a rule, is not installed), it is important to follow its operation through the presence of indicators, and the same model that is being described is fundamentally not suitable for portable computers such as notebooks that are lightweight profile body i In most cases, do not use expansion sockets. At the same time, the internal modem costs a few tens of dollars, is cheaper than existing analogues, does not take up space on the table and does not create a tangle of wires. The external modem transmits that the receiving computer has the latest serial port control (UART) microcircuits installed. UART microcircuits appeared in the first PCs, and then it became clear that exchanging data through the last port is a very complex operation and should be entrusted to a special controller. Since then, a number of UART models have been released. In computers such as IBM PC and XT, and also in most cases with them, the 8250 microcircuit was replaced, in AT it was replaced by UART 16450. Most computers based on i386 and i486 processors until the end were equipped with controller 16550, where they showed up internal hardware buffers. drawing", and today the standard is the UART 16550A - a microcircuit that is similar to the previous one, but with the shortcomings removed. The presence of buffers in all microcircuits, except for the rest, leads to the transmission of data through the serial port At speeds of 9600 bit/s it becomes unstable ( MS Windows Wikipedia lowers this threshold to 2400 bps).

If you need to connect a high-speed external modem to a computer that uses an old UART chip, then change the multicard or add a special expansion card (which will take one bus slot and add another This modem is of great importance). Internal modems do not have this problem - the COM port is not affected (more precisely, the COM port is not affected). The infection of internal modems reveals another advantage, also related to the speed of operation. Due to the V.42bis specification, data may be compressed by approximately four times during transmission, so the modem, which operates at a speed of 28800 bps, is required to retrieve the data from the computer or send it to new Swiss speed 115600 bps, so є interface for the PC serial port. However, 28,800 bps is not the limit for a telephone line, where the maximum lies around 35,000 bps, and on digital lines (ISDN) the capacity exceeds 60,000 bps. However, in this situation, the last port will become the “bottleneck” of the entire system, and the potential capabilities of the external modem cannot be realized. At the same time, modem manufacturers are releasing models that could connect to a larger parallel port, but it is obvious that devices sold at a time are impossible to achieve.

At the same time, a lot of modems can be upgraded to work at high speeds, even to the point of being able to run on ISDN. But everything fits into the boundary barrier on the side of the computer, which for an internal modem is significantly more than 4 MB/s (ISA bus bandwidth). Before speaking, all ISDN modems are internal. True, everything will be the same tomorrow (and maybe the day after tomorrow), but today we can say one thing: choose the type of device you need - no functionalities between internal modems and their external ones There are no taxes.

What a modem vibrati ta yak yogo vibrati

The modem may be unique. Your modem may be similar to other modems. This means that the modem must maintain the maximum number of standards in order to correct errors, data exchange methods and their compression. The most advanced standard is V.32bis for modems with a speed of 14000 bps. For modems with high speed 28,800 bps, the standardized protocol is V.34.

Moreover, it is necessary to note that modems that provide data exchange speeds of 16800, 19200, 21600 or 33600 are not standard.

The exact correction of amends is not to blame but the program. Everything is sewn into the modem by the printer.

About the outside and about the inside. The external modem is connected to the serial port through a special cord. Such a modem, as a rule, contains a volume regulator, information indicators, a life unit, etc., and other devices. If you are a professional, then it is all the same for you, which modem you choose - internal or external. Rest assured, a good internal modem through special software completely eliminates all the features of an external modem.

Do not buy purely imported modems. These little ones don’t get along well on our old lines. Buy non-certified modems, so that they are specially installed for our telephone exchanges.

Russia has very little such choice. This market was captured by two companies: ZyXEL from sunny Taiwan and U.S. Robotics in the USA. The modems of the remaining companies are chosen by the master (Courier), the first ones are chosen by all others, and all the same companies who choose the so-called over-the-top ZyCell protocol.

Well, choose Courier. And believe me, this is not advertising.

Modemi (the name comes from the combination of two words – modulator and demodulator)- these are devices that allow you to organize connections between computers that are located on the same station. If you have access to a computer, you can organize connections between them, via serial port, parallel port, USB, Blutooht. However, such a connection is less likely to occur at nearby stations, which are significant for the port. At large distances, the signal weakens and special devices are required that can change the signal visually, allowing the signal to be transmitted over large distances. What is the purpose of a device called a modem - from the word Modulator-DEMOdulator. The modulator allows you to convert a digital signal into an analogue one, and the demodulator allows you to create a gateway to convert from analogue to digital form(For more precise sensory modulation, it involves changing the characteristics of a non-carrying signal (usually low-frequency periodic vibrations) with a high-frequency carrier signal, which allows the transmission of necessary information). Demodulation is the process of seeing an information signal from the totality of non-carrier and information signals). Faxing operates on practically the same principles; modems that are available with fax transmission capabilities are called fax modems. Modems can be internal (inserted into expansion slots), external (connected to COM, LPT, USB ports or with a border cable to the RJ-45 connector of the computer's connection card, depending on the external power supply unit), installed on a laptop or at You can see cards for connecting to a PCMCIA connector for laptop computers(the remaining one is also called the expansion card PC Card and practically outdated. Currently the standard is being vicorized ExpressCard From connections to buses USB and PCI Express ). In the near future, there will be a widespread expansion of droneless modems (called modules or gateways), which will support the connection lines of steel operators (they have lost the greatest popularity USB modem) . The operating principles of all devices are the same.

Modems can be used analogі digital. Analog modems (dial-up) became the first to be used. Because the speed of data transmission through these modems was low (up to 56 Kbit/sec), they began to switch to digital modes (from an operating frequency of 4 KHz to 2 MHz and a similar speed of up to several megabits/sec). In addition, during the transmission of data over an analog modem, it is not possible to communicate.

Most companies used telephone networks to transmit data. In order to be able to use the digital type of transmission, it is necessary for the sender and receiver to have a digital telephone exchange. In addition, there is no need for a paired telephone and a security alarm on the telephone line. Many people use analog modems.

Main characteristics of modems:

- internal or else external. An internal modem is a card that is inserted into the connectors on the motherboard. This modem is inserted as a primary card, but you need to connect the card as indicated below. An internal modem is usually cheaper than an external one. It takes up space on the table and does not occupy the next port of the computer.

External modems (new) are connected to a USB connector, PCMCIA or ExpressCard and do not require additional life, as long as it is removed from the connector.

The external modem (old) is connected to the serial port and is located in an adjacent housing. This type requires connection to the electrical circuit via a transformer. Before this, you need to add that it does not take up an expansion slot, making it easy to transfer from one computer to another.

Encouragement standardі transmission speed;

Size of RAM and flash memory.

Additional capabilities of modems: digitizing the voice and converting it into an analog signal for speech when transmitting data; Fax; automatic telephone number assignment; auto-show; electronic secretary and other capabilities that telephone devices have.

As a rule, the current modem may phone number, as we will guide you. This: negotiations with a number of subscribers; Turning on the microphone instantly; inclusion of external Guchnomovites; memory of subscriber numbers; subscriber rings again; auto dialer; automatic number assignment; memory of numbers and ringing hours; the appointment of another jingle at the hour of prayer; protection from unnecessary calls; recording of deleted notifications; auto-show; distance therapy; on the phone panel there may be buttons with functions: auto-repeat, listening to unnecessary notifications, connecting the phone, turning on external speakers, etc.; There may be indicators on the telephone panel that indicate the robotic mode when picking up the handset; There may be a display with information about the entrance and exit calls, the hour of service, etc.; voice dialing, the operator calls the subscriber's nickname by voice, and the modem connects with the number; speed dialing, dialing a number using one or two buttons; auto attendant, answer calls that were found when communicating with another subscriber; collection of statistics about the number of calls that were found, their numbers, the hour of the call and the duration of the day; Other functions, for example, dialing the same number at the beginning of the day, alarm clock, etc.

If the modem is frozen, you can see that there is no need to remove the data (remove and insert), in which case you do not need to reset the computer. In addition, there is an indication, which can be used to determine the status of the modem.

Digital modems.

At this hour the decal is being vikorized formats: ADSL, HDSL, IDSL, ISDN, HPNA, SHDSL, SDSL, VDSL, WiMAX and drone-free modems with wireless wireless communication (Wi-Fi). They are often called xDSL (Digital Subscriber Line).

ADSL(Asymmetric Digital Subscriber Line - asymmetric digital subscriber line) appeared in 1987 and is one of the first and most extensive digital data transmission formats. Allows you to send data from the client up to a speed of 16 to 640 kbit/sec (standards 0.5, 0.8, 1.2, 1.3, 3.5 Mbit/sec, and receive data at a speed of 1.5, 0.8, 5, 8, 12, 25 Mbit/ sec). So, since the buyer takes away the data, and does not send it, then the amount of liquidity is not perceived by the buyer, except for the video connection. Therefore, over time, other types of formats began to appear using coaxial cable (cable TV, speed up to 100 Mbit/sec) and Ethernet connector (local connection with speed up to 1 Gigabit/sec). In lower European countries, the ADSL standard has become the standard for denying access to the Internet.

The primary telephone line is used to pass frequencies from 0.3 to 3.4 KHz, the ADSL modem sets the lower frequency for the output stream to 26 kHz, and the upper frequency to 138 KHz, and for the input stream from 138 kHz to 1.1 MHz. In this way, you can talk over the phone, send and receive data instantly.

Prote, the first modems did not allow you to comfortably communicate with the phone, because the high-frequency part of the modem introduced extraneous noise into the telephone (and also interfered with the transmission of data). To make matters worse, they began to install a frequency filter (Splitter), which lets extra low frequencies through to the phone.

HDSL (H igh D ata rate digital Subscriber Line High-speed digital subscriber line) is divided up like the 80s. It uses not one, but two pairs of wires and has a speed of 1.5 Mbit/s (American standard) or 2.0 Mbit/s (European standard) and allows you to transmit a signal up to 4 kilometers, and in some cases up to 7 kilometers. Vikorist is important for an organization.

IDSL(ISDN Digital Subscriber Line - IDSN digital subscriber line) allows data transmission at a speed of 144 Kbps.

ISDN(Integrated Services Digital Network - digital network with integration of services) was announced in 1981 and has a transmission speed of 64 Kbit/sec.

HPNA(Home Phoneline Networking Alliance - the name of the association of non-profit industry companies) works with either standard telephone or coaxial cable. The remaining standard (3.1) allows data transmission at speeds of up to 320 Mbit/s, with standard 2.0 – 10 Mbit/s.

SHDSL (Symmetric High-Speed ​​DSL-Simetrichna Kosokoshvidkizna DSL) Permanent Pass on the Odniy Parіvyv Zi Shvidkistya VID 192 kbit up to 2.3 MBIT/s, and in pairs of airborne vIDSTSTANS up to 6 km.

SDSL(Symmetric Digital Subscriber Line) uses one pair of cables with speeds ranging from 128 to 2048 Kbps. The distance is 3 to 6 km.

VDSL(Very-high data rate Digital Subscriber Line) has a high speed of data transmission from 13 to 56 Mbit/s at the limit of up to 11 Mbit/s at the return line up to 1.2-1.4 km .

WiMAX(Worldwide Interoperability for Microwave Access) is a drone-free connection in the range from 3.5 to 5 GHz for the 802.16-2004 standard (or WiMAX fixes) and 2.3-2.5, 2.5-2.7, 3.4-3.8 GHz for the 80 WiMAX standard). There are many similar parameters with Wi-Fi, but it is also possible to transmit a signal to a large station and, in addition, it is much more expensive.

Bluetooth(Translation - blue tooth) was split up in 1998 and is vicorized for drone-free communication with a computer in the freely licensed range 2.4 - 2.4835 GHz. It does not connect to a connector and is installed in the middle of the computer (device), used to transmit data via radio transmission between different types of computers, mobile phones, printers, cameras, keyboards, mice, joysticks, MFPs, scanners and others .The essence of the method lies in the fact that in the singing range the frequency changes pseudo-floptically at a rate of 1600 times per second. Such a frequency change occurs simultaneously to receive and transmit, which operate synchronously behind such a circuit.The devices can be one at a time up to 200 meters away from the passage between them (walls, furniture, etc.).

The receive-transmit device is located in the middle of the computer and is not visible. If your computer does not have such a device, you can connect an external device via a USB connector that allows you to use this type of data transfer.

Є standards: 1.0 (1998), 2.0 EDR (2004) with high speed data transmission of 3 Mbit/s, practically close to 2 Mbit/s, 2.1 (2007) with highly energy-saving technology, simplified there is an established connection between the devices, as well as more stolen, 2.1 EDR began to consume even less electricity, the connection of devices became even simpler and reliability increased, 3.0 HS (2009) with speedy transmission up to 24 Mbps . 4.0, which became available on the iPhone in 2011, allows you to transfer data at a speed of 1 Mbps. in portions of 8 to 27 bytes.

Create profiles for this standard, which is a set of functions. In order for devices to target a specific profile, the device's offenses must support that profile. For example, A2DP (two-channel transmission of stereo audio data), AVRCP (transmission of standard TV functions), BIP (forwarding images), BPP (forwarding text, electronic sheets to a printer) and so on

WiFi Vikorist is used to create a dartless line. Founded in 1991, NCRCorporation and AT@T are supported by the Wi-Fi Alliance and comply with the IEEE 802.11 standard. Vikoryst is used to connect to a network (local and Internet) of computers and mobile phones.

The receive-transmit device is located in the middle of the computer and is not visible. If your computer does not have such a device, you can connect an external device via a USB connector that allows you to use this type of data transfer.

The following standards: 802.11a vicoristic frequency 5 GHz, providing speed (theoretically) up to 54 Mbps; 802.11b uses the 2.4 GHz frequency band, providing speed (theoretically) up to 11 Mbit/sec. (Practically not vikorist); 802.11g uses a 2.4 GHz frequency, providing speed up to 54 Mbps. (maximum expansion); 802.11n uses frequencies of 2.4 and 5 GHz, providing speeds of 150 to 600 Mbit/sec. (Recently, the fragmentation begins to gain strength). This standard has a longer transmission range and fewer membranes on the connections. The Danish standard uses MIMO (Multiple Input Multiple Output) technology, which allows for multiple installations on walls. Since the device has one antenna, it can operate at a speed of 150 Mbit/sec, two antennas – 300 Mbit/sec, three – 450 Mbit/sec, others (not yet released) – 600 Mbit/sec. The stated speed of transmission differs from the real one. So, instead of 300 Mbit/s, the output is about 100-130 Mbit/s (about half of the information is service symbols), which is also sufficient for work. And due to the presence of walls, the speed drops further, for example, for three walls it will drop to 50 Mbit/sec.

Since businesses operate at a frequency of 2.4 GHz (for example, Microwave Pich), smells can be caused by disturbances. This is why there are devices that operate at two frequencies: 2.4 and 5 GHz.

You will also need cable modems to connect to a cable TV channel.

Call digital modems can contain elements that are subject to change Gateway Between the local boundary and the Internet: router, boundary screen, etc.

Modem indicators

The presence of attacks is possible indicators:

A.A.(Auto Answer – auto-answer) – auto-answer mode, which will ensure that the subscriber’s request is answered automatically;

CD(Carrier Detect – designated DCD) - lights up during a connection session;

CTS or else C.S.(Clear To Send) – the modem is ready before receiving data from the computer. The hour of the withdrawal of these data goes out;

DATA– light up during the hour of data transmission;

DC (Data Compression) – squeeze tributes ;

FAX– between modem and fax;

H.S.(High Speed ​​- high speed) – lights up during an hour of operation of the modem at maximum speed;

E.C. (Error Control or ARQ) – error correction mode;

M.R.(Modem Ready – modem readiness or DSR) - indicates that the modem is still active and ready for operation;

OH(Off Hook – off-hook) - lights up when the handset is off-hook;

ON(PWR) – vitality indicator;

PWR (PoWeR) – inclusion of life;

R.D.(Recieve Data - selecting data or RX or else RXD) - shows that data is being used on the computer;

SD(Send Data – collection of data or SX or else TXT) - indicates that data is being received from the computer;

TEL– light up when the parallel connected telephone is off-hook;

RTS (Request To Send) – the modem is ready to receive data from the computer. Lights up when data is collected from the computer, goes off when data is being transferred;

T.D. (Transmit Data or else TXD) – lights up or lights up when the data is being transferred from the computer to the modem. May light up when transmitting data at maximum transmission speed;

TST (TeST) - shines during testing;

TR(Terminal Ready - readiness for installation or DTR) - Lights up when the core signal is removed;

USB– lights up when the modem is connected to the computer via USB.

The modem body may have a volume control.

On the back panel The external modem can be identified by the following icons:

A.C. IN – connecting the power adapter;

LINE – connection to a telephone line;

ON / OFF – modem turned on/off;

PHONE – phone connection;

R.S. -232 – connector for connecting to the serial port of a computer;

USB – A connector for connecting to a USB bus.

Analog modem

Transfer of data. Telephone lines are connected to analog signals. Through those that people use in the range of 30 Hz to 10 KHz (music has a larger range), then to save money, the telephone line passes a signal from 100 Hz to 3 KHz. This exchange itself relates to the possibility of transmitting data at high speeds. Computers can be connected not only through a telephone line, but also via wireless radio transmission and infrared transmission. Whose bastard doesn't need any darts.

At the end of the package, the data sent in the parallel channel is converted into serial transmission with start-stop bits in the serial port, transmitted to the modem, where they are modeled, so that they are superimposed on the frequency that is not transmitted along the line signal , then try to switch to another modem. Then they are converted to digital form, sent to the next port, converted to a parallel view, and then sent to the processor for processing.

Digital data is processed simultaneously, and the acquisition can be of two types: synchronous and asynchronous. During synchronous transmission, the data packet consists of a header, which includes the destination addresses, the data itself and the check sum. In asynchronous transmission, a start bit, 8 data bits, possibly a parity check bit, and a stop bit are transmitted to indicate the end of the transmission. This type of vicor is used in the serial channel.

In addition, when transmitting data, three modes can be used: duplex, in which data can be transmitted in both directions simultaneously, full-duplex, in which data can be transmitted in both directions, but at any time in one direction, and simplex - transmission of data only in in one direction.

Transferring data from the modem to the modem and from the modem to the computer is very fluid, so that the data is not lost, the modem maintains a buffer, and data that is removed is saved.

Some modems compress the data before sending it, and when it is extracted, another modem decrypts the data. If files are already compressed, this method may prevent transfer time. To avoid data wastage, the speed of data transfer from the modem to the computer is the most important thing among modems that is practically implemented.

When transmitting, one is often vikorized baud, as they wander from bits/sec for hours. In fact, there are different values. 1 baud is one character that can be sent per hour, and not only data, but also signals that can be controlled. The symbol can be a number of bits. Since the signal consists of two types: 0 and 1, the symbol means 1 bit, if 512, then 9 bits (2 9 = 512). When transmitting at low speed, 1 baud is approximately equal to 1 bit/sec. With high speed, the modem sends data at many frequencies, and at any given time not one, but many bits are transmitted, so the speed is measured in bits/sec, and not baud/sec, which will be more often than not there are bodas . The speed in bauds is often indicated, but the speed in bits/sec is also indicated.

When transmitting via a modem, you can estimate approximately how many hours it takes to transmit by dividing the transmission speed by 10, for example, if the transmission is transmitted at a speed of 28800 bps, then approximately 2880 bytes or characters will be transmitted per second ( 28800/10 = 2800).

The modem connects to the serial port of the computer and processes the serial data. If the modem is used for working on the Internet, it can also serve to connect two separate computers directly. Modems can be used in the same way as fax machines for transmitting fax messages. You can use an adapter to create voice notifications in auto-speak mode.

When connected, the modem sends signals that are also output to the speakers, and from them the sound may seem to change, which will last for several seconds. The modem that receives it indicates the standard that can be processed, as well as adjust the clock frequency, and then adjust the phase model. After this, the speaker turns off, and the signals continue to be heard, but they can be heard through the parallel phone.

There are two types of modems: internal and external. The internal connections of the expansion cards are inserted into the motherboard socket, the external ones are connected to their case and behind an additional cable connecting to the serial port. Other types of modems can be connected via the USB bus (and they drain the power supply from the computer), which means that the computer is running during the hour, disconnecting the connector, and performing other tasks. When connecting a modem to the serial port, high-speed models require that the port be wired. So, for modems with a speed of 56 Kbit/sec, the speed of the serial port is 115 Kbit/sec. Higher bandwidth is required for the port in order to handle communication signals between the computer and the modem, rather than being transmitted over a telephone line. If the port does not support high fluidity, the data may be destroyed. External devices can be turned on by turning on the power supply unit, and the internal one can only be turned on when the computer is disabled, which is not easy for the modem to freeze up.

Modems can be divided into two categories: the first type (Class2) has an internal processor that processes the data; in the other, the data is processed by the central processor (Class1), also called Windows modems, Cheaper than the first type. Such a modem, like an old processor, can greatly improve the performance of the computer, but if the user rarely accesses the Internet and only sends a small amount of email every hour, then it is acceptable. This is entirely due to the fact that the computer has a heavy-duty processor.

Often the modem is characterized protocol with what kind of wine it works. Is scurrying signal modulation protocols, error correction protocols, squeezed dataі robots with fax call (fax). The modem carries a number of protocols for the skin of many types. The correction protocols include V.42, MNP2-4, MNP10, data abbreviation – V42bis, MNP5.

One of the main characteristics of the modem is the speed of data transmission, and the maximum speed that is indicated can be 33.6 or 56 Kbps for current devices. When a speed of 33.6 Kbps is specified, all data is processed and data is transmitted in both directions at a speed of 33.6 Kbps. as the line does not allow. If the line does not allow this, a switch to a lower liquid is required. Bandwidth 56 Kbit/sec. will ensure that data is retrieved with greater speed, less when sending it, since there are more reception frequencies here, which are lower for transmission, and transmission to the modem occurs with less speed.

In addition, it is necessary for modems to have small characteristics, otherwise data transmission will not reach maximum speed. To do this, before purchasing a modem from your provider, you need to clarify the type of modem that will work best. Below is a table of the differences between different protocols and the transmission speed of each one.

The prefix bis means that the standard has been revised. Starting at a speed of 14400, all protocols are duplex, so that notifications are transmitted to both parties instantly. The symbol V can begin with the names of standards, the original transmission protocol, and other types of protocols, for example, V.24 contains a list of signals between two modems, V.25bis is a command and control modem, etc. and, for example, MNP, may begin with the symbol V, but then there are not numbers, but symbols, for example, V.FC.

These are the following MNP protocols: MNP1і MNP2- outdated and not vikoristic; MNP3- Ensure synchronous transmission; MNP4- transmits data in synchronous mode in packets of 32 to 256 bytes of data, the size of the packet being stored in the telephone line. For a smaller clear line, a smaller package size is required, for a larger one, a larger one; MNP5- ensures a synchronous mode, in which the data is compressed, there are two compression algorithms that are repeated; MNP6- Provides synchronous mode, as well as data compression; MNP7, MNP8, MNP9- Ensures synchronous mode, in which vikoryst uses more thorough compression methods; MNP10- is detected when the data line is unclear. At the moment the cob of the robot reaches the lowest fluidity, and as the line begins to work with advanced transmission, the fluidity increases.

There are also the following protocols:

Xmodem- protocol issued in 1977. The modem that transmits sends a special NAK signal, then, after receiving it, the receiving modem sees the NAK signal until it receives the data packet, which consists of the character on the head of data (SOH), the block number, data of 128 bytes and a check sum. (CS) When data is removed and verified for the correctness of the checksum, a signal is sent for data that is received (ACK), and if data is received incorrectly, a signal (NAK) is sent. If there are a number of recent data, the session begins to connect. Once the transfer is complete, the EOT symbol is added to indicate the end of the session.

There is a need for modification of this protocol, for example, Xmodem CRC The check sum has been increased to 16 bytes, which improves the reliability of the transfer, Xmodem 1k- The size of the data block is up to 1 kilobyte, Xmodem G- Transfers data, and the control sum is located at the end not of the data block, but of the file.

Ymodem- based on the Xmodem protocol, with a data size of 1 kilobyte, which is transferred, transfers the file name and its attributes. In addition, the first block contains information about those who have such transfer files.

Kermit- Vikorist data packets up to 94 bytes are important, which is important for Unix systems.

Zmodem- transmits data ranging in size from 64 to 1024 bytes in its own format. In the event of a murder, tribute is sent from the moment the murder occurs.

Bimodem– further development of the Zmodem protocol with the ability to strengthen data in two directions simultaneously.

Others may be needed command the modem for example, for yogo testing. Below is a list of active commands for the modem (it is important that modifications of modems can require a different set of commands):

ATA- The modem is ready for operation;

ATADP number- Pulse dialing of a telephone number;

ATADT number– tone dialing;

ATW– ochіkuvannya not bitches;

ATMx- robot guchnomovtsya, de 0-vimkneniy, 1-inclusion;

ATLx- The strength of the machine gun is from 0 to 7;

ATQx- Inform the modem about the following commands: 0-on, 1-off;

ATHx- 0-connection to the modem per line, 1-connection;

ATZ- Updating the cob robot mode;

AT&W- Recording specific modem parameters into memory;

ATSx=value- Variation of modem characteristics;

+++ - Switching the modem to command mode;

A\- Repeat the remaining command.

When transmitting data via a modem, special protocols are used to compress the data, for smooth transmission and data correction methods. These standards are referred to as MNP (Microcom Networking Protocol), as well as those standards that begin with Letter V (V.41, V42 and V42bis).

To transmit data, a special protocol is used to define the rules by which data is transmitted and received. For normal operation, it is necessary that both modems (which send and receive) can handle these protocols. With data correction methods, in addition to them, a special CRC combination is used to serve for the identification of corrections. Upon receipt, the data is verified, so that the calculation and alignment of CRC blocks (calculated and verified) is carried out, and during normal operation, a signal is added about those that the data has been received correctly.

Respect. The country code on the computer is saved with the international telephone prefix. The telephone number is made up of the following digits: Country code (10 for Russia) + region code (495 or 499 for Moscow) + PBX number (3 digits) + telephone number in the middle of the PBX (4 digits)

If you experimented with the modem and it doesn’t work, then to reset the parameters, you can reboot the computer, then turn on the modem, or enter the AT&F command, and to change the parameters for the modem, enter AT&V.

The transmission of text information via telephone channels is called day phone call.

Modemi take revenge you have: I/O port adapter for operation with a telephone line; I/O port adapter for robots and computers; a processor that modulates/demodulates the signal and ensures communication protocol; memory, where the chip control program is saved, modem parameters and RAM are maintained; a controller in charge of the computer and components of the modem.

The modem can take part of these components, and the missing part will be modeled by a central processor, for example, a controller. Such modems are called software modems.

The most important characteristic is transmission speed. Recently, the standard was a speed of 14.4 Kbps (initially, there were also lower speeds), then devices appeared that allowed the transfer of information at speeds of 28.8 and 33.6 Kbps. In addition, the maximum transmission speed reached 128 Kbps and ensured the maximum transmission capacity over the telephone network.

Apparently, devices that operate at a speed of 33.6 KB can operate at higher speeds, such as 28.8 and 14.4 KB/sec., but not in the same way. So, if one end uses a modem that has a transmission speed of 28.8 Kb/sec, and the other - 14.4, then the transmission will be carried out at a speed of 14.4 Kb/sec.

Installation of the modem

Installed modem. Installing a modem, as a rule, does not pose any big problems, since after installing the operating system, the system itself installs the standard driver. If the modem needs a driver, you need to install it, as long as it is the same as the standard driver, it will provide additional capabilities.

To install you need to follow the following sequence of actions:

Turn off the computer (either an internal modem or an external one is connected to the serial port);

If you have an internal modem, install it as an extension. When doing this, trim the board by the edges, without sticking out the conductors and microcircuits on the boards. If you have an external modem, connect to the serial port or USB port. If the number of pins on the serial port connector is not reduced, you will need an adapter, as one of the ports may no longer be occupied;

If the modem has one output for the telephone, then you need to connect the wire with one end to the modem, and the other end to the telephone socket. This type can be equipped with a special type of socket, which has two outputs: one for the telephone, the other for the modem. The type of this type of socket is indicated on the little one, which is right-handed; she has two of these types of socket.

One follows the standard that exists in our region, and the other is the one adopted in Zakhad, which is found in many modems that are sold.

You can quickly use a special splitter, which has one rose on one end and two on the other. One connector is installed into the telephone, up to two others are connected to the telephone socket and the modem.

If the modem has two telephone sockets, then one needs to be connected to the telephone socket (write line to the socket), the other to the phone (write phone). If I can’t write, look at the back wall of the modem, you can see the contact diagram, or go to the documentation. If the connection is made incorrectly, the modem will not function. At this time, change your contacts. The external modem also needs to be connected to the network through the life block. To install an internal modem, follow the description of the installation of boards in the system unit;

After installation, turn off the computer and install the security program that comes with the modem.

Laptops have one output for connecting a telephone line. When working with a modem, it is better not to use a parallel telephone or connect through an external socket on the modem, otherwise the connection to the telephone line may fail and noise may appear.

On a Windows system, after installing a modem, a notification will appear on the screen that the system has detected a new device, after which the system itself will try to identify its characteristics. Follow the instructions for the modem. It is necessary to make the settings correctly so that there are no conflicts through the use of system resources.

Installed The modem vibrates the same way as other devices. Since the modem supports the Plug & Play standard, when you turn on the computer, a “installation wizard” will appear on the screen, which will help you install the modem for additional power and connections. If the modem does not support the Plug & Play standard (for even older models), then you need to quickly go to the following mode: Start → Settings → Control panel → Modems (2) → Power (modems) → Add → (do not specify the modem type) Further. If there is a disk to the modem, you need to quickly select the “Install from Disk” mode or, if necessary, select the manufacturer (unknown, “Standard modem types”) and Model → Further → having selected a suitable model, press i → (select the required port) Dali.

One of the most important parameters that you need to set is the type of dialing, which can be pulse, because in our region the other type is not supported. To install, you need to go to the Power window: Modem: Press “Installation parameters” and select pulse dialing.

Shchob re-verify Once installed correctly, speed up the mode: Start → Settings → Control Panel → System (2) → Devices, where there is a list of devices. If you name “Modem” there will be a plus sign, you need to click on that icon to open the list of modems. After this, the trace will be recontoured, so that there is no sign of power and hail in the installed device.

Modem parameters can be marvelі change For additional help: Start →Settings →Control Panel →Modems →Power →Settings, where the port is changed, the volume of the speaker is indicated, the maximum speed is indicated. In this case, the maximum speed is transferred between the modem and the computer, and not between modems. Make sure to set the maximum fluidity, and change the binder if necessary.

Other foods

The channels of the connection are divided into:

Analogue (for example, telephone), in which information is transmitted as a continuous signal;

Digital, transmission of digital (discrete and pulse) signals

or else

Simplex,

Full duplex

Duplex

or else

Switched, started timely transmissions, then switched off;

Uncommuted (seen), seen in a trivial term

or else

Low speed (telegraph) speed 50-200 bytes/sec;

Average data (telephone) with speed 300-56,000 bytes/sec.;

Visokoshvydkisny, over 56,000 bits/sec.

To transmit data at high speed, a twisted pair cable (connected to each other), a coaxial cable (like a TV antenna), fiber optic (glass fiber) and a radio channel (via radio channels) are used.

Radio waves can be long (3-30 kHz), long (30-300 kHz), medium (300-3000 kHz), short (3-30 MHz), ultra-short (30 MHz-3 GHz), submillimeter (300-6000 Gg)

When transmitting data, a number of types of modulation are used: frequency (V21), phase (V22), amplitude and quadrature amplitude modulation, in which the phase and amplitude change, greater resistance to transgression, lower forward And, therefore, it is used in the V22.bis standard and higher.

The protocol also allows for the possibility of breaking the information into blocks, updating the link, correcting the blocks, etc. They are referred to as Xmodem, Ymodem, Zmodem, Kermit and others. The most extensive is Zmodem.

Merezhevi cards serve as a connection between a computer and a network of computers and as an intermediary between the computer and the transmission network. The Merezheva card has its own processor and memory. The main characteristics of the edge card are the bus to which it is connected, the size of the memory, the card capacity (8, 16, 32 bits), the type of connector for thin and thick cables. Merger cards require an installed interruption line (often 3 or 5), a DMA channel, and a memory address (C800).

Cable for hedging There can be several types:

Twisted pair. Consists of several twisted copper conductors in one cable, which can be unshielded (UTP) or shielded (STR).

Coaxial cable consists of central and screen wires, between which there is insulation. There are two types of cable: thin (0.2 inches long) and thick (0.4 inches long).

Fiber optic cable It consists of two darts, which are made of light fiber fibers. The throughput of the building is high, although it is expensive, it is rarely used.

When the cable is short-circuited, the cable runs on a high-voltage support, often 50 ohms. When laying, it is necessary to use cables of the same brand, from the same generator. After laying a thin cable, connectors are installed, such as the Russian type (CP50) or crimped BNC connectors. A plug is installed at the ends and one of them is firmly grounded.

The laying of thick cables is carried out through transceivers, whereby one transceiver is connected to one computer, and at the ends of the cables that go to the computer there are 15-pin DIX (or AUI) connectors. At the ends of the cables there are installed: N-terminators, one of which is grounded. To increase the length of the local distance (for a thin cable it can be more than 185 meters), use repeaters.

The torsion cable is connected simultaneously with the concentrator or hub (Hub), from which the cable is laid to the computer for no more than 100 meters. At the ends there is an RJ-45 connector, which is similar to a telephone connector, but there are 8 contacts (not 4). Hubs can have a different number of ports, for example, 8, 12, 16, which indicates the maximum number of connected computers.

When using the modem, fax He follows his own standards. When sending faxes at a speed of 14.4 Kbps, the standard V.17 (14400), V27 ter (4800), V29 (9600) and T.30 for the protocol itself is used. When transmitting an image of a sheet, the following modes can be used separately for fax transmission: Standard - 100x200 dpi; yellow (Fine) – 200x200 dpi; high-quality (Superhigh) - 400x200dpi; Photo mode conveys 64 gradations of gray color.

The current modem supports more standards, in any case, those that work for less than the maximum speed of this modem.

In addition to basic modems, there may be even specific modems, for example, cable modems, if the signal is transmitted through TV cable. In this case, the cable is connected to a special socket, which is the socket for the TV and the serial channel of the computer. The operation of cable networks allows data to be transmitted with great speed. However, over time, if the number of skin cells grows, the throughput of the skin cells may appear low. And at the same time, while there are not enough koristuvachs, they will give a small number of koristuvachs great advantages in working on the Internet.

May be vikoristani satellite devices In this case, clients send notifications to the provider via telephone about which pages they want to view, and they are retrieved via a satellite.

Nowadays, there is more and more use of information to transmit information. mobile connection. In this type of connection, the modem communicates with the mobile phone via a special cable.

We have the greatest expansion in data transmission - voice and digital, and standard GSM- Global System for Mobile Communication, which can be translated as “a global system for mobile communications.” The essence of such a standard lies in the fact that all information that is transmitted is divided into so-called frames that are subdivided at all intervals. Depending on how busy the line is, there may be one interval or another. This is a method of mobile communication of destinations before transmitting voice notifications, which may take priority over digital data. The average speed of data transfer does not exceed 9.6 Kbit/s.

Higher standard GPRS(General Packet Radio Service) allows you to increase this speed to 50 Kbps, and theoretically can reach 100 Kbps. In case of GSM substitution, in order to send information it is possible to obtain other hourly intervals in the frame, up to all eight, and this situation increases the speed of sending data. In addition, this option of mobile communication will ensure a quicker payment for the customer, since you are paid for the information that is transferred to the administrator via GSM.

GPRS devices are divided into three classes according to their capabilities:

Class A. Such devices transmit different types of information – voice and digital – every single hour.

Class V. These models allow you to work through the Internet, either with digital data or with voice data.

Klas S. This is where the overpowering of digital data comes into play.

An internal modem is a device installed in the middle of a desktop or laptop computer that allows the computer to communicate with other connected computers. There are two types of internal modems: switching and WiFi® (dromeless). The first one works through the phone line and pulls up a phone number to access the network and cloud data to log in to the system. The rest can be connected using a dartless network and in some situations without cloud data.
The term “internal modem” tends to refer to a switched modem, as modern technologies use classifiers to differentiate them. The current internal modem, also available as an external device, uses the v.92 protocol for communication with copper telephone lines. The modem sends and receives data via modulated audio frequencies, which converts the data into digital bits. The word modem comes from the words modulator and demodulator, which are the same functions.

External modems were transferred to internal models and used for proprietary purposes for a decade until 1981, which marks the release of the first affordable and practical modem for the public domain. Hayes® Smartmodem® is revolutionary through its built-in controller, which allows the device to receive, save and save commands generated by the user. This modem can only dial the number on its own, or accept a call from another modem. Before the advent of Smartmodem, modems were used to operate either as a server or as a client (director or owner), but not simultaneously, and a telephone number had to be dialed manually on a telephone base, and then received locations on an acoustic connection.

An inexpensive Smart-modem with a speed of 300 baud worked with a speed of 300 bps and produced anonymous clones. The useless services of the boards have become a ubiquitous phenomenon, to such an extent that private border services have become so popular that they have created graphic environments where people can point out and push their way through closed content. Over the course of the new decade, as online content moved from text boards to the surface of the graphic medium, the lack of work at greater speeds became obvious.

Modems have not only become new, they have become standard equipment, available as internal models that were always included in a new computer. The current 9600 baud dial-up modems, which operate at a maximum speed of 56 kilobits (kbps), have used a combination of techniques to maximize technology interchange. Server-side compression, which includes an additional protocol known as v.44, can provide theoretical text transmission speeds of up to 320 kbps.

Regardless of the constant reduction, interconnection of the internal dial-up modem, digital subscriber line (DSL) modems, cable modems and fiber optic modems, which use the advantages of new technologies for delivering content to tens of hundreds of Once again, there is no connection via a telephone line. This is no less an internal modem, as before, it is standard equipment as a spare device for use in desktop computers and laptops. Regardless of its age, the call, as before, is respected as the most reliable means of online access, including phones, depending on the available routes, if high-speed access is available daily.

Telecommunication features in the current computer world

I. Entry

Quite often in computer literature we come across such concepts as a modem.

There are no personal computers in the world. It is logical to think about a quick and easy way to connect between them. This method is now possible for a modem. It allows you to transfer information from one computer to another in an encrypted manner via a telephone line. The computers will exchange signals of song frequency and volume.

What can be done to the modem?

You can connect to another wireless modem and exchange files with it, regardless of its reinstallation. Or play a computer game with it, which supports the modem.

If your modem is a fax modem, you can exchange fax messages.

You can use the services of the BBS - Bulletin Board System (English - Electronic Board), retrieve and receive files, interact with other users, and play on-line games, etc. Play with the modem in real time.

You can connect to global networks. For example, FidoNet, or Internet/Relcom. By connecting to them, you can become a participant in anonymous teleconferences, which gives you the opportunity to exchange information with people in your same interests.

If you are a businessman, then using an additional modem you will always be aware of the latest news and updates.

II. How does the modem work?

Not a lot of hidden facts

Then what if they guessed the first modem board?

In the 80s, the American company Hayes released the first modem for the IBM PC.

Of course, telephone lines were designed to transmit only the sounds of the human voice. All apparent, natural sounds are characterized by varying pitch and intensity that are constantly changing. To transmit telephone stench, they are converted into an electrical signal with continuous and constant changes in frequency and strength of the current. Such a signal is called analog.

The computer in charge of the modem understands the digital signal, then. current is less than two equals. Each of them means one of two reasonable values ​​for the computer - logical “0” and “1”. To transmit a digital signal over a telephone line, you need to give it an analog appearance that is pleasing to it.

The modem itself does the work. The same applies to the reversal procedure. transfer an analog signal from a human to a digital computer. The word “modem” is a shorthand for two terms: Modulator/DEMOdulator. The modem organizes the space between the digital signal, which is seen by the computer, and the analog signal, which, as stated above, is the telephone line.

When transmitting data from a computer to a modem, the first one sees a sequence of zeros and ones, and the remaining one converts it into an analog signal. Then the data is sent to the telephone line, and it is received by the modem at the other end of the phone. When the modem receives data, it filters out the red information from line noise. And therefore there are special protocols for correction of cuts. The one that sticks out the most is MNP10. There are MNP1, MNP2, MNP3, MNP4, MNP5, MNP7. Nini of the greatest expansions of MNP5, because MNP7 and MNP10 are installed on special modems that operate behind visible lines. For example, at the global Internet. After the modem adds the necessary information from the noise on the line, it selects data to be pumped as service information. The file, which has already undergone such extensive processing, is recorded on the computer’s hard drive. This is how data is exchanged when connecting via Zmodem, Sealink, Ymodem and many other single-direct protocols.

Of course, computers can instantly receive and add data. Because they are singing songs about frequencies, differences between input and output signals. For which special bidirectional protocols are needed. For example Bimodem, Puma, Janus, Zedzap.

MNP protocols

MNP (Microsoft Network Protocols) is a series of the most advanced hardware protocols, first implemented on Microsoft modems. These protocols ensure automatic correction of data and compression of data transmitted. There are 10 protocols:

MNP1. The error correction protocol uses an asynchronous full-duplex transmission method. This is the simplest of the MNP protocols.

MNP2. The error correction protocol is an asynchronous duplex transmission method.

MNP3. The error correction protocol is a synchronous duplex transmission method between modems (the modem-computer interface becomes asynchronous). So, since with asynchronous transmission, ten bits per byte are transferred - most of the data bit, the start bit and the stop bit, and with synchronous transmission only all of them, then it is possible to speed up data exchange by 20%.

MNP4. The protocol, which is a synchronous transmission method, ensures optimization of the data phase, which further reduces the inefficiency of the MNP2 and MNP3 protocols. In addition, when changing the number of messages on a line, the size of the data blocks that are transmitted also changes. With an increased number of cuts, the size of the blocks changes, increasing the likelihood of successful completion of adjacent blocks. Its efficiency is close to 20% when simply transferring data.

MNP5. In addition to the MNP4 methods, MNP5 often uses a simple method of compressing the information that is transmitted. Characters that are often condensed in the transmitted block are encoded with lanyards of the minor ones, and lower characters that are rarely condensed. In addition, many new symbols are encoded. All text files are compressed to 35% of their output. A combination of 20% MNP4 results in an increase in efficiency up to 50%. Please note that if you are already transferring files, and for the most part, there is no additional increase in efficiency due to the modem's compression.

MNP6. In addition to MNP5 methods, the MNP6 protocol automatically switches between duplex and full-duplex transmission methods depending on the type of information. The MNP6 protocol also provides the same functionality as the V.29 protocol.

MNP7. Similar to earlier protocols, Vikorist has an effective method of data compression.

MNP9. Vikorist's V.32 protocol is an advanced operating method that ensures compatibility with low-bandwidth modems.

MNP10. Used to secure tying on noisy lines, such as steel tying lines, interstitial lines, rural lines. You can use the following methods for help:

Once again, try to install the connection

Changing the size of the packages is necessary before changing the level of the line crossing

Dynamic changes in transmission speed depending on the level of line crossover

All MNP protocols are incompatible with each other. When the connection is installed, the highest level of the MNP protocol is installed. If one of the modems that communicate does not support the MNP protocol, then the MNP modem operates without the MNP protocol.

MNP modem modes

The MNP modem provides the following transmission modes:

Standard mode. Ensures data buffering, which allows you to process different transmission speeds between a computer and a modem and between two modems. As a result, to improve the efficiency of data transfer, you can set the speed of computer-to-modem communication higher than the modem-to-modem. In standard mode, the modem does not suffer from hardware corrections.

Direct transmission mode. This mode corresponds to a primary modem that does not support the MNP protocol. Data buffering is not affected and hardware correction of errors is not affected.

Mode with correction of cuts and buffering. This is a standard mode of operation where two MNP modems are connected. Since the remote modem does not support the MNP protocol, connections are not established.

Mode with correction of errors and automatic adjustment. The mode is selected if it is not known whether the remote modem supports the MNP protocol. At the beginning of a connection session, after the remote mode is assigned to the modem, one of three other modes is installed.

Internal and external modems

There are internal and external modems (there are also special types of modems in the form of PC cards (PCMCIA), but they are also intended for computers such as laptops, and therefore they are not visible here.). Internal Wikonian modems, as expansion cards, are inserted into a special expansion slot on the computer’s motherboard. An external modem, to replace the internal one, will be connected to the adjacent device, then. in an adjacent case and with its own power supply unit, if the internal modem removes the electrical power from the computer power supply unit. So what are the advantages and disadvantages of external and internal modems?

Internal modem

Advantages

1. All internal models without fault (as opposed to external ones) can have an integrated FIFO. (First Input First Output - first arrivals, first acceptances). FIFO is a microcircuit that ensures data buffering. The primary modem, as soon as a byte of data passes through the port, immediately powers up the computer's power supply. The computer, using special IRQ (Interrupt Request) lines, interrupts the modem's operation for an hour, and then resumes it again. This improves the computer's performance. FIFO allows you to edit multiple times less often. There is great significance in the hour of work in task-rich environments. Such as Windows95, OS/2, Windows NT, UNIX and others.
2. When the internal modem is switched off, the number of wires stretched at the most unconnected places changes. So the internal modem itself does not take up valuable space on the desktop.
3. Internal modems are the last port of the computer and occupy the main ports of the computer.
4. Internal modem models are always cheaper than external ones.

1. Occupy an expansion slot on the computer's motherboard. This is even more difficult on multimedia machines, on which a large number of additional cards are installed, as well as on computers, which operate servers in a network.
2. There are no indicator lights, which allow you to follow the processes running in the modem.
3. If the modem is frozen, you can restore functionality by pressing the “RESET” computer reset button.

Advantages

1. They do not occupy an expansion slot, and if necessary, they can be easily plugged in and transferred to another computer.
2. There are indicators on the front panel that help you understand how to operate the modem.
3. If the modem is frozen, there is no need to restart the computer, just turn off and turn on the computer.

1. A multicard is required due to the inserted FIFO. Without a FIFO, the modem will work better, but the speed of data transfer will decrease.
2. The external modem takes up space on the desktop and the necessary additional parts for connection. This creates innocence.
3. It occupies the last port of the computer.
4. An external modem is always more expensive than a similar internal one, because includes a housing with indicator lights and a living unit.

1. MR(Modem Ready)

1. TR(Terminal Ready)

1. HS(High Speed)

1. CD(Carrier Detect)

1. AA(Auto Answer)

1. OH(Off Hook)

1. RD(Receive Data)

1. SD(Send Data)

Modem brands

Today, the actual standard is a 14400 speed modem with data transfer protocols V32 and V32bis (abbreviated, for example, HST and V32terbo). Today's products focus on this standard. Ale and vin, like everything in the computer world, are unstable and gradually dying. Of course, the best way to use a modem is to connect 28800 with speed and with V34 data transfer protocols (and its subset of V.Fast and V.Everything). There are also different types of protocol V34+. It allows you to receive/transmit at speeds up to 33600. Modems from various companies have special protocols for special operating minds (Ring on very noisy lines. These protocols can be used on them without warning. Otherwise, this is normal. clean lines? These protocols are HST , developed by USRobotics® . So there are two protocols, separated Zyxel ® . Tse Zyx and ZyCell. Zyx has a protocol that can communicate with similar models on speeds 16800 and 19200. And ZyCell is a special protocol for satellite and telephone communication. The only drawback of such protocols is that they communicate on proprietary protocols only with similar models.).

Now you can look at the brands of modems.

This company knows that we want to buy inexpensive ones and get reliable models.

For example, the GVC 14440 F1114HV model is a model that has been well recommended in our minds. It is practical to catch the BUSY signal without any delay. This is a fax modem and is a class II fax machine. So in this case, the adjustment of the signal level to the line core is realized. One of its advantages is the silent reed relay.

ZyXEL

Unfortunately, it was one of the most popular and most prestigious models, but today the company has greatly strengthened its position, mainly in the reach of USRobotics.

All types of modems from the company ZyXEL divided into series.

Series 1496 - including standard protocols V32 and V32bis, and standard protocols: Zyx and ZyCell. These models have a voice mode (VOICE) in order to send and receive voice notifications. There is also a number assignment mode (AVN - Automatic number assignment).

Models of the 1496 series have adaptive fax, which means that the modem allows you to automatically identify the subscriber and switch between fax, modem or voice.

Also a modem ZyXEL can operate on multi-wire lines, resulting in transmission speeds of up to 115,200 baud.

This company produces a number of series of modems: USR Sportster, USR Courier, USR WorldPort and others. WorldPort models are designed for portable computers. Through the tsevony there was no wide expansion. The highly productive Courier series, due to various reasons, has not experienced great expansion in our region. The Sportster series will no longer be available. The modems of the Service of the whole Gamu Shvidkosty VID 14400 to 33600. The stench is Buvayy Yak inside, so I called the Imaychy Modifykaty, and the yak is in programly, so і Aparatno. It is important to know that Sportster series modems can be upgraded to a more expensive and richly functional Courier series. After the upgrade, the original USR Sportster is transformed into a Courier. In this case, such important advantages arise as the implementation of the HST (High Speed ​​Technology) protocol.

In 1991, several Canadian programs began to wonder: why is the Sportster so similar to the old Courier? If they have installed a number of modems, then they realize that Sportster and Courier are limited by firmware, which automatically detects the type of modem behind tricky jumpers and NVRAM (Non Violatible Random Access Memory - non-volatile memory of the modem) and for the Sportster series it is simply includes HST and all others Possibility Courier.

III. Visnovok

Before our eyes there is a real communication boom, completely equalized by the scale and the legacy of the emergence of the first personal computers. A simple and effective device - a modem that combines the potential of two of the greatest resources of mankind, the telephone and the personal computer, giving everyone necessary access to the world's most important information and providing a truly modest personal computer fantastic possibilities.

The ignorant computer literacy that we were talking about just recently is now a more-less proven fact. There is no doubt that telecommunications literacy is needed at the same time: without it it is simply impossible to keep up with the civilized world, neither in business, nor in science, nor in education, nor in wealth x other areas. Now the modem’s availability can be equalized with the printer’s availability – and this in another significant way provides the computer with sense. And the hour is not far off when a self-made computer will be no more crusty than a microcalculator.

Wikorystan literature:

1. Berliner E.M. ta in. Microsoft Windows 95. Microsoft Plus! Russian version. View. ABF, Moscow, 1996
2. Zeldner G.A. ta in. Computer on call! Fax modem, modem, global networks, E-Mail, BBS. View. ABF, Moscow, 1996
3. Kirsanov D.. Fax modem: from purchase and connection to access to the Internet. View. "Symbol-Plus", St. Petersburg, 1995