Nowadays, the Internet is needed almost always and everywhere. And this applies not only to urban everyday life, when we can catch 3G or 4G from a smartphone or tablet almost anywhere in the city. If we talk about a laptop, then we can, of course, find a Wi-Fi network or distribute the Internet from a smartphone. But you must admit that it is not possible everywhere and not so convenient. And what can we say about country trips, when catching 2G is already not bad, and we can only dream of free Wi-Fi networks. Okay, even a smartphone or tablet, but what about a laptop? And if there is a stationary computer in the country? Will they call from work? It would be possible to complete urgent tasks right outside the city, but there is no Internet, you have to go home.
On long trips, you also need the Internet: on business trips - for work, on tourist trips - to study maps, search for interesting places, post photos on Instagram and other social networks. Do you really have to always look for Wi-Fi or distribute the Internet from your phone?
Modems and mobile routers will come to the rescue. The principle of their work is simple: insert a SIM-card and enjoy the Internet. The signal strength depends only on the coverage area of your operator. “Excellent!” - you will say and open the page with modems. And there are so many of them ... And such different prices ... How to choose? It all depends on how exactly you want to use the gadget. It is important what devices you will connect to it, as well as where you will use it.
An important point is the choice of the operator. The signal level, and, consequently, the data transfer rate depends on it. Many operators offer their own "branded" modems. They have two drawbacks. First, they are often more expensive. Second, you can only use the services of this operator. If in the place where you are, its networks do not work - well, alas. Therefore, we suggest considering third-party modems and mobile routers.
How are modems different?
USB modem or mobile router
A USB modem is a transceiver that uses the networks of mobile operators to transmit and receive information. It connects to the USB port of the computer and after a little setup allows you to use the Internet. It can also be used with a regular router. A SIM card is inserted into the USB modem, the choice of which depends only on the coverage of the operator's network in the place you need. All USB modems are very small and light, allowing you to carry them in your bag or pocket.A mobile router is a device that works on the principle of an ordinary modem. A SIM card is inserted into it, the device receives a signal from a mobile operator and, unlike a USB modem, provides mobile Wi-Fi. Such a gadget is usually powered by a battery that requires regular charging. Mobile routers are not as small as USB modems. Some models can be put in a pocket, and some will only fit in a bag.
To choose from these two types of gadgets, answer the question: what do you need this device for? If you want to use it only with a laptop to have internet anywhere, or with a desktop computer, get a USB modem. If you are interested in portable Wi-FI - an access point for connecting a number of devices, it is better to purchase a mobile router.
3G or 4G
3G and 4G are wireless communication technologies that allow you to get high-speed Internet access from mobile devices. The letter G in their names is from the word "generation", that is, "generation". Therefore, 3G is the third generation of wireless communication, and 4G is the fourth.
The main difference between these two generations is the data transfer speed. 3G networks are capable of transmitting data at different speeds, which depends on the operating frequency of the mobile operator. The leading operators have an operating frequency of 15 MHz, while some smaller ones have only 4.5 MHz. Therefore, the speed range of 3G networks ranges from several hundred kilobits to several tens of megabits per second.
The main advantage of 3G networks is their coverage area, which covers most of the territory of Russia. Also, the low cost of modems that work only with 3G will be a plus.
4G networks are capable of transmitting data at much higher speeds - up to 1 Gbps. True, it depends on the type of device: for example, not all mobile devices will be able to achieve speeds of 100 Mbps.
The downside of 4G networks is poor coverage in Russia: it only applies to large cities. Also, because of the high-speed data transfer, devices that work with 4G have a higher power consumption.
So when choosing a gadget for a summer residence or trips, it is better to stop at a 3G modem, since you are unlikely to catch 4G anyway, and spend less money on the device. For the city, a 4G modem is better suited.
GSM, GPRS, EDGE, HSPA, LTE
All these terrible abbreviations are nothing but communication standards and technologies of different generations.
GSM is the main communication standard of the second generation. For it, a GPRS packet data transmission technology has been created, the transmission speed of which can reach 115 kbps.
EDGE is a packet data transmission technology that uses the second generation CDMA communication standard. The speed with it reaches 384 kb / s. By the way, this is the same E,
which is displayed on the screen of a smartphone or tablet when it does not catch either 4G, or 3G, or H.
HSPA is a third-generation communication standard that allows packet data rates of 42.2 Mb/s to be achieved. And this is the same H.
LTE is a fourth-generation data transmission technology with a speed of up to 1 Gb / s.
All these standards and technologies are actively used by Russian telecom operators. In the absence of the latest and fastest networks, devices typically switch to the previous generation networks. Therefore, it is better that all of them are supported by the modem, although this is almost always the case.
Nutrition
As we already mentioned, USB modems do not need a separate power supply. Thanks to this, they can be used at any time, you just need to insert them into the USB port of your computer.
Mobile routers run on batteries. The larger their volume, the longer the gadget will work. However, do not forget about such important factors of battery consumption as work in 4G networks and the presence of additional sensors and functions.
Ethernet port
This is the connector that will allow you to connect your modem to your computer using an Ethernet cable. Such a connection will ensure stability and the highest possible speed between the device and the modem. This function is only available for mobile routers, since USB modems are already connected to a computer.
Interface for external antenna
An external antenna is needed in order to better catch the network. After all, the signal is unstable, especially outside the city; it depends on time of day, weather and many other factors. The main disadvantage of the antenna is its low mobility. Therefore, this option is suitable only for those who decide to equip a stationary Internet point, for example, in the country.Additional functions
Mobile modems have additional features. But they may not be useful to everyone. In addition, many of them are quite energy-intensive. So decide right away which of the following you need.
A microSD card slot is useful for owners of laptops with a small number of USB connectors. By inserting a flash card into the modem, you can use it as a drive and, for example, store programs related to the Internet and connecting to it (to free up space on your computer and be able to immediately run all the necessary programs on another device by simply inserting the modem ).
Support for the SMS service allows you to receive and send SMS messages using a special program installed on your computer. This feature is only available for USB modems.
Sensors and a display will help determine the level of charge, the presence of networks, the number of connected users, etc. But you need to remember that with them the battery runs out faster.
An application for smartphones and tablets helps to control the level of charge, connected users, transfer data to the modem's flash drive. This feature is only available on mobile routers.
Dimensions
If we talk about USB modems, then they are all no more than 100 mm in length and 40 g in weight. With mobile routers, everything is different. Their weight can reach 700 g, and dimensions - 250 x 100 mm. But there are also compact models that can be easily carried in your pocket.Setting
For many users, this will be an important parameter. After all, you want to launch the gadget and immediately use it. Moreover, for many it will be a real problem to set up a modem - not everyone is fluent in technology. Therefore, based on this parameter, it is better to give preference to USB modems, and the simplest ones.
Criterias of choice
We examined the main parameters of mobile modems and found out that the selection of characteristics depends on the needs of the user. It is necessary to determine where and with what devices the modem will be used, as well as what additional functions will be needed. Based on the needs of users, we classified mobile modems.For use in the city with a desktop computer worth buying
So, modems and modulation-demodulation...
The term "modem" is an abbreviation for the well-known computer term modulator-demodulator. A modem is a device that converts digital data from a computer into analog signals that can be transmitted over a telephone line. This whole thing is called modulation. The analog signals are then converted back into digital data. This business is called demodulation.
The scheme is very simple. The modem receives digital information in the form of zeros and ones from the computer's central processor. The modem analyzes this information and converts it into analog signals, which are transmitted through the telephone line. Another modem receives these signals, converts them back to digital data, and sends the data back to the remote computer's CPU.
Modulation type (Modulation type), which allows you to select frequency or pulse modulation. Pulse modulation is used throughout Russia.
Analog and digital signals
Telephone communication is carried out through the so-called analog (sound) signals. An analog signal identifies information that is transmitted continuously, while a digital signal only identifies data that is determined at a particular stage of transmission. The advantage of analog information over digital is the ability to fully represent a continuous flow of information.
On the other hand, digital data is less affected by various kinds of noise and rattles. In computers, data is stored in individual bits, the essence of which is 1 (start) or O (end).
If the whole thing is represented graphically, analog signals are sine waves, while digital signals are represented as square waves. For example, sound is an analog signal because sound is always changing. Thus, in the process of sending information over the telephone line, the modem receives digital data from the computer and converts it into an analog signal. The second modem, located at the other end of the line, converts these analog signals into the original digital data.
Interfaces
You can use the modem on your computer using one of two interfaces. They are:
MNP-5 RS-232 serial interface.
MNP-5 Four-pin RJ-11 telephone cable.
For example, an external modem is connected to a computer via an RS-232 cable, and to a telephone line via an RJ11 cable.
Data compression
In the process of data transfer, a speed greater than 600 bits per second (bps or bps) is required. This is due to the fact that modems must collect bits of information and transmit them further through a more complex analog signal (a very tricky scheme). The very process of such a transfer allows the transfer of many bits of data at the same time. It is clear that computers are more sensitive to transmitted information and therefore perceive it much faster than a modem. This circumstance generates additional modem time corresponding to those data bits that need to be somehow grouped and applied to them by certain compression algorithms. So there were two so-called compression protocols:
MNP-5 (transmission protocol having a compression ratio of 2:1).
V.42bis (transmission protocol having a compression ratio of 4:1).
The MNP-5 protocol is usually used when transferring certain already compressed files, while the V.42bis protocol is applied even to uncompressed files, since it can speed up the transfer of just such data.
I must say that when transferring files, if the V.42bis protocol is not available at all, then it is best to disable the MNP-5 protocol as well.
Error Correction
Error correction is a method by which modems test transmitted information for the presence of any damage that occurred during transmission. The modem breaks this information into small packets called frames. The transmitting modem appends a so-called checksum to each of these frames. The receive modem checks if the checksum matches the information sent. If not, the frame is retransmitted.
Frame is one of the key terms of data transfer. A frame is understood as a basic block of data with a header, information attached to this header, and data that completes the frame itself. The added information includes frame number, transmission block size data, sync characters, station address, error correction code, variable volume data, and so-called indicators. Start of transmission (start bit) / End of transmission (stop bit). This means that a frame is a packet of information that is transmitted ^ as one.
For example, in Windows 98, in the modem settings, there is an option Stop bits (Stop bits), which allows you to set the number of stop bits. Stop data bits are one of the varieties of so-called boundary service bits. The table bit determines the end of the cycle for asynchronous transmission (the time interval between transmitted characters varies) of data in a short cycle.
MNP2-4 and V.42 protocols
Although error correction can slow down data transmission on noisy lines, this method provides a reliable connection. The MNP2-4 and V.42 protocols are error correction protocols. These protocols define how modems validate data.
Like data compression protocols, error correction protocols must be supported by both transmitting and receiving modems.
Flow Control or Flow Control
During a transmission, one modem can send data much faster than another modem can receive the data. The so-called flow control method allows you to tell the receiving modem the information that this modem should stop receiving data at some point in time. Flow control can be implemented both in software (XON/XOFF - Start signal/Stop signal) and in hardware (RTS/CTS) levels. Flow control at the program level is carried out through the transfer of a certain character. After the signal is received, another character is transmitted.
For example, in Windows 98, in the modem settings, there is an option Data bits (Data bits), which allows you to set the information data bits used by the system for the selected serial port. The standard computer character set consists of 256 elements (8 bits). Therefore, the default option is 8. If your modem does not support pseudo-graphics (only works with 128 characters), indicate this by selecting option 7.
In the same place in Windows 98, in the modem settings, there is an option Use flow control,
which allows you to determine how the data exchange is implemented. Here you can correct possible errors that occur when transferring data from the computer to the modem. Default setting XON/XOFF means that data flow control is carried out by software methods through standard ASCII control characters, which send a command to the modem pause / resume transmission.
Flow control at the software level is only possible if a serial cable is used. Since the flow control at the software level regulates the transmission process by sending some characters, a failure or even termination of the communication session may occur. This is explained by the fact that one or another noise in the line can generate a completely similar signal.
For example, with software-level flow control, binary files cannot be transferred because such files may contain control characters.
Through hardware-level flow control, RTS/CTS transfers information much faster and more securely than through software-level flow control.
FIFO buffer and UART chips
The FIFO buffer is somewhat similar to a transshipment base: while the data is entering the modem, some of it is sent to the buffer capacity, which gives some gain when switching from one task to another.
For example, Windows 98 only supports the 16550 series Universal Asynchronous Receiver Transmitter (UART) chips and allows you to control the FIFO buffer itself. With a checkbox Use FIFO buffers requres 16550 compatible UART (Use FIFO buffers) you can lock (prevent the system from accumulating data in the buffer capacity) or unlock (allow the system to accumulate data in the buffer capacity) the FIFO buffer. Pushing a button advanced, you turn to the dialogue Advanced Connection Settings, whose options allow you to configure your modem's connection.
S-registers
S-registers are located somewhere inside the modem itself. It is in these same registers that settings are stored that in one way or another can affect the behavior of the modem. There are a lot of registers in the modem, but only the first 12 of them are considered standard registers. S-registers are set in such a way that they send a command to the modem ATSN=xx, where N corresponds to the number of the register to be set, and xx specifies the register itself. For example, through the SO register, you can set the number of rings to answer.
IRQ interrupts
Peripherals communicate with the computer's processor through what are known as IRQs. Interrupts are signals that cause the processor to suspend an operation and transfer its execution to the so-called interrupt handler. When the CPU receives an interrupt, it simply suspends the process and hands over the interrupted task to an intermediary program named Interrupt Handler. The whole thing works regardless of whether an error was detected in the operation of a particular process or not.
Information communication port or simply COM port
The serial port is very easy to find out. You can do this by simply looking at the connector. The COM port uses a 25-pin connector with two rows of pins, one of which is longer than the others. At the same time, almost all serial cables have exactly 25-pin connectors on both sides (in other cases, a special adapter is required).
The COM port (serial port) is the port through which computers communicate with devices such as a modem and mouse. Standard personal computers have four serial ports.
COM 1 and COM 2 ports are normally used by the computer as external ports. By default, all four serial ports have two IRQs:
COM 1 bound to IRQ 4 (3F8-3FF).
COM 2 bound to IRQ 3 (2F8-2FF).
COM 3 is tied to IRQ 4 (3E8-3FF).
COM 4 is tied to IRQ 3 (2E8-2EF).
This is where conflicts can arise, since external ports of other 1/0 I / O devices or controllers can use the same IRQs.
Therefore, after assigning a COM port or IRQ to the modem, you should check other devices to see if they have
the same serial ports and interrupts.
I must say that devices connected to the telephone line in parallel with the modem (especially AON) can significantly degrade * the quality of your modem. Therefore, it is recommended to connect telephones through the jack in the modem designed for this purpose. Only in this case, he will disconnect them from the line during operation.
Your modem's flash memory
Flash memory is read-only memory or PROM (Read Only Memory) that can be erased and reprogrammed.
All modems with the string "V. Everything" in their name are subject to reprogramming. In addition, "Courier V.34 dual standart" modems are subject to software upgrade if the line Options the response to the ATI7 command contains the V.FC protocol. If the modem does not have this protocol, then the upgrade to "Courier V. Everything" is done 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. Each of them has its own firmware versions, and they are not interchangeable, i.e. firmware from the 20.16 MHz model will not work for the 25 MHz model, and vice versa.
User Programmable NVRAM
All modem settings come down to the correct setting of NVRAM register values. NVRAM is a user-programmable memory that retains data when the power is turned off. NVRAM is used in modems to store the default configuration loaded into RAM at power on. NVRAM programming is done in any terminal program using AT commands. A complete list of commands can be obtained from the modem documentation, or obtained in the terminal program by commands AT$ AT&$ ATS$ AT%$. Write to NVRAM factory settings with hardware data control - AT&F1 command, then make adjustments to the modem settings in conjunction with a specific telephone line and write them to NVRAM by command AT&W. Further initialization of the modem must be done through the command ATZ.4.
Application Software for Data Communication
Data programs allow you to connect to other computers, BBS, Internet, Intranet and other information services. You may have a very extensive set of such programs at your disposal. For example, in Windows 98, you have at your disposal a very good terminal client, Hyper Terminal.
If you are having problems communicating with other modems
First you need to evaluate the nature of the communication line. To do this, after a successful session, before reinitializing the modem, enter the commands ATI6- communication diagnostics, ATI11- connection statistics, ATY16- amplitude-frequency characteristic. The received data must be written to a file. After analyzing the received data, it is necessary to make changes to the current configuration and then write them to NVRAM using the command AT&W5.
Russian telephone lines and imported modems
The choice of modems today is quite large, and the difference in their cost is very significant. Transfer rates of more than 28,800 bps on Russian telephone lines are usually unattainable. Above 16,900 bps can only be obtained if the Internet service provider has lines on the PBX to which your phone is connected. In other cases, working on the Internet is too tedious, because at a typical (and even not always achievable) speed of 9,600 bps, it turns into a continuous wait. Therefore, for stable data transmission with interference in the telephone line, you need a high-end modem that costs at least $400.
Which modem is better - internal or external?
The internal modem is installed in a free expansion slot on the computer motherboard and connected to the built-in power supply, while the external modem is a stand-alone device connected to the computer via a standard serial port.
Each of the designs has its own advantages and disadvantages. The internal modem occupies a system bus slot (and there are usually not enough of them), it is difficult to monitor its operation due to the lack of indicators, moreover, the models described are fundamentally not suitable for laptop computers such as notebooks, which have a narrow profile case and in most cases do not with expansion slots. At the same time, the internal modem is several tens of dollars cheaper than external analogues, does not take up space on the table and does not create a mess of wires. Using an external modem means that the computer to which it is connected has the most modern serial port control chips (UART). UART chips appeared in the first PCs, because even then it became clear that data exchange via a serial port is too slow and complicated operation and it is better to entrust it to a special controller. Since then, several UART models have been released. In computers like IBM PC and XT, as well as in fully compatible with them, the 8250 chip was used, in AT it was replaced by the UART 16450. turn", and today the UART 16550A becomes the standard - a microcircuit similar to the previous one, but with the defects eliminated. The lack of buffers in all microcircuits, except for the last one, leads to the fact that data transfer through the serial port at speeds above 9600 bps becomes unstable (using MS Windows reduces this threshold to 2400 bps).
If you need to connect a high-speed external modem to a computer that uses an obsolete UART chip, you must either change the multicard or add a special expansion card (which will occupy one bus slot and deprive the external modem of a major advantage). Internal modems do not have this problem - they do not use the COM port (more precisely, they contain it). Now internal modems have another advantage, also related to speed. According to the V.42bis specification, data can be compressed by about a factor of four in transmission, so a modem operating at 28800 bps must receive data from or send data to the computer at 115600 bps, which is the limit for serial PC port. However, 28800 bps is not the limit for a telephone line, where the maximum lies somewhere in the region of 35,000 bps, and on digital lines (ISDN) the throughput exceeds 60,000 bps. Therefore, in this situation, the serial port will become the "bottleneck" of the entire system, and the potential capabilities of an external modem will not be realized. Modem manufacturers are now developing models that can connect to a faster parallel port, but it is clear that the devices sold now will not be able to adapt to this.
At the same time, many modems can be upgraded to work at high speeds, up to the ability to work on ISDN. But everything rests on a restrictive barrier on the part of the computer, which for an internal modem is significantly higher than 4 MB / s (the throughput of the ISA bus). By the way, all ISDN modems are internal. True, all this will be tomorrow (and maybe the day after tomorrow), but today one thing can be said: choose a device of the type that you like - there are no functional differences between internal modems and their external counterparts.
Which modem to choose and how to choose it
The modem cannot be unique. Your modem must be understood by other modems. This means that the modem must support the maximum number of standards, that is, error correction, communication methods and data compression. The most common standard is V.32bis for 14000 bps modems. For 28800 bps modems, the standardized protocol is V.34.
In addition, it must be emphasized that modems with a data rate of 16800, 19200, 21600 or 33600 are not standard.
No error correction should be programmatic. Everything must be sewn into the modem by its manufacturer.
About the outside and the inside. An external modem is connected to your serial port via a special cable. Such a modem, as a rule, has a volume control, information indicators, a power supply and other sometimes useful gadgets. If you are a professional, then it should not matter to you which modem you choose - internal or external. Usually, a good internal modem through special software emulates well all the visibility of an external modem.
Do not buy purely imported modems. These pieces of iron do not get along on our ancient lines. Purchase only certified modems, that is, hardware specially stitched for our dirty telephone exchanges.
In Russia, this choice is very small. This market was filled by two companies: ZyXEL from sunny Taiwan and U.S. Robotics from USA. Modems of the last firm are chosen by professionals (Courier), the first - by all the rest, that is, all those users who choose the so-called ultra-reliable ZyCell protocol.
So, choose Courier. And believe me, this is not advertising.
Modem (an acronym made up of the words modulator-dem odulator) is a device used in communication systems and performing the function of modulation and demodulation. The modulator performs modulation, that is, changes the characteristics of the carrier signal in accordance with changes in the input information signal, the demodulator performs the reverse process. A special case of a modem is a widely used peripheral device for a computer that allows it to communicate with another computer equipped with a modem through the telephone network (telephone modem) or cable network (cable modem).
Modem types:
By execution:
External - connected to a COM or USB port, usually have an external power supply (there are USB modems powered by USB and LPT modems).
Internal - installed inside the computer in the ISA, PCI, PCMCIA, AMR, CNR slot
Embedded - are the inside of a device, such as a laptop or docking station.
According to the principle of work:
Hardware - all signal conversion operations, support for physical exchange protocols, are performed by a calculator built into the modem (for example, using a DSP, controller). Also in the hardware modem there is a ROM, which contains the firmware that controls the modem.
Winmodems are hardware modems without ROM with firmware. The firmware of such a modem is stored in the memory of the computer to which the modem is connected. It works only in the presence of drivers, which were usually written exclusively for operating systems of the MS Windows family.
Semi-software (Controller based soft-modem) - modems in which part of the modem functions is performed by the computer to which the modem is connected.
Software (Host based soft-modem) - all operations for signal encoding, error checking and protocol management are implemented in software and are performed by the computer's central processor. At the same time, the modem contains an analog circuit and converters: ADC, DAC, interface controller (for example, USB).
Type:
Analog - the most common type of modem for ordinary dial-up telephone lines
ISDN - modems for digital switched telephone lines
DSL - used to organize leased (non-switched) lines using a regular telephone network. They differ from dial-up modems in signal coding. Usually, they allow the use of a telephone line in the usual way at the same time as data exchange.
Cable - used to exchange data over specialized cables - for example, through a cable for collective television using the DOCSIS protocol.
Main article: Wireless modem
Satellite
PLC - use the technology of data transmission over the wires of a household electrical network.
The most common at present are:
Internal soft modem
Built-in modems in laptops.
External hardware modem
Main elements of the modem
I / O ports are circuits designed to exchange data between a telephone line and a modem on the one hand, and a modem and a computer on the other. A transformer is often used to interface with an analog telephone line.
Digital Signal Processor (DSP) Normally modulates outgoing signals and demodulates incoming signals at the digital level according to the communication protocol being used. It may also perform other functions.
The controller controls the exchange with the computer.
Memory chips: ROM - non-volatile memory that stores the modem control firmware - firmware that includes a set of commands and data for modem control, all supported communication protocols and an interface with a computer. Updating the modem firmware is available in most modern models, for which there is a special procedure described in the user manual. To enable flashing, flash memory (EEPROM) is used to store the firmware. Flash memory makes it easy to update the modem's firmware, fixing developers' mistakes and expanding the device's capabilities. In some models of external modems, it is also used to record incoming voice and fax messages when the computer is turned off.
NVRAM is non-volatile electrically reprogrammable memory that stores modem settings. The user can change the settings, for example using the AT command set.
RAM is the modem's RAM, used for buffering received and transmitted data, for the operation of compression algorithms, and other things.
Modems with additional features
Fax Modem - Allows the computer to which it is connected to send and receive fax images to another fax modem or a regular fax machine.
This allows you to:
Using such a modem as an answering machine and for organizing voice mail.
Story
AT&T Dataphone Modems in the United States was part of SAGE (Air Defense Systems) in the 50s. It connected terminals at various air bases, radars and control centers to SAGE command centers throughout the US and Canada. SAGE used leased lines, but the devices at each end of those lines were the same in principle as modern modems.
The first modem for personal computers was a device from Hayes Microcomputer Products, which in 1979 released the Micromodem II for the Apple II personal computer. The modem cost $380 and ran at 110/300 bps.
In 1981, Hayes released the Smartmodem 300 bps modem, the command system of which became the de facto standard.
Good day to you my dear friends. Today I will nostalgic with you, remembering what a modem is. Oh, what a time it was ... I feel that not everyone understands me now, especially young readers who first heard the name of this device.
Then I explain by referring to history.
Let's say that you have a PC, but there is no Internet, none at all. Are you bad without it? Yes, especially considering that you know its limitless possibilities. So. In the 90s, computer owners in Russia first learned about such a Wonder of the World as the global web. And it turns out that you can connect to it over a simple telephone network. Which was at that time the only means of wired communication, laid even in remote villages.
But this required that there was a provider in your city that provides access to the Internet. And the user had a device called a modem, and connected between the PC and the telephone line.
How did it all start?
It just so happened that after the fall of the Iron Curtain, the Internet came to our country with ready-made hardware and software solutions. But in reality, both the network itself and the devices serving it had to go through a thorny path of finding optimal solutions.
The history of the emergence of modem data processing begins in the post-war mountains in the United States. In 1950, between military air defense bases located throughout North America, was laid, which connected radars, terminals, command centers. The signal processing at the ends of the lines was carried out using modulating transformations.
This principle became the basis for the creation of similar devices for network communication between personal computers.
In 1979, the Micromodem II appeared, designed exclusively for the Apple II PC. So the device got its name "modem", formed from the names of the two operations it performs: MODulation and DEMODulation.
I will now explain the purpose of these functions and the principle of operation. So that the digital code pulses, which are a “rectangular” graph, can be transmitted over a channel intended for audio communication, they are pre-modulated, after which the analog signal familiar to a telephone line successfully passes through the network.
In turn, the computer is not able to perceive analog information unusual for it. Therefore, the smooth voltage change in the line is demodulated back into pulses that are understandable for reading by the processor.
But if you study the operation of the modem in more detail, then you should pay attention to its interaction with the network and PC, which implies a system of requests, recognition, changing connection parameters and other control operations.
All this is recorded by a special program code. In 1981, Hayes introduced the Smartmodem 300. It used a system of such commands, which later became the standard in the modem industry.
What are modems and how are they arranged
But, since we began to delve into such subtleties. Then I propose to immediately consider the modem device, consisting of:
- power supply unit;
- two connectors for connecting a telephone cable (incoming from the socket and a branch to the telephone) and a network LAN or serial LPT port for connecting to a computer;
- a controller responsible for exchanging streaming data with a PC;
- a signal processor that directly performs signal conversion operations;
- a memory chipset that includes operational RAM and two types of non-volatile: ROM (with firmware, drivers) and NVRAM with working settings.
I must say right away that this “set” was taken from the design of an external modem, which were the most common during their greatest popularity. Someone probably remembers such models as Courier or Zyxel.
Over time, there were also internal modems inserted into the motherboard. They no longer required a power supply and an external com-port. But a connector was used that could be useful for other needs. Some manufacturers even made built-in modems integrated into the motherboard.
Connection method that determines the speed of the Internet
The conversation about modems will not be complete if you ignore the ways they connect to the Internet. And the first, of course, is Dial-up - the usual dialing, dialing. Of course, this function was performed by the electronic filling of the device, accompanying its work with characteristic sounds coming from the speaker. They were not specifically turned off (despite the annoying) in order to control the process. Dial-up connection had its own characteristics:
- dialing took a long time, and in the process of working on the network, using the phone was impossible;
- very low connection speed of 40 - 45 kbps, which, moreover, strongly depended on the quality of the telephone line;
- billing was often per minute, and given the slow speed - expensive ...
As an alternative to corporate and wealthy users, a dedicated Dial-up line was offered. The advantage of which was the lack of dial-up and the best quality of the channel.
The practice of using the Internet has shown that the amount of information downloaded by the user is much higher than that transmitted to the network. Therefore, ADSL technology was proposed - asynchronous frequency division of data streams using a multiplexer and a modem capable of working with such a signal. This provided new opportunities and clear benefits:
- it became possible to use the phone in parallel in the process of working with the Internet;
- speed increased to 25 Mbps;
- significantly reduced connection time;
The transfer of information with the help allowed a fresh look at the possibilities of high-speed Internet, but, unfortunately, the bandwidth of telephone lines turned out to be a limiting factor at this stage. Providers began to directly lay communication lines (twisted pair or fiber) to the user, bringing the connection speed to 100-300 Mbps.
Not relevant now?
And what about our modems, you ask, are gone? Well, not quite. Still, laying a new line is troublesome, and the telephone cable is already lying. It's a sin not to use them. Therefore, providers still have such a service. Another thing is that telephone communication has changed, digitized, become mobile and provided newer perspectives in the face of 3G / 4G USB modems.
Now you can connect to the Internet at any point within the coverage area of your mobile operator. Moreover, the data transfer rate will allow you to safely watch streaming video. Over time, USB modems also had competitors - these are smartphones. Which in skillful hands easily distribute the Internet via wi-fi.
But that is another story. And this one, I think it is possible to finish. See you soon, my dear readers.
They started a new era of communications and played a major role in the development of the Internet. It will be about modems.
modem- (abbreviated from modulator-demodulator) - a device that, due to the modulation and demodulation of signals, transmits digital data through analog channels - mainly telephone wires.
In this way, modem converts one type of signal to another. With the help of modulation, one or more characteristics of an analog signal are changed: amplitude, frequency, phase. The demodulator performs the reverse function. Currently modems associated with the Internet. They are used to communicate with the provider through various channels (telephone lines, Cable TV lines, base stations of mobile operators). Those. the modem acts as a kind of bridge, because in telephone lines, only an analog signal is possible, and a computer perceives only a digital signal.
History of modems.
The first digital modems began to be developed back in the 50s in North America in order to convert signals for air defense. Modems were used to transmit data over conventional telephone networks. In 1962 the first commercial modem, was created by AT&T. It was a model Bell Dataphone 103. The data transfer rate over the telephone line was 300 bps.
Subsequently the speed modems went through values such as 1200, 2400, 4800 and 9600 bps. The speed of modems increased to 14.4 kb / s only to 1991 year. In 1994 it reached 28.8 kb/sec. The next speed threshold is 33.6 kb/s, which has become the limit for the telephone network. V 1996 56K modem appears, invented by the company Dr. Brent Townshend, which further developed modems. However, back to 70s gg. V 1977 year the first was invented modem for personal computer - 80-103A. It was a real success. Later there were a number of other models, it was Hayes Microcomputer Products.
V 1981 year, Hayes released modem became legendary - Smartmodem 300 bps. For him, a special command system was developed, which is used now. Then the real race for speeds and prices unfolds. modems. The company is in the lead U.S. Robotics. She releases a whole series modems Courier: Starting in 1986 with the Courier HST - 9600 bps.
Types and types modems.
By design, modems are:
- internal modems - located inside the device, they do not have their own power supply.
- external modems - have their own case and power supply, are connected to the computer via a cable, have their own indicators;
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| Internal modems |
According to the principle of work:
- hardware - all signal conversion operations are carried out by itself modem;
- software - all signal conversion operations are implemented in software and are performed by the computer's central processor;
By type of connection:
- analog modems - work through a conventional telephone network;
- cable modems - use a regular television cable or coaxial cable to connect to the Internet;
- radio modems allow the user to work with the network through the radio;
- cellular modems- work on cellular communication protocols - GPRS, EDGE, etc. They often have versions in the form of a USB key fob;
- ADSL modems- a new generation of modems, also work with the telephone network, however, unlike analog ones, they use their own range.
