Whats a real modem

A modem (modulator-demodulator) is a device that modulates an analog carrier signal to encode digital information and demodulates the signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Modems can be used with any means of transmitting analog signals, from light emitting diodes to radio. The most familiar type is a voice band modem that turns the digital data of a computer into modulated electrical signals in the voice frequency range of a telephone channel. These signals can be transmitted over telephone lines and demodulated by another modem at the receiver side to recover the digital data. Modems are generally classified by the amount of data they can send in a given unit of time, usually expressed in bits per second (bit/s or bps), or bytes per second (B/s). Modems can also be classified by their symbol rate, measured in baud. The baud unit denotes symbols per second, or the number of times per second the modem sends a new signal. For example, the ITU V.21 standard used audio frequency shift keying with two possible frequencies, corresponding to two distinct symbols (or one bit per symbol), to carry 300 bits per second using 300 baud. By contrast, the original ITU V.22 standard, which could transmit and receive four distinct symbols (two bits per symbol), transmitted 1,200 bits by sending 600 symbols per second (600 baud) using phase shift keying.

Examples of real modems . . .Acoustic Coupler, very oldschool

A Fax modem present in the 1990's & late 1980's

Computer uses a terminal program to dial the fax modem & the fax modem can then send files down the telephone line to another modem connected to a computer usually running a BBS, Bulletin Board System on standby. A Fax modem is a real modem.

The next picture below is a slot in modem which is actually slotted into one of the computers input slots. Its exactly the same as the modem above but does not use a serial port, it uses a ISA or PCI slot in the computer. A slot in modem is a real modem that can dial numbers.

The Modem above is a USB 56k fax modem, it has a USB port instead of a serial port, it can still dial numbers. It looks abit like a DSL splitter but it isn't.

The Modem below is another USB 56k fax modem, it has a USB port instead of a serial port, it can still dial numbers. It looks abit like a DSL splitter but it isn't.

The modem in the next picture is not a real modem its called a dsl modem or ADSL modem, it can not dial numbers like the modems above

Below are the internals of a DSL or ADSL modem, Digital Subscriber Line, its called a embedded system . . . An embedded system is a computer system with a dedicated function within a larger mechanical or electrical system, often with real-time computing constraints. It is embedded as part of a complete device often including hardware and mechanical parts. By contrast, a general-purpose computer, such as a personal computer (PC), is designed to be flexible and to meet a wide range of end-user needs. Embedded systems control many devices in common use today. Modern embedded systems are often based on microcontrollers (i.e CPUs with integrated memory and/or peripheral interfaces) but ordinary microprocessors (using external chips for memory and peripheral interface circuits) are also still common, especially in more complex systems. In either case, the processor used may be types ranging from rather general purpose to very specialised in certain class of computations, or even custom designed for the application at hand. A common standard class of dedicated processors is the digital signal processor (DSP). The key characteristic, however, is being dedicated to handle a

particular task. Since the embedded system is dedicated to specific tasks, design engineers can optimize it to reduce the size and cost of the product and increase the reliability and performance. Some embedded systems are mass-produced, benefiting from economies of scale. Physically, embedded systems range from portable devices such as digital watches and MP3 players, to large stationary installations like traffic lights, factory controllers, and largely complex systems like hybrid vehicles, MRI, and avionics. Complexity varies from low, with a single microcontroller chip, to very high with multiple units, peripherals and networks mounted inside a large chassis or enclosure.

ADSL or DSL modem internals . . . a embedded system, more like a computer than a modem.

Below is a ADSL modem bank at a ISP, Internet Service Provider, remember ADSL or DSL modems can not dial numbers . . .

[EOF] End Of File . . .