Understanding the Synergy: How Modems and Multiplexers Boost Data Transmission

Modem

A modem is a device or program that enables a computer to transmit data over, for example, telephone or cable lines. Computer information is stored digitally, whereas information transmitted over telephone lines is transmitted in the form of analog waves. A modem converts between these two forms. Fortunately, there is one standard interface for connecting external modems to computers called RS-232. Consequently, any external modem can be attached to any computer that has an RS-232 port, which almost all personal computers have. There are also modems that come as an expansion board that you can insert into a vacant expansion slot. These are sometimes called onboard or internal modems.

While the modem interfaces are standardized, a number of different protocols for formatting data to be transmitted over telephone lines exist. Some, like CCITT V.34, are official standards, while others have been developed by private companies. Most modems have built-in support for the more common protocols -- at slow data transmission speeds at least, most modems can communicate with each other. At high transmission speeds, however, the protocols are less standardized. Aside from the transmission protocols that they support, the following characteristics distinguish one modem from another:

1. Bps: How fast the modem can transmit and receive data. At slow rates, modems are measured in terms of baud rates. The slowest rate is 300 baud (about 25 cps). At higher speeds, modems are measured in terms of bits per second (bps). The fastest modems run at 57,600 bps, although they can achieve even higher rates by compressing the data. Obviously, the faster the transmission rate, the faster you can send and receive data. Note, however, that you cannot receive data any faster than it is being sent. If, for example, the device sending data to your computer is sending it at 2,400 bps, you must receive it at 2,400 bps. It does not always pay, therefore, to have a very fast modem. In addition, some telephone lines are unable to transmit data reliably at very high rates.
2. Voice/data: Many modems support a switch to change between voice and data modes. In data mode, the modem acts like a regular modem. In voice mode, the modem acts like a regular telephone. Modems that support a voice/data switch have a built-in loudspeaker and microphone for voice communication.
3. Auto-answer: An auto-answer modem enables your computer to receive calls in your absence. This is only necessary if you are offering some type of computer service that people can call in to use.
4. Data compression: Some modems perform data compression, which enables them to send data at faster rates. However, the modem at the receiving end must be able to decompress the data using the same compression technique.
5. Flash memory: Some modems come with flash memory rather than conventional ROM, which means that the protocols can be easily updated if necessary.
6. Fax capability: Most modern modems are fax modems, which mean that they can send and receive faxes. To get the most out of a modem, you should have a communications software package, a program that simplifies the task of transferring data.

What does Multiplexer (MUX) 

A multiplexer (MUX) is a device allowing one or more low-speed analog or digital input signals to be selected, combined and transmitted at a higher speed on a single shared medium or within a single shared device. Thus, several signals may share a single device or transmission conductor such as a copper wire or Fiber optic cable. A MUX functions as a multiple input, single output switch.

In telecommunications the combined signals, analog or digital, are considered a single output higher speed signal transmitted on several communication channels by a particular multiplex method or technique. With two input signals and one output signal, the device is referred to as a 2-to-1 multiplexer; with four input signals it is a 4-to-1 multiplexer; etc. This term is also known as a multiplexor.

1. For analog signals in telecommunications (and signal processing), a TDM (time division multiplexer) may select multiple samples of separate analog signals and combine them into one PAM (pulse amplitude modulated) wide-band analog signal.
2. For digital signals in telecommunications on a computer network or with digital video, several variable bit-rate data streams of input signals (using packet mode communication) may be combined, or multiplexed, into one constant bandwidth signal. With an alternate method utilizing a TDM, a limited number of constant bit-rate data streams of input signals may be multiplexed into one higher bit-rate data stream.

A multiplexer requires a de multiplexer to complete the process, i.e. to separate multiplex signals carried by the single shared medium or device. Often a multiplexer and a de multiplexer are combined into a single device (also often just called a multiplexer) allowing the device to process both incoming and outgoing signals. Alternately, a multiplexer’s single output may be connected to a de multiplexer’s single input over a single channel. Either method is often used as a cost-saving measure. Since most communication systems transmit in directions, the single combined device, or two separate devices (in latter example), will be needed at both ends of the transmission line.

Other types of multiplexing technologies and processes include (not a comprehensive listing):

1. Inverse Multiplexing (IMUX)
2. Wavelength Division Multiplexing (WDM)
3. Dense Wavelength Division Multiplexing (DWDM)
4. Conventional Wavelength Division Multiplexing (CWDM)
5. Reconfigurable Optical Add-Drop Multiplexer (ROADM)
6. Frequency Division Multiplexing (FDM)
7. Orthogonal Frequency Division Multiplexing (OFDM)
8. Add/Drop Multiplexing (ADM)

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Sandeep Ghatuary

Finance & Accounting blogger simplifying complex topics.

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