Jumat, 09 Juli 2010

Modem (modulator-demodulator)

Modem (modulator-demodulator) is a device which is currently the most widely used to connect to the internet, particularly through the phone line. Physically, the modem can be distinguished as an internal modem and external modem. Besides, we know the division based on speed and how it works, whether it be software or hardware modem. There are a few bonus more technical nature, such as error control, data compression protocol Internal and External modems

As shown from its name, an external modem device outside

CPU. external modem connected to the CPU via COM or USB port. modem of this type typically use a separate voltage source adapter. The advantage of this type of modem usage is a good enough portability easily removable for use on other computers. Besides using an external modem, there should be no expansion slots that were sacrificed so that it can be used for other purposes, especially if the mainboard is used only to provide a bit expansion slot. external modem is also equipped with an indicator light that enables us to monitor modem status. The disadvantage is more expensive than internal modems. external modems also require a separate place to put it even smaller.

Unlike an external modem, internal modem installed directly inside the CPU. Physically, the form of an internal modem card plugged into one of the expansion slot on the mainboard, usually on the ISA or PCI slot. Use of this type of modem has several advantages, among other places and is more efficient in terms of price is more economical than an external modem. Because they have been installed in the CPU, the modem type does not require an adapter as an external modem so impressed with the system more compact without a lot of milling about the cable that could give the impression of less tidy. However, the internal modem has a weakness as the absence of indicators that can be found on external modems. As a result somewhat difficult to monitor the status of the modem (though it can be done via software). In addition, the internal modem is not using their own voltage source to be supplied from the power supply to the CPU. Heat from the components in a series of internal modems will also increase the temperature within the CPU box.

Modem Speed

The speed of a modem is measured in units bps (bits per second) or kbps (kilobits per second). The amount varies between 300 bps to 56.6 kbps, but the speed commonly used today ranges from 14.4 to 56.6 kbps. The higher the speed the better course because it will shorten the connection time and save on telephone costs. The connection speed is also very dependent on the quality of phone lines used. 56.6 kbps modem is usually very rarely reach top speed. Generally, the fastest connection that can be achieved through conventional phone lines are ranging from 45-50 kbps for downstream, depending on the distance from the central telephone lines are used (of course the closer the better), whereas for the upstream maximum of only 33.6 kbps. This deals with the limitations of phone lines that are basically not designed for high speed data communications.

Hardware and Software-based modems

In addition to the second division of the above, we also know the terms of hardware or software modem. modem that works in hardware using a special chip to handle data communications functions, while on a software modem, this job was taken over by a driver program. Using software modems will be enough CPU work load, and thus would require a system with a fast processor (Pentium processor recommended minimum using 200 Mhz). Loss in performance will be felt when using this type of modem. A Celeron 400-based machines, for example, is only able to work like a PC Pentium Classic while online by using a software modem. Physically there is almost no striking features that distinguish between these two types of modems. However, nowadays almost all PCI-based internal modems on the market is a software modem. These types of modems are generally sold at a price much cheaper than hardware-based modems. Because of the availability factor of the driver, then the software modems are generally only works in Windows OS environment so that the type of modem is also often referred to as Winmodems.

Meaning of indicator light on external modems

OH: Off Hook
Indicates that the modem was working. If likened to a telephone, OH will light up when the receiver was appointed and die when the receiver is placed.

CD: Carrier Detect
Indicates whether there are carriers that are sent from the modem to be contacted or not. When there is a connection with another modem, CD lamp is lit.

AA: Auto Answer
Modem facility that can automatically answer the call from another modem. If the AA indicator lights up, the modem can perform handshaking automatically.

EC: Error Control
Modem facilities for error correction. EC indicators are illuminated to show the modem error correction facility is active.

TD: Transmit Data
The indicator will light when the modem is sending data.

RD: Receive Data
The indicator will light when the modem receives the data.

DTR: Data Terminal Ready
The indicator shows the modem is ready for use to connect to another modem

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