Definition of Modem and its Types in Computer Networks

The definition of Modem comes from the acronym Modulator Demodulator. The modulator is the part that converts the information signal into a carrier signal and is ready to be sent, while the demodulator is the part that separates the information signal (which contains data or messages) from the received carrier signal so that the information can be received properly. Modem is a combination of the two, meaning that the modem is a two-way communication device. 

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Modem Types

A. ADSL modem

ADSL (Asymetric Digital Subscribe Line) modem technology that allows surfing the internet and using analog phones simultaneously. The method is very easy, for ADSL given a device called a splitter or line splitter. Splitter position is placed in front when the telephone line comes in. This means that you shouldn't branch out the line modems for ADSL with direct voice. Splitter tool is useful for eliminating distractions when you are using an ADSL modem. With the Splitter both of them can run simultaneously, so that users can answer and call someone with a regular telephone. On the other hand, users can still connect to the internet via an ADSL modem.ADSL MODEM

 ADSL splitter
ADSL modems generally have two types of connections to computers:
1. USB (Universal Serial Bus)
Universal Serial Bus
2. Ethernet /LAN port 
ethernet LAN
There is also an ADSL modem that is combined with the Wireless feature so that it can distribute connections to wireless devices or to laptops directly.
ads modem wireless

ADSL connection to ClearOS can use external static type (specified ip address manually), external dynamic (DHCP server enabled modem) or external PPPOE (bridge mode modem, input user and password from ISP on ClearOS Server). For external static and dynamic, user and password are entered in modem, modem mode router.

B. GSM / CDMA modem

GSM / CDMA modem supports GPRS / EDGE and 3G / HSDPA network types, which are internet services from cellular operators. GSM / CDMA modem uses a USB connection to connect to the client computer.
usb modem gsm cdma

usb modem dma gsm

To strengthen the signal, you can add an external antenna with a connection using an induction connector or using a pigtail (depending on the type of modem)
Various types of external antennas
Various types of external antennas
Yagi type external antenna
Yagi type external antenna
Pigtail Connector

Pigtail Connector
Induction Connector
Induction Connector
Officially ClearOS doesn't support USB connections. So if you want to use a GSM / CDMA modem, you need a router to change the connection type to Ethernet.
modem router

C. Satellite Modem / VSAT Modem

VSAT (in English, stands for Very Small Aperture Terminal) is a station that receives signals from a satellite with a dish-shaped receiving antenna less than three meters in diameter. The main function of the VSAT is to receive and send data to the satellite. The satellite functions as a signal successor to be sent to another point on the earth. Actually the VSAT dish is facing a geostationary satellite. Geostationary satellites are satellites that are always in the same place in line with the earth's rotation on its axis, which is possible because it orbits at the same point on the earth's surface, and follows the earth's rotation on its axis.
VSAT Parabolic Antenna

VSAT Parabolic Antenna

VSAT components, consisting of:

Outdoor Unit (ODU):

  • 1. Antenna / dish / parabolic 2 to 4 feet (0.55-2.4 m) in size, mounted on a roof, wall or on the ground.
  • 2. BUC (Block Up Converter), which delivers information signals to satellites. Also often referred to as Transmitter (Tx).
  • 3. LNB (Low Noise Block Up), which receives information signals from satellites. Also often referred to as Receiver (Rx).

• Indoor Unit (IDU):

  • Modem (Modulator / Demodulator), a device called the Return Channel Satellite Terminal that connects from the outside unit with an IFL cable measuring no more than 50 meters long.
  • IFL (Inter Facility Link). Is a media liaison between ODU & IDU. The physical type is usually a coaxial cable and usually uses a BNC (Bayonet Neill-Concelman) connector.
VSAT Modem
VSAT modem
VSAT Parabolic Antenna
VSAT Modem Connection to Outdoor Unit (via Coax Cable)
The output of the VSAT modem is in ethernet form so that it can be connected to ClearOS with a choice of external static or external dynamic.

D. Cable Modem

A cable modem is used for internet connection via cable TV channels. The cable used is the coaxial type.
Cable Modem Connection Scheme
Cable Modem Connection Scheme
Cable Modem

Cable Modem
Cable Modem
ClearOS supports cable modems with both external cable and external static / dynamic connection types.
Thus a little knowledge about the definition of modems and the types of modems which are an important part of network equipment.

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