10-11-2012, 05:18 PM
modem
A modem.docx (Size: 104.63 KB / Downloads: 46)
introduction
A modem (modulator-demodulator) is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier 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 over any means of transmitting analog signals, from light emitting diodes to radio. The most familiar example is a voice band modem that turns the digital data of a personal 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). Modems can alternatively 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, that is to say, tones of different frequencies, 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 was able to transmit and receive four distinct symbols (two bits per symbol), handled 1,200 bit/s by sending 600 symbols per second (600 baud) using phase shift keying.
Specifspec
MODEM – (MODulate/DEModulate) An input/output device that converts digital data from a computer to analog data for transmission over the telephone lines by modulating it into waves; at the other end, the modem converts the analog data back to digital form so that it can be read by the computer. Modems are made for different frequencies from 28.8k bps to 56k bps (bps –Bit Per Second)
Item
Description
External Modem – This particular modem uses a serial interface (connection):
(compare the pros and cons)
+ Easy to install with serial
cable
+ Does not occupy internal slot
+ Does not draw from computer’s power
supply
+ Has LED indicator light, which make it
easier to diagnose problem
+ Can be turned off without turn off the
computer
• Uses a serial port for connectivity
• Slightly higher because of case, power supply, and cable.
Internal Modem – This particular modem goes inside your PC in an ISA or PCI expansion slot. (compare the Pro and Cons)
+ Usually supply it own port
+ Provides own high-speed UART
+ Slightly Less Expensive
• Occupy an internal expansion slot
• Some Models offers a windows display of progression for connectivity.
• In some situation, lockup of modems can only be cured by resetting entire computer.
1. Rent a Modem from BSNL
2. Modem outright purchase form BSNL (one time payment)
3. Modem purchase from BSNL (Through installements)
4. Use your own ADSL Modem (purchased from open market)
There are four types of ADSL Modems
• Type 1: Type -I Modems are with one Ethernet Port and One USB Port (Eg: Nokia siemens C 2110, Utstar UT 300R, Smart AX MT 882 Utstar UT 300RTU, DLink GLB 502, 802 Etc)
• Type 2: Type -II Modems having one Ethernet and one Wi Fi port each (Eg: Quidway WA 1003 A, Utstar WA3002-G1 etc)
• Type 3: Type-III Modems are with four Ethernet ports (Eg: Smart Ax MT 841 type 3)
• Type 4: Type-IV Modems are with Four Ethernet ports and with WI FI (ZTE ZXDSL 531, Siemens SL2-141, Smart AX MT 841 Type 4 etc)
DSL modem:
DSL (Digital Subscriber Line) modem is exclusively used for connections from a telephone switching office to the user. DSL modem is a device used to connect a single computer or router to a DSL phone line, in order to use an ADSL service. Like other modems it is a type of transceiver. It is also called a DSL Transceiver or ATU-R. The acronym NTBBA (network termination broad band adapter, network termination broadband access) is also common in some countries. Some of the ADSL modems also manage the connection and sharing of the ADSL service with a group of machines: in this case, the unit is termed a DSL router or residential gateway