Modem

Seminar onSeminar onMODEMSMODEMS

MODEMSMODEMS

Converts analog signals to Converts analog signals to digital and vice-versadigital and vice-versa

MODEMSMODEMS

A modem is a device or program that enablesA modem is a device or program that enables

computer to transmitt data over telephone lines.computer to transmitt data over telephone lines.

Computer information is stored digitally, whereasComputer information is stored digitally, whereas

information transmitted over telephone lines is information transmitted over telephone lines is

transmitted in the form of analog waves.A modem transmitted in the form of analog waves.A modem converts between these two forms. converts between these two forms.

IntroductionIntroduction

Modulator – converts digital Modulator – converts digital information to analoginformation to analog

Demodulator – converts analog Demodulator – converts analog information to digitalinformation to digital

Basic PrincipleBasic Principle

01010101

Basic StructureBasic Structure

How Modulation How Modulation is used for data is used for data

transfer ?transfer ?10100101011001010 - the 10100101011001010 - the

transmitted symbol sequence transmitted symbol sequence will be: 6 4 5 1 2. will be: 6 4 5 1 2.

Classification of ModemsClassification of Modems

Range Range Line Type Line Type Operation ModeOperation Mode SynchronizationSynchronization Modulation Modulation Data RateData Rate

Range Line Range Line TypeType

Short HaulShort Haul Voice GradeVoice Grade Wide BandWide Band

Dial-up Dial-up LeasedLeased PrivatePrivate

Operation Mode Operation Mode ModulationModulation

SimplexSimplex Half-DuplexHalf-Duplex Full-DuplexFull-Duplex

AMAM FMFM PMPM TCMTCM

CABLE MODEMCABLE MODEM

Cable Modems make access to TV cable, Cable Modems make access to TV cable, and let you get  high-speed internet access. and let you get  high-speed internet access.

Availability is still limited in many areas, Availability is still limited in many areas, but is growing rapidly. but is growing rapidly.

EXTERNAL MODEMEXTERNAL MODEM It usually plug in through a serial port, or  a It usually plug in through a serial port, or  a

USB port. USB port. 

External modems cost the most, but have the External modems cost the most, but have the benefits of being easily installed. benefits of being easily installed.

Also plugs into telephone line.Also plugs into telephone line.

External power supply is needed.External power supply is needed.

Holder case is required.Holder case is required.

Often they have the  indicators that tell the Often they have the  indicators that tell the status of your connection there is one status of your connection there is one standard interface for connecting external standard interface for connecting external modems to computers called RS-232.modems to computers called RS-232.

TYPICAL INDICATERS ON EXTERNAL MODEMS FRONT TYPICAL INDICATERS ON EXTERNAL MODEMS FRONT PANALPANAL

HS = HIGH SPEEDHS = HIGH SPEED AA = AUTO ANSWERAA = AUTO ANSWER CD =CARRIER DETECTCD =CARRIER DETECT OH =OFF HOOKOH =OFF HOOK RD =RECIVED DATARD =RECIVED DATA SD =SEND DATASD =SEND DATA TR =TERMINAL READYTR =TERMINAL READY MR = MODEM READYMR = MODEM READY

INTERNAL MODEMINTERNAL MODEM It can insert into a vacant It can insert into a vacant

expansion slot. expansion slot.

No external power supply is No external power supply is needed.needed.

No holder case is required.No holder case is required.

Least expensive at given speed.Least expensive at given speed.

Incompatible with different kind Incompatible with different kind of PCs.of PCs.

These modems go inside the These modems go inside the computer, and usually plug computer, and usually plug directly into the motherboard. directly into the motherboard.

ISDN MODEMISDN MODEM ISDN is an abbreviation for Integrated Services Digital Network. ISDN is an abbreviation for Integrated Services Digital Network.

There is no such thing as a noisy or fuzzy line.  There is no such thing as a noisy or fuzzy line.  always runs at 64kbps. always runs at 64kbps.

Ability to bond multiple "B" channels to get speeds of 128kbps. Ability to bond multiple "B" channels to get speeds of 128kbps.

Call Setup is very fast (dialing, handshake and authentication), Call Setup is very fast (dialing, handshake and authentication), usually under 2 seconds (compared with 15 seconds at least for usually under 2 seconds (compared with 15 seconds at least for most analog modems). most analog modems).

Ability to get 2 calls at the same phone number (one line is for Ability to get 2 calls at the same phone number (one line is for voice, and the other line for your internet connection). voice, and the other line for your internet connection).

WIRELESS MODEMWIRELESS MODEM Convert digital data into  radio Convert digital data into  radio

signals and back.  signals and back.  Support a maximum data Support a maximum data

transmission rate of 19.2Kbps transmission rate of 19.2Kbps (kilobits per second). (kilobits per second).

Wireless modems can be used up Wireless modems can be used up to 20-30 miles (30-50 KM).to 20-30 miles (30-50 KM).

Operation is in the 900 MHz and Operation is in the 900 MHz and 2.4 GHz.  2.4 GHz. 

Modem names include – Modem names include – BreeseLINK, LATNET-Radio BreeseLINK, LATNET-Radio

Data Links, AirLink Wireless Data Links, AirLink Wireless Modems, and Open Minds. Modems, and Open Minds.

FAX MODEMFAX MODEM

A fax modem in PC can send data to a standard A fax modem in PC can send data to a standard fax machine, which converts data into hard copy fax machine, which converts data into hard copy form. form.

On the other hand a PC fax system can receive a On the other hand a PC fax system can receive a transmission from a standard fax machine and transmission from a standard fax machine and capture the image into graphic file. capture the image into graphic file.

The fax server eliminates the need for each PC in The fax server eliminates the need for each PC in the network to be equipped with its own fax the network to be equipped with its own fax modem and telephone line.modem and telephone line.

DSL MODEMDSL MODEM DSL Modems: DSL (Digital Subscriber Line)  service is DSL Modems: DSL (Digital Subscriber Line)  service is

usually offered through  the phone the company/ISP. usually offered through  the phone the company/ISP.

You can leave your Internet connection open and still use You can leave your Internet connection open and still use the phone line for voice calls.the phone line for voice calls.

The speed is much higher than a regular modem (up to The speed is much higher than a regular modem (up to 1.5 Mbps )1.5 Mbps )

DSL doesn't necessarily require new wiring; it can use the DSL doesn't necessarily require new wiring; it can use the phone line you already havephone line you already have

56K MODEMS56K MODEMS The latest modems are equipped with many facilities The latest modems are equipped with many facilities

they have a speed which can even reach a data transfer they have a speed which can even reach a data transfer speed of 56.6 kbps . They have all facilities like fax, auto-speed of 56.6 kbps . They have all facilities like fax, auto-answering, auto-dialing etc. answering, auto-dialing etc.

They are asymmetrical in that the downloadingThey are asymmetrical in that the downloading is a maximum of 56kbps. is a maximum of 56kbps.

The uploading can be maximum of 33.6 kbps.The uploading can be maximum of 33.6 kbps.

Modem SpeedModem Speed

The Modulation SpeedThe Modulation Speed The Serial Port SpeedThe Serial Port Speed

SPEED OF MODEMSPEED OF MODEM

Modem speed is rated in bps (bits per Modem speed is rated in bps (bits per second).  So a 56k modem transmits at second).  So a 56k modem transmits at 56,000 bits per second in theory. While 8 56,000 bits per second in theory. While 8 bits make a byte, and 1024 bits equal one bits make a byte, and 1024 bits equal one kilobits, a 56k modem will transmit a kilobits, a 56k modem will transmit a maximum of approximately 7 kilobytes of maximum of approximately 7 kilobytes of information every second.   A modem will information every second.   A modem will never connect higher than what it is rated never connect higher than what it is rated for. for.

Modem InstallationModem Installation

Modem Cable SelectionModem Cable Selection Selection of PortSelection of Port

STANDARDSSTANDARDS

ITU ITU :-- International Telecommunication. :-- International Telecommunication. Union.Union.

ISO ISO :-- International Standard Organization. :-- International Standard Organization.

CCITTCCITT :-- International Consultative :-- International Consultative Committee For Telephone And Telegraphy.Committee For Telephone And Telegraphy.

DIFFERENT CCITT DIFFERENT CCITT STANDARDSSTANDARDS

Bell 103 & 212ABell 103 & 212A: :

Bell 103 transmits at 300 bps at 1 bit per baud. Bell 103 transmits at 300 bps at 1 bit per baud. Bell 212A was the next step up, capable of two Bell 212A was the next step up, capable of two bits per baud. It was capable of 1200bps at 600 bits per baud. It was capable of 1200bps at 600 baud. baud.

V.21:V.21:

It was a sort of international standard. It is not It was a sort of international standard. It is not compatible with Bell protocols, and is only compatible with Bell protocols, and is only capable of 300bps. capable of 300bps.

V.22V.22:: Shares the features of V.21, but was capable ofShares the features of V.21, but was capable of 1200bps ,ran at 4 bits per baud for a total of 2400bps 1200bps ,ran at 4 bits per baud for a total of 2400bps

V.23:V.23: This allowed the modem to send and receive data at This allowed the modem to send and receive data at

the same time, although it could send data only at the same time, although it could send data only at 75bps. This standard was developed to lower the cost 75bps. This standard was developed to lower the cost of modems. A 1200 bps modem was very expensive at of modems. A 1200 bps modem was very expensive at the time.the time.

V.29V.29:: A half-duplex standard, meaning one-way. It works at A half-duplex standard, meaning one-way. It works at

9600bps. The standard is not laid out well for modems, 9600bps. The standard is not laid out well for modems, therefore isn't much used. The protocol is most often therefore isn't much used. The protocol is most often used for fax machines used for fax machines

V.32V.32:: It was a full-duplex standard and operated at It was a full-duplex standard and operated at

9600bps, with a 2400 baud rate. 9600bps, with a 2400 baud rate.

V.32bisV.32bis:: It transmitted 6 bits per baud, allowing It transmitted 6 bits per baud, allowing

throughputs of 14,400 bps.throughputs of 14,400 bps. V.32 Fast:V.32 Fast: Better known as the 28,800 bps modem. Better known as the 28,800 bps modem.

V.34V.34:: The latest real modem standard. It provides a The latest real modem standard. It provides a

reliable 28,800 bps connection. the standard is reliable 28,800 bps connection. the standard is often used for 33,600 bps transmissions. often used for 33,600 bps transmissions.

Error Correction :Error Correction : Error Correction is an important feature in the Error Correction is an important feature in the

fastest modems. It allows fast reliable fastest modems. It allows fast reliable connections over standard phone lines, even past connections over standard phone lines, even past noise. noise.

Modems use the V.42 error correction protocol. Modems use the V.42 error correction protocol. With it, the modem can detect damaged data With it, the modem can detect damaged data streams, and the data will be resent. streams, and the data will be resent.

The V.42bis protocol is just like V.42, but The V.42bis protocol is just like V.42, but incorporates data compression. A 14.4 modem, incorporates data compression. A 14.4 modem, with data compression, can boast transmission with data compression, can boast transmission rates of 57,600 bps. rates of 57,600 bps.

PROTOCOLSPROTOCOLS

V.34 -  for 28.8k and 33.6k communications.  V.34 -  for 28.8k and 33.6k communications.  K56Flex - for 56k communication,  created by Lucent K56Flex - for 56k communication,  created by Lucent

and Rockwell.  and Rockwell.  X2 - for 56k communication,  created by US Robotics X2 - for 56k communication,  created by US Robotics

(3com).  (3com).  V.90 - This is the International Standard for 56k V.90 - This is the International Standard for 56k

modems.   modems.   V.92 - This is an  ITU (international V.92 - This is an  ITU (international

Telecommunication Union) standard for 56K modems, Telecommunication Union) standard for 56K modems, but three new features have been added -- faster but three new features have been added -- faster connections (on 50%), better uploading, and data and connections (on 50%), better uploading, and data and voice support: voice support:

ERROR CORRECTION ERROR CORRECTION PROTOCOLPROTOCOL

There are 2 protocols that are used to correct There are 2 protocols that are used to correct errors on a connection:errors on a connection:

V.42 (LAPM) – This is the International Standard V.42 (LAPM) – This is the International Standard for doing Error Correction .for doing Error Correction .

MNP –  an old protocol that most modems MNP –  an old protocol that most modems support.  support. 

Today’s Status & Future Today’s Status & Future TrendsTrends

Semiconductor modems introducedSemiconductor modems introduced Increased speedIncreased speed Less complicationLess complication More use due to internetMore use due to internet Frequent use of internal modemFrequent use of internal modem

LATEST TRENDS OF MODEMSLATEST TRENDS OF MODEMS

They have a speed which can even reach a data They have a speed which can even reach a data transfer speed of 56.6 kbps . transfer speed of 56.6 kbps .

They have all facilities like fax, auto-answering, They have all facilities like fax, auto-answering, auto-dialing etc.auto-dialing etc.

The latest facility available in modems is caller id, The latest facility available in modems is caller id, Distinctive ring detection, Faxing. etc.Distinctive ring detection, Faxing. etc.

BibliographyBibliography

Hardware Bible Winn.L.Rosch

Data Communications Prakash .C. Gupta

Data Comm. & Networking Behrouz .A. Forouzan

Internet