Modems Flashcards
What does modem stand for ?
Modulator - demodulator
Define my modem ?
A device that modulates an analogue carrier signal and encodes the information in digital format
It also demodulates the carrier signal to enable decoding of the transmitted information
What are the two types of modem ?
Serial and parallel
What is a serial modem ?
It is a modem that transmits and receives one bit at a time
What is a parallel modem ?
It is a modem that transmits and receives data via a number of levels and more than one bit at a time
What are the advantages of serial modems ?
Reduces the cable size needed and often less expensive
There is. I requirement for synchronisation between terminals - better over a long distance
What is the disadvantage of a serial modem ?
They have much slower transmitter times
What are the advantage of parallel modems ?
Faster transmission times
What are the disadvantages of parallel modems?
They require an internal clock to maintain synchronicity
Require signalling commands to transmit data
Where are modems employed ?
Computes, teleprinters, digital speech, narrow band phone dial up, broadband internet
In narrow band/ phone dial up modems what are its two basic functional parts ?
An analogue section for generating signals and operating the phone
A digital section for set up and control
What two modes can an narrow band / phone dial up modem be in while operational ?
Data mode- data is sent to and from the compute over the phone line
Command mode - the modem listens to data from the computer for commands, then carries them out
What is a typical session for a narrowband/dial up modem ?
Powering up the modem which automatically is in command mode … command for dialling a number ….. once connection is established it will go into data mode
What uses radio modems ?
Direct broadcast satellite
Wifi
Mobile phones
Where are radio modems commonly deployed ?
High speed computer network links to outlying areas where the laying of fibre cable may not be economical
Where are wireless data modems used ?
In wifi and WiMAX standards which operate at microwave frequencies
Where is wifi principally used ?
In laptops for internet connections and in wireless application protocol
When can a wifi enabled devices connect to the internet ?
When it is in range of a wireless network connected to the internet
What is the coverage of one or more access points called ?
A hot spot
What area can a hot spot comprise ?
As small as a few rooms to as large as many square miles
What does WiMAX stand for ?
Worldwide interoperability for microwave access
What is WiMAX ?
A telecommunications protocol that provides fixed and fully mobile internet access
What is the advantage of WiMAX over wifi ?
WiMAX enables data transfer between nodes at greater distances and greater speeds
What does WiMAX utilise ?
Orthogonal frequency division multiplexing
What are three types of mobile/cellular modem ?
Gprs- general packet radio service
Umts- universal mobile telecommunications systems
Hspa- high speed packet access
What is a benefit of a cellular router ?
It allows multiple people to connect to it
What is a modem made for ?
One connection
Explain broadband modems ?
They are more advanced than dial up modems , as they can modulate/ demodulate hundreds of channels simultaneously
What does ITU stand for ?
International telecommunications union
Expand ITU-R and describe thier focus ?
International telecommunications union - radio communications
Responsible for the management of international radio frequency spectrum and satellite orbit resources
Expand and describe the focus of ITU-T
International telecommunications union- T standardisation
Set the standard relating to modems that utilise telephone circuitry
Expand and describe ITU -D
International telecommunications union - development sector
Help spread equitable, sustainable and affordable access to information and communication technologies
What does the ITU-T V series recommendations do ?
Provides recommendations for data communications over the telephone network,
Specifically protocols that given approved modem communications, standards and interfaces
What are the v.23 recommendations ?
Half duplex between to analogue modems using FSK modulation.
600-1200 bands
600-1200 bits
What are the v.90 recommendations ?
Modem allowing 56.4 kbits download to 33.6 kbits upload
What three types of data do modems typically send ?
Digital facsimile
High speed data
Telemetary and telecontrol
Expand gprs
General packet radio service
Expand Umts
Universal mobile telecommunications systems
Expand hspa
High speed packet access
