• Define modulation and its four basic versions
• Define the different types of multiplexing techniques, their benefits, and hardware requirements
• Discuss the fundamental types of switching used in voice and data communications
• Identify the differences between local and tandem switching
• Identify modern signaling techniques used to route calls to their destination
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1. Modulation - A signal-processing technique in which an information wave is imposed on a carrier wave to create a unique wave pattern. Amplitude modulation is a method of modulation in which the amplitude of the carrier signal is modified by the addition of the information signal. Frequency modulation is a method of modulation in which the frequency of the carrier signal is modified by the addition of the information signal. Phase modulation is a type of modulation in which an information wave modifies a carrier wave's phase. Pulse code modulation is used to record instruments playin on a compact disc or to record voice messages on a digital answering machine.
In circuit switching, a connection is established between two nodes before they begin transmitting. The bandwidth is is dedicated to this connection during the entire transmission. In packet switching, data is broken into pieces before they are transported individually. Each packet is free to follow any path to their destination, where they are put back together.
L. Campbell
Differences between local and tandem switching:
Local: provide dial tone; accept and interpret signals from local subscriber; receive signals from destination local switch about when to terminate call; record local subscriber billing info; store information about subscribers in a database; test and manintain subscriber local loop; modify subscriber account and line configuration; provide caller id, call waiting, number blocking, and voice mail; provide operator assistance and access to emergency services.
Tandem: terminates trunks at Class 1,2,3,4 CO; gather and transmit info about telephone network traffic and congestion; determine fastest path over PSTN for long distance; carries data and voice signal between CO; test and maintain trunks; assist in trunk configuration.
Local switches handle signals from a local loop.
Tandem switches handle calls between central offices
Tandem does not deal with subscribers,and local switches do.
Tandem switches are only digital,and local switches deal with analog and digital.
The modern signaling techniques used to route calls to their destination are: Public switching and Local Switching Systems. Public switching routes calls and interconnects telephone subscriber across the PSTN. Local switching systems receives and interprets the signal from subscriber's telephone.
J Otey.
Modulation: Technique for processing signals in which two waves are combined. To produce a wave with the characteristics of both and can be decoded to separate the characteristics.
Modern signaling: changes digital into analog (transmitted) change analog back to digital sends analog over the telephone line. When computer picks up analog signal and translate them back into digital signals the computer can use.
. Frequency Division Multiplexing
2. Time Division Multiplexing
3. Statistical multiplexing
4. Wavelength Division Multiplexing
Multiplexing techniques makes it possible to send more information over a single channel in a shorter period of time relying on simplex transmission.
Hardware:
Multiplexer
Demultiplexer
Andrew G. Mark K. and John N.
1. Modulation is a technique for processing signals in which 2 waves are combined to produce a wave that possesses characteristics of both and can be decoded to seperate these characteristics. AM FM PM PCM
2. Each type needs a multiplexer and a demultiplexer
FDM, TDM, Statistical multiplexing, WDM- Needs a Fiber Optic Modem, DWDM
3. Circuit switching is on while the Call is connected, Message switching- Store and Forward, Packet switching sends information in groups.
4. Tandem switching is switching used between central offices. local switching is used by ILEC's, CLECs and local wireless telephone carriers.
5. Subscriber loop signaling, Interoffice signaling, Common Channel Signaling, Signaling System # 7.
Types of switching- Circuit switching, bandwidth is dedicated during the whole transmission.
Message switching, Store and forward. (e-mail)
Packet switching, Makes it possible to find the fastest circuit available at any instant.
Packets may take a diffrent route to the destination
Define the different types of multiplexing techniques, their benefits, and hardware requirements.
FDMis a analog signal used for Radio & Cable Broadcast.
TDM is used with data networks it assigns time slots.
Statistical is similar to TDM it assigns time slots but does not use them.
WDM is a new technology that uses fiber optics.
Modulation processes signals into which two waves are combined to produce a wave that has characteristics of both. The four types are: Amplitude Modulation (AM), Frequency Modulation (FM), Phase Modulation (PM), and Pulse Code Modulation (PCM).
Frequency Division Multiplexing(FDM) is sending multiple analog signals simultaneously over one channel by separating the channel into bands. The guardband reduces noise. It's used for voice, video and data. The hardware requirements are coaxial cable, telephone line or the airways.
Time Division Multiplexing(TDM) assigns time slots to every device that exchanges signals. It is inefficient because some time slots are left empty. T-carriers, SONET and cell phones use it.
Statistical Multiplexing is similar to TDM. It is more efficient because if a slot is empty, it sends that slot to another device that needs it. ISDN, ATM and frame relay use it.
Wave Division Multiplexing(WDM) uses a single strand of fiber optic cable. It separates it into subchannels according to wavelength. A Fiber Optic Modem(FOM) is used instead of a mux and demux. It is much more efficient.
Dense Wavelength Division Multiplexing (DWDM) is same as WDM except it supports a larger number of different wavelengths. Fiber optic cables are used.
Circuit switching is a method in which a connection must be established between 2 devices before transmission can occur. The bandwidth is dedicated. All data travels over one path.
Packet switching breaks data into packets before they are transported. They can travel over different paths.
Message switching is also called "store and forward". It receives the entire message before it forwards it. It is used in email.
Local switching is switching over a local loop.
Tandem switching is between central offices.
The 4 types of signaling include: Subscriber loop signaling, Interoffice signaling, Common Channel Signaling(CCS) and Signaling System #7(SS7).
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