03-03-2008, 09:57 PM
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 | | | Join Date: Sep 2007 Location: near Govt College of Science Multan Pakistan
Posts: 9,693
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 Re: Assignment on Applications of FDM,WDM,TDM
MY Assignment (Applications...)
FDM:
- Analog telephone system employed FDM to combine multiple voice conversations onto one line. The analog telephone backbones gave way to digital, thus FDM has been replaced with TDM for backhaul trunks.
- Frequency Division Multiple Access used in the analog cellular telephone network that divides the spectrum into 30 kHz channels.
- FDM transmitting multiple data signals simultaneously over a single wire by using multiple carriers, each having a unique center frequency.
- Cable TV companies use FDM to transmit hundreds of channels of analog and digital TV as well as Internet over a single coaxial cable.The cable modem both modulates and demodulates the appropriate carriers to provide bi-directional operation for Internet access.
TDM:
- A network that transmits data in dedicated end-to-end circuits comprising 64 Kbps digital channels. TDM networks evolved from the analog voice networks of the telephone companies. They are widely used for digitized voice and data in the form of digital signal (DS) circuits made up of T1, E1 and OC-1 lines and multiples thereof.
- TDM enabled the telephone companies to migrate from analog to digital on all their long distance trunks, and later to the local loops.
- TDM is widely used to combine multiple 64 Kbps streams into the 1.544 Mbps capacity of a T1 channel.
- A channel bank converts 24 analog voice conversations into digital and then multiplexes them via TDM onto the T1. Contrast with FDM
- A satellite and cellular phone technology that interleaves multiple digital signals onto a single high-speed channel.
- Channel banks use TDM (time division multiplexing) to combine the different signals into one by interleaving the bits.
- Channel banks converted 24 analog voice lines into digital and multiplexed them onto one T1 line.
WDM:- WDM wavelengths can each carry independent signals - OC-3 voice on one wavelength, analog video on another wavelength, and OC-12 ATM on yet another one.
- WDM systems can carry as many as two dozen channels, but in the future, capacity should increase to 128 channels or more on a single fiber. The potential bandwidth on WDM systems is mind boggling. For example, a system with 24 channels, each running at OC-48, would have a total capacity of 60Gbits/sec, and a system with 40 such channels would carry 100Gbits/sec.
- DWDM systems contain many more channels, and therefore much more bandwidth capacity. But most discussions of WDM and DWDM don't strictly define how many channels constitute one or the other, so the terms have become interchangeable (although DWDM is more commonly used).
- DWDM is starting to attract interest in the medium-haul market, which could include metropolitan area networks.
- In the future, fiber networks will probably have a combination of SONET/SDH that runs over a DWDM infrastructure.Most wide area traffic, including IP, is converted to ATM cells and then transported over SONET.
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