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WDM – Wavelength Division Multiplexing technology and its variations DWDM, UDWDM and CWDM
How to economically send more traffic over only single fiber

20121116143834643464Fiber optic is the most reliable medium and it is out of question. But, can we do something in case when our network is growing up really fast, we have more and more sites to hook up, our infrastructure starts to suffer for lack of usable fibers and we have no additional place in the pipes to put another fiber optic cables? Sure we can, WDM (Wavelength Division Multiplexing) technology will come forward !

Wavelength Division Multiplexing technique enables us use many light waves with different wavelength of transmission in single fiber optic.That technology may by classified in a view of number of used channels and spacing between channels in the field of length of the light wave. Nowadays we distinguish 4 kinds of WDM technique : WDM, DWDM, UWDM and CWDM


Characterizes with a small number of used wavelengths (2,4,8). These days the most often are being used 2 wavelengths 1310nm and 1550nm. Both channels are sent via single optical link. Usually you get a pair of biderictional WDM SFP modules with switched RX/TX



DWDM – Dense Wavelength Division Multiplexing
In case of DWDM the number of usable channels is equal of several dozens and standard spacing between channels is 0,8nm. Another evolution of that technique is UWDM (Ultra Dense Wavelength Division Multiplexing) where spacing between channel is 0,4nm and number of usable channels is equal of several hundreds.Currently experimental works with spacing between channels equal 0,1nm are being conducted, but the rules of work for them are the same. Nowadays DWDM systems based on frequency grid with spacing 50GHz (0,4nm), 100GHz (0,8nm) and 200GHz (1,6nm) and are applied with frequency reference equal 193,1 THz.



CWDM Coarse Wavelenght Division Multiplexing
Technology, which gives us  the best solution from the economic point of view, creating the networks with using wave multiplexing is CWDM. It enables us sending from 4 up to 16 optical channels, so less then DWDM technique, but thanks to relatively large spacing between channels (20nm) allows us applying cheaper transceivers and elements of the optical line. CWDM are based on 20nm spacing between channels. Mandatory wavelengths amount to: 1470, 1490, 1510, 1530, 1550, 1570, 1590, 1610. Surprisingly CWDM can carry DWDM wavelengths owing to wider wavelength spacing, so we may pack up a couple of DWDM systems into one CWDM.



Multiplexer and Demultiplexer


Mux and Demux appliances will be needed in order to combine and separate traffic which come from particular switch ports. It happens because each port in MUX and DEMUX work on different wavelength according what I described above, but they are all send via only one single fiber.


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