WDM & DWDM?

I’ve recently been in quite a few meetings where the acronyms WDM and DWDM have been used. Now I know what WDM is wavelength division multiplexing, but I didn’t agree with them being swapped in and out as one is different from the other.

OK WDM is straight forward enough; Multiplexing is used To combine multiple signals (analogue or digital) for transmission over a single line or media. In the case of the media being fibre, then WDM is used whereby each signal is assigned a particular wavelength.

WDM is the optical equivalent of FDM, short for frequency division multiplexing, a multiplexing technique that uses different frequencies to combine multiple streams of data for transmission over a communications medium. FDM assigns a discrete carrier frequency to each data stream and then combines many modulated carrier frequencies for transmission. For example, television transmitters use FDM to broadcast several channels at once.

DWDM is short for Dense Wavelength Division Multiplexing, an optical technology used to increase bandwidth over existing fibre optic backbones. DWDM works by combining and transmitting multiple signals simultaneously at different wavelengths on the same fibre. In effect, one fibre is transformed into multiple virtual fibres. A key advantage to DWDM is that it’s protocol- and bit-rate-independent. DWDM-based networks can transmit data in IP, ATM, SONET /SDH, and Ethernet, and handle bit rates between 100 Mb/s and 2.5 Gb/s. Therefore, DWDM-based networks can carry different types of traffic at different speeds over an optical channel

So for networks where VoIP is requirement then from a QoS standpoint, DWDM-based networks create a lower cost way to quickly respond to customers’ bandwidth demands and protocol changes.

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