Submitted by

MURTADHA ALI NSAIF SHUKUR

(M.Tech (ECE))

Second semester (1ST year)

WDM(Wavelength-Division Multiplexing)

WDM is based on a well-known concept called frequency

division multiplexing or FDM. With this technology, the

bandwidth of a channel (its frequency domain) is divided

into multiple channels, and each channel occupies a part

of the larger frequency spectrum. In WDM networks, each

channel is called a wavelength. This name is used because

each channel operates at a different frequency and at a

different optical wavelength (and the higher the

frequency, the shorter the signal's wavelength)

Con.WDM The wavelengths on the fiber are separated by unused

spectrum. This practice keeps the wavelengths separated

from each other and helps prevent their interfering with

each other. This idea is called channel spacing, or simply

spacing. It is similar to the idea of guardbands used in

electrical systems. In Figure below, the small gaps

between each channel represent the spacing. The relationbetween frequency and wavelength is ( c = ƛ*f)Mean ƛ c f when increasing (ƛ) performance

decreasing (f) and vice versa .

Con.WDM

(TDMA) Time Division Multiple Access

Time division multiplexing (TDM) provides a user thefull channel capacity but divides the channel usageinto time slots. Each user is given a slot and the slotsare rotated among the users. A pure TDM systemcyclically scans the input signals (incoming traffic)from the multiple incoming data sources(communications links, for example). Bits, bytes, orblocks of data are separated and interleaved togetherinto slots on a single high-speed communications line.

TDMA

Combining WDM and TDM

Most optical networks (or, for that matter, most networks in general) use a combination of WDM and TDM by time-division multiplexing fixed slots onto a specific wavelength, as shown in Figure below. This concept is quite valuable because it allows multiple users to share one WDM wavelength's capacity. With some exceptions, the capacity of one wavelength exceeds an individual user's traffic capacity needs.

Combining WDM and TDM

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