Presentation ON A Brief Introduction to WDM and TDM

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.WDMThe 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 relation between 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 the full channel capacity but divides the channel usage into time slots. Each user is given a slot and the slots are rotated among the users. A pure TDM system cyclically scans the input signals (incoming traffic) from the multiple incoming data sources (communications links, for example). Bits, bytes, or blocks of data are separated and interleaved together into slots on a single high-speed communications line.

TDMA

Combining WDM and TDMMost 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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