What is WDM and DWDM (Densed Wavelength Division Multiplexing)

Mumbai University > Electronics Engineering > Sem 8 > Advanced Networking Technologies

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  1. Wavelength Division Multiplexing WDM is a technology which multiplexers a number of optical fibre by using different wavelengths of laser light.
  2. This technique enables bidirectional communication over one stand of fibre as well as well as multiplication of capacity.
  3. DWDM refers to optical signals multiplexed within 1550nm band and has a greater overall capacity than WDM
  4. DWDM allows 160 wavelengths to be segmented per fibre with higher number of possible, where each wavelength can support anywhere from 2.5 to 10Gbps.

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DWDM allows 160 wavelengths to be supported per fibre with higher number possible, where each wavelength can support anywhere from 2.5 to 10Gbps.

DWDM Hardware

DWDM equipment typically works only in the optical domain.

  1. DWDM Multiplexer / Demultiplexer

    • Combines multiple optical signals into a single optical fibre and separates optical signals.
  2. Optical Add / Drop Multiplexers (OADM)

    • Acts like a SADM except that if functions exclusively in the optical domain. It allows a wavelength to be split or added to a DWDM fibre
  3. OXC Optical Cross Connect

    • Acts as a cross connect between input ports and m-output ports
    • It provides efficient network management of wavelengths at the optical layer.
    • The functions that can be performed are signal monitoring, grooming, provision, restoration etc.
  4. Optical amplifier

    • Amplifies the optical signals so that the signalling strengths can travel over long distances.
    • It increases the power of signal and regeneration produces the original signals.
    • An optical amplifier is a cost effective method for extending the distance between end devices or regeneration
    • Optical amplifier works in optical domain and can amplify all the wavelengths.
    • They are placed in every line 80-120km.


A DWDM is not as interfaces specific as SONET but if can support many interfaces like

  • Ethernet
  • Fibre Cable
  • ATM

Optical network configuration

  • Point to Point
  • Ring
  • Mesh (Partial or full)

Advantages of DWDM

  • Every wavelength is independent of others
  • Optical amplifier can act on all wavelengths, providing cost savings over a single amplifier per fibre.
  • The capability to support 160 wavelengths means that over 1Tbps of traffic can be used.
  • Each wavelength can be a different traffic type such as SONET, gigabit, Ethernet or IP can be operated at different speeds.
  • This provides Bandwidth and protocol flexibility with payload efficiency.


  • Some fibre plants are not suitable for DWDM
  • Vendor Inter-operability issues exist
  • DWDM systems can be extremely difficult to troubleshoot, manage and provision.
  • Service providers typically run SONET over DWDM to utilize SONETS’s network management capabilities but DWDM equipment’s need to be managed.
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