Continued… DWDM Part IV

To recap, DWDM technology has been developed to increase the capacity of a single fiber SONET/SDH technology, which transmits information via a single channel or wavelength of light via each fiber optic strand. The term “dense” refers to high-wavelength or high-channel count per fiber. In essence, each wavelength represents a different transmission channel and can transmit data at 10 Gbps.

DWDM can offer potentially unlimited bandwidth at multi-gigabit and multi-terra-bit rates by carrying multiple light waves of different frequencies on a single fiber. A single fiber can carry up to 128 wavelengths and researchers/technologists are working on DWDM technologies that could carry more than 1,000 channels within a single fiber.

Operationally, optical network deployments represent a significant CAPEX (Capital Expenditures) investment. However, the rapidly falling cost of raw fiber will accelerate the adoption of this technology.

For today post, I’ll discuss on the capabilities and merits of DWDM as practical considerations for the service providers to deploy DWDM networks.

  • Extendibles:

DWDM is a more cost-effective alternative to SONET/SDH, which employs Time Division Multiplexing (TDM). A highway analogy, where one fiber can be considered as a multi-lane highway, can be used to explain the difference between the two. TDM relates to traffic flow on single lane of the highway. To increase the throughput of autos, one can increase their speed that is equivalent to time multiplexing.

DWDM, on the other hand, relates to the accessing the unused lanes on the highway. Another way to increase auto throughput is to add more lanes that is equivalent to wavelength multiplexing.  DWDM combines multiple optical signals so that they can be amplified as a group and transported over a single fiber to increase capacity. Each signal transmitted can be at a different rate (OC–3/12/24, etc.) and in a different format (SONET/SDH, ATM, IP, WDM, and Gigabit Ethernet, etc.).

[I’ll discuss further on TDM-DWDM analogy with graphical illustrations in future post for a better understanding]

The operations associated with TDM electronic-to-optical and optical-to-electronic somehow rather slow the performance of SONET/SDH networks. These operations convert data signals from the electronic network to optical format, route the signals to their proper destinations within the optical part of the infrastructure, and then convert them back again for their continued journey over the electronic portion of the network.

DWDM technology, on the other hand, employs an Erbium Doped Fiber Optic Amplifier (EDFA) with advanced filtering techniques to amplify optical signals without converting them to electrical signals.DWDM uses Optical Bi-directional Line Switched Ring (OBLSR) topologies to optimize bandwidth capacity of the in-place fiber optic plant and the traffic volumes transported via the Optical Layer. A DWDM infrastructure also increases the distances between network elements – a big benefit for long-distance (long-haul) service providers looking to reduce their initial network investments significantly.

DWDM uses advanced wavelength routing protocols and gigabit routers for provisioning of wavelength or channel capacity. DWDM employs tunable lasers for enabling development of multiple, independent, narrowly spaced transmission channels or wavelengths on a single fiber optic strand.

Source:  DWDM: Technologies and Initiatives by Khoa Duc Tran

To be continued… DWDM Part V – Capabilities and Merits


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