2016年12月28日星期三

CWDM Comparison With DWDM


Wavelength Division Multiplexing (WDM) is a technique, which uses a special property of fiber-optics. This property allows the combination of multiple signals onto a single strand of fiber. Each signal is assigned to a different wavelength of light. Since one wavelength does not affect another wavelength, the signals do not interfere. It is the technology enabling cost efficient upgrade of capacity in optical networks. Coarse WDM (CWDM) and Dense WDM(DWDM) are different wavelength patterns of WDM systems. This tutorial is going to compare CWDM and DWDM in many aspects covering features, transmission distance, applications and cost etc.

CWDM Introduction

CWDM, namely Coarse WDM, was introduced as a low-cost approach to increasing bandwidth utilization of the fiber infrastructure. By using several wavelengths (colours) of the light, 18 channels are viable in the spectrum grid from 1270 nm to 1610 nm with a 20 nm channel spacing which is defined in the ITU-T standard G.694.2. However, for different applications, there are different ITU-T standard to define the specific wave range and channels. For instance, according to the ITU-T G.695, CWDM increases fiber capacity in either 4, 8, or 16 channel increments. By increasing the channel spacing between wavelengths on the fiber, CWDM allows for a simple and affordable method of carrying up to 16 channels on a single fiber.

Benefits of CWDM:
Passive equipment that uses no electrical powerMuch lower cost per channel than DWDMScalability to grow the fiber capacity as neededWith little or no increased costProtocol transparentEase of use

Drawbacks of CWDM:
16 channels may not be enoughPassive equipment that has no management capabilitiesCosts significantly more per channel than BWDM

DWDM Introduction

Dense WDM (DWDM) is the technology of choice for transporting extremely large amounts of data traffic over metro or long distances in telecom networks. Optical networking and especially the use of DWDM technology has proven to be the optimal way of combining cost efficient transport with advanced functionality, which can cope with the bandwidth explosion from the access network.

DWDM typically has the capability to transport up to 80 channels (wavelengths) in what is known as the Conventional band or C band spectrum, with all 80 channels in the 1550 nm region. DWDM takes advantage of the operating window of the Erbium Doped Fibre Amplifier (EDFA) to amplify the optical channels and extend the operating range of the system to over 1500 km. This denser channel spacing requires tighter control of the wavelengths and therefore cooled lasers as opposed to Coarse Wavelength Division Multiplexing (CWDM) which has broader channel spacing un-cooled lasers.

Benefits of DWDM:

Up to 32 channels can be done passivelyUp to 160 channels with an active solutionActive solutions involve optical amplifiersTo achieve longer distances

Drawbacks of DWDM:
DWDM solutions areQuite expensiveActive solutions require a lot ofSet-up and maintenance expenseVery little scalability forDeployments under 32 channels



CWDM VS DWDM

According to the respective introduction to CWDM and DWDM above, we know that CWDM is defined by wavelengths and DWDM is defined in terms of frequencies. This is the basic difference between these two kinds of technologies.

CWDM VS DWDM
For applications, DWDM's tighter wavelength spacing fit more channels onto a single fiber, but cost more to implement and operate. CWDM match the basic capacities of DWDM but at lower capacity and lower cost. CWDM enable carriers to respond flexibly to divers customers needs in metropolitan regions where fiber may be at a premium. The point and purpose of CWDM is short-range communications. It uses wide-range frequencies and spreads wavelengths far apart from each other. DWDM is designed for long-haul transmission where wavelengths are packed tightly together. Vendors have found various techniques for cramming 32, 64, or 128 wavelengths into a fiber. DWDM system is boosted by Erbium-Doped Fiber Amplifier, so that to work over thousands of kilometers for high-speed communications.

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