need for DWDM and CWDM

Unanswered Question
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 5 (2 ratings)
viyuan700 Thu, 04/08/2010 - 10:25


1)am still confused a bit about DWDM and CWDM,where and when we need such this technology?mean for customer requirments

CWDM- Your office are 30-40miles away and you have few channels (e.g upto 8 channels). If you dont use CWDM then you need 8 pais of fiber between your offices and you leased 1 pair from SP.

DWDM-Your offices are beyond the reach of Long haul optics cards or you have more channels offered by CWDM. Then you need DWDM as you can amplify signal if your distance is too much or you have too many channels.

2)What is the benefits of Channels e.g up to 40 channels now?

If you need that many channels then you dont need 40pair of fiber. If your distnace are too far then you dont need repeater for every channel (means 40 repeaters )as in DWDM one amplifier can amplify all 40 channels.

3)whose offere this services?its is offered by ISPs Goverments?

Service provider offere wavelengths and deploy DWDM as they have lots of traffic.

DO you have specific requirement or you are just trying to learn. Use google to learn more and specific questions are welcome. As very difficult to type from scratch what DWDM/CWDM is or their advantage.

Tom Randstrom Thu, 04/08/2010 - 10:27

Challenging to answer this in a forum such as this, but I will try to help.

/* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin;}

1)      am still confused a bit about DWDM and CWDM,where and when we need such this technology?mean for customer requirments

I am not clear regarding “customer requirements”. 

Typically, xWDM is used to expand the capacity of installed fiber optic cables.  It is used extensively by telecom service providers (AT&T, BT, etc.) and ISP’s (Comcast, Cable & Wireless, etc.) over their long-haul fiber routes (between cities) as well as some metro networks (within a city or region) to interconnect their central offices. These service providers aggregate and transport data for a large number of customers, which is growing quickly.  It is very expensive to install new fiber cables, especially in large cities, so it is important to use the installed fiber wisely.

Service providers are not installing xWDM (xPON or Passive Optical Network) for transporting services into customer’s home and many small to medium businesses.

Companies, such as service providers, governments, enterprises, etc., many lease dark fibers to interconnect their facilities.  These fiber leases are quite expensive and the customers will typically use xWDM to expand the fiber’s bandwidth capacity and lower their cost per transported bit.

2)      What is the benefits of Channels e.g up to 40 channels now?

The major benefit for xWDM is based on each user’s network requirements.  If you have a network whose bandwidth requirements are modest and there is plenty of unused fiber between the equipment facilities, then xWDM may not be of any benefit.  If you have a situation where your network bandwidth exceeds your trunk interface’s line speed and you do not have dark fiber pairs between your equipment to add another link, then deplying xWDM may be more cost effective than installing new fiber cables. 

Think of each “channel” in a xWDM as a virtual strand of fiber.  Without xWDM, a pair of fiber strands can carry one signal (i.e. GE, 10GE, Fiber Channel, etc.) between two devices (switch, router, etc.).  With a 40 channel xWDM system, the same fiber pair can support 20 signals used by many devices.   

3)      whose offere this services?its is offered by ISPs Goverments?

There are telecom service providers (Level 3, AboveNet, etc.) that sell “wavelength” services to customers. This service allows the customer access to one channel over a pair of fibers. Governments use xWDM to provide their various agencies/departments with dedicated bandwidth within a wavelength. 

There are many situations where xWDM becomes an important tool to lower the overall cost of a data network. 

freebirdking Tue, 08/24/2010 - 21:40

CWDM - Coarse Wavelength Division Multiplexing. WDM systems with
fewer than eight active wavelengths per fiber.

DWDM - Dense Wavelength Division Multiplexing. WDM systems with more
than eight active wavelengths per fiber.
CWDM is defined by wavelengths. DWDM is defined in terms of
frequencies. DWDM’s tighter wavelength spacing fit more channels
onto a single fiber, but cost more to implement and operate
CWDM can—in principle—match the basic capabilities of DWDM but at
lower capacity and lower cost. CWDM enables carriers to respond
flexibly to diverse customer needs in metropolitan regions where
fiber may be at a premium. However, it’s not really in
competition with DWDM as both fulfill distinct roles that largely
depend upon carrier-specific circumstances and requirements anyway.
The point and purpose of CWDM is short-range communications. It
uses wide-range frequencies and spreads wavelengths far apart from
each other. Standardized channel spacing permits room for wavelength
drift as lasers heat up and cool down during operation. By design,
CWDM equipment is compact and cost-effective as compared to DWDM


This Discussion