BLOG

By Guilherme Salvadori – Presales Engineer

Introduction

The need for high bandwidth capacity is increasing in the ISP market. Finding a solution to extend link capacity by optimizing existing fiber optic infrastructure is critical to business competitiveness.

What it is and what it is for

XWDM technology has been around since the late 1970s. The technique consists of multiplexing wavelengths, thus enabling the transmission of multiple optical channels on only one pair of fibers. The best known xWDM standards in the industry are Coarse Wavelength Division Multiplexing (CWDM) and Dense Wavelength Division Multiplexing (DWDM).

The CWDM standard allows transmission of up to 18 channels ranging from 1271nm to 1611nm, with 20nm spacing (ITU-T G.694.2). This standard allows transmission of channels with bandwidths up to 2.5Gb and distance up to 60km, not allowing EDFA optical amplification due to channel spacing.

Dense Wavelength Division Multiplexing (DWDM) multiplexing has denser channel spacings that can range from 1.6nm to 0.2nm. This allows more channels to be multiplexed than CWDM and can transmit more than 128 channels on a single fiber pair. The technology allows a channel transmission capacity of up to 100Gb and can reach hundreds of kilometers using amplifiers.

When to use

Noteworthy is the popularization of equipment with 10Gb Ethernet interfaces for data transmission, but end consumers are demanding ever larger internet connections, which eventually clog the existing 10Gb links.

This gives you the options to invest in switches with 40Gb or 100Gb ports (such as Datacom switches: DM4170, DM4250 and DM4270 or use more 10Gb ports than existing switches.

In case of using more 10Gb ports there is the problem of physical infrastructure, in this scenario comes the DWDM that optimizes the existing optical fiber by passing multiple 10Gb channels just adding a passive equipment at the ends, without having to change anything on the uplink optical fiber.

Datacom Solution

Datacom has a compact and passive solution that extends the fiber optic transmission capacity, making it possible to transport up to 08 10Gb channels transparently over a single fiber pair.

The DM936 Mux / Demux is compact equipment that can be rack mounted 19 ”via the MA-26 adapter, which can hold up to 3 units of equipment at 1U in height. Because it is passive, the DM936 does not require power to operate, simply connect the optical cords from the color DWDM transceivers installed on the customer switch.

Datacom's solution allows you to reach a distance of up to 65km with mux/demux only, without optical amplification:

There is also the 1U high EDFA optical amplifier module with redundant power supply and SNMP management. With the addition of the optical amplifier, links up to 80km can be reached:

In very long links, we have the effect called chromatic dispersion, which is the widening of the optical signal due to the different speeds of wavelengths that are traveling in the fiber. Datacom has the DM936-DCM40 module that corrects the effect of chromatic dispersion, using this module together with the EDFA amplifier can reach up to 110km:

Some interesting observations about the solution:

• Links should be peer-to-peer, for ring topology always consider two sets of DM936 per site.
• DWDM works on layer 1 of the OSI (physical) model, so no configuration is required on the device, it's plug and play.
• The technology is transparent, that is, the equipment does not handle the protocols that are trafficking in the links. It is fully possible to have the most diverse protocols and services working on the same optical fiber without any interference from each other.
• It is compatible with any Ethernet equipment (no manufacturer restrictions), just add the color DWDM transceiver to the ethernet equipment and connect it to the DM936.
• The Datacom solution has no transponder (module that converts standard wavelength 1310 / 1550nm transceivers into DWDM wavelengths), DWDM modules must be used at specific wavelengths, there are a total of 08 discrete modules that go from the channel 33 to channel 40 of band C. Only one transceiver of each channel should be used per mux / demux.
• It is the market practice to swap erased fiber, in the case of DM936 it is possible to swap a DWDM port and will have almost the same effect as an erased fiber (limited to 10Gb).
• Allows greater distance to 40Gb and 100Gb switch solutions, which reach around 40km without amplification.

For more details, see the datasheet by clicking this link, or contact our presales team: suporte.prevendas@datacom.com.br. We are available to assist you in designing your network topology and choosing the product that best suits your needs.

For questions and request for proposal, do not hesitate to contact the Datacom sales team: sales@datacom.com.br (+55) 51 3933 3000.

UPDATED ON 6/10/2020:

In 2020, Datacom launched new passive DWDM models, which in addition to the 8-port model reported in this article, include the following configurations:

• 32-channel 10Gb Mux / Demux, using two fibers
• 16-channel 10Gb Mux / Demux, using only one fiber

Further details can be found in the article New solutions for expanding 10Gb optical links.