A QSFP28 is a combination of transmitter and receiver for the transfer of optical signals. The QSFP28 uses an electronic to optical converter to translate the signals within the QSFP28 . For the transmission, the QSFP28 uses LEDs or lasers. https://www.cbo-it.de/shop/QSFP28-Transceivers

1. 100G DWDM QSFP28: The Enabler of 100G End-to-
End Long Distance Connectivity!
Standard optical transmission transceivers including CFP and QSFP28 transceiver modules are
quite efficient for 100G transmission within data centers. However, it becomes an issue as they
cannot be used for transporting data over long distances like in cases where traffic is needed to
be carried between multiple data centers, geographically dispersed and situated far from one
another (say over 60 kilometers). Here comes the role of 100G DWDM QSFP28 transceivers.
DWDM technology is not new in the industry as DWDM SFP transceivers are widely used for the
expansion of 10G network capacity. Regarding functionality, the 100G DWDM is quite similar
to its predecessor. Though, it is typically used in 100G networks for transmission over longer
distances.
100G DWDM QSFP28: The Broader Reach,
More Agile Solution
100G DWDM QSFP28 works on an advanced and state-of-the-art modulation technique called
PAM4. Moreover, it takes a form factor similar to QSFP transceiver modules and can directly be
used on switches with available QSFP28 ports – capitalizing on the IEEE CAUI-4 4x 25G electrical
interfaces. One of the significant benefits of DWDM QSFP28 PAM4 is its lower power consump-
tion which makes it into a practical solution for data center interconnect applications.
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2. Benefits of the PAM4 method
Before PAM4 (pulse amplitude modulation), binary NRZ modulation format is used for 100G
long-haul and 40G data transmission networks. PAM4 is a better choice as it comes with four
distinct levels for the encoding of two data bits. Thus, with this modulation format, the band-
width of a connection can be double. These days, the single-wavelength PAM4 modulation
technique is being used as it is considered as the most efficient and cost-effective enabler of
100G data transportation.
Customers who are willing to construct an embedded DWDM data network can employ these
transceivers in their switches directly. Therefore, it is a cost-effective and simple solution. How-
ever, PAM4 requires amplification, and you cannot go beyond the range of 5 to 6 kilometers
without using dispersion compensation. Thus, a dedicated DWDM multiplexer in combination
with dispersion compensation and an amplification system is necessary to connect data centers
using PAM4.
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The advent of Pluggable 100G DWDM QSFP28 Transceivers
In the past few years entire focus remained on coherent DWDM optical transceivers including
but not limited to CFP and CFP2. Back in 2016, Inphi (a leading vendor in communications indus-
try) launched the pluggable 100G DWDM QSFP28 transceivers for the very first time.
The introduction of pluggable DWDM QSFP28 transceivers was received like a strong alterna-
tive for 100G DWDM coherent transceivers. It triggered a major shift as a significant number of
network operators started shifting to 100G DWDM QSFP28 transceivers.

3. 100G DWDM QSFP28 – an Ultimate Answer for the anticipated Data
Centers Interconnect Boom
The growth of e-commerce, social networking, and big data is driving the demand for band-
width between data centers. This factor is motivating data center operators to deploy low pow-
er, high-density and low latency DWDM links to connect their multiple data centers. In fact,
Data centers interconnect (DCI) today has become a basic necessity of businesses.
Far located data centers are connected to meet various crucial needs such as: disaster recov-
ery, cluster computing, large-scale data transfers and also for the erection of metro data center
topologies. Data-intensive applications including Artificial intelligence, server-less compute and
machine learning are inducing a rapid growth in the construction of cloud networks.
As per AGC research, in 2019 the global market for optical data center interconnect (DCI) will
hit the $4.7 billion mark. You can suggest that the QSFP28 form factor compatible 100G DWDM
modules are ready to replace 10G DWDM technology which is still being used in a significant
portion of sub 80 kilometer lines.
Large Data Centers vs. Regional Data Centers
Restraints in the building of massive data centers are enforcing cloud service providers (CSPs)
to move towards distributed regional architectures. It is because the construction of large-scale
data centers is not always achievable due to:
• Power constraints
• Real estate limitations
• Legal issues
• Cost-related issues
In short, to provide applications agility and to maintain seamless content delivery interconnect-
ing geographically dispersed or regional data centers becomes a practical and more affordable
solution.
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4. Implementation of the 100G DWDM QSFP28 Transceiver
With its capability to deliver as much as 4Tbps of bandwidth for up to 80 kilometers spread
between data centers the 100G DWDM QSFP28 can be considered as a perfect solution. The
construction of a 100G DWDM QSFP28 based long distance interconnection setup requires:
• Optical Multiplexer/Demultiplexer
• Optical Pre-Amplifier and Post-Amplifier
• Dispersion Compensator ( for greater then 5-kilometer applications only)
In this arrangement, the Optical Multiplexer (MUX) syndicates various wavelengths of light into
a single fiber strand, and Erbium-doped fiber amplifiers aka EDFAs are employed to boost the
signal. For applications greater then 5 kilometers, a dispersion compensator is required (as
shown in Case II). Whereas no dispersion compensator is needed in scenarios where the dis-
tance remains less than 5 kilometers.
Case I: under 5 km Applications
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Case II: over 5 km Applications
(up to 80km)

5. General Characteristics of available 100G DWDM QSFP28
Pluggable Modules:
The 100G DWDM QSFP28 pluggable modules are widely considered as a viable solution for
Metro Data Center Interconnect (DCI) with a possibility of transmission over 80 kilometers at a
speed of 100 Gigabits/s.
These transceivers employ an IEEE CAUI-4 4x25G interface, and they come compatible with
standard 100G QSFP28 ports. As far as their optical capabilities are concerned, the 100G QSFP28
pluggable modules can combine two different wavelengths into a single duplex fiber with its
center wavelength aligned with the 100GHz grid.
The DWDM QSFP28 is obtainable in 40 diverse channels on the 100GHz ITU-T based grid to
offer up to 4Tbps maximum bandwidth over a single fiber pair. Following features can be antic-
ipated by a 100G DWDM QSFP28 module:
• Easy integration with existing optical line infrastructure
• PAM4 modulation format possible for smaller size QSFP28 setups
• High capacity, reliable bandwidth throughout metro reach optical fiber network
• Scalable solution for 100Gbps to 4Tbps
• Offered in the form of hot-swappable pluggable devices
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The Beauty of Pluggable 100G DWDM QSFP28 Transceivers
Enterprisesanddatacenterscandeploypluggabletransceiversandtranspondersinvariouscom-
binations according to their specific requirements. The extension of a handy embedded DWDM
approach to 100G line speeds can keep complexities and costs out of Datacom networking.
Pluggable 100G transceivers allow enterprises to experience the comprehensive benefits of
open, flexible line networking. Moreover, pluggable 100G transceivers available on the market
are relevant and practical with various already existing network configurations.

6. © 2019 CBO - All rights reserved.
BlueOptics and BlueLAN including their Logos are trademarks from CBO registered in Germany and/or other countries. Other names and brands mentioned
in this document may be claimed as the property of others.
This document is for informational purposes only and does not set forth any warranty, expressed or implied, concerning any equipment, equipment fea-
tures, or service offered or to be offered by CBO. The publication of information in this data sheet does not imply freedom from patent or other protective
rights of CBO or others. In accordance with the CBO policy of continuous improvement specifications may change without notice.
Contact a CBO sales office for information on feature and product availability.
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