The occurrence of 25GbE changes the data center Ethernet landscape of some enterprises and organizations, creating a viable market for high-speed, reasonably-priced connectivity. How much do you know about this 25GbE network?

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Fiberstore (FS.COM) | 25GbE: How Much Do You Know About it?
Over the years, data center bandwidth requirements are expanding at double-digit rates, along with
the equally urgent push not to compromise the cost-to-performance ratio. To accommodate the
needs of web-scale data centers and cloud-based services, efforts have been made by leading cloud
and telco providers to define and drive 25Gigabit Ethernet (GbE) technology. As such, the latest
Ethernet speed upgrade path would be 10G-25G-100G, or the possible 10G-25G-50G-100G, instead
of 10G-40G-100G. The occurrence of 25GbE changes the data center Ethernet landscape of some
enterprises and organizations, creating a viable market for high-speed, reasonably-priced
connectivity. How much do you know about this 25GbE network? You may have few insights on it.
Don’t worry, this article gives an detailed description about it.
What Is 25GbE?
25GbE is defined for 100GbE which is implemented as four 25Gbps lanes running on four fiber or
copper pairs. 100G optics (e.g. QSFP28 transceivers) have four lasers, each transmitting at 25Gbps.
The twisted pair standard was derived from 40GbE standards development. Using 25GbE with
QSFP28 transceivers results in a single-lane connection similar to existing 10GbE technology—but it
delivers 2.5 times faster performance. It’s a proposed standard for Ethernet connectivity that will
benefit cloud and enterprise data center environments, enabling the transmission of Ethernet
frames at 25Gbps, and promoting the standardization and improvement of the interfaces for
applicable products. The following table provides a summary of key 25GbE interfaces.
25GbE: How Much Do
You Know About it?

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Fiberstore (FS.COM) | 25GbE: How Much Do You Know About it?
How 25GbE Standard Comes?
One of the main challenges in data centers is the insatiable hunger for more bandwidth. In 2010,
the IEEE ratified a 40GbE and 100GbE standard, and launched a new study group to work on a
400GbE standard to keep up with bandwidth demand.
However, for some cloud providers and other large-scale data center operators, the requests are not
more than the simple raw capacity. 10GbE is no longer fast enough. For server to top-of-rack
network connections to keep up, you would need to double the number of switches in each rack
and use 10GbE NICs. This would lead to impractical budget. The 40GbE isn't cost-effective or
power-efficient in top-of-rack (ToR) switching for cloud providers and others that operate at a
similar scale.
In such a condition, 25GbE was proposed as a standard for Ethernet connectivity, using a single-lane
25Gbps Ethernet link protocol to deliver the best price per performance ratio. In June 2014, the
25GbE Consortium was formed to promote the technology, and subsequently an IEEE 802
workgroup was formed to develop the standard.
Why Consider 25GbE?
Compared with 40GbE solutions, 25GbE technology provides superior switch port density by
requiring just one lane (vs. four with 40GbE), along with lower costs and power requirements. Since
40G short-reach QSFP+ interface (ie. QFX-QSFP-40G-SR4) is constructed from four parallel links.
Extending QSFP+ onto fiber requires four parallel 10Gb streams to transport this to the receiving
QSFP+ parallel optics. And long-reach QSFP+ interfaces utilize Wave Division Multiplexing (WDM) to
transport the four 10Gb streams over a single pair of fiber (image below). The requirement of four
lanes significantly reduces switch port density per switching chip and increases the cost of cabling
and optics. While the 25GbE standard requires only a single lane, while delivering 2.5 times more
throughput compared to current 10GbE solutions, saving the cost compared to 40GbE solutions.

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Fiberstore (FS.COM) | 25GbE: How Much Do You Know About it?
Besides, deploying 25GbE networks enables organizations to significantly reduce the required
number of switches and cables, along with the considerations for the reduction of facility costs
related to space, power, and cooling compared to 10GbE and 40GbE technology. Fewer physical
network components reduce ongoing management and maintenance costs.
Additionally, the 25GbE physical interface specifications support the form factors, including QSFP28
and SFP28. QSFP28 has four lanes and each lanes supports 25Gbps speed. Each lane requires a
serializer/deserializer (SerDes) chipset. The proposed 25GbE standard uses the same physical silicon
from a single 25Gbit/s lane, which simplifies the process with just minor changes for forward error
correction and lane alignment.
25GbE standard helps reduce capital expenditures (CAPEX) and operational expenditures (OPEX)

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Fiberstore (FS.COM) | 25GbE: How Much Do You Know About it?
compared to 40GbE, while meeting the necessary I/O bandwidth requirements in data centers. In
addition, some blade server chassis solutions today are limited to only two SerDes lanes for their
LAN on Motherboard (LOM) networking ports and therefore cannot implement a four-lane 40Gbps
interface.
Conclusion
25GbE specification enables network bandwidth to be cost-effectively scaled in support of
next-generation server and storage solutions residing in cloud and web-scale data center
environments. At present, Fiberstore supplies many 25G solution products, including QSFP28 to
4xSFP28 DAC cables which serve as the alternative solutions to QSFP28 to QSFP28 DAC (QSFP28
cable). With the technology being much maturer, more and more 25G products will be made
available to users.

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Fiberstore (FS.COM) | 25GbE: How Much Do You Know About it?
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Notice: This document is for informational purposes only and does not set forth any warranty, expressed or
implied, concerning any equipment, equipment features, or service offered or to be offered by Fiberstore.
Fiberstore reserves the right to make changes to this document at any time, without notice, and assumes no
responsibility for its use. This information document describes features that may not be currently available.
Contact a Fiberstore sales team for information on feature and product availability.
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