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Fiberstore (FS.COM) | Development of 40GBASE-iSR4 QSFP+
Transceiver
Nowadays, 40G QSFP+ transceiver modules are widely deployed in
optical network with variousadvantages, such as delivering
excellent high speed optical/electrical performance coupled with
lowpower dissipation. Using bundled fiber cables and MPO
connectors, the port density of QSFP+modules is triple that of SFP+
modules. Moreover, the power consumption is reduced from
1000mWmaximum per lane for SFP+ to 375 mWmaximum per lane for
QSFP+.
In order to further expand the portfolio of innovative parallel
fiber optic transceivers, a new QSFP+transceiver was launched,
which is named 40GBASE-iSR4 QSFP+ transceiver. The letter i refers
tothe ability of inter-operation. It is not only 40Gb Ethernet
compliant, but also inter-operable withany 10GBASE-SR compliant
transceiver at link distances up to 100 meters over OM3 multimode
fiber.This article will focus on the development process of this
40GBASE-iSR4 QSFP+ transceiver.
Background
The volume of digital information flowing through data network
develops at an ever increasing rateday by day. So the growth of
cloud computing, server virtualization and the trend toward
networkconvergence is forcing todays networks to be more efficient
and faster than ever. 1Gbps Ethernetaccess links have been replaced
by 10Gbps links due to the increases in server utilization
obtainedthrough Virtualization. To keep up, higher performance
switching hardware is needed to providesufficient I/O
(Input/Output) bandwidth to avoid blocking. In order to meet this
demand, manynewer access switches could support 48 ports of 10G
Ethernet for connection to downstreamservers, and 2 or 4 ports of
40G Ethernet for connection to the core switches. These
40Ginterconnects are implemented by using QSFP+ transceivers and
could provide sufficient bandwidthto enable fully non-blocking
switch fabrics.
Potential Opportunity
The release of IEEE 802.3ba-2010 standard for 40G Ethernet
specifies the optical and electricalrequirements for various
physical layer link implementations. The 40GBASE-SR4 PMD
(physicalmedium dependent) variant defines a 4-lane parallel
optical interconnect for operation over OM3multimode fiber with
transmission distance up to 100 meters. Each of the four lanes
works at a datarate of 10.3125 Gbps which is the same serial bit
rate that was defined for 10G Ethernet links.
Development of40GBASE-iSR4 QSFP+Transceiver
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WHITE PAPER
Fiberstore (FS.COM) | Development of 40GBASE-iSR4 QSFP+
Transceiver
The 40GBASE-SR4 PMD addresses the need for 40Gbps interconnects
in the data center. It takesadvantage of the widely-deployed and
low-cost 850nm VCSEL (vertical cavity surface emitting
laser)technology. Because each of the 4 lanes in 40GBASE-SR4 have
the same serial bit rate of 10GEthernet link, there is an
opportunity for switching hardware vendors to utilize 40GBASE-SR4
as 4separate 10G Ethernet interconnects.
The Issue
The standard of 40GBASE-SR4 provides an opportunity to further
address the growing need forbandwidth. It is not defined to be
backward compatible with the preceding 10G Ethernet shortreach
interconnect standard. Although both 40G Ethernet and 10G Ethernet
included a PMDdefinition for short reach VCSEL based optical links
operating at 10.3125 Gbps per lane,interoperability cannot be
guaranteed (see the picture below).
The following analysis of 40GBASE-SR4 and 10GBASE-SR
specifications tells why inter-operabilitycannot be guaranteed over
all specified operating conditions.
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WHITE PAPER
Fiberstore (FS.COM) | Development of 40GBASE-iSR4 QSFP+
Transceiver
From the above chart, we could see that many of the transmitter
and receiver specificationsgoverning the 10GBASE-SR standard are
equal or more stringent than those for 40GBASE-SR4standard. This is
not surprising because the 40GBASE-SR4 specification is written to
covertransmission links up to 100 meters, while the 10GBASE-SR
specification is intended to satisfy amaximum transmission link
length of 300 meters over OM3 multimode fiber. Except the
distance,the main specification gap preventing guaranteed
inter-operability relates to receiver overload.
The Solution
40GBASE-iSR4 QSFP+ transceiver was released to tackle the issue
of an overload condition whenconnecting a 40GBASE-SR4 transmitter
to a 10GBASE-SR receiver. It is intended to be fully compliantto
the 40GBASE-SR4 specification but with a lower maximum transmit
optical output power. Themaximum specified output power has been
lowered from +2.4 dBm to -1 dBm allowing it tointerface with
10GBASE-SR receivers without fear of overload.
The VCSEL design combined with superior laser programming and
control algorithms allow for areduction in the module maximum
specified optical output power without compromising any of
themodule high speed electro-optic performance. And the result (see
the following two charts) is afully compliant 40GBASE-SR module
which can interoperate with legacy 10GBASE-SR transceivers.
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WHITE PAPER
Fiberstore (FS.COM) | Development of 40GBASE-iSR4 QSFP+
Transceiver
Summary
40GBASE-iSR4 QSFP+ transceiver provides an effective solution
for users who seek to increase thecapacity of their switching
networks. With the reduced maximum specified output power, theQSFP+
iSR4 is able to support standard 40G Ethernet links up to 100
meters over OM3 and10GBASE-SR links over the same distances. The
QSFP+ form factor increases the effective 10GEthernet port count
density by a factor of 3 over the standard SFP+, while allowing for
a decrease inoverall power dissipation.
Contact UsManufacturing R & D (China)
Eastern Side, Second Floor, Science &Technology Park, No.6,
Keyuan Road,Nanshan District, Shenzhen 518057,ChinaTel: +86 (755)
8300 3611Fax: +86 (755) 8326 9395Email: [email protected]
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1220 Tung Chun Commercial Centre,438-444 Shanghai Street,
Kowloon,Hong KongTel: +852 81763606Fax: +852 81763606Email:
[email protected]
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331 Andover Park East Ste330, Tukwila,WA 98188,United StatesTel:
+1-425-226-2035Fax: +1-253-246-7881Email: [email protected]
London Office (United Kingdom)
Third Floor 207 Regent Street, London,W1B 3HH, United
KingdomTel: +44 2081441980
Notice: This document is for informational purposes only and
does not set forth any warranty, expressed orimplied, 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
noresponsibility 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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