Optical Transport - A Primer on Form
Factors and Optical Specifications
Gerard Powers & Chris Crotteau / Network Hardware Resale
Bill Jensen / University of Wisconsin-Madison
Contents
•
•
•
•
Introduction
10GbE Pluggable Types
10GbE optical specifications
40GbE pluggable types and optical
specifications
• 100GbE Pluggable types and types and
optical specifications
• Summary
Introduction
• This is a high-level overview of the different
10GbE, 40GbE and 100GbE form factors and
optics types
• There are MANY different 10GbE options and
combinations and this is a common source of
confusion and implementation issues for
customers deploying 10GbE
• 10GigabitEthernet form factors have gone
through several different revisions over the years
as 10GbE demand increased
XENPAK
X2
Contents
XFP
SFP+
XENPAK
• Used primarily by Cisco and Juniper. The 4-port
Cisco module WS-X6704-10GE is still very
popular
• Very large module that includes some PHY logic
in the package (example – WAN PHY capability
on a XENPAK card is placed on the optic, while
this capability on an XFP or SFP+ based
interface is placed on the linecard)
• Uses SC connector for fiber or CX4 (Infiniband)
for copper
10G Form Factors (Cont.)
X2
•
•
•
•
Reduced-size evolution of the XENPAK
Used almost exclusively by Cisco and HP
Same general capabilities as XENPAK
30% reduced footprint allowed 10G port densities to
increase by 2X and then 4X in Cisco modules
• Introduced a converter module to convert X2 modules to
2X1G or 1XSFP+ (please note the TwinGig converters
have many compatibility restrictions)
• Uses SC connector for fiber or CX4 (Infiniband) for
copper
• X2 form factor is the ONLY option for pluggable 10GbE-T
10G Form Factors (Cont.)
XFP
• Small form factor optic, no PHY logic
• Moving the PHY logic to the linecard gave made
it possible to make 10G/OC192 dual-rate optics
• Uses LC fiber connector
• XFP is currently the smallest form factor tunable
DWDM optic that is available
• Used mostly in WAN applications, due to dualrate 10G/OC192 and Tunable DWDM offerings
10G Form Factors (Cont.)
SFP+
• Same form factor as SFP
• SFP+ ports are often 1G/10G, offering huge
flexibility in deploying mixed environments
(Note: some chassis have restrictions on
which ports are 10G-only and which are
1G/10G)
• All major vendors are moving towards SFP+
for common 10GbE applications, especially in
the Data Center
10G Form Factors (Cont.)
Optics Types
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SR
LRM
LX4
LR
LW
ER
ZR
CU
CX4
T
10GBase-SR
• Uses 850nm laser assembly
• Most common and least expensive
multimode 10GbE optic
• Available in ALL form factors
• When deploying, make sure you know what
grade of multimode is installed!
• Max distance varies based on fiber grade
(see next slide)
10GBase-SR (Cont.)
Wavelength
850nm
Core Size (microns)
Modal Bandwidth
Cable Distance
62.5
160 (FDDI)
26m
62.5
200 (OM1)
33m
50
400
66m
50
500 (OM2)
82m
50
2000 (OM3)
300m
50
4700 (OM4)
400m
10GBase-LX4
• Original standard for longer runs over multimode
fiber
• 4 lane (4x 2.5Gbps) optic, working over multiple
wavelengths in the CWDM plan
• Large laser assembly precludes use in XFP and
SFP+ form factors
• Long LX4 runs need to use a mode-conditioning
patch cable to ensure signal integrity
• Obsolete; replaced by 10GBase-LRM
10GBase-LRM (“Long Reach Multimode”)
• LRM optics use a 1310nm laser assembly
• LRM provides up to 220m reach over FDDIgrade multimode fiber
• Higher fiber grades do NOT provide longer
reach
• Long LRM runs need to use a modeconditioning patch cable to ensure signal
integrity
• Available in all form factors (not all vendors do,
though)
10GBase-LR
•
•
•
•
1310nm laser assembly
10km over singlemode fiber
No minimum distance
Most commonly implemented 10GbE optic for
singlemode runs
• Available in all form factors
10GBase-ER
• 1550nm laser assembly
• 40km maximum distance
• “Minimum distance” requirement; attenuation
needed for short runs using ER optics
• Highly recommended to verify the optical
power budget for deployments beyond 30km
• Available in all form factors
10Gbase-ZR
• 1550nm laser assembly
• 80km maximum distance
• “Minimum distance” requirement; attenuation
needed for short to medium runs using ZR optics
• Always qualify the ZR run to verify the proper
optical power budget
• Not an IEEE standard; however, all major
vendors have agreed upon the same
specifications for interoperability
• Available in all form factors (SFP+ is very new,
though)
10G over CWDM
• It is a common misunderstanding that there
are established 10GbE CWDM
implementations
• NO OEM makes a pluggable 10GbE CWDM
optic; they are only available through 3rd
parties manufactures for use with an external
media converter
10G over DWDM
• Optics are available in all form factors that
output at fixed wavelengths (100GHz DWDM
plan)
• XFP form factor optics are available that can be
tuned to any wavelength in the DWDM C band
(50GHz DWDM plan)
• The advantage of XFP-based DWDM optics
means you can plug directly into the DWDM
plant, without the requirement of a transponder
10G over DWDM (Cont.)
• The advantage of using pluggable based
DWDM optics means you can plug directly
into the DWDM plant, without the requirement
of a transponder.
• Tunable optics are very popular from a
sparing perspective as you only need to
spare one type of optic instead of a pair of 32
different wavelengths
10GBase-CX4
• Designed as a drop-in replacement for
Infiniband networking; uses 4 lane Infiniband
cables
• Bulky cabling and connector restrict CX4 to
XENPAK and X2 form factor or fixed interfaces
• Maximum distance of 15m
• Was primarily used as a cheap server-to-switch
interconnect
• Mostly obsolete
Part 2 – Optics Types (Cont.)
Part 2 – Optics Types (Cont.)
10GBase-CU/10GBase-CX1
• AKA: direct attach cables, “DAC”)
• Cable with SFP+ ends plugs directly into an
SFP+ slot
• Both devices must present SFP+ connectors
• Unsuitable for connecting different
vendors’ networking equipment to each
other due to vendor ID checks on the SFP
portion of the cable
10GBase-CU/10GBase-CX1 (Cont.)
• Ultra low latency (no electrical-optical-electrical
conversion); in fact, for ultra low latency switches
such as the Nexus 3548, published latency figures
are ONLY achievable via DAC.
• Cable is permanently attached to the SFP+
• Max lengths is 5 meters (passive) or 10 meters
(active)
• Active = 850nm laser and multimode assembly
• Passive = fully electrical
• Almost exclusively used to connect server to switch
10Gbase-T
• Primarily fixed interface
• Very high power consumption of PHY logic
means no pluggable SFP+ at this time
• Only Cisco offers a pluggable 10GBase-T
optic in the X2 form factor (X2-10GB-T)
• Most switches offer 1G/10G operation, some
go further and offer 100/1000/10G operation.
Make sure to check documentation before
you assume support!
The Future is Now - 40GbE
• Currently, 40GbE optics are found in two form
factors – QSFP for common applications, and
CFP for specialty applications.
• Most 40GbE ports are capable of operating
either in 40GbE mode or a 4x10GbE mode.
• With few exceptions, current 40GbE optics
are built using multilane technology so as to
reuse existing commodity 10GbE optical
elements.
Example of a QSFP
40GBase-SR4
• 40GBase-SR4 uses four 850nm laser
assemblies over multimode fiber
• SR4 dominates current 40GbE deployments
• As 10GBase-SR technology has been
reused, distance limits are the same as SR
with the caveat that OM2 or better fiber is
require
40GBase-SR4 (cont.)
• The use of four SR lasers requires the use of
specialized multilane cabling when deploying
SR4 optics.
• A single 10 lane MTP/MPO (“Multi-fiber Push
On”) cable is used for SR4, where 4 fibers
are used for transmit, 4 for receive, and two
fibers are unused.
• Connecting SR4 optics back to back requires
a crossed MPO cable.
40GBase-SR4 (cont.)
• When SR4 is operated in 4x10GbE mode, a
MPO to 8x SC or LC breakout cable is
needed
40GBase-LR4
• 40GBase-LR4 uses four lasers at different
wavelengths centered around 1310nm.
• This use of WDM allows the use of any
existing singlemode fiber run with LC (QSFP)
or SC (CFP) ends.
• Maximum distance is 10km
40GBase-FR
• 40GBase-FR is a very new optical standard
• Single lane optic
• Currently only available in CFP form from
select networking OEMs
• 1550nm laser, 2km reach
40GBase-CR4
• CR4 is the direct attach cable standard for
40GbE.
• 4 twinax cables are used between the QSFP
ends
• 5m max distance for passive cables
• Breakout cable is available for 4x10GbE port
operation
Sample CXP to 3 x QSFP Cable
Sample QFP to 4xSFP+ cable
100GbE – the fastest there is
• Currently, 100GbE optics are available in two
pluggable types, as well as fixed optics for
specialty applications.
• CFP optics are the most common
• Some vendors have implemented CFP ports
as 40/100GbE
• CXP optics are the current small form factor
100GbE optic, but very few vendors have
CXP based cards
An example of a CFP and CXP:
100GBase-SR10
• Like the 40GbE SR4 standard, this is a
multilane optic. 10x 10Gbps optical elements
are used for SR10.
• The use of the same SR elements means
cabling requirements for distance are the
same as SR4
• SR10 is cabled using either 2x 10 lane MPO
cables or 1x 24 lane MPO cable
100GBase-SR10 (cont.)
• Some vendors have produced 100GbE
interfaces that can operate in 10x 10GbE
mode, 3x 40GbE mode, or both.
• Like SR4, special breakout cables are
required for this mode of operation
• SR10 interfaces presented as a single 24
lane MPO cable must use a crossed cable
when connected back to back
100GBase-LR4
• Uses 4 25Gbps lanes at the same 1310nmcentered wavelengths that 40Gbase-SR4 uses.
• As this standard uses WDM, a standard pair of
singlemode fiber is sufficient for connectivity.
• This is only available in CFP form factors
• LR4 is commonly deployed, as 100GbE is
currently used primarily for inter-site connectivity.
100GbE over DWDM
• As 100GbE is currently the fastest available
interface of any type, there has been a strong
need by the large carriers to have 100GbE
capable DWDM equipment.
• 100GbE over DWDM interfaces on
networking equipment is available only
through a few select vendors, and at extreme
cost.
Summary
• When implementing 10GbE, there are many
form factor choices. The best options will
depend on the particulars of your
implementation.
• When implementing 10GbE over multimode,
fiber grade matters!
• SFP+ is very attractive because of the price
point, the port density and the backwards
compatibility with GigabitEthernet
Summary (Cont.)
• 40GbE is starting to gain momentum,
especially in the data center environment
• High density 40GbE switches are available
from most vendors at this time
• There are 40GbE QSFP to SFP+ breakout
options for more interface options
• Cabling 40GbE for multimode presents
additional complexity due to the multilane
natures of the current optics
Summary (Cont.)
• 100GbE is the popular choice for carrier who have
outgrown 10GbE technologies
• Some vendors have 100GbE ports that can break
out to 40GBE or 10GbE
• Like 40GbE, multimode options are available,
however cabling because even more complex as
there are 20 lanes
• CFP is too large of a form factor to support high port
densities
• It remains to be seem s if the industry will shift from
CFP in favor of the CXP form factor
Q&A
Thank you!
Review: Optics Form Factors
Optic Type and
Form Factor
XENPAK
X2
XFP
SFP+
SR
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
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
LRM
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LX4

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
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LR
LW
ER
ZR
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Review: Optics Form Factors (Cont.)
Optic Type and
Form Factor
XENPAK
X2
XFP
SFP+
CU
CX4








10GBASE CWDM
T



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DWDM
Tunable
DWDM

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Review: Optics Specs
Optic Type
MMF
SR
LRM
LX4
LR
LW
ER
ZR
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
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SMF

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
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CAT6+
Twinax Infiniband 850nm
1310nm
1550nm
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Review: Optics Specs (Cont.)
Optic Type & Media
MMF
CU
CX4
10GBASE-T
CWDM
DWDM
Tunable DWDM





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SMF






CAT6+
Twinax Infiniband 850nm
1310nm
1550nm



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