Application
Notesenko.com

CS® and SN®
Connector
SEPTEMBER 2021
Rev. 01

Issued by:Engineering
Department

Created by:Andrei Vankov
Emmanuel Kolczynski

Application NoteCS® and SN® Connector
Challenge
Data center growth has created challenges and opportunities for component and system vendors. The
primary challenges include supporting increased bandwidth, density along with superior manageability
without increasing the physical layer connectivity footprint of existing data centers.
Networking switch faceplate density is doubling with new product introductions from multiple vendors
using the QSFP-DD as a transceiver interface. 128 single lanes (channels) ports or 32 quad lane ports havebeen the maximum network switch faceplate density in data center switches since 2012. Recently most
networking switch ASIC vendors have been able to double the channel count on a single switch ASIC to 256
lanes. Several MSA’s (QSFP-DD, OSFP, and SFP-DD) have been created with double-density transceivers tomanage the increased bandwidth density while still maintaining a 1RU switch faceplate form factor. With
these new double-density transceivers the fiber count has doubled from four lanes to having up to eight fiber
pairs. Many of the transceiver implementations have split the eight lanes into two separate quad interfaces
to maintain compatibility with the rest of the installed fiber and network switch infrastructure. When one ofthese new switches are deployed, the immediate need is to increase the number of fiber pair terminations inthe same physical space as the current infrastructure in both the rack and the rest of the structured cabling
infrastructure.
Looking at the optical interconnects in both enterprise and hyperscale data centers, the duplex LC and MPO
connectors have been fundamental components in most of that infrastructure. Both the duplex LC andMPO are used extensively in structured cabling, and down to the individual transceiver interconnects. The
emerging trends in the data center growth to increase bandwidth is to start migrating to double density
pluggable optical modules that match network faceplate bandwidth with capable bandwidth delivered by
the underlying network switch ASICs.

1

CS® and SN® Connector

The MPO has been used for parallel optical engines that drive single wavelengths onto multiple fibers. Duplex
fiber (CWDM or DWDM) solutions can take advantage of duplex LC connector.
A four-lane quad interface transceiver has a total of eight active fibers in a MPO-12. To support the double
density transceivers with eight fiber pairs (16 fibers total), a different MPO would need to be used. Either an
MPO-16 (single row of 16 fibers) or an MPO-24(two rows of 12 fibers each) could be used. Increasing the fiber
density on MPO connectors has led to other problems associated with the MPO connector. Keeping the end
face of MPO clean has been one of the industry’s more controversial topics. Most of the cleaners for MPO canclean only a limited area of the MPO connectors end face due to the existence of built in guide pins. Dust or
particles which are left on the surface even after cleaning can cause the performance to worsen as the dust
particle will cause a gap between mated fibers thus resulting in a loss of physical contact.
In addition to cleanliness challenges with parallel fiber connectors, getting consistent IL (Insertion Loss)between all fibers within the connector has been problematic. Repetitive mating cycles on a single connector
can lead to different insertion losses between different fibers. MPO connectors require more operator
interaction to get both a dust free connection that allows all fibers to conduct light, and an interconnect thathas all fibers with acceptable insertion loss. If either problem exists, a MPO connector cleaning operation isrequired and repeated until insertion loss and fiber connectivity at the MPO interconnect meets the systemdesign requirements. Adding more fibers in an MPO connector by either increasing the fiber density in asingle row or adding a second row of fibers increases the effort of getting optical performance on all fibers forconnectivity and insertion loss. Another method to address the best performance of MPO connectivity is touse MPO HighDura connectors. The advantages include better performance, less maintenance and obtaining
optimal signal integrity.
LC connectors have been used for duplex (single pair) fiber attach with single or multiple wavelengths usedon the single pair of fibers. The limitation of the duplex LC connector has been its physical size. The size ofthe existing duplex LC connector does not allow double density solutions with the existing form factors oftoday’s QSFP form factor transceivers. Duplex LC connectors have been more robust in today’s enterprise andhyperscale data center environments than the MPO connector. Duplex LC connectors have been developedwith a zirconia ferrule and end face fiber that makes field cleaning simple and quick with traditional cleaning
methods. The CS® and the SN® connectors like the duplex LC connector are constructed with a zirconia ferrulethat is spring loaded to ensure that an adequate mating force is applied to get a reliable fiber connection witha consistent low insertion loss.

New Solutions
There are two new solutions that have been designed to address the needs of the enterprise and hyperscaledata center. These new connectors are called the CS® and the SN® connectors. Both connectors are leveraged
from the parent duplex LC connector with 1.25mm O.D. Zircona ferrules. The pitch of the CS® and SN®
connectors have been changed to allow getting a 2-4x increase in fiber density at the transceiver.

2CS® and SN® ConnectorCS® Connector
The CS® connector was introduced as a replacement to current duplex LC connectors which are too big
for newer generation transceiver interfaces and to increase the connector density in patch panels. The CS®
connector is operated with a push-pull mechanism having two cylindrical, spring-loaded 1.25mm ferrules,
within a single housing. The CS® connector’s two ferrules are pitched at 3.8mm apart, which is the minimum
possible spacing to meet today’s TOSA and ROSA optics requirement. The CS® connector can be used witheither 2mm or 3mm jacketed cable.
Compared to a standard duplex LC connector, the CS® connector has a 40% width reduction, which is a highvalue proposition especially in data centers where space is a premium. Furthermore, CS® has an advantage inheight over a duplex LC connector. The duplex LC’s latching lever design requires adequate vertical spacing
between adapters to get physical access to the release lever. The CS® connector comes with an integrated
push pull tab which allows the adapters to be more densely stacked vertically. CS® can more than double thedensity in the patch panel compared to duplex LC, with the features of narrower adapter width and denser
vertical stacking of the CS® adapter. The CS® connector is currently undergoing standardization process in the
Telecommunications Industry Association (TIA). The new connector will be standardized under a new Fiber
Optic Connector Interface Standard (FOCIS) FOCIS-19 standard for a duplexed 2 ceramic ferrule connector.
The CS® connector is designed to be available in OM3, OM4, OM4+, and OM5 Multi-mode, as well as Singlemode(OS2) and Single-mode APC varieties. The connector design utilizes current industry processes for
ferrule polishing, cleaning and visual qualification techniques. In addition, the connector also uses existingmaterials capable of extended service life qualifications. As the CS® connector is designed for applicationin data centers, telecoms, and enterprise industry, the connector is tested against standard performance
qualifications. The main industry standard testing performed on the CS® connector has been GR-326 (Genericrequirements for Single-mode optical connectors and jumper assemblies), IEC 61300-3-34 (Fiber optic
interconnecting devices and passive components – Basic test and measurement procedures – Attenuationof random mated connectors - Grade B), and TIA 568 (Structured cabling system standards for commercial
buildings, and between buildings in campus environments).
The CS® connector in addition to allowing a double density interconnect at the transceiver, it is also well suited
to allow more than a doubling of fiber interconnect density within the structured cabling infrastructure space.

2X LC STYLE FERRULE
increase reliability

3CS® and SN® Connector

2mm
Ruggedized
cable
PUSH-PULL TAB
for superior manageability in highdensity applications comes invarious length and styles

7 mm

40% higher density compared
to LC Connector

10.7 mm

CS® Connector compared to an LC connector

3.8 mm

6.25 mm7.85 mm

12.3 mm

CS® Connector

LC Duplex

SN® Connector
SN® connector is a new duplex optical fiber connector designed for Data Center 400G optimization. The
SN® connector was designed to provide individual and independent duplex fiber breakout at a quad styletransceiver (QSFP, QSFP-DD, OSFP) as a more efficient, increased reliability, and a lower cost alternative thanthe MPO connector. SN® has two (2) LC style 1.25mm O.D. Zirconia ferrules in a single housing, pitched 3.1mm
apart vs 6.25mm in a duplex LC connector. Each of the SN® connector ferrules can be individually prepared,polished, and tested. This allows the manufacturer to easily control each fiber connection of the connectors.
In addition, the use of a widely deployed 1.25mm ferrule allows for a simpler manufacturing process withan already streamlined manufacturing process. In comparison, MPO connectors are manufactured with all
12 fibers terminated into a single MT ferrule. The preparation, polishing, and testing are done for all 12 fibers
simultaneously which can result in varying performances of each of the fiber connection. Since SN® uses thesame zirconia ferrules as on the duplex LC, the entire end face can be easily cleaned by traditional cleaning
methods. The SN® connector supports up to 1.6mm jacketed cable.
Another valuable feature of the SN® like CS® and LC connectors is the ability to support polarity changes thatcan be easily made in the field. This is something that is not achievable with MPO connectors for SM. MPO
connectors for SM are angle-polished, angled top to bottom where the connector key is on top side. Due tothis, SM MPO connectors cannot be flipped to change the polarity. Care must be exercised in planning MPO
cabling infrastructure to ensure that the correct polarity of Tx and Rx and lane order are preserved throughthe cabling environment with the proper choice of MPO connector options. At times an additional MPO
connector pair needs to be added into the link to ensure that proper polarity is preserved.
The design of the SN® connector allows users to have four individual connectors with eight fibers in total,
within a single QSFP, QSFP-DD and OSFP transceiver interface. The SN® connector can be used for fiber
applications such as PSM4, SR4, DR4, DR4+ and SR4.2 modules at the transceiver where MPO is commonlyused now.
SN® is a push-pull style connector which allows for high density layout. Even though SN® allows up to 4 times
higher density compared to duplex LC connector, the required quality, optical, and mechanical performancecan be maintained.
SN® has some advantages compared to MPO• Easy break out/simple network structure• Easy cleaning/maintenance of the ferrule end face
• Proven stable optical performance
Today’s MPO based transceivers with parallel links are used for communications links up to 500m. This is a
4CS® and SN® Connectortypical usage for leaf-spine or leaf to top-of-the rack switches network in Data Centers. To implement a meshfabric network, signals coming out from one transceiver are split and directed to different switches. This will
require a single MPO connector to be fanned-out to four (4) duplex LC connectors into a cross connect patch
panel (or breakout box) that is connected to another duplex LC connector which is then fan-into a single MPO
connector at the far end transceiver. This method requires the use of fan-out cables, jumpers, and cassettemodules which take up rack space, and increases link optical attenuation. The additional connectors also
become potential points of failure due to poor connector hygiene practices. This increases the deployment
cost, and complexity with the use of more components in the network. Some of these components, suchas the MPO-duplex LC fan-out cables, must be custom made for each application with different staggeredlengths, thus increasing the logistical complexity.
Cassette/Rack

SFP Module

SFP Module

Crossconnect

MPO/LC Fan Out

Switch (Leaf )MPO/LC Fan Out

Switch (Leaf )The SN® connector can simplify and reduce the overall cost of this structure, as SN® based transceivers are alreadybroken out by having four (4) individual SN® connectors at the transceiver interface. To make a mesh fabriccross connection, it only requires SN® to SN® jumpers that can be connected point to point at the transceiver.

5CS® and SN® Connector

Application solutions for CS® and SN® Connectivity
The enterprise and hyperscale data centers physical infrastructure structured cabling plant have not changed
for many years with the use of duplex LC and MPO connectors. The recent requirements to increase the
networking bandwidth in both the enterprise and hyperscale data centers provides additional advantages
and benefits with the deployment of the CS® or SN® connectors.
Both the CS® and SN® connectors allow for increased density of interconnects over duplex LC in the rack andstructured cabling infrastructure. The CS® and SN® also meet the needs of providing increased patch panel
break out capabilities with new network switch densities within a 1RU form factor.
The CS® connector provides multiple physical layer cabling schemes such as point to point and central network
point of administration(CPNA) through CS®/CS® and CS®/MPO trunk cables, CS®/CS and CS®/LC Jumpers. The
CS® connector solid body structure provides superior mechanical strength as compared to an LC connector.
This ruggedized construction is well suited for both outside plant as well as inside data center applications.
The CS® exceeds the GR-326 requirements.

Example of Enterprise ribbon array Fiber Trunk Cable Data Center Layout
In this application all the patch panels in the infrastructure are CS/MPO instead of LC with the trunk cables being MPO/MPO
all the patch panel cross connect jumpers in the main area of administration are CS/CS. The jumpers to the end devices form
the Zone cabinets are hybrid CS/LC. The two arrays to the mainframe and directors/Switches are MPO/LC

CS patch panels utilizing
CS/CS jumpers for cross connect

Main Distribution
CabinetPatch panel to Switch connectivity
is Hybrid to CS/LC jumpers

Mainframe

MPO/LC external harness

Directors

MPO/MPO Trunk cable

Under Floor Box

MPO/LC Trunk cable

Servers

Zone Cabinet

CS/LC Hybrid Trunkor Jumper cable

SAN
Under Floor Box
MPO/LC Trunk cable

Switch Rack
Cabling Legend
MPO/LC external harness

BSC Cabinet

MPO/LC Trunk cable
CS/LC Hybrid Trunk or Jumper cable
CS/CS Trunk or Jumper cable6CS® and SN® Connector

CS/LC Hybrid Trunk or Jumper cableExample of Enterprise Trunk Cable Data Center Layout
In this application all the patch panels in the infrastructure are CS instead of LC with the trunk cables now being CS/CS and all
the patch panel cross connect jumpers are CS/CS. The jumpers to the switch in the main area of administration as well as theservers and end device jumpers are hybrid CS/LC

CS patch panels utilizing
CS/CS jumpers for cross connect

Main Distribution
CabinetPatch panel to Switch connectivity
is Hybrid to CS/LC jumpers

E n d Device
such as SAN,
switches, etc.

S erver

CS/CS Trunk or Jumper cable

Server(s)S erver

Zone Cabinet

CS/LC Hybrid Trunk or Jumper cable

CS/LC Hybrid Trunkor Jumper cable

Cabling Legend
CS/LC Hybrid Trunk or Jumper cable
CS/CS Trunk or Jumper cable

CS CONNECTOR

SN CONNECTOR

2x

4x• Designed for 2x breakout• Total 4 Fibers (2Fx2)• Designed for 4x breakout• Total 8 Fibers (2Fx4)

in QSFP Footprint

in QSFP Footprint

Hyper-Scale data center applications are more compact therefore a ruggedized connector is not a primaryconsideration. The SN® connector provides greater routing and capacity than current hyper-scale data center
configurations have today. This increased capacity allows for future growth while not having to change out
the entire infrastructure.
CS® is available in serial, parallel, and WDM optical cabling schemes while SN® is available in parallel cabling
schemes.

7

CS® and SN® Connector

*MDI (Media Device Interface)SN® Connector MDIQSFP FootprintQSFP FootprintCS® Connector MDI• 2x100G• 2x200G• 4x100G• 4x200GCS

3.8 mm
3.85 mmLC Duplex

MPO

10.7 mm

5.3 mm

3.1 mm

9.46 mmSN

7.85 mm

6.25 mm
13 mm

The CS® connector was optimized as a robust higher density replacement over the duplex LC connector inboth the rack and structured cabling environments.
The SN® connector provides increased density over the CS® connector, and the ability to do individual
breakout at the transceiver. In addition to breakout capabilities at the transceiver, the SN® connector allows
direct cross connection without the need for additional breakout cables or fiber shuffles that add up to four
fiber connections into the overall link. Additional fiber connections add increased insertion loss, creates
points of failure, and increases overall cost.

Connector Type
LC
CS®
SN®

8

CS® and SN® Connector

1RU Patch Panel
72-channel / 144-fiber
168-channel / 336-fiber
192-channel / 384-fiber - 256/264-channel / 512/528-fiber

Both CS® and SN® uses single-mode quality zirconia ferrules which provides optical signal integrity. Easy
cleaning and maintenance is similar to what is done today with the duplex LC connector. The CS®connector
supports either 2mm or 3mm jacketed cable, where the SN® connector can only support a 1.6mm jacketedcable. In some co-located or enterprise data centers that have point-point connections between different
racks, a 1.6mm cable might not be suitable for all applications. The minimum supported jacketed cable
thickness requirements would need to be validated with the customer.
The CS® connector is a replacement to current duplex LC connectors which are too large for next generationtransceiver interfaces for dual optics engine transceivers, and also facilitates the need for increased connector
density in patch panels. CS® is compatible in dual duplex transceivers supporting 2 x 100GE, 2 x 200GE, and 2
x 400GE when they become available. The SN® connector provides a replacement for the MPO connector inquad fiber applications such as PSM4, SR4, DR4 and SR4.2 modules. The SN® connector will support 4 x 100GE(400GBASE-DR4) and 4 x 200GE transceivers when they become available.

Summary of CS vs. SN data center applications

CS® Connector - Enterprise Co-Lo, Cloud & Edge

SN® Connector - Hyper-Scale

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Serial, Parallel and WDM optical cabling schemes
Central Network Point of Administration cross-connect
Trunk cabling to Zone Cabinets, switches and servers
CS/CS trunk cables
MPO/MPO trunk cables
CS/MPO trunk cables
CS/CS jumpers 2.0mm O.D.
CS/LC jumpers 2.0mm O.D.
Patch panel channel counts in 1RU - 128Ch, 144Ch & 160Ch
matches uo to either 32 channel and 36 channel port
counts• 10G, 40G, 100G, 200G & 400G

Double Density MSA’s reference:
QSFP-DD		 http://www.qsfp-dd.com/
SFP-DD		http://sfp-dd.com/
OSFP			https://osfpmsa.org/index.html

9CS® and SN® Connector

Parallel optic cabling schemes
Central Network Point of Administration cross-connect
Trunk cabling to Zone Cabinets, switches and servers
MPO/MPO trunk cables
SN/SN jumpers 1.6mm O.D.
Patch panel channel counts in 1RU - 128Ch, 160Ch, 192Ch,
256Ch matches up to either 32 or 64 channel port counts• 400G

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