Optical Transceivers Information

Optical Transceivers Information
Industrial-grade optical transceivers and optical interconnection components.

2017年3月21日星期二

SFP Transceivers Options for Brocade 5100 Switch

Nowadays, many small and medium business and organizations such as local government, campus and some agencies etc., require fast and frequent access to database the files. A storage Area Network (SAN) with Fibre Channel (FC) switching technology (Figure 1) offers the speed and reliability for them. Brocade 5100 switch is an ideal Fibre Channel switch used for those organizations and can meet a variety of SAN environments.


Brief Introduction to Brocade 5100
The Brocade 5100 is a 1U Enterprise class Fibre Channel switch which combines 1, 2, 4, and 8 Gbps Fibre Channel technology in configurations of 24, 32 or up to 40 ports, getting an overall bandwidth of 320 Gbps. It is very flexible to users since it enables organizations to use 4Gbps SFPs today and upgrade to 8Gbps SFPs when required. By utilizing the sixth-generation ASIC (Application Specific Integrated Circuit) technology featuring five 8-port groups, it can reduce congestion and increase bandwidth. Because an ISL (Inter-Switch Link) trunk can supply up to 64 Gbps of balanced data throughput within these groups. In addition, enhanced Brocade ISL Trunking also utilizes ISLs more efficiently to preserve the number of usable switch ports. As shown in Figure 2, the port side of the Brocade 5100 includes the system status and power LED, console port, Ethernet port and LEDs, USB port, and FC ports and the corresponding port status LEDs. And the FC ports are numbered from left to right, in eight-port groups from 0 to 39, as illustrated in Figure 3.


Brocade 5100 ISL Trunking
As mentioned above, the Brocade 5100 can benefit from the trunking features which optimizes the use of bandwidth by allowing a group of ISL to merge into a single logical link. As we know, when ISL configured, there are certain issues like congestion. The congestion of Fibre channel links will eventually lead to performance issue and severe production impact. In this case, ISL trunking is an ideal solution to solve this issue.
As Figure 4 shown, when two switches get connected, there is a ISL link and the network traffic starts to flow through this link to the other switch. Without trunking, the congestion caused in the ISL which resulted in frames loss and bandwidth waste.
Using ISL trunking configurations, shown as Figure 5 (a), at 2Gbps speeds, the trunking delivers ISL throughput of up to 8 Gbps, avoiding the ISL congestion at the same time. In the same way, using 4 Gbps with 8 trunks can reach up to 32 Gbps, as Figure 5 (b) displayed.


Transceiver Options for Brocade 5100
Cable runs require transceivers at each end in SAN. In the SAN with Brocade Fibre Channel switches, Fibre Channel transceivers are used. Since the Brocade 5100 can support 1/2/4/8Gbps Fibre Channel, the transceiver options for Brocade 5100 are available in 1G, 2G, 4G and 8G Fibre Channel transceiver modules. Among these options, the transceivers with the data rate of 2, 4 and 8 Gbps are most commonly used in today’s Fibre Channel deployment. In addition, you can select either single-mode or multimode implementations by using the corresponding optics.
The following table shows the 2/4/8G transceiver modules that are available in infiberone.com. With strict coding technology and test assurance, these transceiver modules are highly compatible with Brocade and can achieve high performance in your Brocade 5100 switch in a cost-saving manner.

2017年3月13日星期一

How To Clean The Recommendation for MPO MTP Connectors

MPO/MTP connectors are common throughout the high-density network today, giving us the power to add, drop, move and change the network. Thus, inspection and cleaning are very important for them since that issues with connector cleanliness and contamination are the greatest cause of network failure. However, you may find that you cannot get the expected result even though you have already cleaned the MPO/MTP connector before connection. Why? Keep reading this post, you may find out what the trouble is and how to solve it.


Understanding MPO/MTP Connector
MPO/MTP connector is the most common multi-fiber connector type used in today’s high-density networks, e.g. 40/100 Gigabit Ethernet. It usually contains one or two rows of fibers (12-fiber MPO/MTP or 24-fiber MPO/MTP) in a single connector. Compared to the single-fiber connectors, a MPO or MTP connector has a larger contact area (Figure 1), and alignment of the fibers is achieved by the connection of male connector (pinned connector) which has outer pins and female connector (unpinned connector) which has alignment holes (Figure 2).

When cleaning a MPO/MTP connector, all fibers on the connector must be clean for it to function properly. Because contamination of one fiber can cause signal degradation on other fibers. Additionally, due to the presence of the alignment pins, the cleaning of the extreme sides of the MPO/MTP connector end-face is often overlooked by users (Figure 3). This is also why we cannot get the expected result in spite of repetitive cleaning. For these reasons, we should choose the right cleaning method and tools for proper cleaning.


Cleaning Method—Dry or Wet?
Inspection should be done first before cleaning as it can decide if you need to clean. Once cleaning is required, dry cleaning which is an efficient method to remove dusts and finger grease is usually the preferred method to use due to the possibilities of residue when using alcohol based products.

However, dry cleaning method is not always sufficient to completely remove all contaminants. Thus, if the second inspection reveals that the MPO/MTP connector is still contaminated after the first dry cleaning, wet+dry cleaning method (Figure 4) is recommended to use for second cleaning. If the connector is still contaminated after second cleaning using wet+dry method, you could try to redo it once more. But in this case, permanent damage of the connector must be excluded. Once permanent damage is detected, the connector has to be replaced.

The one-click MPO/MTP cleaner (Figure 6) is an easy-to-use cleaning tool for MPO/MTP accessible connector and adapter cleaning. If connector and adapter are both required to clean in your system, it is a good choice for you. Just with a simple “one-click”, the cleaning is done. A one-click MPO/MTP cleaner can be used up to 600 cleans.


In addition to the cleaner, other cleaning accessories such as lint-free wipe, optical grade dust remover, lint-free swab, etc. are necessary to achieve dry or wet+dry cleaning.

Conclusion
Fiber optic cleaning is a key part in whole fiber optic systems. MPO/MTP connector is more susceptible to contamination due to its larger contact area and multiple fiber design. Thus, choosing a right cleaning method and cleaning tool is very important for MPO/MTP cleaning. This post recommended cleaning methods and tools for MPO/MTP cleaning. All the products mentioned above can be ordered in our on-line shop www.infiberone.com. Please visit the website or contact us for more information.

More Optical Transceivers Knowledge: www.infiberone.com/Plate_49.html

2017年3月1日星期三

Fiber Patch Panels Used in Data Center Interconnection Structured Cabling solution

To facilitate Data Center Interconnection structured cabling, intermediate link connections are usually made at patch panels to accommodate reconfigurations. In a structured cabling, all switches, servers and storage throughout the data center are represented by individual ports on the front of the patch panels in a centralized patching location often called the main distribution area (MDA). Connecting two ports is accomplished by a simple patch cord on the front side of the patch panels at the MDA, allowing for instant device to device connectivity.


Common Fiber Patch Panels Used in Data Center Interconnection
Structured cabling is the key to cable plant that is easy to document, manage, and grow with the current and future demands of data center connections. Three most common fiber patch panels used in structured cabling are LC adapter panels, MTP to LC cassettes, Cloud Optical Transceivers, Active Optical Cables, Direct Attach Cables and MTP adapter panels.

LC Adapter Panel – This type of patch panel module is also known as an LC-LC module and requires trunk cables with LC termination. The LC adapter panel offers the lowest connector loss of any of the patch panel modules.

MTP-LC Module – This patch panel module is also called an MTP to LC cassette and converts MTP trunk cables to LC connections. This module type has LC connectors in front and MTP connectors in back.


MTP Adapter Panel – This patch panel module supports MTP trunk cables and each MTP connection supports 8-12 fibers. The MTP adapter panel can easily support 12 MTP connections and 144 fibers or more.
Fiber Patch Panels Connections in Data Center Interconnection
In the 1 rack unit (1RU) patch panel drawn in figure below, LC adapter panel, MTP-LC module and MTP adapter panel are supported. These three types of patch panels support trunk cables terminated with MPO or LC connections. The trunk cables plug in the back of the patch panels and LC or MPO patch cords connect to the front of the patch panel. This modular patch panel architecture enables easy installation and scales well. With standard LC interfaces, this modular patch panel architecture supports 36 LC connections in a 1U patch panel. A 42RU rack full of these patch panel modules can support over one thousand fiber optic ports (42X36 = 1,512 LC ports).

Fiber Patch Panels Applications in Data Center Interconnection
Data centers often use four patch panel links that have two trunk cables radiate out from the patch panels in the MDA (shown in the figure below). In this case, each end of a trunk cable terminates in a patch panel, so four patch panels are associated with a link that has two trunk cables in it. Two of the patch panels are located in the MDA to connect any port to any port. One patch cord is needed in the MDA to connect the two trunk cables and another patch cord is needed on each end of the link to connect to the optical modules. This four fiber patch panel link has two trunk cables, three patch cords and four patch panels in all.


Conclusion
Fiber optic links are used to connect thousands of ports in massive data centers. Most data center links use MMF and support links with 2 trunk cables and four patch panels. In large deployments, more connections in more patch panels are also needed in a link and the insertion loss and link length must be managed. As the most three common patch panels used in data centers, LC adapter panels, MTP to LC cassettes and MTP adapter panels play a crucial role in structured cabling deployment. All these three patch panels are provided in INFIBERONE.COM with high quality and low price. For more details, welcome to visit www.infiberone.com or contact us over sales@infiberone.com.

2016年12月27日星期二

The Method of Install or Remove SFP Transceiver Modules on Cisco Device

The SFP (small form-factor pluggables) transceiver modules are hot-pluggable I/O devices that plug into module sockets. The transceiver connects the electrical circuitry of the module with the optical or copper network. SFP transceiver modules are the key components in today's transmission network. Thus, it is necessary to master the skill of installing or removing a transceiver modules to avoid unnecessary loss. This tutorial are going to guide you how to install or remove SFP transceiver module in a right way.


Things Should Be Know Before Installing or Removing SFP

Before removing or installing a Transceiver Module you must disconnect all cables, because of leaving these attached will damage the cables, connectors, and the optical interfaces. At the same time please be aware that do not often remove and install an SFP transceiver and it can shorten its useful life. For this reason transceivers should not be removed or inserted more often than is required. Furthermore, transceiver modules are sensitive to static, so always ensure that you use an ESD wrist strap or comparable grounding device during both installation and removal.

Required Tools

You will need these tools to install the SFP transceiver module:
1.Wrist strap or other personal grounding device to prevent ESD occurrences.
2.Antistatic mat or antistatic foam to set the transceiver on.
3.Fiber-optic end-face cleaning tools and inspection equipment
Installing SFP Transceiver Modules


SFP transceiver modules can have three types of latching devices to secure an SFP transceiver in a port socket:

1.SFP transceiver with a Mylar tab latch.
2.SFP transceiver with an actuator button latch.
3.SFP transceiver that has a bale-clasp latch.

Types of SFP Latching

Determine which type of latch your SFP transceiver uses before following the installation and removal procedures.


To install an SFP transceiver, follow these steps:
Step 1. Attach an ESD-preventive wrist strap to your wrist and to the ESD ground connector or a bare metal surface on your chassis.
Step 2. Remove the SFP Transceiver Module from its protective packaging.
Note: Do not remove the optical bore dust plugs until directed to do so later in the procedure.
Step 3. Check the label on the SFP transceiver body to verify that you have the correct model for your network.
Step 4. Find the send (TX) and receive (RX) markings that identify the top side of the SFP transceiver.
Note: On some SFP transceivers, the TX and RX marking might be replaced by arrowheads that point from the SFP transceiver connector (transmit direction or TX) and toward the connector (receive direction or RX).
Step 5. Position the SFP transceiver in front of the socket opening.
Note: Different Cisco devices have different SFP module socket configurations. Your Cisco device could have either a latch-up or a latch-down orientation. Ensure that you are installing the SFP transceiver in the correct orientation for your Cisco device. Refer to the hardware installation instructions that came with your Cisco device for more details.
Step 6. Insert the SFP transceiver into the socket until you feel the SFP Transceiver Module connector snap into place in the socket connector.
Note: For optical SFP transceivers, before you remove the dust plugs and make any optical connections, observe these guidelines:
a. Always keep the protective dust plugs on the unplugged fiber-optic cable connectors and the transceiver optical bores until you are ready to make a connection.
b. Always inspect and clean the LC connector end-faces just before you make any connections. See the Required Tools section of this document for more information.
c. Always grasp the LC connector housing to plug or unplug a fiber-optic cable.

Step 7. Remove the dust plugs from the network interface cable LC connectors. Save the dust plugs for future use.
Step 8. Inspect and clean the LC connector’s fiber-optic end-faces.
Step 9. Remove the dust plugs from the SFP transceiver optical bores.
Step 10. Immediately attach the network interface cable LC connector to the SFP transceiver.
Step 11. Connect the 1000BASE-T SFP transceivers to a copper network.

Caution: In order to comply with GR-1089 intrabuilding lightning immunity requirements, you must use grounded, shielded, twisted-pair Category 5 cabling.

Complete these steps in order to connect the transceivers to a copper network:
a.Insert the Category 5 network cable RJ-45 connector into the SFP transceiver RJ-45 connector.
Note: When you connect to a 1000BASE-T-compatible server, workstation, or router, use four twisted-pair, straight-through Category 5 cabling for the SFP transceiver port. When you connect to a 1000BASE-T-compatible switch or repeater, use four twisted-pair, crossover Category 5 cabling.
b.Insert the other end of the network cable into an RJ-45 connector on a 1000BASE-T-compatible target device.
c. Reconfigure and reboot the target device if necessary.

Step 12. Observe the port status LED:
a. The LED turns green when the SFP transceiver and the target device have an established link.
b. The LED turns amber while STP discovers the network topology and searches for loops. This process takes about 30 seconds, and then the LED turns green.
c. If the LED is off, the target device might not be turned on, there might be a cable problem, or there might be a problem with the adapter installed in the target device. Refer to the Troubleshooting section of your switch hardware guide for solutions to cabling problems.


Removing SFP Transceiver Modules
Step 1. Attach an ESD-preventive wrist strap to your wrist and to the ESD ground connector or a bare metal surface on your chassis.
Step 2. Disconnect the network fiber-optic cable or network copper cable from the SFP Transceiver Module connector. For optical SFP transceivers, immediately reinstall the dust plugs in the SFP transceiver optical bores and the fiber-optic cable LC connectors.
Tips: For reattachment of fiber-optic cables, note which connector plug is send (TX) and which is receive (RX).
Step 3. Release and remove the SFP Transceiver Module from the socket connector.
a. If the SFP transceiver has a Mylar tab latch, pull the tab gently in a slightly downward direction until the transceiver disengages from the socket connector, and then pull the SFP transceiver straight out. Do not twist or pull the Mylar tab because you could detach it from the SFP transceiver.

Removing-SFP-with-Mylar-Tab
b. If the SFP transceiver has an Actuator button latch, gently press the actuator button on the front of the SFP transceiver until it clicks and the latch mechanism releases the SFP transceiver from the socket connector. Grasp the actuator button between your thumb and index finger, and carefully pull the SFP transceiver straight from the module slot.
Removing-SFP-with-Actuator-Button-Latch
c. If the SFP transceiver has a Bale-clasp latch, pull the bale out and down to eject the SFP transceiver from the socket connector. If the bale-clasp latch is obstructed and you cannot use your index finger to open it, use a small flat-blade screwdriver or another long narrow instrument to open the bale-clasp latch. Grasp the SFP transceiver between your thumb and index finger, and carefully remove it from the socket.

Removing -SFP-with-a-Bale-Clasp-Latch
Step 4. Place the removed SFP transceiver in an antistatic bag or other protective environment.

2016年12月26日星期一

Fundamentals of DWDM Optical Passive Components Technology

The emergence of DWDM is one of the most recent and important phenomena in the development of fiber optic transmission technology. This tutorial will introduce the fundamentals of DWDM technology, such as the components, optical amplifiers used in DWDM system, etc.


Components and Operation
DWDM is a core technology in an optical transport network. The essential components of DWDM can be classified by their place in the system. On the transmit side, there are lasers with precise, and stable wavelengths. On the link, there is optical fiber that exhibits low loss and transmission performance in the relevant wavelength spectra, in addition to flat-gain optical amplifiers to boost the signal on longer spans. On the receive side, there are photodetectors and demultiplexers using thin film filters or diffractive elements. Besides these components, optical add/drop multiplexers and optical cross-connect components may be used.

The main job of optical fibers is to guide lightwaves with a minimum of attenuation (loss of signal). Multimode fiber and single-mode fiber are the general two categories of optical fiber in use today. Single-mode fiber has a much smaller core that allows only one mode of light at a time through the core. As a result, the fidelity of the signal is better retained over longer distances, and modal dispersion is greatly reduced. These factors attribute to a higher bandwidth capacity than multimode fibers are capable of. For its large information-carrying capacity and low intrinsic loss, single-mode fibers are preferred for longer distance and higher bandwidth applications, including DWDM.

Erbium Doped Fiber Amplifier (EDFA)

By making it possible to carry the large loads that DWDM is capable of transmitting over long distances, the EDFA was a key enabling technology. Erbium is a rare-earth element that, when excited, emits light around 1.54 micrometers—the low-loss wavelength for optical fibers used in DWDM. The picture below shows a simplified diagram of an EDFA. A weak signal enters the erbium-doped fiber, into which light at 980 nm or 1480 nm is injected using a pump laser. This injected light stimulates the erbium atoms to release their stored energy as additional 1550-nm light. As this process continues down the fiber, the signal grows stronger.

Multiplexers and Demultiplexers
As DWDM systems send signals from several sources over a single fiber, they must include some means to combine the incoming signals. This is done with a multiplexer, which takes optical wavelengths from multiple fibers and converges them into one beam. At the receiving end, the system must be able to separate out the components of the light so that they can be discreetly detected. Demultiplexers perform this function by separating the received beam into its wavelength components and coupling them to individual fibers. Demultiplexing must be done before the light is detected, because photodetectors are inherently broadband devices that cannot selectively detect a single wavelength.

In a unidirectional system, there is a multiplexer at the sending end and a demultiplexer at the receiving end shown in the following picture. Two system would be required at each end for bidirectional communication, and two separate fibers would be needed.

unidirectional system
In a bidirectional system, there is a multiplexer/demultiplexer at each end and communication is over a single fiber pair.

bidirectional system
Multiplexers and demultiplexers can be either passive or active in design. Passive designs are based on prisms, diffraction gratings, or filters, while active designs combine passive devices with tunable filters.


Optical Add/Drop Multiplexers (OADM)
Between multiplexing and demultiplexing points in a DWDM system, there is an area in which multiple wavelengths exist. It is often desirable to be able to remove or insert one or more wavelengths at some point along this span. An optical add/drop multiplexer performs this function. Rather than combining or separating all wavelengths, the OADM can remove some while passing others on. OADM is a key part of moving toward the goal of all-optical networks.

There are two general types of OADMs. The first generation is a fixed device that is physically configured to drop specific predetermined wavelengths while adding others. The second generation is reconfigurable and capable of dynamically selecting which wavelengths are added and dropped.

Operation of a Transponder Based DWDM System

Within the DWDM system, a transponder converts the client optical signal. The following picture shows the end-to-end operation of a unidirectional DWDM system.
anatomy of dwdm system

The following steps describe the system shown in the picture above.
1. The transponder accepts input in the form of standard single-mode or multimode laser. The input can come from different physical media and different protocols and traffic types.
2. The wavelength of each input signal is mapped to a DWDM wavelength.
3. DWDM wavelengths from the transponder are multiplexed into a single optical signal and launched into the fiber. The system might also include the ability to accept direct optical signals to the multiplexer; such signals could come, for example, from a satellite node.
4. A post-amplifier boosts the strength of the optical signal as it leaves the system (optional).
5. Optical amplifiers are used along the fiber span as needed (optional).
6. A pre-amplifier boosts the signal before it enters the end system (optional).
7. The incoming signal is demultiplexed into individual DWDM lambdas (or wavelengths).
8. The individual DWDM lambdas are mapped to the required output type (for example, OC-48 single-mode fiber) and sent out through the transponder.

FAQ about Video SFP Transceivers

1. What is SDI?
SDI, the abbreviation for Serial Digital Interface, is a digital video interface standard made by SMPTE organization. This serial interface transmits every bit of data word and corresponding data through single channel. Due to the high data rate of serial digital signal(a kind of digital baseband signal), it must be processed before transmission.

2. What are the categories of video transceiver modules?
It can be divided traditionally by operating rate into HD-SDI, 3G-SDI, 6G-SDI, 12G-SDI; by transmission mode into single Tx, single Rx, dual Tx, dual Rx and TR transceivers; by standards into MSA and non-MSA; by operating wavelength into 1310nm, 1490nm, 1550nm and CWDM wave length. It also exists video modules of electrical interfaces that adapting mini BNC port to coordinate with SFP slot-supporting digital matrix. Currently there are also on the market some crossover video transceivers, for example, transfer the encoded SG-SDI to IP protocol conversion module can be used in traditional Ethernet switch, replacing video codec equipment.


3. What are the data rate of digital SDI?



4. What is 3G-SDI Pathological Patterns? 
SDI Proving Ground(also called Pathological Patterns) is a whole test signal, thus it must be done during blackout. SDI proving ground signal is difficult to handle by serial digital system, and significant to check the system performance. Regularly SDI Proving Ground contains the richest low-frequency energy which statistically happens one per frame. One component of SDI proving ground is, 19 zeros in a sequence, followed by a one (or 19 ones followed by a zero), can be used to test the working condition of equalizer. This sequence produces vast DC component to strengthen the analog ability of equipment and transmission system processing signal. The test signal appears with purple background on the top of the image display. The another component of SDI Proving Ground signal is used to check the phase lock loop performance. It is an unusual signal sequence, consists of 20 zeros followed by 20 ones. It has minimum zero crossing point used for clock extraction. This signal appears with Grey background on the bottom of the image display. Pathological Patterns test is also an important indicator of video SFP modules.

5. What are 6G-SDI and 12G-SDI applied in?
Generally in HD digital broadcasting field, such as digital output port of TV station HD professional camera. One-channel 6G-SDI can transmit 36fps 4K resolution zero-compressed video, while one-channel 12G-SDI can transmit 60fps 4K resolution zero-compressed video.

6. What are the main differences between HDMI and SDI?
a. Different transmit mode: Adapting parallel mode, HDMI cables contain up to 19 pairs of wires; while SDI adapts serial mode and contains only one pair of wire.
b. HDMI is applied for consumer products, like DVO from consumer camera, game machine and HD digital Set Top Box; when SDI applied in broadcast market, like TV stations and studio.
c. HDMI interface supports HDCP encryption HD digital copyright protection, but not SDI.

7. What is SDI digital video matrix? What main functions it has?
Digital video matrix arbitrarily exports m channel video signal to the electronic device on n channelmonitor equipment by switching array method, realizes video switch function through digital Cross-point chip, which realized by artificially plugging the copper shaft joint of distribution frame before the digital video matrix appearance. Presently digital matrix has been distinguished by working bandwidth, such as the type supporting 3G-SDI high-speed signal; usually each input-output port supports automatic equilibrium function; and high-end model has CDR clock regeneration function, on port types it has BNC copper shaft joint, also video SFP supportable fiber interface. With module design, it is more flexible to deploy and convenient to use.

8. What long-distance transmission solutions applying 3G-SDI, 6G-SDI and 12G-SDI?
3G-SDI, 6G-SDI and 12G-SDI both are digital baseband signal, thus limited with long-distance transmission on copper cable, for instance, 3G-SDI signal can transmit up to 55 meters on premium copper cables, but that will be much decreased to within 10 meters as for 6G-SDI and 12G-SDI, what’s more, copper cable transmission is susceptible to outside electromagnetic interference. If high-speed baseband signal proceeds optics and electrics conversion, then it can be greatly solved through optic-fiber cables. Currently the generic 3G-SDI video transceivers in marketplace is with transmission distance up to 40km on singlemode optical cables, and it will be easily to solve long-distance transport with 3G-SDI transmitter. Meanwhile there are many optical module options supporting CWDM waveband, which save much fiber resource by carrying WDM(wavelength division multiplexing) on single fiber. Now 6G-SDI and 12G-SDI optical transceivers gradually are commercially available.

9. What’s the difference between MSA and Non-MSA standards of 3G-Video SFP optical transceiver modules? What will be the consequence if they match wrongly to host machine?
The gold finger of 3G-Video SFP transceivers have 20 pins, MSA ans Non-MSA differ in I2C pin definition: MSA standard defines I2C definition on the fourth pin (SDA) and the fifth pin (SCL); while Non-MSA standard defines it on the fifth and sixths pins.

I2C pins failing to match the host machine can directly lead to SFP module communication connecting error to host machine I2C, it comes out the SFP DDM function is unavailable and EEPROM unreadable by host machine.

25GbE VS 40GbE Cabling


In 2015 data center optics market, the 40GbE transceivers is ubiquitous and the market of 40GbE is encouraging. However, with 100GbE rapidly becoming the new standard in transport, the rules of game seems to have changed. A new voice is announcing: 25GbE is more preferred and the death of 40GbE was never in doubt. Why? This tutorial will make a comparison of 25GbE and 40GbE cabling.

40GbE Cabling Overview
40 GbE, namely 40 Gigabit Ethernet, is a standard developed by the IEEE 802.3ba Task Force to support sending Ethernet frames at 40 Gbps (Gigabits per second). The official development of 40GbE standards began most early in January 2008, and the standards were officially approved in June 2010.
IEEE 802.3 Standard Interfaces that Specify 40GbE
At the heart of the 40GbE network layer is a pair of transceivers connected by a cable—OM4 or OM3 fiber cable. The transceivers, in turn, are plugged into either network servers or a variety of components, including interface cards and switches.

40GbE Optics & Cables
There are several standard form factors of 40GbE transceivers in the whole evolution. The CFP (C Form-Factor Pluggable) transceiver uses 12 Tx and 12 Rx 10Gbps lanes to support one 100GbE port, or up to three 40GbE ports. With its larger size, it can meet the needs of single-mode optics and can easily serve multimode optics or copper. But it is gradually falling behind since the increasing demands for high density. Another form factor is the CXP. It also provides twelve 10Gbps lanes in each direction, but is much smaller than the CFP and serves the needs of multimode optics and copper. At present, the most commonly used 40GbE form factor is the Quad Small Form-Factor Pluggable since it is similar in size to the CXP but can provide four Tx and four Rx lanes to support 40GbE applications for single-mode, multimode fiber and copper.
Fiber optic cabling or copper cabling are both available for 40 GbE. The supportable channel length depends on the cable and the transceiver type. For data center 40GbE fiber optic cabling, OM3 and OM4 multimode cabling is generally recommended because its reach supports a wider range of deployment configurations compared to copper solutions. In addition, compared to single-mode solutions, it costs lower. For connector type, it is no longer the duplex LC in this case. In the 802.3ba standard, MPO/MTP connectors are used at the multimode transceivers to support the multifiber parallel optics channels.



25GbE Cabling Overview
25GbE is a standard developed by IEEE 802.3 Task Force P802.3by in July 2014, using for Ethernet servers and switches connectivity in a datacenter environment. The upcoming IEEE 802.3by 25GbE standard is technically complete and expected to be ratified by June of 2016. Meanwhile, the industry expects that 25GbE hardware will be available as early as 2015 with the standard finalized by 2016.
IEEE 802.3 Standard Interfaces that Specify 25GbE.

25GbE Optics & Cables
The 25GbE physical interface specification supports two main form factors—SFP28 (1x25 Gbps) and QSFP28 (4x25 Gbps).
The 25GBASE-SR SFP28 is an 850nm VCSEL 25GbE transceiver available in the market. It is designed to transmit and receive optical data over 50/125µm multimode optical fiber (MMF) and support up to 70m on OM3 MMF and 100m on OM4 MMF (LC duplex). In fact, using an SFP28 direct attach copper (DAC) cable for switches direct connection is more commonly used now. In addition, a more cost-effective solution is recommended that is to use a QSFP28 to connect a 100GbE QSFP28 switch port to four SFP28 ports. DAC cable lengths are limited to three meters for 25GbE. Thus, the active optic cable (AOC) solutions are also used for longer lengths of application.
25GbE Cabling vs 40G Cabling
Compared to 40 GbE, the 25GbE seems to be more suitable and cost-effective for cloud and web-scale data center applications. Using 25GbE with QSFP28 transceivers, users can deliver a single-lane connection that is similar to existing 10GbE technology, but with 2.5X faster performance. In addition, 25 GbE can provide superior switch port density by requiring just one lane (vs. 4 x lanes with 40 GbE). Thus, it costs less and requires lower power consumption.

Benefits of 25 GbE when compared to 40 GbE are shown as below:
Maximum switch I/O performance and fabric capability
2.5 times the performance of 10 GbE
Greater port density vs 40 GbE (one lane vs. four lanes)
Reduced capital expenditures (CAPEX)
Fewer ToR switches and fewer cables
Lower cost versus 40 GbE
Reduced operational expenditures (OPEX)
Requires less power, cooling, and footprint
Leverage of existing IEEE 100GbE standard


Summary
No matter the market research or the attitude of users, 25 GbE seems to be the preferred option in the next step. Actually, coming back to reality, there will be a significant increase in 100GbE and 25GbE port density this year. However, will 40 GbE be replaced and dead? We do not know what will happen in the future. But the trends will always be higher speed, wider band, and higher port density. 25 GbE vs 40 GbE, let's wait and see how things play out.