10GbE (Gigabit Ethernet) is no longer enough for the increasing need for high speed transmission with applications like Big Data, Cloud and Internet of Things being introduced in a variety of industries. Transmission network migration to 40/100G has already been the industry consensus. As the cost for 100G is far beyond what most companies can afford and the technology for 100G is still not mature, there is still a gap to reach the transmission speed of 100 Gb/s. However, to satisfy the current need for data rate, 40G could be a better and more economic solution. Currently the servers in many data centers are ready to carry the transmission of 40 Gb/s. The core technologies of 40G are gradually mature. In addition, more manufacturers are battling for the 40G market, which drives down the 40G deployment price.

Unlike 1G migrating to 10G, 10G migration to 40G get across a much larger span in terms of not only transmission data rate but also technologies. Thus, the deployment of 40G migration is much more complicated than that of 10G. Three factors should be considered to increase the reliability and manageability for 40G migration. They are fiber optic transceiver, transmission media, and pre-terminated MPO assemblies.

Fiber Optic Transceiver

Fiber optic interconnection is indispensable in today’s telecommunication network. Photoelectric conversion is a necessary part in fiber optic network. The function of fiber optic transceiver is photoelectric conversion, which makes it one of the most commonly used components in the data center. Without it, the data center cannot run normally.

As for 40G migration, transceivers of two different package forms are commonly used: QSFP+ transceiver (Quad Small Form-factor Pluggable Plus transceiver) and CFP transceiver (C Form-factor Pluggable transceiver). QSFP+transceiver is more popular in 40G application. A single 40G fiber optic transceiver may not be expensive. However, to a medium-sized data center, thousand of optical transceivers might be needed. The total cost on optical transceivers is a large sum of money. The switch market has already been monopolized. Luckily, the transceiver market is not. Third party transceivers that are compatible with a variety types of switches can be found in today’s market. They have the same performances that the original brand transceivers have, but cost less money. Selecting compatible transceivers has become the choice of many data centers. Cost is one aspect that should be considered in 40G optical transceiver selection. Quality is also very important. Not all the third party transceivers are created equal. Selecting the compatible 40G transceivers from a company that assures 100% compatibility and interoperability is necessary. The above picture shows the testing of Cisco compatible QSFP-40G-LR4 transceivers on a Cisco switch to ensure its compatibility and interoperability.

Transmission Media

40G standards of IEEE have already been announced several years ago. To meet various situations, there are standards for different transmission media. Although fiber optic cable is becoming more and more popular, there is still a place for copper cable in data center. Standards for both copper and fiber optic are being used. Commonly used 40G Ethernet media systems include the following:

• 40GBASE-CR4: 40Gb/s Ethernet over copper cable in short transmission distance.
• 40GBASE-SR4: 40Gb/s Ethernet over four short-range multimode fiber optic cables.
• 40GBASE-LR4: 40Gb/s Ethernet over four wavelengths carried by a signal long-distance single mode fiber optic cable.

It comes to the old question: fiber optic cable or copper cable, which should be used in 40G migration? Copper is cheaper. But it can only support 40G transmission limited to several meters. Single mode fiber optic cable supports the longest 40G transmission distance up to 10 km. For multimode fiber optic cables, OM3 and OM4 are suggested to support short distance transmission. The longest distance that OM3 can support for 40G transmission is 100 m. OM4 can support a longest 40G transmission distance of 150 m. The selection of transmission media should depend on the specific applications.

MPO Assemblies for 40G

According to the IEEE standards, the 40G multi-mode Ethernet transmission uses four multi-mode fiber optic cables. The IEEE 802.3ba standard also specifies multi-fiber push-on (MPO) connectors for standard-length multi-mode fiber connectivity. Most of the 40G multi-mode Ethernet transceivers are based on the MPO technology. It is wise to increase fiber optic density by using MPO technology, but a new problem is coming up. As the fiber number increased, the cabling and splicing difficulty in data center increased. Unlike traditional two-strand fiber connections, MPO connectors cannot be field terminated easily. Most of the data centers choose the pre-terminated MPO assemblies (as shown in the above picture) in 40G deployment, which is more reliable and can save more human labor. Before cabling, determine the cabling lengths and customized pre-terminated MPO assemblies with manufacturers would save a lot of time and money.

Conclusion

Selecting a compatible third party transceiver of high quality in 40G transmission would save a lot of money. Combining specific applications and characteristics of 40G transmission media, would help to determine the most economic and reliable 40G deployment plan. Pre-terminated MPO assemblies are necessary for flexible and manageable cabling in 40G deployment. 40G migration is happening now and it will become a milestone in the history of network transmission.

MPO / MTP Harness & Fanout Cable Assemblies

Optec's MPO / MTP harness & fanout cable assemblies, part of the High Density Multifibers solutions portfolio, utilizes the high density MPO / MTP connector and fans out using a fanout kit to conventional generic fiber optic connectors such as SC, ST, LC, E2000 and MTRJ.

Benefits:

• Factory terminated & tested with guaranteed quality
• High density to dramatically save space
• Installer-friendly to save time & money
• Optimize network performance
• Maximize lifespan
• Design cater for up-scaling needs and future technologies growth
• The best solution covers all fiber optic cabling needs in all areas of Data Center 

How to Upgrade From 10GbE to 40GbE for Multimode Fiber?

Scenario 1—if upgrading from 10G to 40G, one or more of the LC Duplex cassette(s) can be replaced with 12 MPO adapters. The MPO adapters are designed to fit in the same opening as the cassettes. This easy upgrade path uses the 8-fiber harness cable to connect to the 10G SFP+. From Figure 1, we can see that 4 10G SFP+ modules like SFP-10GB-SR are connected with MPO adapter by MTP harness cable. It does not require any additional space and reuses the same patch panels. Additional 12-fiber cable assemblies (or any fiber counts in multiples of 12 fibers) are provided as needed for backbone or horizontal cabling.

Scenario 2—if it is required to add some 40G connections while retaining the 10G connections, like Figure 2 shows, use one MPO/MTP LGX Cassette to connect four 10G SFP+ links. Then a Type-B female MPO/MTP trunk cable should be used between the cassette and 40G QSFP+ transceiver. QSFP+ transceiver like QSFP-40G-SR4 is needed here to provide a cost-effective solution for smoothly migrating to 40G connectivity.

Module Types

QSFP/QSFP28

QSFP form factor optics are the primary way of delivering 40GbE and are now appearing in 100GbE in QSFP28 form. These present either MPO or LC connectors.

• QSFP28 is a new variant published to support 100Gb. QSFP and QSFP28 are both the same form factor.

• LC Variants are also available on Bi-Directional (BiDi) Multi-Mode QSFPs allowing QSFPs to use existing OM3/OM4 multi-mode fiber plants

• MPO variants are also available for (some) Single-Mode QSFP transceivers used to breakout 1x MPO/MTP port to multiple LC connections

• *Multi-Mode QSFP transceivers typically support a breakout mode as well.
  
   

Media Dependent Interface (MDI)

Media dependent interface is an Ethernet port connection that connects network devices such as switches and hubs without using a null-modem or crossover cable. A suitable MPO (multi-fiber push-on) adapter is often used as the MDI for multimode fiber cables. The benefit of using an MPO connector is that it can support up to 24 fibers in one ferrule. With the 40 GbE transmission, a 12-position MPO connector is used. Only four transmit fibers are used on each side of the MPO connector, leaving the middle four unused.

For 100 GbE transmission, a 24-position MPO connector with 12 fibers in each row is used. But only ten fibers on the top and another ten on the bottom rows are used, leaving the middle four unused. Besides MPO connects, you can also use LC connectors. The latter comes with one fiber in each ferrule but supports wideband multimode fiber technology for higher transmission speeds of up to 400GbE.

As fiber optic density increases, field termination and splicing become much more hectic. You can save time & energy by choosing custom cable lengths and pre-terminated MPO and LC assemblies.

 

Migration Path for 40/100 GbE

A practical and seamless migration to a higher Ethernet speed ensures minimal disruption with little to no replacement of existing connectivity components and fiber optical cabling. The latter is often deployed for the switch to switch connections, switch to server, and SAN connections.

Some components needed during migration include modules, harnesses, adapter plates, and trunks. 40/100 GbE migration uses nearly the same components except for the MPO connectors. Using pre-terminated optical fiber cabling is often preferred as it eliminates rework and testing and minimizes cost during installation. It also allows for convenient replacement or the addition of new connections in the future.

When choosing between 12 and 24-fiber trunks, always pay attention to the network density and congestion. Often, high-density connectivity needs more active equipment, but the space could be limited. 24-fiber cabling will work best as it will allow for more connections without increasing the number of ports. It also reduces the cables needed compared to a 12-fiber model, translating into a lighter load, convenient management, and reduced cooling costs.

The use of parallel optics in 40GbE multimode fiber cabling (MMF cabling) require more fiber strands than the 10GbE infrastructures. Thus, data center will require a cabling upgrade to meet the requirement of migration. In this case, cost is a big factor. To help user solve the fiber cost issue, many vendors developed a new transceiver alternative that allow zero-cost fiber migration by reusing the current 10Gbps multimode fiber-optic cabling plant for 40Gbps connectivity. 
 

Overview on Multimode and Single-mode Fibers

Since the establishment of multimode fiber in the early 1980s, there has been OM1 and OM2, and laser optimized OM3 and OM4 fibers for 10GbE, 40GbE and 100GbE. OM5, the officially designated wideband multimode fiber (WBMMF), is a new fiber medium specified in ANSI/TIA-492AAAE. The channel capacity of multimode fiber has multiplied by using parallel transmission over several fiber strands. In terms of single-mode fiber, there are only OS1 and OS2; and it has been serving for optical communications without much change for a long time. Compared with the constant updates of multimode fiber and considering other factors, some enterprise customers prefer to use single-mode fiber more over the past years and for the foreseeable future. With the coming out of the new OM5 fiber, it seems that multimode fiber might last for a longer time in the future 200G and 400G applications.

 

FAQ: 40Gb/s Ethernet extended optical multimode fiber cable for link distances up to 400 meters

When using multimode fiber (MMF) optical cable for 40Gb/s Ethernet (40GbE) extended connections, the distance between the host or switch and the storage system can be up to 400 meters. This extended distance capability enables customers to have much greater flexibility in the physical location of the host or switch.
To deploy optical MMF 40Gb/s Ethernet connectivity for extended distances, customers must adhere to the following requirements:

• Must use 50-micron optical cable that meets this specification:

MPO-MPO duplex 50/125 Plenum, Type B, min 3500Mhz/Km @ 850 nm, OM4 MMF Cable.

• For cable lengths greater than 30 meters, customers must purchase them directly from cable vendors. See the Ordering Information for 40GbE MMF Optical Cable below for details.

• To achieve the maximum 400-meter distance, the interconnect must be a direct point-to-point optical cable with no intervening devices (i.e. patch panel, optical coupler).

• The distance will be reduced when the interconnect is routed through intermediate passive devices (such as a patch panel) due to degradation in optical signal quality (about 0.3 dB loss per passive device). The actual distance reduction will vary. The only practical way for establishing the maximum supported distance is to test the desired configuration in the actual customer environment.