40G Ethernet Migration Strategy Over Multimode Fiber

With the increasing network bandwidth to meet the global IP traffic demand, there will be a need to upgrade to 40G Ethernet links for switch to server and storage area network connections in data centers. And the biggest market for 40G Ethernet (40 GbE) is in data centers for interconnection links with servers and storage area networks. So this article will talk about migration strategy for 40G Ethernet over multimode fiber.

40G Ethernet Standard

 

IEEE published the IEEE 802.3ba standard for 40 Gigabit Ethernet in June 2010. The following table illustrates the capabilities of different grades of multimode fibers (OM1, OM2, OM3 and OM4) to support different Ethernet applications. Only the laser optimized multimode fibers OM3 and OM4 are capable of supporting 40G Ethernet. The cabling requirements for 40GBASE-SR4 will be focused and guidance on an effective migration strategy to transition form 10G to 40G will be provided.

 

40G Ethernet Over Multimode Fiber

 

40G Ethernet over multimode fiber uses parallel optics at 10Gb/s per lane. One lane uses 1 fiber for each direction of transmission. 40G requires 8 fibers. The concept of parallel transmission at 10 Gigabits per lane is illustrated below. The minimum performance that is needed to support 40G over multimode fiber is OM3 fiber for a distance of 100 meters. Cabling with OM4 fiber provides the capability to extend the reach up to 150 meters.

 

Media Dependent Interface (MDI)

 

The MDI is the physical interface that connects the cabling media to the network equipment. For multimode fiber, the media dependent interface is the MPO adapter that meets the dimensional specifications of IEC 61754-7 interface 7-3. The corresponding MPO female plug on the optical fiber cable uses a flat interface that meets the dimensional specifications. 40 GbE uses the MPO connector interface at the MDI and uses a 12 position MPO connector interface that aligns 12 fibers in a single row. Four transmit fibers are used on one side and four receive fibers are used on the opposite side of the MPO connector, for a total of eight fibers. The middle four fiber positions are not used.

Migration Path From 10G to 40G for Multimode Fiber

 

Migrating from 10G (that uses two fibers in either a SC Duplex or a LC Duplex connector) to 40G will require a lot more fibers and a different type of connector. The way that optical fiber cabling is deployed for 10G can facilitate an easier migration path to 40G. An effective migration strategy needs to provide a smooth transition to the higher Ethernet speeds with minimum disruption and without wholesale replacement of existing cabling and connectivity components.

Optical fiber cabling is commonly deployed for backbone cabling in data centers for switch to switch connections and also for horizontal cabling for switch to server and storage area network connections. The use of pre-terminated optical fiber cabling can facilitate the migration path to 40G. A pre-terminated cable assembly containing 24 OM4 multimode fibers with two 12-fiber MPO connectors at both ends plugs into the back of a breakout cassette that splits the 24 fibers into 12 LC duplex connectors at the front of the cassette. It is necessary to provide some 40G connections, either as a replacement of or as an addition to the existing 10G connections.

The first case: if upgrading from 10G to 40G, one or more of the LC duplex cassette/cassettes can be replaced with 12 MPO adapters. The MPO adapters are designed to fit in the same opening as the cassettes. Fiberstore offers a high-density 18 MPO adapter with the same overall physical dimensions as 12 MPO adapter. This is an upgrade path from 10G to 40G that does not require any additional space and reuses the same patch panels. For instance, the 12 LC duplex cassettes could be replaced with either a 12 MPO or 18 MPO adapters as needed.

The second case: if it is required to add some 40G connections while retaining the 10G connections, a high-density cassette containing 18 LC duplex connections in the same space as a 12 LC duplex cassette would be used. Three of the 12 duplex cassettes can be replaced with three 18 LC Duplex cassettes, thus maintaining the 48 10G connections while freeing space for either a 12 MPO or 18 MPO adapter providing up to 18 additional 40G connections. The requisite number of additional fiber cable assemblies in multiples of 12 fibers are provided as needed.

Summary

 

Pre-terminated optical fiber cabling provides a seamless migration path to 40 Gigabit Ethernet using the same infrastructure by adding pre-terminated trunk cable assemblies and MPO adapter frames as needed. The use of Fiberstore’s pre-terminated cabling facilitates the migration to 40G Ethernet from 10G Ethernet networks today.

Article source: www.fiberopticshare.com/40g-ethernet-migration-strategy-over-multimode-fiber.html

Which to Choose for 40GBASE-LR4 QSFP+ Transceiver: PSM or CWDM?

It is well known that 40GBASE-SR4 QSFP+ transceiver uses a parallel multimode fiber (MMF) link to achieve 40G. It offers four independent transmit and receive channels and each channel is capable of 10G operation for an aggregate data rate of 40G with distances up to 100 meters on OM3 MMF or 150 meters on OM4 MMF. However, for 40GBASE-LR4 QSFP+ transceivers, two kinds of links are available. One is parallel single-mode fiber (PSM), and the other is coarse wavelength division multiplexing (CWDM). What is the difference between the two? Keep reading this article and you will find the answer.

40GBASE-LR4 PSM QSFP+ Transceiver

PSM QSFP+ transceiver is a parallel single-mode optical transceiver with an MTP/MPO fiber ribbon connector. Moreover, it offers four independent transmit and receive channels and each channel is capable of 10G operation for an aggregate data rate of 40G on 10 km of single-mode fiber. The guide pins inside the receptacle could ensure proper alignment. Usually, the cable cannot be twisted for proper channel to channel alignment. For a PSM QSFP+ transceiver, the transmitter module accepts electrical input signals compatible with common mode logic (CML) levels. All input data signals are differential and internally terminated. The receiver module converts parallel optical input signals via a photo detector array into parallel electrical output signals. The receiver module outputs electrical signals are also voltage compatible with CML levels. All data signals are differential and support a data rates up to 10.3G per channel.

40GBASE-LR4 CWDM QSFP+ Transceiver

The 40GBASE-LR4 CWDM QSFP+ transceiver like QSFP-40GE-LR4 is compliant to 40GBASE-LR4 of the IEEE P802.3ba standard. It has a duplex LC connector for the optical interface and its maximum transmission distance is 10 kilometers. Single-mode fiber (SMF) has to be used to minimize the optical dispersion in the long-haul system. This transceiver converts 4 inputs channels of 10G electrical data to 4 CWDM optical signals by a driven 4-wavelength distributed feedback (DFB) laser array, and then multiplexes them into a single channel for 40G optical transmission, propagating out of the transmitter module from the SMF. Reversely, the receiver module accepts the 40G CWDM optical signals input, and demultiplexes it into four individual 10G channels with different wavelengths. The central wavelengths of the four CWDM channels are 1271, 1291, 1311 and 1331 nm as members of the CWDM wavelength grid defined in ITU-T G694.2. Moreover, each wavelength channel is collected by a discrete photo diode and output as electric data after being amplified by a transimpedance amplifier (TIA).

Differences Between the Two

From the perspective of an optical transceiver module structure, PSM seems more cost effective as it uses a single uncooled CW laser splitting its output power into four integrated silicon modulators. Moreover, its array-fiber coupling to an MTP connector is relatively simple. However, from the perspective of an infrastructure, PSM would be more expensive when the link distance is long, because it uses 8 optical single-mode fibers while CWDM only uses 2 optical single-mode fibers. The following table illustrates the main differences between CWDM and PSM.

In addition, the caveat is that the entire optical fiber infrastructure within a data center, including patch panels, has to be changed to accommodate MTP connectors and ribbon cables, which are more expensive than conventional LC connectors and regular SMF cables. Moreover, it is not a straightforward tack to clean MTP connectors. So CWDM is a more profitable and popular 40G QSFP link.

Summary

For 40GBASE-LR4 QSFP+ transceivers, either CWDM link or PSM link, the maximum transmission distance is both 10 km. 40GBASE-LR4 PSM QSFP+ transceiver uses an MTP/MPO fiber ribbon connector via 8 optical single-mode fibers to reach 40G, while 40GBASE-LR4 CWDM QSFP+ transceiver uses a duplex LC connector via 2 optical single-mode fibers to achieve 40G. Thus, CWDM QSFP+ enables data center operators to upgrade to 40G connectivity without making any changes to the previous 10G fiber cable plant, which is more cost-effective and widely used by people.

 Article source: www.fiberopticshare.com/which-to-choose-for-40gbase-lr4-qsfp-transceiver-psm-or-cwdm.html

Data Center 40G Migration with OM3 and OM4 Optical Connectivity

Why Migrate to 40G

With the quick development in data center, cabling infrastructures should provide manageability, flexibility and reliability. Deployment of optical connectivity solutions enables for an infrastructure meeting these requirements for current applications and data rates. Scalability is another key factor that needs to consider when choosing the type of optical connectivity. It refers to not only the physical expansion of the data center with respect to additional servers, switches or storage devices, but to the scalability of the infrastructure to support a migration path for increasing data rates. As technology evolves and standards are completed to define data rates such as 40G/100G, Fibre Channel (32G and beyond) and InfiniBand (40G and beyond), the cabling infrastructures installed today need to provide scalability to accommodate the need for more bandwidth in support of future applications. Moreover, current data rates cannot meet the needs of the future with the rising demand to support high-bandwidth applications. 40G technologies and standards, however, can support future networking requirements. Thus, a migration to 40G is required.

40 Gigabit Ethernet Standard

Ratified in June 2010, 802.3ba standard provides a guidance for 40G transmission with multimode and single-mode fibers. And this standard does not have guidance for Cat UTP/STP copper cable. OM3 and OM4 are the only multimode fibers included in the standard. Due to the 850nm VCSEL modulation limits, multimode fibers utilize parallel optics transmission instead of serial transmission. Single-mode fiber guidance utilizes duplex fiber WDM (wavelength-division multiplexing) serial transmission.

Compared to single-mode fiber, multimode fiber offers a significant value proposition for short length interconnects in the data center. Unlike traditional serial transmission, parallel optics transmission utilizes an optic module interface where data is simultaneously transmitted and received over multimode fibers. The 40GBASE-SR4 supports 4 x 10G on four fibers per direction.

Cabling Performance Requirements for OM3/OM4

When evaluating the performance needed for the OM3 and OM4 cabling infrastructure, the following criteria should be considered. Each of the criteria would have an impact on the cabling infrastructure’s ability to meet the standard’s transmission distance of 100 meters over OM3 fiber and 150 meters over OM4 fiber.

Bandwidth is the primary criteria. OM3 and OM4 fibers are optimized for 850nm transmission and have a minimum 2000 MHz∙km and 4700 MHz∙km effective modal bandwidth (EMB). Fiber EMB measurement techniques are utilized today. The minimum EMBc (Effective Modal Bandwidth calculate) method combines the properties of both the source and fiber. With a connectivity solution using OM3 and OM4 fibers that have been measured using the minEMBc technique, the optical infrastructure deployed in the data center will meet the performance criteria set forth by IEEE for bandwidth.

Insertion loss is a critical performance parameter in current data center cabling deployments. Total connector loss within a system channel impacts the ability to operate over the maximum supportable distance for a given data rate. The supportable distance at data rate decreases with total connector loss increasing. The 40G standard specifies the OM3 fiber to a 100m distance with a maximum channel loss of 1.9 dB, which includes a 1.5 dB total connector loss budget. OM4 fiber is specified to a 150m distance with a maximum channel loss of 1.5 dB, which includes a 1.0 dB total connector loss budget. The maximum cable fiber attenuation is 3.5 dB/km at 850 nm. So the insertion loss specifications of connectivity components should be evaluated when designing data center cabling infrastructures. With low-loss connectivity components, maximum
flexibility can be achieved with the ability to introduce multiple connector matings into the connectivity link.

Summary

Cabling deployed in the data center today must be selected to provide support of data rate applications of the future. To achieve this purpose, OM3 or OM4 is a must. They provide the highest performance for today’s needs. With 850nm EMB of 2000 MHz∙km and 4700 MHz∙km, the fibers provide the extended reach required for structured cabling installations in the data center. Except the performance requirements, the choice in physical connectivity is also important. Utilizing MTP-based connectivity in today’s installations provides ways to migrate to multifiber parallel optic interface when needed. Therefore, MTP-based connectivity using OM3 and OM4 fiber is the ideal solution in the data center. It can be installed for use in today’s applications, while providing an easy migration path to future higher speed technologies.
 

Article source: www.fiberopticshare.com/data-center-40g-migration-with-om3-and-om4-optical-connectivity.html

Data Center 10 Gigabit Ethernet Cabling Options

With the dramatic growth in data center throughput, the usage and demand for higher-performance servers, storage and interconnects have also increased. As a result, the expansion of higher speed Ethernet solutions, especially 10 and 40 Gigabit Ethernet has been ongoing. For 10 Gigabit Ethernet solution, selecting the appropriate 10-gigabit physical media is a challenge, because 10GbE is offered in two broad categories: optical and copper. This article will introduce both optical and copper cabling options for 10 Gigabit Ethernet.

Fiber Optic Cables

Two general types of fiber optic cables are available: single-mode fiber and multimode fiber.

Single-mode Fiber (SMF), typically with an optical core of approximately 9 μm (microns), has lower modal dispersion than multimode fiber. It is able to support distances of at least 10 kilometers, depending on transmission speed, transceivers and the buffer credits allocated in the switches.

Multimode Fiber (MMF), with an optical core of either 50 μm or 62.5 μm, can support distances up to 600 meters, depending on transmission speed and transceivers. 

When planning data center cabling requirements, be sure to consider that a service life of 15-20 years can be expected for fiber optic cabling. Thus the cable chosen should support legacy, current and emerging data rates.

10GBASE-SR — a port type for multimode fiber, 10GBASE-SR cable is the most common type for fiber optic 10GbE cable. It is able to support an SFP+ connector with an optical transceiver rated for 10GbE transmission speed. 10GBASE-SR cable is known as “short reach” fiber optic cable.

10GBASE-LR — a port type for single-mode fiber, 10GBASE-LR cable is the “long reach” fiber optic cable. It is able to support a link length of 10 kilometers.

OM3 and OM4 are multimode cables that are “laser optimized” and support 10GbE applications. The transmission distance can be up to 300 m and 400 m respectively.

Copper Cables

Common forms of 10GbE copper cables are as follows:

10GBASE-CR — the most common type of copper 10GbE cable, 10GBASE-CR cable uses an attached SFP+ connector and it is also known as a SFP+ Direct Attach Copper (DAC). This fits into the same form factor connector and housing as the fiber optic cables with SFP+ connectors. Many 10GbE switches accept cables with SFP+ connectors, which support both copper and fiber optic cables.

Passive and Active DAC — passive copper connections are common with many interfaces. As the transfer rates increase, passive copper does not provide the distance needed and takes up too much physical space. So the industry is moving towards an active copper type of interface for higher speed connections. Active copper connections include components that boost the signal, reduce the noise and work with smaller gauge cables, improving signal distance, cable flexibility and airflow.

10GBASE-T — 10GBASE-T cables are Cat6a (category 6 augmented). Supporting the higher frequencies required for 10GbE transmission, category 6a is required to reach the distance of 100 meters (330 feet). Cables must be certified to at least 500 MHz to ensure 10GBASE-T compliance. Cat 6 cables may work in 10GBASE-T deployments up to 55 meters (180 feet) depending on the quality of installation. Some 10GbE switches support 10GBASE-T (RJ45) connectors.

When to Use Different Type of 10GbE Cables

To summarize, currently the most common types of 10GbE cables use SFP+ connectors.

• For short distances, such as within a rack or to a nearby rack, use DAC with SFP+ connectors, also known as 10GBASE-CR.
• For mid-range distances, use laser optimized multimode fiber cables, either OM3 or OM4, with SFP+ connectors.
• For long-range distances, use single-mode fiber optic cables, also known as 10GBASE-LR. 

Originally published: www.fiber-optic-components.com/data-center-10-gigabit-ethernet-cabling-options.html

50µm and 62.5µm Multimode Optical Fiber: Which Is More Preferable?

Multimode optical fiber is a type of optical fiber mainly used for transmission over short distances, such as in a building or on a campus. Typical multimode optical fibers support data rates from 10 Mbps to 10 Gbps over link lengths of up to 600 meters. It can offer reliable, flexible and cost effective cabling solutions for local area networks, central offices and data centers.

What Are 50/125µm and 62.5/125µm Multimode Optical Fiber?

According to the core and cladding diameters, multimode optical fiber can be divided into 50/125 µm and 62.5/125 µm. 50 µm and 62.5 µm refer to the diameters of the fiber core, which is the area that carries light signals. 125 µm means the cladding diameter of the fiber. The cladding confines the light to the core as it has a lower index of refraction. Cable construction is shown in the following diagram indicating the cable core, cladding and outer jacket diameters. Currently, there are four types of multimode optical fibers: 62.5µm multimode optical fiber (OM1), 50µm multimode optical fiber (OM2), laser-optimized 50µm multimode optical fiber (OM3) and laser-optimized 50µm multimode optical fiber (OM4). 

Why Two Core Diameters?

When optical fiber was introduced for 10Mbps and then 100Mbps Ethernet, light-emitting diode (LED) light sources and 62.5µm fiber were used. LEDs overfill the fiber core, so larger core diameters mean more light is collected, and thus data can be carried farther as shown in the following picture A. 

In order to achieve 1Gbps performance, the light source was upgraded to vertical-cavity surface-emitting laser (VCSEL). VCSELs can switch more rapidly than LEDS, which makes them better for higher data rates. Moreover, VCSELs emit much smaller and more sharply focused beams, coupling more power into the fiber for greater efficiency as the following picture B shown. With a VCSEL light source, all of the light is coupled into the fiber, so a larger core diameter does not gather more light. In fact, a larger core diameter transmits the light less efficiently as a result of modal dispersion. Using 50µm fiber decreased modal dispersion and then increased the reach of 1Gbps fiber cabling.

Which Is More Preferable?

62.5µm fiber could support 2km campuses at 10 Mbps because more light for LEDs could be coupled into its larger core. And it dominated the premises market for more than a decade. However, with faster transmission rates and higher bandwidth demands, changing market conditions was imperative. So 50µm fiber has been established as the best solution for applications > 10 Mbps. The 100Mbps Fast Ethernet standard invited the use of LEDs that take advantage of lower fiber attenuation at 1300nm wavelength, which offset the LED coupling loss into 50µm fiber caused by its smaller core diameter. Hence, 50µm fiber could support the same 2km reach at 100 Mbps as 62.5µm fiber.

As data rates rise to Gigabit speeds, 62.5µm fiber is stretched beyond its performance limit because of its lower bandwidth at 850 nm. By contrast, 50µm fiber has as much as ten times the bandwidth of the 62.5µm fiber, which enables support of 1Gbps and 10Gbps applications. As 1Gbps and 10Gbps transmitters use small spot-size lasers, concerns over power coupling efficiency into 50µm fiber are no longer an issue. Moreover, the laser-optimized 50µm multimode optical fiber can offer the most secure and least-cost upgrade path to higher-speed networks as it is able to support 40 and 100Gbps data transmission.

Conclusion

As stated above, 50µm multimode optical fiber is more preferable than 62.5µm multimode optical fiber. Using 50µm multimode optical fiber can bring benefits of faster transmission rates and higher bandwidth. If you have not put 50µm multimode optical fiber into use, it is time to employ 50µm multimode optical fiber for higher performance on your network.

Article source: www.fiber-optic-components.com/50%C2%B5m-and-62-5%C2%B5m-multimode-optical-fiber-which-is-more-preferable.html