Category: Fiber Transceivers

Optical transceivers, Active Optic Cables, data center switches, and cable management in data centers.

How does bending effect a Fiber Patchcord?

by http://www.fiber-mart.com

Fiber optic cables by their nature and the way they are manufactured are designed to be enduring the stress applied to them during their installation and maintenance, however as they are made of glass and are highly fragile it is highly advisable by the manufacturers to lower this stress to a minimum. Bending the fiber cables and the amount of quality loss depends on the type of the cable, if it’s Single- mode or Multi- mode cable, their design, their core diameter and their transmission wavelength. Usually longer wavelengths are more sensitive to stress and bending losses.
The process of bending or pulling loss starts inside the cable as the optical signal within the cable is not guided through the core of the fiber, instead a big part of the light itself is lost and bouncing in the walls and the cladding in the cable thus creating a high loss in optical light. Bending would most probably permanently damage the fiber cable by causing cracks in it. This would compromise the quality of the signal and the integrity of the data transmission. This is easily put to the test with the help of a visible laser put in the fiber itself and bending it at a certain point. The light loss will be visible where the cable is being bent.
During the last couple of years manufacturers and the Fiber Optic Association started developing a new type of cables that are more durable and can withstand higher stress and bending. This was firstly developed for the Single- mode fibers and after a couple of years for the Multi- mode fibers. The way they were testing the bending and the endurance of the cables was with the help of a piece of wood and bending the cable around it in front of a wide audience.
The bending of the fiber optic cables is measured by the bend radius. Only in the last couple of years this bending radius has been industry standardized by the Fiber Optic Association. In contrary before it was standardized the bending radius have been governed by the cable manufacturers. The new standard defined by the ANSI/TIA/EIA-568B.3 named “Optical Fiber Cabling Components Standard” sets exact performance specifications concentrated on the minimum bend radius and the maximum pulling tensions for 50/125 micron and 62.5/125 micron fiber optic cables. With the new standard introduced the manufacturers have the obligation to specify the minimum bending radius to which the cable could be safely bent during the installation. Most commonly the minimum bend radius of 1.6mm and 3.0mm fiber cables is around 3.5cm and the minimum bend radius for patch cable is around ten times the cable diameter. If referring to the manufacturer’s recommended bend radius is not possible, the general guideline for cable bending is no more than 20 times the diameter of the cable itself.
There are two types of bending radius: micro bends and macro bends. As the name suggests macro bends are larger than micro bends. Even though the two terms are very similar there is a significant difference in differentiating them. Macro bends are usually the bends that would be visible by the naked eye and micro bends are small microscopic deviations along the fiber itself.
However, it doesn’t take much for a micro bend to happen as it could be also caused by the fiber coating squeezing the cable because of very low temperatures. There is a standardized micro bend test procedure defined by the Fiber Optics Association named “FOTP-68 Optical Fiber Micro bend Test Procedure”. One way of developing and manufacturing more micro bend enduring fiber optic cables is by applying several layers of primary coating which would eventually protect the fibers of being bent.
Macro bends on the other hand, as aforementioned, is tested by wrapping the fiber cable around a specific material of a specified diameter. The standardized macro bend testing defined by the Fiber Optics Association is called “FOTP-62 IEC 60793-1-47 Measurement Methods and Test Procedures – Macro bending Loss”.
Another aspect of the bend radius that would affect the fiber cable performance is the path of the patch cable. This should be clearly defined by the manufacturer. If this is not properly done it would cause increased congestion in the termination panel possibly violating the band radius threshold. The patch cable should be easily accessed, easier to be maintained at all points of its path. Because the patch cables are commonly kept together with cable ties, manufacturers advise these cable ties be used with caution. Tightening the cable ties with an installation tool is harmful to the fiber optic cables and could very easily cause a full fiber breakage. Manufacturers advise the cable ties to be hand tightened but in the same time to leave them loose enough to be moved along the cable by hand.
The patch cable path should be well-defined and reduce the risk of stressing the cable. This way the patch cable path would be easier and quicker to be accessed by the engineer for maintenance works. The reduced fiber twists would ensure the optic light in the cable travels in the core of the cable thus minimizing the escape through the walls and the coating of the cable.
As the proper fiber management would affect the network’s reliability, performance and the cost, a well-defined cable paths could ensure a safe ground for future maintaining and network upgrading.

What interconnection solutions are available for QSFP28?

by http://www.fiber-mart.com

The Quad Small Form-factor Pluggable (QSFP) is a compact, hot-pluggable transceiver. The data rates are from 4×1 Gb/s for QSFP and 4×10 Gbit/s for QSFP+  and to the highest rate of 4×28 Gbit/s known as QSFP28[3] used for 100 Gbit/s links.

The QSFP28 standard is designed to carry 100 Gigabit Ethernet, EDR InfiniBand or 32G Fibre Channel. This transceiver type is also used with direct-attach breakout cables to adapt a single 100GbE port to four independent 25 gigabit ethernet ports (QSFP28-to-4x-SFP28). Sometimes this transceiver type is also referred to as “QSFP100” or “100G QSFP”  for sake of simplicity.

QSFP28 transceiver not only have the same physical size as the QSFP+ used for 40G traffic, but the lowest power consumption among those that are capable of handling 100G traffic.

Basically, there are two types of transceivers: QSFP28-SR4 and QSFP28-LR4.

QSFP28-SR4 transceivers is specially designed to support connections of up to 100 meters over multimode fiber. This approach is similar to using AOC cables, but here it is possible to use structured cabling. They use more expensive non-standard MPO (multi push-on/pull-off cable) connectors which cancel out some of the cost savings of the transceiver.

QSFP28-LR4 versions support connections up to 10km over single-mode fiber. They use standard LC connectors and the existing structured LC cabling.

QSFP28 Cable Assemblies

QSFP28 cable (DAC or AOC cables) is the more convenient, low-cost method of connecting 100G equipment. Using cable assemblies removes many of the problems associated with dirty connectors. DAC is suitable for applications within 15m and AOC up to 70m. AOC cable assemblies provide similar performance to discrete transceivers and fiber cables.

Active Direct Attach Copper Cable

Active copper cables are designed in the same cable type as the passive one, but they contain low power circuitry in the connector to boost the signal and are driven from the port without additional power requirements. The active version provides a low cost alternative to optical transceivers, and are generally used for end of row or middle of row data center architectures for interconnect distances of up to 15 meters.

The main difference between active DAC and passive DAC is that there is a driving chip in the design of active DAC.

Active Optical Cable

Active optical cable (AOC) incorporates active electrical and optical components. It can achieve longer distance than the copper assemblies. In general, active optical cable can reach more than 100m via multimode fiber. Compared to direct attach copper cable, AOC (eg. Cisco SFP-10G-AOC10M) weighs less and can support longer transmission distance. It is immune to electromagnetic energy since the optical fiber is dielectric (not able to conduct electric current). And it is an alternative to optical transceivers and it can eliminate the separable interface between transceiver module and optical cable. However, it costs more than copper cable. 100GbE QSFP28 AOC is composed of an OM4 multimode cable connecting two QSFP28 connectors on each end. Using the same port as transceiver optics, direct attach cables can support Ethernet, Infiniband and Fibre Channel but with independent protocols. In general, direct attach cable assemblies are divided into three families—direct attach passive copper cable, direct attach active copper cable and active optical cable (AOC).

Advantages of Active Optical Cables

The AOC assemblies provide the lowest total cost solution for data centers by having the key advantages as following:

  • Low weight for high port count architectures;
  • Small bend radius for easy installations;
  • Low power consumption enabling a greener environment.

For the 100G longer distance, the CFP and CFP2 offer DWDM Coherent technology and enable multi-channel long distance connectivity of more than 1000km. One thing we can’t miss is that the CFP is too big to be used in an Ethernet switch in volume.

Fan-out cable or breakout cable is considered as one of the the latest enabling technologies to help increase port densities and lower costs. Taking one (large bandwidth) physical interface and breaking it out into several (smaller bandwidth) interfaces, it has been highly recommended to be used in network migration. Breakout cables are also possible on most 100GbE QSFP+ ports where each of the 4 optical lines are broken out to 4 individual 25GbE or 10GbE interfaces. This solution requires either the deployment of a breakout cable that has 4 physical 25G / 10G endpoints, or the use of a breakout mux where an SR4 optic with MPO / MTP cable is deployed.

What is the Low Smoke Zero Halogen Cable?

by http://www.fiber-mart.com

Cables are predominant components in tree structure of a digital data center, ensuring the flow of vital information from one active device to another. In order to have products that have fire resistance properties in data center, it is important to focus on each LAN or WAN component to see the standard fire compliant standards that are present in such a catastrophic scenario.
A PVC cable (made of polyvinyl chloride) has a jacket that gives off heavy black smoke, hydrochloric acid, and other toxic gases when it burns. Low Smoke Zero Halogen (LSZH) cable has a flame-resistant jacket that doesn’t emit toxic fumes even if it burns.
On the cable industry market, there are two standards that are predominant for non-PVC cables in the fire conditions:
Historically, the European product safety standards have focused on cable designs that exclude halogens in their designs. The IEC 60332-1 governs the flame retardant
grade specifications for cables for LANs, WANs and other networking products. IEC 60332-1 applies to the majority of medium and large-scale installations in Europe. It requires LSZH jackets on cables installed near places where people congregate or anywhere there is exposed wire.
U.S. standards, on the other hand, have focused on the product’s fire resistance properties and its resistance to propagation of flame during fire conditions.
The current cost-effective compound technology available for the industrial wire and cable market forces engineers to choose either excellent flame performance or halogen-free, low-smoke performance without sacrificing electrical performance.
Wire and cable insulations are generally broken down into two distinct types, thermoplastic and thermoset.
The primary difference being that a thermoplastic material will melt when exposed to high heat or fire conditions, while a thermoset material will not melt when exposed to heat, will better resist softening and degrading, and will turn to a char under high heat or fire conditions.
As thermoset materials inherently provide better emergency performance at elevated temperatures, electrical overload conditions, and better flame propagation resistance than a thermoplastic material, they are generally preferred in industrial applications, as the conductor will have a greater propensity to see these types of operating temperatures during normal operation.
The properties of a thermosetting compound are created by an irreversible chemical reaction during processing which causes the molecules to link (cross-link), thereby “strengthening” their molecular structure. While these cross-linking properties are extremely beneficial to cable performance, they also make the development of thermosetting compounds with comparable properties to thermoplastic materials more difficult and have historically presented a greater challenge to the industry.
European standards tend to focus on cable designs generating low-smoke and containing zero-halogens (LSZH) and specific electrical requirements, while the North American standards primarily focus on a combination of fire retardancy and specific electrical performance, with a high degree of emphasis on wet electrical qualifications.
The term “low-smoke, zero-halogen” describes two distinct properties of a cable compound. The term “low- smoke” describes the amount of smoke which a compound emits when burned, while “zero-halogen” describes the amount of halogens used to make the compound. Designated halogen-free cables, hand, do not produce a dangerous gas/acid combination when exposed to flame.
In Data Center cabling and specially in patching, we may find the Cat5e UTP LSZH cable that  is performance optimized with 4 balanced twisted pairs on 24 AWG insulated solid bare copper conductors. SCP Cat5e UTP LSZH cables are constructed to create a round and flexible cable for easy pulling and stripping of the LSZH jacket.
How are cables tested or what are the main functional tests that have to be passed by the LSZH cables?
Electrical performance.
Flame propagation
Smoke measurement
Certified and listed by a nationally recognized independent testing laboratory Halogen content measurement. The thermoset insulations are rated for use at 90°C wet and dry conditions.

What is the Low Smoke Zero Halogen Cable?

by http://www.fiber-mart.com

Cables are predominant components in tree structure of a digital data center, ensuring the flow of vital information from one active device to another. In order to have products that have fire resistance properties in data center, it is important to focus on each LAN or WAN component to see the standard fire compliant standards that are present in such a catastrophic scenario.
A PVC cable (made of polyvinyl chloride) has a jacket that gives off heavy black smoke, hydrochloric acid, and other toxic gases when it burns. Low Smoke Zero Halogen (LSZH) cable has a flame-resistant jacket that doesn’t emit toxic fumes even if it burns.
On the cable industry market, there are two standards that are predominant for non-PVC cables in the fire conditions:
Historically, the European product safety standards have focused on cable designs that exclude halogens in their designs. The IEC 60332-1 governs the flame retardant
grade specifications for cables for LANs, WANs and other networking products. IEC 60332-1 applies to the majority of medium and large-scale installations in Europe. It requires LSZH jackets on cables installed near places where people congregate or anywhere there is exposed wire.
U.S. standards, on the other hand, have focused on the product’s fire resistance properties and its resistance to propagation of flame during fire conditions.
The current cost-effective compound technology available for the industrial wire and cable market forces engineers to choose either excellent flame performance or halogen-free, low-smoke performance without sacrificing electrical performance.
Wire and cable insulations are generally broken down into two distinct types, thermoplastic and thermoset.
The primary difference being that a thermoplastic material will melt when exposed to high heat or fire conditions, while a thermoset material will not melt when exposed to heat, will better resist softening and degrading, and will turn to a char under high heat or fire conditions.
As thermoset materials inherently provide better emergency performance at elevated temperatures, electrical overload conditions, and better flame propagation resistance than a thermoplastic material, they are generally preferred in industrial applications, as the conductor will have a greater propensity to see these types of operating temperatures during normal operation.
The properties of a thermosetting compound are created by an irreversible chemical reaction during processing which causes the molecules to link (cross-link), thereby “strengthening” their molecular structure. While these cross-linking properties are extremely beneficial to cable performance, they also make the development of thermosetting compounds with comparable properties to thermoplastic materials more difficult and have historically presented a greater challenge to the industry.
European standards tend to focus on cable designs generating low-smoke and containing zero-halogens (LSZH) and specific electrical requirements, while the North American standards primarily focus on a combination of fire retardancy and specific electrical performance, with a high degree of emphasis on wet electrical qualifications.
The term “low-smoke, zero-halogen” describes two distinct properties of a cable compound. The term “low- smoke” describes the amount of smoke which a compound emits when burned, while “zero-halogen” describes the amount of halogens used to make the compound. Designated halogen-free cables, hand, do not produce a dangerous gas/acid combination when exposed to flame.
In Data Center cabling and specially in patching, we may find the Cat5e UTP LSZH cable that  is performance optimized with 4 balanced twisted pairs on 24 AWG insulated solid bare copper conductors. SCP Cat5e UTP LSZH cables are constructed to create a round and flexible cable for easy pulling and stripping of the LSZH jacket.
How are cables tested or what are the main functional tests that have to be passed by the LSZH cables?
Electrical performance.
Flame propagation
Smoke measurement
Certified and listed by a nationally recognized independent testing laboratory Halogen content measurement. The thermoset insulations are rated for use at 90°C wet and dry conditions.

Will QSFP28 be a better way to 100G?

by http://www.fiber-mart.com

The Quad Small Form-factor Pluggable (QSFP) is a compact, hot-pluggable transceiver used for data communications applications. The form factor and electrical interface are specified by a multi-source agreement (MSA) under the auspices of the Small Form Factor Committee. It interfaces networking hardware to a fiber optic cable or active or passive electrical copper connection. It is an industry format jointly developed and supported by many network component vendors, allowing data rates from 4×10 Gbit/s.The format specification is evolving to enable higher data rates; as of May 2013, highest possible rate is 4×28 Gbit/s (also known as QSFP28).
4 x 28 Gbit/s QSFP+ (QSFP28)
The QSFP28 standard is designed to carry 100 Gigabit Ethernet, EDR InfiniBand or 32G Fibre Channel. This transceiver type is also used with direct-attach breakout cables to adapt a single 100GbE port to four independent 25 gigabit ethernet ports (QSFP28-to-4x-SFP28) Sometimes this transceiver type is also referred to as “QSFP100” or “100G QSFP”  for sake of simplicity.
The 100G QSFP28 transceiver modules are designed for use in 100 Gigabit Ethernet, 128GFC and 4x28G OTN links over multimode fiber. They are compliant with the QSFP28 MSA, 128GFC, IEEE 802.3bm 100GBASE-SR4 and CAUI-4. Digital diagnostics functions are available via the I2C interface as specified by the QSFP28 MSA.
An optical transceiver form factor is specified by a multisource agreement (MSA). An MSA is an agreement between multiple manufacturers to make optical transceivers that can plug into switches.
QSFP28 module uses four lanes for 100G optical signal transmitting like 40G QSFP+. However, each lane of QSFP28 can transmit 25G optical signal. To fit the various requirements in practical applications, IEEE and MSA standards that support different transmission distances and fiber types are being published.
100Gbase-SR4 QSFP28
100Gbase SR4 QSFP28 module uses eight multimode fibers for 100G dual-way transmission over 850nm. It can support a transmission distance up to 70m over OM3 and 100m OM4 with a MTP interface. 12-fiber MTP OM3/OM4 trunk cables are suggested to be used with QSFP-100G-SR4 modules. 100Gbase-SR4 QSFP28 is the most popular QSFP28 module according to research.
100Gbase-LR4 QSFP28
It focuses on longer transmission distance over single-mode fiber. 100Gbase-LR4 QSFP28 has a duplex LC interface and uses WDM technologies to achieve 100G dual-way transmission over four different wavelengths around 1310nm. It can support distances up to 10km.
The 100G-QSFP-LR4 module can support 10km, which is too much for a lot of single-mode applications. It would be uneconomical to buy a 10km module for just 1km or 2km application. MSA has published two 100G standards — 100Gbase-PSM4 and 100Gbase-CWDM4, which can help to decrease the cost of 100G deployment.
100Gbase-PSM4 QSFP28
100Gbase-PSM4 QSFP28 module has a MTP interface working on wavelength of 1310nm for 100G transmission over single-mode fibers. It can support transmission distance up to 500 meters. 100Gbase-PSM4 QSFP28 module is much cheaper than 100Gbase-LR4 QSFP28 module. And 500 meter’s transmission distance can cover a wide range of applications.
100Gbase-CWDM4 QSFP28
For longer transmission distance, 100Gbase-CWDM4 QSFP28 is suggested, which supports a distance up to 2km over single-mode fiber optic cable. 100Gbase-CWDM4 standard is published by MSA, which is a more cost-effective solution for a wide range of applications compared with 100Gbase-LR4. This module uses CWDM technologies to transmit the 100G optical signal via a duplex LC interface over wavelengths near 1310nm.
100G QSFP28 DAC
100G QSFP28 family also includes a series of direct attach cables. There are mainly two types of QSFP28 DAC, which are QSFP28 to QSFP28 DAC and QSFP28 to SFP28 DAC. These QSFP28 DACs are cost-effective solution for 100G transmission less than 5 meters.

Will QSFP28 be a better way to 100G?

by http://www.fiber-mart.com

The Quad Small Form-factor Pluggable (QSFP) is a compact, hot-pluggable transceiver used for data communications applications. The form factor and electrical interface are specified by a multi-source agreement (MSA) under the auspices of the Small Form Factor Committee. It interfaces networking hardware to a fiber optic cable or active or passive electrical copper connection. It is an industry format jointly developed and supported by many network component vendors, allowing data rates from 4×10 Gbit/s.The format specification is evolving to enable higher data rates; as of May 2013, highest possible rate is 4×28 Gbit/s (also known as QSFP28).
4 x 28 Gbit/s QSFP+ (QSFP28)
The QSFP28 standard is designed to carry 100 Gigabit Ethernet, EDR InfiniBand or 32G Fibre Channel. This transceiver type is also used with direct-attach breakout cables to adapt a single 100GbE port to four independent 25 gigabit ethernet ports (QSFP28-to-4x-SFP28) Sometimes this transceiver type is also referred to as “QSFP100” or “100G QSFP”  for sake of simplicity.
The 100G QSFP28 transceiver modules are designed for use in 100 Gigabit Ethernet, 128GFC and 4x28G OTN links over multimode fiber. They are compliant with the QSFP28 MSA, 128GFC, IEEE 802.3bm 100GBASE-SR4 and CAUI-4. Digital diagnostics functions are available via the I2C interface as specified by the QSFP28 MSA.
An optical transceiver form factor is specified by a multisource agreement (MSA). An MSA is an agreement between multiple manufacturers to make optical transceivers that can plug into switches.
QSFP28 module uses four lanes for 100G optical signal transmitting like 40G QSFP+. However, each lane of QSFP28 can transmit 25G optical signal. To fit the various requirements in practical applications, IEEE and MSA standards that support different transmission distances and fiber types are being published.
100Gbase-SR4 QSFP28
100Gbase SR4 QSFP28 module uses eight multimode fibers for 100G dual-way transmission over 850nm. It can support a transmission distance up to 70m over OM3 and 100m OM4 with a MTP interface. 12-fiber MTP OM3/OM4 trunk cables are suggested to be used with QSFP-100G-SR4 modules. 100Gbase-SR4 QSFP28 is the most popular QSFP28 module according to research.
100Gbase-LR4 QSFP28
It focuses on longer transmission distance over single-mode fiber. 100Gbase-LR4 QSFP28 has a duplex LC interface and uses WDM technologies to achieve 100G dual-way transmission over four different wavelengths around 1310nm. It can support distances up to 10km.
The 100G-QSFP-LR4 module can support 10km, which is too much for a lot of single-mode applications. It would be uneconomical to buy a 10km module for just 1km or 2km application. MSA has published two 100G standards — 100Gbase-PSM4 and 100Gbase-CWDM4, which can help to decrease the cost of 100G deployment.
100Gbase-PSM4 QSFP28
100Gbase-PSM4 QSFP28 module has a MTP interface working on wavelength of 1310nm for 100G transmission over single-mode fibers. It can support transmission distance up to 500 meters. 100Gbase-PSM4 QSFP28 module is much cheaper than 100Gbase-LR4 QSFP28 module. And 500 meter’s transmission distance can cover a wide range of applications.
100Gbase-CWDM4 QSFP28
For longer transmission distance, 100Gbase-CWDM4 QSFP28 is suggested, which supports a distance up to 2km over single-mode fiber optic cable. 100Gbase-CWDM4 standard is published by MSA, which is a more cost-effective solution for a wide range of applications compared with 100Gbase-LR4. This module uses CWDM technologies to transmit the 100G optical signal via a duplex LC interface over wavelengths near 1310nm.
100G QSFP28 DAC
100G QSFP28 family also includes a series of direct attach cables. There are mainly two types of QSFP28 DAC, which are QSFP28 to QSFP28 DAC and QSFP28 to SFP28 DAC. These QSFP28 DACs are cost-effective solution for 100G transmission less than 5 meters.