Overcoming OM3 Performance Challenges

Transcription

1 White Paper Overcoming OM3 Performance Challenges First Third-Party Test of Pre-terminated OM3 MTP System Demonstrates Flexibility in 10G Network Designs Gary Bernstein, RCDD Director of Product Management Fiber and Data Center Leviton Network Solutions Dennis Manes Senior Applications Engineer - Fiber and Data Center Leviton Network Solutions

2 Abstract 10 Gigabit Ethernet (10GbE) introduces a challenging 2.6 db insertion loss limit on OM3 fiber cabling. This tight limit has led some industry observers to suggest it s not possible to meet the standard using regular, as opposed to low-loss, MTP cassettes. These observers have also suggested it s not possible to run fiber cabling the full 300-meter distance specified in the 10GBASE-S standard when using MTP cassettes, whether standard or low-loss. To test these assumptions, Leviton contracted with Intertek Testing Services (ETL) to perform benchmark testing of OM3 fiber system performance. The testing proved that the 10GBASE-S standards can easily be met with the latest generation of OM3 fiber systems using standard MTP cassettes and up to the full 300-meter length limit. In addition, the results show that Leviton s OM3 system will support future migration to 40GbE/100GbE applications. Leviton Network Solutions 2

3 Multimode Fiber Standards, Applications, and Challenges For many years 62.5/125 µm (OM1) and conventional 50/125 µm (OM2) multi-mode fiber have dominated shorter distance communication applications, such as within a building or on a single-site campus. The fibers easily support applications ranging from 10 Megabit Ethernet (MbE) to Gigabit Ethernet (GbE). Their relatively large core sizes simplify connections and are ideal for use with low cost light-emitting diode (LED) transmitters. With the introduction of, and demand for, 10 Gigabit Ethernet (10GbE), typical in data centers, the physical limitations and properties of multimode optical fiber are being severely tested. Multimode fiber provides many allowable paths for light to travel down the fiber, and due to intermodal dispersion not all pulses arrive at the destination simultaneously. This characteristic, as well as other issues, ruled out the use of OM1 and OM2 fiber with 10GbE. To address this, the Institute of Electric and Electronic Engineers (IEEE) created the 10GBASE-S (the S stands for short wavelength) multimode fiber specification with the goal of providing 10GbE operating distances of 300 meters. Laser-optimized OM3 fiber was specified in TIA-492AAAC to support both the IEEE standard and economical vertical cavity surface emitting lasers (VCSELs) that operate at the 850 nm and 1300 nm wavelengths. Fiber that meets the standards delivers an effective modal bandwidth of 2000 MHz*km at the 300 meter distance. The TIA-568-C.0 standard allows for a maximum 2.6 db insertion loss and 300 meter length with OM3 fiber cabling systems. While manufacturers frequently submit their copper cables for third-party testing to verify performance that meets or exceeds applicable standards, they typically have not had fiber cabling systems, including OM3, tested. As a result, designers and operators of OM3 fiber networks are uncertain what the true parameters are in designing premises applications. Leviton Network Solutions 3

4 For example, the maximum insertion loss for MTP-LC cassettes or modules as stated in the TIA specification is 1.5 db, as shown in Figure A below. An unusually complicated (but not extreme) configuration might consist of four cassettes with a total of eight mated pairs. If each of these cassettes were at the headroom limit then the insertion loss at 6.0 db would exceed the allowable limit. Some vendors have addressed this possibility by offering low-loss cassettes. However, these cassettes come at a considerable cost premium approximately 50%. MTP Cassette Type Leviton Typical Leviton Maximum TIA Maximum Allowable LC SC MU Connector Mated Pairs Type Leviton Typical Leviton Maximum TIA Maximum Allowable LC SC MU MTP Figure A: OM3 fiber insertion loss performance (dbs) Channels approaching the 300-meter maximum allowable distance for 10GbE have the same potential issue. Insertion loss for OM3 cable is typically 3.0 db per kilometer. The TIA standard allows 0.75 db insertion loss per connector mated pair. For example, a 300-meter channel configuration with six mated pairs could have a maximum insertion loss of 3.9 db, well above the 2.6 db limit. Undoubtedly, this explains why some vendors have recommended that users stay well below the 300-meter length limit. Leviton Network Solutions 4

5 Putting the Latest Generation of Fiber to the Test How much headroom does a 50/125 μm laser optimized fiber system actually provide relative to the specification, and what is the impact to the network designer? To address these questions, Leviton contracted with Intertek (ETL) to test Leviton s OM3 fiber system including MTP trunk cables, MTP-LC cassettes and harnesses, MTP adapter brackets and LC-LC OM3 patch cords. Testing included three different OM3 channel configurations: meters, 6 mated pairs meters, 8 mated pairs meters, 9 mated pairs All channels were set up and bidirectionally tested with readings measured against maximum allowable insertion loss as specified in TIA-568-C.0, using Annex E guidelines (see appendix for detailed test setup description and diagram). Each test configuration was constructed as shown below in Figures B, C, and D. Storage Core Switch Figure B: Configuration meter channel with 6 mated pairs Average maximum channel insertion loss was 2.04 db, resulting in a 0.57 db margin under the 2.6 db limit. Storage Server Figure C: Configuration 2 53-meter channel with 8 mated pairs Average maximum channel insertion loss was 1.83 db, resulting in a 0.77 db margin under the 2.6 db limit. Storage Server Figure D: Configuration 3 62-meter channel with 9 mated pairs Average maximum channel insertion loss was 1.87 db, resulting in a 0.72 db margin under the 2.6 db limit. Leviton Network Solutions 5

6 Conclusion All three configurations were found to be compliant with all applicable criteria of the TIA-568-C.0 standard. The connectors tested not only meet the maximum published performance requirements, but also the insertion loss specifications shown in Figure A. It is clear that 10GbE specifications can be met without the additional costs of low-loss cassettes. These tests, the first known to provide independent verification of OM3 fiber channel performance, show substantial margin under TIA insertion loss limits for 10GbE using standard cassettes. With the assurance of these results, network designers have the freedom to utilize the complete 10GBASE-S standard including distances up to 300 meters and the maximum number of specified connectors. In addition, the test results show that the latest generation OM3 fiber systems provide a solid foundation for future installations of 40GbE and 100GbE. The IEEE approved the 802.3ba standard in June 2010; it specifies a maximum insertion loss of 1.9 db for 40/100GbE using OM3 cabling. The systems tested here are already right on the border of meeting that specification, indicating that organizations will be able to upgrade with either no or very limited system changes. Download the ETL test documents at Leviton Network Solutions 6

7 References TIA-568-C.0: Generic Telecommunications Cabling for Customer Premises Annex E: Optical Fiber Field Test Guidelines TIA-492AAAC: Detail Specification for 850-nm Laser-Optimized, 50-µm Core Diameter/ 125-µm Cladding Diameter Class 1a Graded-Index Multimode Optical Fibers IEEE 802.3ae/10GBASE-S: 10 Gigabit Ethernet/To support short distances over deployed multi-mode fiber cabling IEEE 802.3ba: Media Access Control Parameters, Physical Layer Specifications and Management Parameters for 40Gb/s and 100Gb/s Operation Test Setup Link under test Loss in db Light source Mandrel Mated connector pair with mating adapter Mated connector pair with mating adapter Optical Power Meter Figure E: Cable Link Channel Testing Configuration Intertek set up the testing as specified in TIA-568-C.0 Annex E. The forward direction link measurement was performed by placing a reference quality jumper on a Rifocs optical meter and measuring the link insertion loss by connecting the test jumper of the source to one end of the cabling link and the test jumper of the meter to the other end of the cabling link. Both ends of the cabling link were disconnected and the ends were interchanged and reconnected to perform the reverse direction measurements. Leviton Network Solutions 7

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