FOCUS on CONNECTIVITY
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.
MTP-LC cassettes or modules as stated in the TIA specification is 1.5 dB, as shown in Figure A. 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%.
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.
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 this question,
Leviton contracted with Intertek (ETL) to test Leviton’s OM3 fiber system including pre- terminated MTP trunk cables, MTP-LC cassettes and harnesses, MTP adapter brackets and LC-LC OM3 patch cords. Testing included three different OM3 channel configurations:
1. 300 meters, 6 mated pairs 2. 53 meters, 8 mated pairs 3. 62 meters,9 mated pairs
All channels were set up and bi-directionally tested with readings measured against maximum allowable insertion loss as specified in TIA-568-C.0, using Annex E guidelines. Each test configuration was as shown in Figures B, C, and D.
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 designershave 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 100 GbE. 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: www.leviton.com/ns/testresults
by Gary Bernstein, RCDD, CDCD, Director, Product Management, Fiber & Data Center Solutions and Dennis Manes, RCDD, Senior Applications Engineer, Fiber & Data Center Solutions, Leviton Network Solutions
*Note: in some cases the insertion loss and the margin do not add up to the limit due to rounding.
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.
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