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TEST & MEASUREMENT
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By Dan Payerle , Business Unit Manager US , IDEAL Networks
www . idealnetworks . net
Selecting the most appropriate fibre optic certification standard isn ’ t always clear-cut . Tier-1 , Tier-2 or both ? Dan Payerle from IDEAL Networks explains …
Unlike copper cabling where only one level of certification is defined by standards , there are two levels , or ‘ tiers ’, available when certifying fibre optic cabling . The different tiers specify which type of test is performed , therefore defining the test equipment to be used and are known as Tier-1 or Tier-2 certifiers .
Tier-1 certification is a measurement of the total insertion loss ( previously called attenuation ) of the cabling from one end of the link to the other . The equipment used to perform Tier-1 certification is an optical power meter and optical light source . An OLTS ( optical loss test set ) is an advanced type of PM / LS with additional capability . In this article ‘ OLTS ’ will be used to refer to both OLTS and PM / LS testers .
Tier-2 certification provides loss information about each component of the link . An OTDR ( optical time domain reflectometer ) is used to perform this certification . The primary advantage of a Tier-2 test is that it provides information about each connection , splice and cable segment in the link and offers a graphical representation of the components and their performance . When testing newly installed cabling the report is a snapshot of the system that can be compared to later tests to identify any changes in the cabling . An OTDR is unrivalled for troubleshooting because it shows the operator exactly where faults are located in the cabling , expediting the repair process .
Tier-1 , Tier-2 or both ? One of the most commonly asked questions is which type of test should be used , and whether performing Tier-2 certification meets the requirements of Tier-1 certification ? Ultimately , the required testing is an agreement between the cabling contractor and their customer . However , when certification is required , it ’ s good practice to always perform a Tier-1 test and optionally do a Tier-2 test . Tier-2 certification supplements Tier-1 certification , it ’ s not a replacement for it . This often confuses people because in addition to the losses for each component in the link , an OTDR will also show the total link loss like an OLTS does . So why then does an OTDR not satisfy the requirement for Tier-1 certification ?
There ’ s a subtle nuance between the total link loss reported by an OLTS and an OTDR . An OLTS measures the true optical loss of the link , while an OTDR calculates the total loss of the link . Although both may provide similar results when testing the same cable , the OLTS is always the most accurate way to determine the end-to-end loss of a link . Absolute accuracy is especially important with high
bandwidth multimode applications such as 100GBASE-SR10 ( 100 gigabit Ethernet ) where the total allowable insertion loss can be as low as 1.5dB .
Tier-1 certification explained Tier-1 certification uses an optical light source and optical power meter to measure the total insertion loss across the cabling under test . This is so the tester will provide one number that ’ s the sum loss of all of the ‘ events ’ in the cabling connected to the tester . Events are components of the optical cabling link that either lose or reflect light as it passes through . Events include cable , connectors , bulkheads , splices , splitters and bends / kinks .
This is a simple and accurate way of determining whether a fibre optic link will support an application or not . The resulting insertion loss measurement can be compared to a specification or standard to provide a pass / fail status of each link for its intended use . As mentioned above , if 100GBASE-SR10 Ethernet allows a maximum channel loss of 1.50dB , a channel that exceeds 1.50dB of loss will fail the test , and a channel with 1.50dB loss or less will pass . It ' s a simple and quick test , and is the most common method of certifying fibre optic cabling .
To perform this certification , the test cord ( s ) used for testing with the PM / LS are first referenced / calibrated out so their loss isn ’ t included in the test results . There are different reference methods available , using either 1 , 2 or 3 test cords . The method used depends on several factors including the
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