Framed and moving
Engineers at Galazar networks simulate telecom networks to test their 2.5-Gbps multiservice framer ICs. Tests involve measuring framing, mapping, bit-error rate, power consumption, and other parameters.
Martin Rowe, Senior Technical Editor -- Test & Measurement World, 12/1/2006 2:00:00 AM
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DEVICE UNDER TEST
2.5-Gbps multiservice framer ICs. The ICs combine Ethernet and PDH frames into synchronous optical network/synchronous digital hierarchy (SONET/SDH) frames for transport. The device can accept two Gigabit Ethernet streams, 28 DS1/E1 lines, three DS3/E3 lines, 24 SPI-3 channels, and four 622-Mbps SONET lanes. The devices also decode in-coming frames from the SONET lanes into their respective tributaries.
THE CHALLENGE
Test each device for functional parameters such as framing, mapping, bit-error rate, jitter, and virtual concatenation of SONET/SDH containers into higher bit-rate streams for transport in 2.5-Gbps SONET/SDH signals. Measure current consumption and clock jitter.
THE TOOLS
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Agilent Technologies: digital data test sets, SONET/SDH testers, logic analyzer. www.agilent.com.
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Anue Systems: network emulator. www.anuesystems.com.
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Fluke: digital multi-meter. www.fluke.com.
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Ixia: Ethernet tester. www.ixiacom.com.
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Spirent Communications: Ethernet tester. www.spirentcom.com.
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Tektronix: oscilloscope. www.tektronix.com.
PROJECT DESCRIPTION
Galazar Networks (Ottawa, ON, www.galazar.com) produces multiservice framer ICs for the telecom industry. Prior to releasing a product to production, Galazar engineers test devices for functional parameters such as throughput, bit-error rate, mapping, and framing. They also test devices for power consumption, clock jitter, setup and hold, and other parameters.
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Ethernet and PDH testers generate bit frames that the service framer under test must aggregate into SONET/SDH frames. |
To verify that a device meets specifications, the engineers use a reference design board that provides support circuitry and a processor running the VxWorks operating system. The processor runs software that performs real-time functions such as performance monitoring and interrupt handling. The board also lets an external PC control the device under test’s (DUT’s) ports and configuration. Finally, it provides shunt resistors for measuring current consumption.
The framer must aggregate both plesiochronous digital hierarchy (PDH) frames from the digital data test sets and asynchronous Ethernet frames from the Ethernet testers into synchronous SONET frames. Engineers measure setup and hold (S&H) of the SONET data signals with an oscilloscope. They perform the test by looping the SONET lines back to the DUT. They measure S&H on a tributary DS1 or DS3 line, send the frames through the DUT, and measure the decoded stream’s S&H.
Ethernet physical-layer hardware (PHY) extracts the clock from incoming streams so that engineers can measure the S&H time. The DUT must extract an embedded clock and make it available for jitter measurements with an oscilloscope. The engineers use the PDH testers to measure bit jitter on signals decoded from SONET frames and sent over the DS1/DS3 lines.
The Galazar engineers also must test for the device’s latency in processing Ethernet frames. They generate time-stamped frames with the Ethernet tester and measure the time between when a frame is sent and when it is returned to the tester. A test also includes measuring lost Ethernet packets, which the engineers perform by breaking the SONET stream.
Engineer David Kirk and others also break the SONET loop so they can emulate an entire network with a network emulator. They can add impairments such as differential delay and bit errors.
Kirk explained that the engineers must automate the measurements by writing scripts for each tester and for the reference board. “When testing a new generation of parts,” said Kirk, “we can spend four to six months because we have to write a new set of scripts. We must find and fix bugs in the scripts, the DUT, and sometimes the tester.”
LESSONS LEARNED
“Scripts are invaluable when we verify new products,” said Kirk. “They let us set up and tear down configurations thousands of times. We can run a test in 24 hours that would take weeks if we operated test equipment manually.”
Kirk also pointed out that it’s important to work with test-equipment makers as they develop new products. Because Galazar engineers worked with Agilent Technologies during the development of enhancements to the SONET/SDH testers, they were able to influence the feature set in the Agilent tester.
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