Testing Ethernet using 56/112 Gbps SerDes and advanced modulation formats like PAM-4 require extra focus on the Physical Layer (Layer 1). At these high speeds, signal integrity degrades quickly after transmission over few meters due to things like frequency dependent loss, inter-symbol interference and cross talk.
Standards and technology evolve rapidly, and developers of semiconductors and network equipment need to verify the performance of their products before they reach the market. Therefore, Ethernet test equipment must include tools for testing at Layer 1 as well as L2 & L3 traffic generation and analysis. Furthermore, test equipment must be future proof with the flexibility to add new test and management features as standards and new use cases evolve.
The Physical Layer functions are handled in the PHY and include the PCS, FEC, PMA, PMD and AN sub-layers.
One of the first things to check for a high speed Ethernet link is the signal integrity. Normally, this involves analysis of an eye diagram but, for 56G/112G PAM-4 receivers a 4-level vertical slicer eye is constructed from the sampled and recovered signal. The better the separation between the four PAM-4 slices, the better the signal integrity.
The PCS sublayer of the PHY operates on a number of parallel PCS lanes. After transmission these lanes need to be identified and aligned relative to each other. A typical test case therefore involves swapping of PCS lanes as well as inserting user-defined skew per Tx PCS lane. Such tests will verify that the DUT’s receiver is able to re-order the PCS lanes and handle skew variations.
The Forward Error Correction (FEC) is an important part of the PCS sublayer that needs to be tested. There are several different types of FEC-schemes dependent on the specific Ethernet speed. To test a new FEC implementation it is necessary to insert errors and check that the FEC corrects them. Also, with PRBS generators and error insertion from the Ethernet test equipment the BER performance both pre- and post-FEC can be verified.
The FEC can only work if the amount of pre-FEC bit errors is not too high. For transmission of high-speed Ethernet over electrical cables equalizers are needed at both the transmitter and the receiver to improve the signal integrity. As part of the physical layer testing, the equalizers must be manually tuned to optimize the signal quality for each lane and the specific transmission medium used.
Auto Negotiation (AN) and Link Training (LT) are key elements of Ethernet transmission over electrical connections and can reduce overall installation time, minimize the risk of configuration mistakes and optimize performance. During the AN process, two connected devices exchange information about their transmission speeds and FEC abilities and agree on a common set of transmission parameters. LT is then used to automatically tune the transmit equalizer settings at each device for minimum BER at the selected transmission speed.
Although the AN and LT protocols are standardized by IEEE802.3 it has proven challenging for developers of semiconductors and network equipment to verify performance of their products. Slight differences in implementations may cause products to fail in interoperability tests against third parties. And often vendors have a hard time troubleshooting to find the root cause of the malfunctioning.
The Z800 Freya ANLT Test Appliance is designed for performance verification and troubleshooting of the AN/LT protocols.
Watch the video below to learn how you can use the XenaManager software with the Z800 Freya to test Layer 1 functionality.
Z800 Freya Test Modules
For advanced Layer 1 testing Xena, offers the Xena Z800 Freya test modules supporting up to 800Gbps over 112G SerDes and PAM-4 and a range of advanced Layer 1 test features. Z800 Freya can be installed in either the robust scalable 4U B2400 chassis (where it occupies two of the 12 slots), or alone in the small, easy-to-transport 1U XenaCompact chassis.
Xena offers a selection of test modules for testing all Ethernet speeds from 10Mbps to 800Gbps.
Our range includes the latest Ethernet technology with 112G-based SerDes and PAM-4 in our Z800 Freya product line. For testing and debugging AN/LT protocols we offer our dedicated Z800 Freya Compact ANLT Test Appliance.
Xena’s test solutions include feature-rich software for generating Ethernet traffic and analyzing the result. The primary tool is XenaManager.
There are also test suites for running standard tests such as RFC2544, RFC2889, RFC3918 and Y.1564, and specialized AN/LT tests along with a comprehensive range of powerful scripting and test automation options such as Xena OpenAutomation (XOA), an open-source test automation framework featuring a Python API that runs on any OS.
Choose between the robust scalable 4U XenaBay with space for up to 12 test modules, or the small, easy-to-transport 1U XenaCompact with just one test module.
All our solutions include the Xena Value Pack which consists of 3 years’ SW updates, 3 years’ HW warranty, free online/email support for the lifetime of the product and free product training.
Together with our low port-pricing, this represents significant savings on the TCO of your Ethernet traffic generation and analysis solutions.
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