Carrier Ethernet technology requires specific testing standards and procedures because Ethernet was not initially designed for carrier networks. These procedures include the RFC 2544 test suite, filtering, truncation and capture triggers.
The RFC 2544 test suite outlines the tests required to measure and prove performance criteria for carrier Ethernet networks. The standard provides an out-of-service benchmarking methodology to evaluate the performance of network devices using throughput, back-to-back, frame loss and latency tests, with each test validating a specific part of a service level agreement. The methodology defines the frame size, test duration and number of test iterations. Once completed, these tests will provide performance metrics of the Ethernet network under test.
The ability to filter Ethernet traffic means capturing only the traffic that fits a specific profile, therefore efficiently using the available memory.
A filter engine is based on basic and advanced filtering capabilities. In the basic mode, the user can filter traffic based on a single trigger value, while the advanced mode provides the ability to customize a filter using up to four triggers combined with logical operands (AND, OR, NOT). In both cases, a complete set of triggers includes MAC, IP, UDP and VLAN.
Truncation means limiting the capture of data to a specific number of bytes and therefore, capturing only the data that is necessary. Since proprietary information cannot be decoded by test equipment, network engineers will limit the capture to the header, or add more bytes to include higher-layer information, for more in-depth testing.
With most typical capture tools, capture starts as soon as the tool is enabled. However, this could mean that an event will occur after the memory buffer is filled up, providing no useful information whatsoever.
Three are three types of capture triggers:
The triggering position determines the position of the triggered frame within the captured data. Specifying where the trigger event is located in a capture is useful when performing pre- and post-analysis because it is important to understand what happened before and after a failure. Traditional capture tools only provide a post-trigger position, but today’s Ethernet capture tools also provide a mid- and pre-trigger.
In Pre-Trigger mode, the last frame of the capture is the trigger event; therefore, the captured output contains all the frames leading up to the event. This mode can be used to determine what led to the specific event.
Mid-Trigger mode is a very powerful application that provides a snapshot of the traffic before and after the trigger event. In this mode, the trigger event is usually in the middle of the captured traffic.
In Post-Trigger mode, the first frame of the capture is always the trigger, and the remaining frames are the frames that follow the trigger event. This mode is typically used to analyze content after the event.