Verify Ethernet networks
Martin Rowe, Senior Technical Editor -- Test & Measurement World, 9/1/2009 2:00:00 AM
Ethernet is everywhere, from home networks to carrier networks. Service providers need to test Ethernet links between their carrier networks and access networks such as DSL. Testing Ethernet-based networks for QoS (quality of service) involves making packet jitter, throughput, latency, and frame-loss measurements.
All of these measurements can indicate delivery problems, particularly when a network carries voice or video. For example, too much packet jitter—the difference in delays between packets in a stream—can result in dropped packets, which can produce gaps in audio reception or blocks in video.
Ethernet testing is based on RFC 2544, which defines a set of test methodologies that carriers use to test Ethernet networks (Ref. 1). The figure shows several test points in the carrier’s access network and at a customer’s network.
 Test points for DSL access range from the customer’s network to the carrier’s core network. |
Tests involve measuring parameters such as latency and throughput at any two points. Depending on the customer (business or residential), an Ethernet packet header may contain QoS bits that define the level of service that the carrier must provide. Three bits, called PCP (priority code point), indicate a frame’s priority. Packets carrying video, for example, will likely get a higher priority than packets carrying data because of video’s susceptibility to lost packets or excessive packet jitter.
To learn more about Ethernet testing, read “Basic connectivity testing and service verification,” by Andy Hight, product manager at Sunrise Telecom.
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