Ethernet Testing Parameters

Testing Ethernet Services

The Ethernet connections must be tested to ensure that they are operating correctly and also they are performing to the required levels. This is done by testing  the bandwidth, the delay and the loss of frames in the  connection. In Ethernet terms these are called Throughput, Latency and Frame Loss.

Throughput

Data throughput is simply the maximum amount of data, that can be transported from source to destination. However the definition and measuring of throughput is complicated by the need to define an acceptable level of quality. For example, if 10% errored or lost frames were deemed to be acceptable then the throughput would be measured at 10% error rate. Here we have generally accepted definition that throughput should be measured with zero errors or lost frames. In any given Ethernet system the absolute maximum throughput will be equal to the data rate, e.g. 10 Mbit/s

100 Mbit/s or 1000 Mbit/s. In practice these figures cannot be achieved because of the effect of frame size.

The smaller size frames have a lower effective throughput than the larger sizes because of the addition of the pre-amble and the interpacket gap bytes, which do not count as data.

Latency

Latency is the total time taken for a frame to travel from source to destination. This total time is the sum of both the processing delays in the network elements and the propagation delay along the transmission medium. In order to measure latency a test frame containing a time stamp is transmitted through the network. The time stamp is then checked when the frame is received. In order for this to happen the test frame needs to return to the original test set by means of a loopback (round-trip delay).

Frame Loss

Frame loss is simply the number of frames that were transmitted successfully from the source but were never received at the destination. It is usually referred to as frame loss rate and is expressed as a percentage of the total frames transmitted. For example if 1000 frames were transmitted but only 900 were received the frame