Different services require different error performance and different data rates. For example, a service such as status monitoring with polling may be able to tolerate more errors and lower transmission speeds than a time-critical application such as video telephony or "twitch" video games where retransmission of errored frames cannot be tolerated. Each service will require different operating characteristics for satisfactory performance.
Three important indicators used to evaluate the performance of modems in a cable television network, in the presence of continuous or impulsive noise, are carrier-to-noise ratio (CNR), frame-loss-ratio (FLR), and bandwidth efficiency (BWE). These three parameters are related to each other and are bounded by the channel capacity limit of Shannon. Actual cable modem performance in different operating modes can be described parametrically using measurements in these three indicated dimensions. When the value of CNR in the transmission channel is known ' the value of BWE at an arbitrarily small FLR can be deduced. The resulting operating point can be compared to minimum service requirements.
This paper describes how these useful performance indicators can be used to evaluate and to compare the performance of different cable modem transmission system modes in the presence of continuous or impulsive noise. Determination of satisfactory regions of operation under various transmission channel conditions is discussed. An example of the use of the described performance indicators for determining satisfactory service delivery is provided.