Which QoS parameter constrains the average rate of excess service frames ingressing the provider's network?

The correct choice is Excess Information Rate (EIR), which is defined as the maximum average rate of excess service frames that can be transmitted into a provider's network beyond the committed rate. In Quality of Service (QoS) in networking, EIR is crucial for managing how excess traffic is handled when the committed traffic is already being processed according to its designated rate.

EIR allows for some flexibility in handling bursty traffic by permitting additional packets to be transmitted when there is available bandwidth. However, it's important to recognize that this excess traffic does not have guaranteed delivery; it can be discarded if the network is congested. This makes EIR essential for understanding quality metrics because it effectively defines how much uncommitted capacity is available for incoming frames without violating the network's service agreements.

The other QoS parameters refer to different aspects of network usage: Committed Information Rate (CIR) relates to the guaranteed bandwidth allocated for traffic, Peak Information Rate (PIR) indicates the maximum allowable bandwidth, and Average Information Rate (AIR) describes the long-term average rate over time. While all these parameters are important, EIR specifically addresses the average rate of excess service frames, making it the most pertinent choice for the question.