Which metric expresses the percentage of lost frames between an ingress UNI and egress UNI?

• A. Inter-frame Delay Variation(IFDV)
• B. Frame Loss Ratio(FLR)
• C. Frame Delay(FD)
• D. Availability

Answer: (B)

Frame loss ratio captures the fraction of frames that do not arrive from the ingress UNI to the egress UNI. It is defined as the number of frames lost divided by the number of frames transmitted, usually shown as a percentage. This metric specifically measures end-to-end loss, which is exactly what the question asks for.

Inter-frame delay variation looks at jitter between arriving frames, not whether any frames were lost. Frame delay concerns how long frames take to traverse the path, not loss. Availability reflects uptime of the service, not the rate of lost frames. So the end-to-end percentage of lost frames is the frame loss ratio.