y available server without any signaling prior to the session/call or any reservation of network resources on the end-to-end path). The end-to-end performance of a path can be estimated if the performances of all subsections on the path are known (Figure 4.9). For that purpose there can be different parameters; however, if one needs to distinguish the most important standardized QoS parameters for IP-based services (from the end-to-end point of view, which is the only point of view for any QoS observation), they will be the following [32]: Mean transfer delay. This refers to the sum of the mean delays (IPTDs) contributed by network sections on the path UNI-UNI. 4 QoS for Fixed Ultra-Broadband router router router router Customer Network Customer Network network section 1 network section N IP network cloud Customer Customer LAN and LAN and terminal terminal equipment Network section Network section equipment End-to-end IP network (network QoS) End-to-end user terminal to user terminal connection (service QoS) Figure 4.9 End-to-end IP network QoS. Delay variation. This is UNI-UNI delay variation which is influenced by IPDV from the network section on the path between the two ends. However, each network section influences this parameter via its traffic management techniques, which may differ from one network section to another. Therefore, it is difficult to estimate accu- rately the delay variation without having considerable information about individual delay distributions in different network sections. Such detailed information can only occasionally be shared among telecom operators (it is not a rule). Therefore, the network end-to-end delay variation (i.e. UNI-UNI IPDV) estimation may have certain limitations regarding accuracy. Error packet ratio. For estimation of IPER across network sections (which have their own IPER) to obtain UNI-UNI performance one should proceed by inverting the probability of error-free packet transfer across n network sections, given as follows: IPERUNI-UNI = 1 - {(1 - IPERNS1).(1 - IPE