3 site 4 MPLS - Multi protocol label switching VPN - Virtual private network Figure 7.6 VPN services: pipes and hoses. VPN sustainable/committed ingress/egress bitrate. That is the average guaranteed bitrate for a given VPN pipe or VPN hose. These parameters are dependent upon the SLA for a given VPN or traffic management decision as well as the number of network providers that particular VPN traverses. VPN service availability. The percentage of time when the VPN is available is compa- rable with the transport network's availability (e.g. 99 999% of time). Regarding KPIs for bitrates used for the VPN, there are different constraints in pipe and hose models. For example, a full mesh of N sites that should be connected requires N X (N-1)/2 VPN pipes. But, VPN pipe model can be inefficient due to low resource utilization in the network. For example, if site-1 provisions 100 Mbit/s to each of the sites 2, 3, and 4 (that is 300 Mbit/s in total), and there is low traffic to site 2 that unused capacity cannot be allocated for carrying traffic between site 1 on one side and sites 3 and 4 on the other (so, 100 Mbit/s network capacity will be idle in this case). However, VPN pipe model can be used for business services where both endpoints of the pipe are in the network of the VPN service provider, while in cases where VPN endpoints belong do different networks (of different providers) then hose model can be more convenient. 7.5.3 KPIs for Mobile Services Mobile networks have different characteristics than fixed access networks. They differ in two main aspects: 7 Broadband QoS Parameters, KPIs, and Measurements Mobile networks have radio-based access which cannot be completely isolated and controlled, SO there is interference between different radio signal in the same spec- trum, higher attenuation of signals due to many obstacles on the path, signal reflec- tions and scattering, multipath propagation (due to signal reflections) which result in time dispersion of signals, SO the bitrates are harder to be guaranteed in mob