referred to as jitter): This is the difference between the one-way delay of IP packet and reference IPTD (e.g. average IPTD as a reference delay). IPLR (IP packet loss ratio). This is calculated as the ratio of the total number of lost IP packets to the total number of transmitted IP packets. IPER (IP packet error ratio). This is calculated as the ratio of the total number of IP packets with some errored bit(s) to the total number of transmitted IP packets. The values of these performance parameters can be different for different traffic types, which are mapped to network QoS classes. Of course, the use of the classes is not manda- tory in all network environments, and may differ from one network to another. One may note that the transfer capacity (typically expressed in bit/s, i.e. Kbit/s, Mbit/s, Gbit/s, etc.) is the network performance parameter that has certainly the highest impact on the performance perceived by the end-user. Why? Because higher 4.5 End-to-End QoS Network Design bitrates end-to-end provide a better user experience due to better performances for most of the services (e.g. higher transfer capacity as well as lower delay and delay variation). Note that the theoretical "net" capacity of a given system (e.g. cable, optical, wireless/mobile) is always larger than the bitrates that can obtained by individual end-user applications. Regarding end-to-end communication, the network model is also referred to as UNI-to-UNI, where UNI is the interface that connects the user premises network such as home network or enterprise network on one side and the telecom operator network on the other side [32]. End-to-end interconnected IP networks may support user-to-user connections, user-to-host connections, and other endpoint variations. In the network presentation, the network sections (NSs) can be represented as clouds with edge routers on their borders and a certain number of interior routers which may have different functions (e.g. routers on the network edges, with additional functions, are referred to as g