on points that the IP traffic traverses (i.e. IP packets from the service flows). End-to-end communication across the Internet is also noted as UNI-to-UNI (where UNI stands for user to network interface). In such QoS big picture (with the end-to-end concept), different IP network sections may be represented as network clouds with edge routers on their borders toward other networks with which they interconnect. Also, each network cloud has many different routers and switches, where some of them are used only to route (or switch) IP packets (i.e. the data) while others have various functionali- ties (e.g. control and management functionalities). When considering end-to-end IP communication, there can be one or multiple IP network sections on that path. Since the Internet is a global network, where clients can be connected through a fixed or mobile access network in one country and servers can be hosted in another country or region, IP connections typically span national or regional boundaries. So, UNI-UNI performance (i.e. end-to-end QoS) for a given service can be estimated or measured by knowing network performances of all network sections across different IP networks on the path of the data. Generally, each network section may have different policies and different QoS approaches, SO end-to-end QoS in IP-based platforms and networks is usually difficult due to their heterogeneity. So, when IP is used as networking transport technology that in practice does not guarantee that various networks are the same or compatible one to another. An extreme case of various configurations among different IP networks will be an end-to-end scenario where each of the networks has different QoS approach (e.g. ISP-A uses DiffServ, Transit provider 1 uses over-provisioning, Transit provider 2 uses multi-protocol label switching, and ISP-B uses Carrier Ethernet QoS, as it is given in Figure 7.4). When there are different QoS mechanisms in each network segment it is hard to provide guaranteed end-to-end QoS for the Internet traffic (w