x (or more) classes. How- ever, at the interconnection point between the network providers there is a need to map classes which are being used by one provider to classes which are being used by the other provider and vice versa. This is usually implemented at the edge routers of each of the network providers. IP Network Architectures for End-to-End QoS There is a fundamental difficulty in the IP-based platforms and networks due to heterogeneity in all aspects, including network infrastructures, type of applications and services carried through the network, management infrastructure, and end-user devices. Simple use of IP as a transport technology does not mean networks and platforms are the same or even compatible. So, QoS is not assured by itself in IP networks, especially for traffic being transported through multiple network providers. There is an excessive number of different configurations among different networks, although all of them are using IP (and Internet networking principles) as a transport means. Thus it is hard to provide certain QoS for different services from one end to the other, simply because each network has different mechanisms and the levels of control and provision are also different. For example, as shown in Figure 2.19, one network 2 Internet QoS Cable access access network network ISP-1 ISP-2 (IntServ) (DiffServ) (MPLS) (Over provisioning) Carrier WiFi Mobile access Optical access (4G) access network BB - Backbone network ISP - Internet service provider DiffServ - Differentiated services MPLS - Multi-protocol label switching IntServ - Integrated services Figure 2.19 IP networks with heterogeneous QoS mechanisms. provider may use an IntServ-based approach, another one on the packets' route may use the DiffServ approach for QoS provisioning, a third one may use MPLS traffic engineering, while a fourth may use over-provisioning (without explicit QoS support for given traffic types). Possible mapping between DiffServ layer 3 marking, MPLS class of services, and Ethernet priority code point