 typical example) an IPX. With the aim of providing end-to-end QoS for the given connection, packets from the end-users should be correctly marked on the inter-provider link and avoid modifications of packets. The two providers, A and B, should have a peering agreement IP packet DiffServ IP packet Customer treatment of Customer Customer packets Customer premises premises network network Provider's Provider edge Core network Provider edge Customer Customer premises premises network network Customer Customer Figure 2.17 Basic model for a single provider. 2.11 IP Network Architectures for End-to-End QoS IP packet IP packet DiffServ treatment Customer Customer of packets Customer Customer premises premises network network Provider A Provider B Provider edge Provider edge network network Customer border border Customer premises router router premises network network Customer Customer Interconnection link between providers AS - Autonomous system Figure 2.18 Basic inter-provider model. for an end-to-end service with the appropriate QoS mechanism applied on their interconnection. Also, when there is a need for monitoring of the customer (of either of the two providers in this scenario), such action is likely to involve both providers. Which solution can be used for the interconnection between two network providers? Well, the interconnection should be possible with MPLS VPN [34], with a simple IP interconnection (with differentiation on the network layer, e.g. by using DiffServ fields in the IP headers), as well as with a layer 2 interconnection. In general, in Internet networking philosophy, each of the networks which is a sepa- rate administrative domain (consisting of one or more ASs) is completely autonomous to choose traffic management mechanisms and QoS techniques, including the number of classes used inside the network provider's administrative domain. So, it is possible for one provider to group (aggregate) the traffic in three classes only (as an example), while the other operator may distinguish among five or si