l is effectively a Policy Decision Point (PDP). The IP policy control makes decisions regarding the network, based on IP policy rules, and communicates these decisions to the IP BS manager in the GGSN, which is the IP Policy Enforcement Point (PEP). A protocol interface between the IP policy control and application servers/proxies (e.g. local SIP proxy) supports the trans- fer of policy related information from the application layer to the policy decision point now under consolidation. A protocol interface (e.g. COPS protocol RFC2748) between the IP policy control and GGSN supports the transfer of information and policy deci- sions between the policy decision point and the IP BS manager in the GGSN. The IP policy control bases policy decisions only on information obtained from nodes/ elements within its domain or from nodes with which it has a trust relationship. The IP policy control needs to be in the same domain 6 as the GGSN or have a trust relationship with the GGSN [7]. 9.9.2.3 Resource Manager In the UMTS network various nodes perform resource management in the admission control decision, usually under the direct control of the UMTS network. Likewise, in IP networks, there also exists resource management to ensure that resources required for a service are available. Because resources for the IP bearer service to be managed are not necessarily owned by the UMTS network. The resource management of those resources would be performed through an external resource management function for the IP net- work. In addition, where the UMTS network is also using external IP network resources as part of the UMTS bearer service, e.g. for the backbone bearer service, it may also be necessary to inter-work with an external IP resource manager. Figure 9.18 illustrates the scenario for control of an IP service using IP Bearer Service (BS) managers in both possible locations, i.e. in the UE and gateway node and an exter- nal resource manager. It also indicates the optional communication path between the IP BS managers in the U