of session and the information may be aggregated to an agreed level. This information may be used for charging purposes, statistics or others. Policy function. The policy function provides capabilities to state and enforce rules to manage the behaviour of heterogeneous systems (in terms of QoS, security etc.), devices, applications and network resources. The enforcement of policies on multiple managed entities is intended to produce aggregate behaviour that enables delivery of service at agreed levels. The policy itself may be stored in a directory. Mobility agent. This function provides support for handling personal mobility, terminal mobility and service mobility. Interconnection 15.1 OBJECTIVES To explain: what is meant by interconnect and interworking relationships between interworking and fundamental technical plans interconnect and roaming, roaming between technologies interconnect and VHE interconnect and e2e performance interconnect and signalling interconnect and charging and accounting interconnect and SLA the need for cooperation between technologies, such as UMTS and WLAN. Figure 15.1 gives a hint on involved areas. Media/border gateway control function Other networks Service network or home network Terminal if any Applications Service enablers Roaming Mobility management (PDP context) network control and intelligence IW signalling Border Access Core connectivity gate- Connectivity Might be visited network Figure 15.1 Dedicated interworking parts of the reference model - in a particular call other 'ordi- nary' parts will be involved as well Understanding Changing Telecommunications - Building a Successful Telecom Business. Edited by A. Olsson © 2004 John Wiley & Sons, Ltd ISBN: 0-470-86851-1 Understanding Changing Telecommunications - Building a Successful Telecom Business 15.2 INTRODUCTION It has been said before: it is the user perception that counts. The main user perceived areas in this book are services, QoS and security, all perceived end to end. The strong relationship between interconnect and 