rtain MGW in order to avoid overload. BICC uses M3UA on top of SCTP. These protocol stacks are given in Figure 14.23. (See also Figure 14.13). 14.10 COMMON SUPPORT FUNCTIONS This section summarizes some common support server functions. Most of the servers can be seen in Figure 14.20. The servers normally belong to a fundamental plan. Therefore Control Network the treatment in the book is distributed to chapters dealing with FP security (Chapter 6) and FP in general (Chapter 8). Gateway location. The main function of gateway location is to provide information that enables the selection of the appropriate gateway. The information provided could include route, cost, congestion and other parameters. Directory server. The main function of a directory server is to provide a listing of information. The most common information model for directories is based on LDAP. LDAP directory services are based on a client-server model. See the Chapter 6. Name server. The main function of the name server is to map names to addresses. This function essentially consists of two parts: a database to store the mapping, and a query resolver program that answers requests to translate the name to an address. The de facto standard for name server function is the DNS, which is briefly described in Chapter 8. Address allocation. See DHCP in Chapter 8. Security function. See AAA in Chapter 6. Accounting function. This function addresses the problem of accounting. Accounting provides information about the utilization of resources by a user. Accounting can be based on providing information at specified intervals, end 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 