rmination of allowed QoS classes is done by means of subscriber profile information At the end of the chapter the distribution of functionality to the numerous individual nodes will be treated at an overview level. Let us have a very brief look at some specific FP features or references concerning the control layer. 14.3.1 SIGNALLING Signaling is a focal point in this chapter. See Section 14.4. 14.3.2 MOBILITY MANAGEMENT: ROAMING Roaming between GSM and UMTS is one of the important tasks, where the control layer is involved. The inter-system roaming solution allows the subscriber to roam from the UMTS net- work to the GSM network and vice versa. The MSC Server supports mobility management in order to enable attachment/detachment and roaming within the UMTS network, between UMTS networks, and between UMTS and GSM networks. See more in Chapter 15. 14.3.3 MOBILITY MANAGEMENT: HANDOVER The MSC server supports inter-MSC and intra-MSC handover from UMTS to GSM and vice versa. The handover function is vital for the offered QoS. 14.3.4 WLAN ISP (WISP): ROAMING Islands of public WLAN coverage have already established roaming between their respec- tive networks, based on unilateral agreements. There are also companies establishing themselves as intermediary roaming players. That can be a choice for many WISP operators who are very local or who want to establish global roaming quickly. Supposing that visited and home WISPs do not have any roaming relations; the roaming broker can make direct agreements with each involved WISP. 14.3.5 MOBILE OPERATOR: WLAN ROAMING For a mobile operator, the well-established GSM (and GPRS) roaming concept can be extended to also cover WLAN roaming traffic. WLAN roaming traffic costs can be integrated with other GSM roaming traffic charges and billed on regular invoices by the home operator. Understanding Changing Telecommunications - Building a Successful Telecom Business 14.3.6 CHARGING The servers provide flexible charging mechanisms. The existing charging capabilities allow the operator to