f a fixed network switching node, e.g. routing path search and signal routing. A public land mobile network can have several Mobile Switching Centres with each one being responsible for a part of the service area. The BSCs of a base subsystem are subordinated to a single MSC. Second Generation Cellular Networks Dedicated Gateway MSC (GMSC) This passes voice traffic between fixed networks and mobile networks. If the fixed network is unable to connect an incoming call to the local MSC, it routes the connection to the GMSC. This GMSC requests the routing information from the Home Location Register (HLR) and routes the connection to the local MSC in whose area the mobile station is currently staying. Connections to other mobile international networks are mostly routed over the International Switching Centre (ISC) of the respective country. Home and Visitor Location Registers (HLR and VLR) A given mobile network has several databases. Two functional units are defined for the synchronisation of registration of subscribers and their current location: a home location register (HLR) and the visitor location register (VLR). In general, there is one central HLR per public land mobile network (PLMN) and one VLR for each MSC. Home Location Register (HLR) The HLR stores the identity and user data of all the subscribers belonging to the area of the related GMSC. These are permanent data such as the International Mobile Subscriber Identity (IMSI) of an individual user, the user's phone number from the public network (not the same as IMSI), the authentication key, the subscribers permitted supplementary service and some temporary data. The temporary data on the Subscriber Identity Module (SIM) may include entries such as: the address of the current VLR; the number to which the calls may be forwarded; some transit parameters for authentication and ciphering. Visitor Location Register (VLR) The VLR stores the data of all mobile stations that are currently staying in the administrative area of the associated MSC. A VLR can be respon