Cellular Network Security 305 call routing information (also called roaming number) from the VLR where the subscriber is currently roaming. The PRN message contains the called number, alerting pattern, and other subscriber call profile data items. The VLR uses the called number to store the alerting pattern and subscriber call profile data items and assign the roaming number for routing the call. This roaming number data item is passed on to the HLR (in message PRN_ACK), which forwards it to the GMSC (in message SRI_ACK). The GMSC uses this roaming number to route the call (message IAM) to the MSC where the subscriber is currently roaming. On receipt of the message IAM, the MSC assigns the called number resources for the call and also requests the subscriber call profile data items, and alerting pattern for the called number (using message SIFIC) from the VLR, and receives the same in the Page MS message. The MSC uses the alerting pattern in the incoming call profile to derive the page type data item. The page type data item denotes the manner in which to alert the mobile station. It is used to page the mobile subscriber (using message Page). Thus subscribers receive incoming calls irrespective of their locations in the network. If data item values are inaccurate, the network can misoperate and subscribers will be