a connection via PLMN, ISDN, or PSTN for the handover. 4. The new MSC requests allocation of a traffic channel from the BSC (new). 5. The BSC (new) allocates the channel and informs the MSC (new). 6. The MSC (new) allocates a handover number and sends it to the MSC (old). 7. The MSC (old) routes a call toward the MSC (new) using the han- dover number as dialed digits. 8. When the routing is complete and channel is established from the anchor MSC to the new cell, the new MSC/VLR commands the mobile station, via the MSC (old), to switch to the new traffic channel (frequency and time slot of the new cell) and MSC (old) to perform switching. 9. The old MSC switches to the new channel and the new MSC and BSC connect the speech path through the reserved channels in the new cell. Notice that the call is still controlled by the old MSC, which has the role of anchor MSC and it, for example, produces charging records. Finally, the channel of the old cell is released. 5.6.4 GSM Security Functions In the GSM special attention is paid to security aspects, such as security against forgery and theft, security of speech and data transmission, and secu- rity of the subscriber's identity. Use of a radio transmission makes the PLMNs particularly sensitive to the misuse of resources by unauthorized per- sons and the eavesdropping of information exchanged on the radio path. Introduction to Telecommunications Network Engineering For security functions the AuC delivers random numbers and precalcu- lated keys for authentication and ciphering to the HLR. It then sends them with other subscriber information to the VLR, where location update is performed. We now review the four most important security functions of GSM net- work, which are shown in Figure 5.15. In addition to these functions, the GSM SIM card is protected by a personal identity number (PIN), similar to a credit card "password." The ME may also provide additional security features. 5.6.4.1 Authentication For authentication AuC provides authentication triplets to the VLR via 