s the new channel, the MSC performs the switching. When the neighbor cell is located under a different MSC, an inter- MSC handover may be required. Then the BSC requests the anchor MSC to establish the connection with the help of a new MSC to the new cell. The anchor MSC performs the switching. The anchor MSC is the exchange via which the call was originally connected. The anchor MSC controls the call until it is cleared even though it may use other MSCs to maintain the call through handovers. Handover can also be executed to arrange traffic between cells to avoid unsuccessful calls due to geographically uneven load. In this case the calls of the MSs that are located close to the border of a loaded cell are switched to a neighboring cell that has more free capacity. As an example we now look at how the most complicated handover, inter-MSC handover, is performed. The handover procedure between two MSCs, shown in Figure 5.14, includes the following main phases: 1. The mobile station moves across the cell border and the BSC (old) decides to initiate handover to another cell (new). The decision is based on the measurement information sent by the mobile and by Anchor MSC PSTN or ISDN VLR (new) VLR (old) (old) (new) Cell (old) Cell (new) Signaling transfer Speech connection Figure 5.14 Handover or handoff between two MSCs. Mobile Communications the BTS. The measurement information includes, in addition to traffic channel measurement results, identifications of neighboring cells and the measurement results of them. The mobile station con- tinuously measures the common channel of each neighbor cell in addition to the traffic channel in use for the call. 2. The BSC (old) notices that the best cell candidate is not under its control and requests the MSC (old) to begin handover preparation to the new cell. The MSC (old) recognizes that the proposed cell (new) is connected to another MSC. 3. The MSC (old) requests a handover number from MSC (new). The handover number is a temporary telephone number that is used to establish 