nhiều kết nối E-1 là cần thiết để kết nối một MSC tới BSS. Trong thực tế, điều này có nghĩa rằng nhiều E-1s được đóng gói và gửi qua các kết nối quang học như STM-1 tới BSS. Một lý do khác để sử dụng một kết nối quang học được rằng các tín hiệu điện chỉ có thể được thực hiện trên một khoảng cách dài với những nỗ lực tuyệt vời | 50 Communication Systems for the Mobile Information Society in a next step. Once the new BSC has prepared the speech channel TCH in the new cell the MSC returns a handover command to the mobile station via the still existing connection over the current BSC. The mobile station then performs the handover to the new cell. Once the new cell and BSC have detected the successful handover the MSC can switch over the speech path and inform the old BSC that the traffic channel for this connection can be released. Inter-MSC handover if the current and new cells for a handover procedure are not connected to the same MSC the handover procedure is even more complicated. As in the example before the BSC detects that the new cell is not in its area of responsibility and thus forwards the handover request to the MSC. The MSC also detects that the LAC of the new cell is not part of its coverage area. Therefore the MSC looks into another table which lists all LACs of the neighboring MSCs. As the MSC in the next step contacts a second MSC the following terminology is introduced to unambiguously identify the two MSCs the MSC which has assigned a MSRN at the beginning of the call is called the anchor-MSC A-MSC of the connection. The MSC that receives the call during a handover is called the relay-MSC R-MSC . See Figure . In order to perform the handover the A-MSC sends a MAP mobile application part see Section handover message to the R-MSC. The R-MSC then asks the responsible BSC to establish a traffic channel in the requested cell and reports back to the A-MSC. The A-MSC then instructs the mobile station via the still existing connection over the current cell to perform the handover. Once the handover has been performed successfully the R-MSC reports the successful handover to the A-MSC. The A-MSC can then switch the voice path towards the R-MSC. Afterwards the resources in the old BSC and cell are released. If the subscriber yet again changes to another cell during the call
