For acquiring system information instances, a method determines if one or more system information instances requested in a request message are received in a reply message from a base station. The request message includes a request bitmap indicating the requested system information instances. The reply message includes a reply bitmap indicating the system information instances in the reply message. The method acquires the system information instances indicated in the request bitmap and the reply bitmap from the reply message. In addition, the method requests the system information instances from the base station that are indicated in the request bitmap and not indicated in the reply bitmap.