Once the GPS Server receives a LU message, it checks the distance between the MN and its current AP. We define the G threshold, which corresponds to the maximum distance between an MN and its associated AP where the MN is not considered to be close to the border of its AP’s coverage. If this distance is below the G threshold, the MN is still in the range of its current AP and is not required to perform a handover. Otherwise the MN is going out of the coverage area of its current AP and the GPS Server has to determine a target AP for the pending handover. Among all APs in the GPS Server list, the GPS Server chooses the closest one to the MN as the target AP. If the target AP is not the same as the current one, the GPS Server sends a Handover Initiate (HI) message to the MN. The HI message contains the target AP’s 802.11 channel, SSID, and sub-network IPv6 prefix. According to the
measurements found in [4], we decided to set the G threshold to 50% of the AP’s range.