Editing Roaming (section)

=== Location update ===
Location updating is the mechanism that is used to determine the location of an [[Mobile station|MS]] in the idle state (connected to the network, but with no active call).
# When the mobile device is turned on or is transferred via a [[handoff|handover]] to the network, this new "visited" network sees the device, notices that it is not registered with its own system, and attempts to identify its home network. If there is no roaming agreement between the two networks, maintenance of service is impossible, and service is denied by the visited network.
# The visited network contacts the home network and requests service information (including whether or not the mobile should be allowed to roam) about the roaming device using the [[International mobile subscriber identity|IMSI]] number.
# If successful, the visited network begins to maintain a temporary subscriber record for the device. Likewise, the home network updates its information to indicate that the cell phone is on the visited network so that any information sent to that device can be correctly routed.