What are UPLMN, OPLMN, FPLMN,IPLMN, HPLMN, VPLMN and EPLMN/EHPLMN?
This tutorial explains the different types of PLMNs in LTE or 3G networks. An earlier PLMN article explains what is a PLMN. A PLMN type changes based on user location and behavior about the network.
User PLMN. This is the planning priority set by the user.
Operator PLMN. This is the PLMN priority set by the mobile operator.
This is forbidden PLMN. In roaming a mobile network try to attach from a PLMN. During attach and location, an update is done with the home network HLR. If a subscriber is allowed to roam then, HLR sends the subscriber data. If a subscriber is not allowed to roam, HLR returns the roaming not allowed error. In case of error, roaming PLMN is put on the forbidden list and FPLMN. Now next time phone does not try with FPLMN. Once a phone is restarted then the list is cleared.
It is Interrogating PLMN. It refers to the MCC and MNC where GMSC and CAMEL node is located. For a dialed subscriber, first, the call hits the GMSC. GMSC interrogates the HLR for further call routing.
The PLMN id is derived from the IMSI. This never changes while roaming, if IMSI is not changing, the HPLMN will not change.
Visited PLMN. The PLMN id is of the roaming network.
EPLMN or EHPLMN:
Equivalent PLMN. If a subscriber roams in Home PLMN there is no roaming. A Subscriber always sees the signals of the home mobile network operator. An operator may not have much coverage, so they do collaborate with other mobile operators, where the roaming will not be applied. This is called EPLMN or EHPLMN. Subscriber has the impression that he is in his home network. E.g The IDEA network in India might not have coverage in some cities. There it can use another mobile operator (e.g Airtel).