This post contains the meaning of different PLMNs in LTE or 3G network. In earlier PLMN Article explains about what is plmn? The PLMN type changes based on user location and behavior about the network.
User PLMN. This is the plmn 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 update is done with the home network HLR. If subscriber is allowed to roam then, HLR sends the subscriber data. If a subscriber is not allowed to roam, HLR returns roaming not allowed error. In error case roaming plmn is put the forbidden list and FPLMN. Now next time phone does not try with FPLMN. One a phone is restarted then 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 to the GMSC . GMSC interrogates with 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 the for roaming network.
EPLMN or EHPLMN:
Equivalent PLMN. If a subscriber roames in Home PLMN there is no roaming. Subscriber always see the signals of the home mobile network operator. An operator may not have much coverage , so they do collaborations with other mobile operators , where the roaming will not be applied. This is call EPLMN or EHPLMN. Subscriber have impression that he is in his home network. E.g The IDEA network in India might not have coverage in some state. There it can use another mobile operator (e.g Airtel).