Why after flight mode OFF and ON device first goes to EPLMN first?

CORE
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1

Hello Experts.

Does anybody know the reason why after flight mode OFF and ON device first goes to EPLMN first?

(Roaming PLMN)

EPLMN
EPLMN767×780 86.3 KB

2

I think this is a standard for the smartphones.

3

Well, yep happening for any type of smartphone brand.

True, but don’t know the reason…

I tried many setting on SIm but failed to solve it.

4

It depends upon what is flashed in usim under eplmn list.

5

eplmn is another operator.

We use as roaming.

Our hpmn is prioritized and EFHPLMNwAcT= our HPLMN.

1 Like
6

Why you mentioned EPLMN as roaming PLMN?

Is it not part of attach accept?

For roaming PLMN we have some definition in Core network.

After airplane mode OFF, UE search first for HPLMN / EHPLMN.

7

ePLMN = 2nd PLMN that we want only UE attaches if our coverage is bad.

HPLMN is prioritized, but the question is why flight mode OFF and ON triggers mostly ePLMN attach?

8

A PLMN type changes based on user location and behavior about the network.

  • UPLMN: User PLMN. This is the planning priority set by the user.

  • OPLMN: Operator PLMN. This is the PLMN priority set by the mobile operator.

  • FPLMN: This is forbidden PLMN. In roaming a mobile network, try to attach from a PLMN. An update is done with the home network HLR during attach and location. 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.

  • IPLMN: 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.

  • HPLMN: The PLMN id is derived from the IMSI. This never changes while roaming. If IMSI is not changing, the HPLMN will not change.

  • VPLMN: 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 collaborate with other mobile operators, where the roaming will not be applied. This is called EPLMN or EHPLMN. The 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).

1 Like
9

When a device is powered on or reconnected to a cellular network, it’s necessary to perform ePLMN scanning to ensure that the device connects to the best available network in terms of signal quality and coverage. This is especially crucial when the device has ran sharing configured, as it needs to identify and select the appropriate network for seamless handover between different radio access technologies. During ePLMN scanning, the IMSI (International Mobile Subscriber Identity) is used to identify the network operator to which the device is attempting to connect. Based on this information, the device can then search for and connect to the available network that corresponds to the operator associated with the IMSI. Device settings may include network preferences that influence the network selection process and roaming configuration, determining how the device connects to mobile networks when outside its home area.

10

Once the ue is powered off or out of coverage it should use the last registered PLMN (LRPLMN) using all access technologies that are capable of so it is expected to select the last registered PLMN once you power on

Please refer to the following specification: 3GPP 23.122 4.4.3.1