My 3GPP TS 22.011 Notes
3.2 Network Selection
See spec for details...
3.2.2 Procedures
3.2.2.1 General
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If registration on a PLMN is successful, the UE shall indicate this PLMN (the "registered PLMN") and be capable of making and receiving calls on it. The identity of the registered PLMN shall be stored on the SIM/USIM. However, if registration is unsuccessful, the UE shall ensure that there is no registered PLMN stored in the SIM/USIM.
If a registration is unsuccessful because the IMSI is unknown in the home network, or the UE is illegal, then the UE shall not allow any further registration attempts on any network, until the UE is next powered up or a SIM/USIM is inserted.
If the registration is unsuccessful due to the lack to service entitlement, specific behaviour by the UE may be required, see clause 3.2.2.4.
To avoid unnecessary registration attempts, lists of forbidden PLMNs, TAs and LAs are maintained in the UE, see clause 3.2.2.4 and 3GPP TS 23.122.
Registration attempts shall not be made by UEs without a SIM/USIM inserted.
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3.2.2.2 At switch-on or recovery from lack of coverage
See spec...
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If successful registration is achieved, the UE shall indicate the selected PLMN.
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3.2.2.5 Periodic network selection attempts
If the Operator controlled signal threshold per access technology is not set on the Universal Subscriber Identity Module (USIM), a UE in Automatic Mode shall make periodic attempts to look for a higher priority PLMN including associated Access Technology of the same country as the currently received PLMN including associated Access Technology or for a higher priority PLMN including associated Access Technology that uses a Shared MCC (e.g. MCC=901). If the currently received PLMN including associated Access Technology uses a Shared MCC, also a higher priority PLMN including associated Access Technology using any non-Shared MCC shall be considered. For the ranking of PLMNs the UE shall use the order used in clause 3.2.2.2. In the case that there is no associated Access Technology identifier, the mobile shall assume that all Access Technologies provided by a PLMN are of equal priority. Moreover, periodic network selection shall not lead to change of access technology within the registered PLMN.
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