Editing My 3GPP 24.501 notes (section)

=== 5.5.1 Registration procedure ===

==== 5.5.1.1 General ====

The registration procedure is always initiated by the UE and used for initial registration as specified in subclause 5.5.1.2.2 or mobility and periodic registration update as specified in subclause 5.5.1.3.2.

When the UE needs to initiate registration over both 3GPP access and non-3GPP access in the same PLMN (e.g. the 3GPP access and the selected N3IWF are located in the same PLMN), the UE:
<ol type="a">
<li>in 5GMM-REGISTERED-INITIATED over 3GPP access shall not initiate registration over non-3GPP access; or</li>
<li>in 5GMM-REGISTERED-INITIATED over non-3GPP access shall not initiate registration over 3GPP access.</li>
:NOTE 1:	To which access (i.e. 3GPP access or non-3GPP access) the UE initiates registration first is up to UE implementation.
</ol>

When the UE is registered with a PLMN over a non-3GPP access, the AMF and the UE maintain:
<ol type="a">
<li>registration state and state machine over non-3GPP access;</li>
<li>5G NAS security context;</li>
<li>5G-GUTI;</li>
<li>registration area for non-3GPP access, which is associated with a single TAI; and</li>
<li>non-3GPP de-registration timer in the UE and non-3GPP implicit de-registration timer in the AMF.</li>
</ol>

A registration attempt counter is used to limit the number of subsequently rejected registration attempts. The registration attempt counter shall be incremented as specified in subclause 5.5.1.2.7 or subclause 5.5.1.3.7. Depending on the value of the registration attempt counter, specific actions shall be performed. The registration attempt counter shall be reset when:
* the UE is powered on;
* a USIM is inserted;
* a registration procedure is successfully completed;
* an EPS attach or combined EPS attach procedure is successfully completed in S1 mode and the UE is operating in single-registration mode. In this case, the UE shall reset the registration attempt counter for 3GPP access;
:NOTE 2:	The registration attempt counter for non-3GPP access is not impacted by the EPS attach and the combined EPS attach procedure.
* a registration procedure is rejected with cause #11, #12, #13, #15, #27, #31, #62, #72, #73, #74, #75, #76, #77 or #78;
* a registration procedure is rejected with cause #3, #6 or #7, the REGISTRATION REJECT message is received without integrity protection and the counter for "SIM/USIM considered invalid for GPRS services" events has a value less than a UE implementation-specific maximum value.
* a network initiated deregistration procedure is completed with cause #11, #12, #13, #15, #27; #62, #72, #74, #75, #76, #77 or #78; or
* a new PLMN or SNPN is selected.

Additionally, the registration attempt counter shall be reset when the UE is in substate 5GMM-DEREGISTERED.ATTEMPTING-REGISTRATION or 5GMM-REGISTERED.ATTEMPTING-REGISTRATION-UPDATE, and:
* the current TAI is changed;
* timer T3502 expires; or
* timer T3346 is started.
When the registration attempt counter is reset, the UE shall stop timer T3519 if running, and delete any stored SUCI.

The lower layers indicate to NAS whether the network supports emergency services for the UE in limited service state (see 3GPP TS 38.331). This information is taken into account when deciding whether to initiate an initial registration for emergency services.

==== 5.5.1.2 Registration procedure for initial registration ====

===== 5.5.1.2.1 General =====

This procedure can be used by a UE for initial registration for 5GS services.

When the UE initiates the registration procedure for initial registration, the UE shall indicate "initial registration" in the 5GS registration type IE. When the UE initiates the registration procedure for emergency services, the UE shall indicate "emergency registration" in the 5GS registration type IE. When the UE initiates the initial registration for onboarding services in SNPN, the UE shall indicate "SNPN onboarding registration" in the 5GS registration type IE. When the UE initiates the initial registration procedure for disaster roaming services, the UE shall indicate "disaster roaming initial registration" in the 5GS registration type IE.

If the MUSIM UE initiates the registration procedure for initial registration and indicates "emergency registration" in the 5GS registration type IE in the REGISTRATION REQUEST message, the network shall not indicate the support of:
* the N1 NAS signalling connection release;
* the paging indication for voice services;
* the reject paging request; or
* the paging restriction;
in the REGISTRATION ACCEPT message.

===== 5.5.1.2.2 Initial registration initiation =====
The UE in state 5GMM-DEREGISTERED shall initiate the registration procedure for initial registration by sending a REGISTRATION REQUEST message to the AMF,
<ol type="a">
<li>when the UE performs initial registration for 5GS services;</li>
<li>when the UE performs initial registration for emergency services;</li>
<li>when the UE performs initial registration for SMS over NAS;</li>
<li>when the UE moves from GERAN to NG-RAN coverage or the UE moves from a UTRAN to NG-RAN coverage and the following applies:
# the UE initiated a GPRS attach or routing area updating procedure while in A/Gb mode or Iu mode; or
# the UE has performed 5G-SRVCC from NG-RAN to UTRAN as specified in 3GPP TS 23.216,
:and since then the UE did not perform a successful EPS attach or tracking area updating procedure in S1 mode or registration procedure in N1 mode;
<li>when the UE performs initial registration for onboarding services in SNPN; and</li>
<li>when the UE performs initial registration for disaster roaming services;</li>
</ol>
with the following clarifications to initial registration for emergency services:
<ol type="a">
<li>the UE shall not initiate an initial registration for emergency services over the current access, if the UE is already registered for emergency services over the non-current access, unless the initial registration has to be initiated to perform handover of an existing emergency PDU session from the non-current access to the current access; and</li>
NOTE 1:	Transfer of an existing emergency PDU session between 3GPP access and non-3GPP access is needed e.g. if the UE determines that the current access is no longer available.
<li>the UE can only initiate an initial registration for emergency services over non-3GPP access if it cannot register for emergency services over 3GPP access.</li>
</ol>

The UE initiates the registration procedure for initial registration by sending a REGISTRATION REQUEST message to the AMF, starting timer T3510. If timer T3502 is currently running, the UE shall stop timer T3502. If timer T3511 is currently running, the UE shall stop timer T3511.

<span style="color:red">During initial registration the UE handles the 5GS mobile identity IE in the following order:</span>
<ol type="a">
<li>if:
<ol type="1">
<li>the UE:</li>
<ol type="i">
<li>was previously registered in S1 mode before entering state EMM-DEREGISTERED; and</li>
<li>has received an "interworking without N26 interface not supported" indication from the network; and</li>
</ol>
<li>EPS security context and a valid native 4G-GUTI are available;</li>
</ol>

then the UE shall create a 5G-GUTI mapped from the valid native 4G-GUTI as specified in 3GPP TS 23.003 and indicate the mapped 5G-GUTI in the 5GS mobile identity IE. The UE shall include the UE status IE with the EMM registration status set to "UE is not in EMM-REGISTERED state" and shall include an ATTACH REQUEST message as specified in 3GPP TS 24.301 in the EPS NAS message container IE.

Additionally, if the UE holds a valid 5G GUTI, the UE shall include the 5G-GUTI in the Additional GUTI IE in the REGISTRATION REQUEST message in the following order:
# a valid 5G-GUTI that was previously assigned by the same PLMN with which the UE is performing the registration, if available;
# a valid 5G-GUTI that was previously assigned by an equivalent PLMN, if available; and
# a valid 5G-GUTI that was previously assigned by any other PLMN, if available;

<li>if:
# the UE is registering with a PLMN and the UE holds a valid 5G-GUTI that was previously assigned, over 3GPP access or non-3GPP access, by the same PLMN with which the UE is performing the registration, the UE shall indicate the 5G-GUTI in the 5GS mobile identity IE; or
# the UE is registering with a SNPN, the UE holds a valid 5G-GUTI that was previously assigned, over 3GPP access or non-3GPP access, by the same SNPN with which the UE is performing the registration, and the UE is not initiating the initial registration for onboarding services in SNPN, the UE shall indicate the 5G-GUTI in the 5GS mobile identity IE;</li>

<li>if the UE holds a valid 5G-GUTI that was previously assigned, over 3GPP access or non-3GPP access, by an equivalent PLMN, the UE shall indicate the 5G-GUTI in the 5GS mobile identity IE;</li>

<li>if:
# the UE is registering with a PLMN and the UE holds a valid 5G-GUTI that was previously assigned, over 3GPP access or non-3GPP access, by any other PLMN, the UE shall indicate the 5G-GUTI in the 5GS mobile identity IE; or
# the UE is registering with an SNPN, the UE holds a valid 5G-GUTI that was previously assigned, over 3GPP access or non-3GPP access, by any other SNPN, and the UE is not initiating the initial registration for onboarding services in SNPN, the UE shall indicate the 5G-GUTI in the 5GS mobile identity IE and shall additionally include the NID of the other SNPN in the NID IE;</li>

<li>if a SUCI other than an onboarding SUCI is available, and the UE is not initiating the initial registration for onboarding services in SNPN, the UE shall include the SUCI other than an onboarding SUCI in the 5GS mobile identity IE;</li>
<li>if the UE does not hold a valid 5G-GUTI or SUCI other than an onboarding SUCI, and is initiating the initial registration for emergency services, the PEI shall be included in the 5GS mobile identity IE; and</li>
<li>if the UE is initiating the initial registration for onboarding services in SNPN, an onboarding SUCI shall be included in the 5GS mobile identity IE.</li>
</ol>
:NOTE 2: The AMF in ON-SNPN uses the onboarding SUCI as specified in 3GPP TS 23.501.

If the SUCI is included in the 5GS mobile identity IE and the timer T3519 is not running, the UE shall start timer T3519 and store the value of the SUCI sent in the REGISTRATION REQUEST message. The UE shall include the stored SUCI in the REGISTRATION REQUEST message while timer T3519 is running.

If the UE is operating in the dual-registration mode and it is in EMM state EMM-REGISTERED, the UE shall include the UE status IE with the EMM registration status set to "UE is in EMM-REGISTERED state".

:NOTE 3: Inclusion of the UE status IE with this setting corresponds to the indication that the UE is "moving from EPC" as specified in 3GPP TS 23.502.
:NOTE 4: The value of the 5GMM registration status included by the UE in the UE status IE is not used by the AMF.

If the last visited registered TAI is available, the UE shall include the last visited registered TAI in the REGISTRATION REQUEST message.

If the UE requests the use of SMS over NAS, the UE shall include the 5GS update type IE in the REGISTRATION REQUEST message with the SMS requested bit set to "SMS over NAS supported".  When the 5GS update type IE is included in the REGISTRATION REQUEST for reasons other than requesting the use of SMS over NAS, and the UE does not need to register for SMS over NAS, the UE shall set the SMS requested bit of the 5GS update type IE to "SMS over NAS not supported" in the REGISTRATION REQUEST message.

See spec for more info...

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If the UE does not have a valid 5G NAS security context, <span style="color:red">the UE shall send the REGISTRATION REQUEST message without including the NAS message container IE.</span> The UE shall include the entire REGISTRATION REQUEST message (i.e. containing cleartext IEs and non-cleartext IEs, if any) in the NAS message container IE that is sent as part of the SECURITY MODE COMPLETE message as described in subclauses 4.4.6 and 5.4.2.3.

If the UE has a valid 5G NAS security context and the UE needs to send non-cleartext IEs, the UE shall send a REGISTRATION REQUEST message including the NAS message container IE as described in subclause 4.4.6. If the UE does not need to send non-cleartext IEs, the UE shall send a REGISTRATION REQUEST message without including the NAS message container IE.


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