Interface: N1 over LTE access / S1-MME control path
Domain: Core-side EPS mobility management signaling for UE identity refresh.
Signaling bearer: NAS signaling
Logical channel: Commonly carried after attach, TAU, or another EMM branch where the MME decides to refresh the UE identity.
Transport / encapsulation: EPS NAS message sent by the MME and delivered to the UE through the eNodeB when the network refreshes the UE's temporary identity.
Security context: Normally protected because the message replaces a sensitive temporary identity and is sent after security context setup.
Message Structure Overview
GUTI Reallocation Command is an EPS mobility-management message rather than an ASN.1 LTE RRC structure.
The practical reading path starts with the new GUTI and then checks whether TAI list context changed at the same time.
ASN.1 Message Syntax for LTE GUTI Reallocation Command
GUTI Reallocation Command
GUTI
TAI list OPTIONAL
DCN-ID OPTIONAL
UE radio capability ID OPTIONAL
UE radio capability ID deletion indication OPTIONAL
How to read this message syntax
Read the new GUTI first. In traces, this message is usually about identity refresh, not about a wider mobility failure.
Start with the new GUTI because that is the reason this message exists.
Then check whether TAI list also changed.
Important Information Elements
IE
Required
Description
GUTI
Yes
Carries the new globally unique temporary UE identity allocated by the MME.
TAI list
Optional
May refresh the tracking-area list that belongs with the new identity context.
DCN-ID
Optional
May carry data-centre-network identity context when used by the network.
Detailed field explanation
GUTI
Carries the new globally unique temporary UE identity allocated by the MME.
Presence: Required
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
TAI list
May refresh the tracking-area list that belongs with the new identity context.
Presence: Optional
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
DCN-ID
May carry data-centre-network identity context when used by the network.
Presence: Optional
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
What to check in logs and traces
Confirm which earlier EMM branch triggered the identity refresh.
Inspect the new GUTI first.
Check whether a matching GUTI Reallocation Complete follows.
Common Issues and Troubleshooting
The UE later uses an unexpected temporary identity.
Likely cause: The network may have refreshed the GUTI in an earlier secure branch.
What to inspect: Check GUTI Reallocation Command and the later GUTI Reallocation Complete.
Next step: Treat the identity change as expected if the command-complete pair is present.
LTE / 5G / Variant Comparison
Compared with Tracking Area Update Accept
Tracking Area Update Accept keeps the UE registered. GUTI Reallocation Command specifically refreshes the stored temporary identity.
FAQ
What is GUTI Reallocation Command in LTE?
It is the EPS NAS message the MME sends when it wants the UE to store a new GUTI.
What should I inspect first?
Start with the new GUTI and then check whether the TAI list also changed.
Decode this message with the 3GPP Decoder, inspect the related message database, or open the matching call flow to see where this signaling step fits in the full procedure.
