PDU Session Release is the 5GSM procedure used to terminate an established PDU session. It may be initiated by the UE or by the network. After completion, the PDU session identity and associated resources are released and the user-plane path for that session is removed.
Signaling Sequence
# | Direction | 5GSM Message | Comment |
1 | UE -> NW | PDU Session Release Request | UE requests regular deactivation of the PDU session. |
2 | NW -> UE | PDU Session Release Command | Network commands release of the session. |
3 | UE -> NW | PDU Session Release Complete | UE confirms that the release procedure is complete. |
Message Structure
The release messages are usually short. The release request and release command include a 5GSM cause. The release complete message may contain only the 5GSM header when there is no additional information to return.
Example : PDU Session Release Request
The following example is based on an Amarisoft MME log. The whole decoded 5GSM message is shown below.
04:10:00.681 [NAS] UL 0065 5GSM: PDU session release request
Protocol discriminator = 0x2e (5GS Session Management)
PDU session identity = 1
Procedure transaction identity = 50
Message type = 0xd1 (PDU session release request)
5GSM cause = 0x24 (Regular deactivation)
Example : PDU Session Release Command
The following example is based on the matching network response in the same Amarisoft MME log.
04:10:00.681 [NAS] DL 0065 5GSM: PDU session release command
Protocol discriminator = 0x2e (5GS Session Management)
PDU session identity = 1
Procedure transaction identity = 50
Message type = 0xd3 (PDU session release command)
5GSM cause = 0x24 (Regular deactivation)
Example : PDU Session Release Complete
The following example is based on the UE completion message from the same Amarisoft MME log.
04:10:00.721 [NAS] UL 0065 5GSM: PDU session release complete
Protocol discriminator = 0x2e (5GS Session Management)
PDU session identity = 1
Procedure transaction identity = 50
Message type = 0xd4 (PDU session release complete)