| Protocol | nas | Network | 5g |
|---|---|---|---|
| Spec | 3GPP TS 24.501 | Spec Section | 8.3.7 |
| Direction | UE to SMF via AMF | Message Type | 5GSM signaling |
| Full message name | 5G NAS - PDU Session Modification Request |
|---|---|
| Protocol | NAS |
| Technology | 5G |
| Direction | UE to SMF via AMF |
| Interface | N1 |
| Signaling bearer / channel | NAS signaling / Usually carried inside UL NAS Transport on the access side |
| Typical trigger | The UE needs to modify an active session because the application, QoS policy, header-compression state, or session capability has changed. |
| Main purpose | Requests a change to an established PDU session so the network can update QoS, configuration, or session capabilities without creating a new session. |
| Main specification | 3GPP TS 24.501, 8.3.7 |
| Release added | Release 15 |
| Procedures where used | 5G PDU Session Modification, QoS Flow Establishment, VoNR service adaptation |
| Related timers | T3581 |
| Related cause values | #43 Invalid PDU session identity, #44 Semantic errors in packet filter(s), #45 Syntactical error in packet filter(s), #46 out of LADN service area, #59 unsupported 5QI value, #67 insufficient resources for specific slice and DNN, #69 insufficient resources for specific slice, #83 Semantic error in the QoS operation, #84 Syntactical error in the QoS operation, #95-111 protocol errors |
PDU Session Modification Request is the 5GSM message the UE sends to change an already active PDU session, such as updating QoS, packet-filter behavior, header-compression settings, or other session parameters.
Requests a change to an established PDU session so the network can update QoS, configuration, or session capabilities without creating a new session.
Call flow position: UE-initiated modification request step for an already active PDU session.
Typical state: The UE already has a live PDU session and is asking the network to revise the session configuration.
Preconditions:
Next likely message: PDU Session Modification Command or PDU Session Modification Reject
Call flow position: Often appears when the UE wants the network to add or adjust QoS-related behavior for the session.
Typical state: The session is already established and the QoS state is being refined.
Preconditions:
Next likely message: PDU Session Modification Command
Previous message(s): PDU Session Establishment Accept, UL NAS Transport, Active PDU session state
Next message(s): PDU Session Modification Command, PDU Session Modification Reject, PDU Session Release Command
Security context: Normally sent while the PDU session is already active and NAS security is established, so the payload is usually integrity protected and often ciphered.
This message is not typically analyzed as ASN.1 on the wire. It is usually read as a NAS or protocol field structure instead.
This is a 5GSM NAS message defined by ordered information elements in 3GPP TS 24.501 rather than ASN.1 syntax.
PDU Session Modification Request
Extended Protocol Discriminator: 5G Session Management
PDU Session ID: 10
PTI: 5
Message Type: PDU Session Modification Request
5GSM Capability:
Reflective QoS: supported
Multi-homed IPv6 PDU session: not supported
Integrity Protection Maximum Data Rate: full data rate
Maximum Number of Supported Packet Filters: 16
Requested QoS Rules:
Rule 1:
QFI: 9
Packet filter: permit out ip from any to any
Precedence: 255
Requested QoS Flow Descriptions:
5QI: 1
GFBR UL/DL: 128 kbps / 128 kbps
Extended Protocol Configuration Options:
DNS IPv4 address request
DNS IPv6 address request
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.