Description
The Fully Qualified Session Endpoint Identifier (F-SEID) is a critical data structure defined within the 5G Core network's Service-Based Architecture (SBA). It serves as a globally unambiguous address for a specific session endpoint, such as a Protocol Data Unit (PDU) session anchored at a Session Management Function (SMF) or a User Plane Function (UPF). The F-SEID is constructed by concatenating two primary components: the Session Endpoint Identifier (SEID) and the IP address of the network function hosting that endpoint. The SEID itself is a locally significant identifier assigned by the network function, but when combined with the node's IP address, it becomes globally unique across the entire network. This composite structure is fundamental for the HTTP/2-based service-based interfaces (e.g., N4, N7) used between Control Plane functions like the SMF and the UPF.
Architecturally, the F-SEID is used within the Packet Forwarding Control Protocol (PFCP) session context, particularly in the N4 interface between the SMF (control plane) and the UPF (user plane). When an SMF establishes a PDU session, it creates a PFCP session and assigns an F-SEID for the session endpoint on the UPF. This F-SEID is then used in all subsequent PFCP messages (e.g., Session Establishment, Modification, Deletion) to uniquely identify the session and the specific UPF instance handling it. The IP address component ensures that messages are correctly routed to the physical or virtualized network function instance, even in a cloud-native, distributed deployment where multiple UPF instances may exist.
The role of the F-SEID extends beyond simple identification; it is integral to session management, mobility, and network slicing. For mobility events like handovers, the SMF may need to redirect traffic by updating the F-SEID to point to a different UPF. In network slicing, the F-SEID helps associate a session with a specific slice instance, as the UPF may be slice-specific. The identifier also supports advanced features like session and service continuity (SSC) modes, where the PDU session anchor (and thus the F-SEID) may change. Its design aligns with the 5G Core's principle of separation of control and user plane, enabling flexible scaling and deployment of user plane resources.
Purpose & Motivation
The F-SEID was introduced to address the need for unambiguous session endpoint identification in the 5G Core's distributed, cloud-native architecture. Previous 4G EPC architectures used identifiers like the Fully Qualified TEID (F-TEID) in GTP-based interfaces, but these were tied to the GPRS Tunnelling Protocol. With 5G's shift to a Service-Based Architecture (SBA) and the introduction of new protocols like PFCP for the N4 interface, a new identifier mechanism was required. The F-SEID provides a standardized way to uniquely identify a session endpoint across potentially numerous, geographically dispersed network function instances, solving the problem of session routing and management in a decomposed network.
Its creation was motivated by the limitations of earlier identifiers that were not fully qualified or were protocol-specific. In a monolithic network, locally significant identifiers might suffice, but in a microservices-based 5G Core, control plane functions (like SMF) need to communicate with specific user plane instances (UPFs) without ambiguity. The F-SEID ensures that even if multiple UPFs use the same local SEID value, the combination with the IP address prevents collisions. This is crucial for automation, orchestration, and fault isolation, as it allows network operators to pinpoint exactly where a session is anchored. The F-SEID thus supports the scalability, resilience, and service differentiation goals of 5G, including network slicing and edge computing.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (111 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-14, normative work from Rel-15.
In Release 15, the F-SEID function was introduced within the newly defined PFCP-based N4 interface procedures for session establishment, modification, deletion, and reporting. Its role was clarified within the fundamental PFCP concepts for CP/UP functions and PFCP Associations, and it became a key identifier used during session restoration procedures following an SMF or UPF restart. Specifically, the F-SEID is included in PFCP Session Report Requests to facilitate the movement of PFCP sessions between SMFs within an SMF set.
- Session establishment on N4 TS 29.244CR0049
- Session Modification on N4 TS 29.244CR0050
- Session deletion on N4 TS 29.244CR0051
- Session Reporting on N4 TS 29.244CR0052
- PDR for Ethernet PDU session TS 29.244CR0112
- Essential clarification on the CHOOSE bit in F-TEID IE TS 29.244CR0122
+ 5 more changes
In Release 16, the F-SEID function was enhanced to support the reestablishment and seamless handover of PFCP sessions within an SMF set after a node failure or restart. This included procedures for a UPF to move PFCP sessions to alternative SMFs in the set using mechanisms like the PFCP Session Report Request with the old CP F-SEID. Furthermore, the release introduced more robust PFCP association handling, allowing sessions to be successively controlled by different SMFs of the same set to maintain service continuity.
- PFCP Association Setup Request with same Node ID TS 23.527CR0017
- Reestablishment of PFCP sessions after a UP function restart TS 23.527CR0018
- Enhancement to the PFCP Association Release Procedure TS 29.244CR0240
- Update the PFCP association setup to support UE IP address Allocation by AAA/DHCP TS 29.244CR0252
- PFCP sessions successively controlled by different SMFs of a same SMF set TS 29.244CR0261
- F-TEID in a PDR TS 29.244CR0278
+ 32 more changes
In Release 17, the F-SEID function was enhanced to support robust PFCP session restoration for both unicast and Multicast-Broadcast Services (MBS) following UPF or NG-RAN failures. This included new procedures for MBS session restoration upon MB-UPF failure, with or without restart, and for home-routed PDU sessions. Furthermore, the release specified that the UPF must set the SEID field to zero and include the old CP F-SEID in PFCP Session Report Requests when moving sessions between SMFs within an SMF set.
- Restoration of PFCP sessions affected by a partial or complete failure TS 23.527CR0030
- MBS session restoration upon MB-UPF failure with restart TS 23.527CR0041
- MBS session restoration upon MB-UPF failure without restart TS 23.527CR0042
- Restoration of a Broadcast MBS session upon NG-RAN failure with or without restart TS 23.527CR0048
- Restoration of a Multicast MBS session upon NG-RAN failure with or without restart TS 23.527CR0049
- Support of Broadcast MBS Session with an AMF set being deployed TS 23.527CR0056
+ 25 more changes
In Release 18, the F-SEID function was enhanced to support more robust session restoration procedures, specifically for split PDU sessions and for scenarios involving an SMF failure within an SMF set. The updates enable a UPF to proactively move a PFCP session to an alternative SMF by sending a Session Report Request with the old CP F-SEID when the original SMF is unresponsive. Furthermore, the release introduced procedures to exclude certain PFCP sessions, like those for RADIUS signaling, from restoration.
- Multicast MBS session (de)activation or update after an AMF failure TS 23.527CR0063
- Update N4 Session modification procedure to support network slice replacement feature TS 29.244CR0730
- PFCP extensions for HR-SBO PDU sessions TS 29.244CR0750
- TL-Containers in PFCP Session Modification/Deletion Request/Response TS 29.244CR0767
- ECN marking during PDU session establishment procedure TS 29.244CR0772
- Support of DL Session AMBR in HR-SBO session TS 29.244CR0824
+ 15 more changes
In Release 19, the F-SEID function was enhanced to support the restoration of PFCP sessions at an alternative SMF within an SMF set upon a failure. The UPF was enabled to move groups of PFCP sessions, identified by attributes like FQ-CSID or Group ID, to designated alternative SMFs using PFCP Session Report Request messages. Furthermore, mechanisms were introduced to allow an SMF to explicitly indicate that specific PFCP sessions should be excluded from such restoration procedures.
- Multicast MBS session restoration procedure for N3mb path failure TS 23.527CR0082
- PFCP sessions excluded from the restoration upon a SMF failure with SMF set being deployed TS 23.527CR0089
- PFCP sessions excluded from the restoration upon a SMF failure with SMF set being deployed TS 29.244CR0895
- Providing alternative SMF(s) per PFCP Session TS 29.244CR0911
- Clarification to the Multicast MBS session restoration procedure for NG-RAN restart TS 23.527CR0086
- Restore PFCP Sessions at an alternative SMF TS 23.527CR0091
+ 4 more changes
Explore further
Broader topics and technologies where F-SEID plays a role.
Defining Specifications
3GPP specifications that define or reference F-SEID, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.527 vj50 | 5G System Restoration Procedures | Rel-19 |
| TS 29.244 vj40 | PFCP Specification for Control/User Plane Separation | Rel-19 |