US-12628050-B2 - Technique for performing a context transfer

US12628050B2US 12628050 B2US12628050 B2US 12628050B2US-12628050-B2

Abstract

A technique for performing a context transfer from a first session management entity to a second session management entity in a mobile communication system is provided, wherein the context transfer concerns a data session associated with a User Equipment, UE, wherein the data session is handled by the first session management entity via a first gateway entity and wherein, after the context transfer, the data session is to be handled by the second session management entity via a second gateway entity. A method implementation of the technique is performed by the second session management entity and comprises, while the UE is in an inactive state, triggering (S 302 ) sending, to the second gateway entity, a session establishment request to establish a new session handling the data session via the second gateway entity, and triggering (S 304 ) providing, to the second gateway entity, an old Internet Protocol, IP, address assigned to the UE as part of an old session handling the data session via the first gateway entity, requesting the second gateway entity to assign the old IP address to the UE as part of the new session, besides a new IP address assigned to the UE as part of the new session, and, when the UE enters an active state from the inactive state, triggering (S 306 ) providing the new IP address to the UE.

Inventors

Attila Mihály
Maria Cruz Bartolomé Rodrigo

Assignees

TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

Dates

Publication Date: 20260512
Application Date: 20200401
Priority Date: 20200218

Claims (18)

1 . A method for performing a context transfer from a first session management entity to a second session management entity in a mobile communication system, the context transfer concerning a data session associated with a User Equipment (UE), the data session handled by the first session management entity via a first gateway entity and, after the context transfer, the data session handled by the second session management entity via a second gateway entity, the method being performed by the second session management entity and comprising: while the UE is in an inactive state: triggering sending, to the second gateway entity, a session establishment request to establish a new session handling the data session via the second gateway entity; triggering providing, to the second gateway entity, an old Internet Protocol (IP) address assigned to the UE as part of an old session handling the data session via the first gateway entity, and requesting the second gateway entity to assign the old IP address to the UE as part of the new session, besides a new IP address assigned to the UE as part of the new session; receiving, from the second gateway entity, tunnel endpoint information regarding the second gateway entity, the tunnel endpoint information comprising a tunnel endpoint identifier of a radio access node and the second gateway entity that is to be used by the first gateway entity; and triggering providing the tunnel endpoint information to the first gateway entity and requesting the first gateway entity to forward DL packets directed to the old IP address to the second gateway entity for further delivery to the UE; and when the UE enters an active state from the inactive state, triggering providing the new IP address to the UE.
2 . The method of claim 1 , wherein, in the inactive state, the UE is in at least one of an unconnected Non-Access Stratum (NAS) state and an inactive Radio Resource Control (RRC) state and wherein, in the active state, the UE is in a connected NAS state and in an active RRC state.
3 . The method of claim 1 , wherein triggering providing the new IP address to the UE is performed after the UE has stopped exchanging traffic.
4 . The method of claim 1 , wherein the first gateway entity maintains forwarding downlink (DL) packets directed to the old IP address according to a forwarding rule by which DL packets directed to the old IP address have been forwarded prior to providing the old IP address to the second gateway entity.
5 . The method of claim 1 , wherein the tunnel endpoint information is provided to the first gateway entity via the first session management entity, and wherein the tunnel endpoint information is included in a context request for the data session sent from the second session management entity to the first session management entity.
6 . The method of claim 5 , wherein the context request for the data session includes a gateway change indication indicating to the first session management entity to request the first gateway entity to forward DL packets directed to the old IP address to the second gateway entity for further delivery to the UE.
7 . The method of claim 1 , further comprising, while the UE is in the inactive state, triggering providing the tunnel endpoint information to a mobility management entity requesting the mobility management entity to configure, using the tunnel endpoint information, an Access Network (AN) node to forward uplink (UL) packets arriving from the UE to the second gateway entity.
8 . The method of claim 1 , further comprising, while the UE is in the inactive state, triggering providing a time indication to the first gateway entity, optionally via the first session management entity, indicating a maintenance time until which a packet forwarding state associated with the old session is at least to be maintained by the first gateway entity.
9 . The method of claim 1 , wherein the old IP address is provided to the second gateway entity in a session modification request sent to the second gateway entity to modify the new session.
10 . A method for performing a context transfer from a first session management entity to a second session management entity in a mobile communication system, the context transfer concerning a data session associated with a User Equipment (UE) the data session handled by the first session management entity via a first gateway entity and, after the context transfer, the data session handled by the second session management entity via a second gateway entity, the method being performed by the second gateway entity and comprising: while the UE is in an inactive state: receiving, from the second session management entity, a session establishment request to establish a new session handling the data session via the second gateway entity; triggering establishing the new session; receiving, from the second session management entity, an old Internet Protocol (IP) address assigned to the UE as part of an old session handling the data session via the first gateway entity; receiving, from the second gateway entity, tunnel endpoint information regarding the second gateway entity, the tunnel endpoint information comprising a tunnel endpoint identifier of a radio access node and the second gateway entity that is to be used by the first gateway entity; and triggering providing the tunnel endpoint information to the first gateway entity and requesting the first gateway entity to forward DL packets directed to the old IP address to the second gateway entity for further delivery to the UE; and triggering assigning the old IP address to the UE as part of the new session, besides a new IP address assigned to the UE as part of the new session, the new IP address provided to the UE when the UE enters an active state from the inactive state.
11 . The method of claim 10 , wherein, in the inactive state, the UE is in at least one of an unconnected Non-Access Stratum (NAS) state and an inactive Radio Resource Control (RRC) state and wherein, in the active state, the UE is in a connected NAS state and in an active RRC state.
12 . The method of claim 10 , wherein the new IP address is to be provided to the UE after the UE has stopped exchanging traffic.
13 . The method of claim 10 , wherein the first gateway entity maintains forwarding downlink (DL) packets directed to the old IP address according to a forwarding rule by which DL packets directed to the old IP address have been forwarded prior to receiving the old IP address from the second session management entity.
14 . The method of claim 10 , further comprising: receiving, from the first gateway entity, DL packets directed to the old IP address; and triggering delivering the DL packets to the UE.
15 . The method of claim 10 , wherein the old IP address is received from the second session management entity in a session modification request to modify the new session.
16 . A method for performing a context transfer from a first session management entity to a second session management entity in a mobile communication system, the context transfer concerning a data session associated with a User Equipment (UE), the data session handled by the first session management entity via a first gateway entity and, after the context transfer, the data session handled by the second session management entity via a second gateway entity, the method being performed by the first session management entity and comprising: while the UE is in an inactive state: triggering providing, to the second session management entity, an old Internet Protocol (IP) address assigned to the UE as part of an old session handling the data session via the first gateway entity, the old IP address is to be provided to the second gateway entity requesting the second gateway entity to assign the old IP address to the UE as part of a new session established by the second gateway entity for handling the data session via the second gateway entity, besides a new IP address assigned to the UE as part of the new session, the new IP address provided to the UE when the UE enters an active state from the inactive state; receiving, from the second gateway entity, tunnel endpoint information regarding the second gateway entity, the tunnel endpoint information comprising a tunnel endpoint identifier of a radio access node and the second gateway entity that is to be used by the first gateway entity; and triggering providing the tunnel endpoint information to the first gateway entity and requesting the first gateway entity to forward DL packets directed to the old IP address to the second gateway entity for further delivery to the UE.
17 . The method of claim 16 , wherein, in the inactive state, the UE is in at least one of an unconnected Non-Access Stratum (NAS) state and an inactive Radio Resource Control (RRC) state and wherein, in the active state, the UE is in a connected NAS state and in an active RRC state.
18 . A method for performing a context transfer from a first session management entity to a second session management entity in a mobile communication system, the context transfer concerning a data session associated with a User Equipment (UE) the data session handled by the first session management entity via a first gateway entity and, after the context transfer, the data session handled by the second session management entity via a second gateway entity, the method being performed by the first gateway entity and comprising: while the UE is in an inactive state: receiving, from the first session management entity, a session release request to release an old session handling the data session via the first gateway entity, an old Internet Protocol (IP) address assigned to the UE as part of the old session, the old IP address being provided to the second gateway entity requesting the second gateway entity to assign the old IP address to the UE as part of a new session being established by the second gateway entity for handling the data session via the second gateway entity, besides a new IP address assigned to the UE as part of the new session, the new IP address provided to the UE when the UE enters the active state from the inactive state; receiving, from the second gateway entity, tunnel endpoint information regarding the second gateway entity, the tunnel endpoint information comprising a tunnel endpoint identifier of a radio access node and the second gateway entity that is to be used by the first gateway entity; and triggering providing the tunnel endpoint information to the first gateway entity and requesting the first gateway entity to forward DL packets directed to the old IP address to the second gateway entity for further delivery to the UE; and maintaining a packet forwarding state associated with the old session at least until an expected time at which the UE enters an active state from the inactive state.

Description

TECHNICAL FIELD The present disclosure generally relates to mobile communication systems. In particular, a technique for performing a context transfer from a first session management entity to a second session management entity in a mobile communication system is presented. The technique may be embodied in methods, computer programs, apparatuses and systems. BACKGROUND Mobile communication systems of the fifth generation (5G), especially their Core Network (CN) architectures, generally make use of the Service Based Architecture (SBA) paradigm in which each Network Function (NF) may provide—as a “producer”—one or more “services” to one or more “consumers”. NF services represent self-contained functionalities that can be modified in an isolated manner without affecting others. In order to cover the possibility of transferring context/session data from a source NF service to a target NF service (e.g., of a different vendor), to thereby be able to resume processing in the target NF service, standardization of a context transfer procedure was taken into consideration in recent 3GPP discussions. Besides some generic operations for context transfer, a method for Session Management Function (SMF) context transfer has been agreed which is illustrated in FIGS. 1a and 1b (e.g., described in 3GPP Change Request S2-1908169 “Update SM context transfer procedure”). As shown in the figure, in step 1, Session Management (SM) context transfer is initiated at the old SMF, e.g., triggered by Operations & Management (O&M), and, in step 2, the old SMF may subscribe to events at the Access and Mobility Management Function (AMF) to be notified when the User Equipment (UE) status enters the CM-IDLE state or the CM-CONNECTED with Radio Resource Control (RRC) inactive state, as defined in 3GPP TS 23.501, such as 3GPP TS 23.501 v16.1.0, for example. The AMF may then wait until the UE becomes CM-IDLE or RRC inactive (i.e., enters an inactive state in the sense of the present disclosure, as will be discussed further below) and send a corresponding notification to the old SMF in step 3. In step 4, the old SMF triggers the actual context transfer procedure by sending an Nsmf_PDUSession_SMContextStatusNotify message to the AMF including an SMF transfer indication as well as a new SMF ID (or SMF set ID) and a Protocol Data Unit (PDU) session ID of the current PDU session associated with the UE. In step 5, the AMF uses the new SMF ID (or SMF set ID) to select the new SMF and sends an Nsmf_PDUSession_CreateSMContext request to the new SMF, requesting the new SMF to establish a context with the same PDU session ID. In step 6, the new SMF sends an Nsmf_PDUSession_ContextRequest request to the old SMF to obtain the context for this PDU session. In step 7, the old SMF releases the N4 session established with the User Plane Function (UPF) (the N4 session being the session established on the N4 interface between the SMF and the UPF which handles the PDU session) by sending a flag notifying the UPF about the expected reestablishment of the N4 session for the same PDU session. In step 8, the old SMF sends an Nsmf_PDUSession_ContextRequest response to the new SMF with the requested SM context in response to the request of step 6. The SM context may include the Internet Protocol (IP) address of the UE if the PDU session is of type IPv4, IPv6 or IPv4v6, for example. If the new SMF is able to transfer the SM context, the new SMF may set up a new policy association towards the Policy Control Function (PCF) in step 9. In step 10.1, the UPF may receive an N4 session establishment request from the new SMF for the same PDU session and, in step 10.2, the new SMF may perform a reestablishment of the N4 session with the UPF (establishing a new N4 session), wherein all information related to the N4 session of the old SMF that is not used by the N4 session of the new SMF is removed from the UPF. In step 11, the new SMF may register at the User Data Management (UDM) function and subscribe to subscription changes for the UE in step 12. As the context transfer is then complete, the new SMF sends, in step 13, an Nsmf_PDUSession_CreateSMContext response to the AMF in response to the request of step 5 and, in step 14, the UDM notifies the old SMF that it is deregistered for the PDU session. If an error occurred in the above context transfer, the old SMF may optionally reestablish the N4 session with the UPF in step 15 and the procedure may end here. Otherwise, in step 16, the old SMF may remove its policy association with the PCF and, finally, in step 17, the old SMF releases all internal resources corresponding to the PDU session. Subscribers to SMContextStatusNotify for the transferred SM context (see step 4) are notified of the context transfer and optionally of the new location of the transferred SM context. The above context transfer procedure does not deal with cases when the context transfer cannot be achieved with the same UPF, however, i.e., with cases when the