Deferred Leg Linking in PCRF During Handover
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Solution Overview
Problem
During handover from one access technology to another in telecommunications networks, the Policy and Charging Rules Function (PCRF) incorrectly links Gateway Control Sessions (GCS) to existing IP-CAN sessions due to unknown handover states, leading to inconsistencies in signaling order between Gxx and Gx interfaces.
Innovation Solution
Incorporating a new indication in the Gateway Control Session (GCS) establishment message to defer leg linking until corresponding control signaling is received over the Gx interface, ensuring that the PCRF waits for confirmation from the Packet Data Network Gateway (PDN-GW) before linking sessions, thereby maintaining the temporal order between Gxx and Gx signaling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the PCRF creates a GCS before receiving handover confirmation on Gx interface, then the signaling order is simplified and implementation is easier, but the PCRF incorrectly links the GCS to the wrong IP-CAN session when handover state is unknown
Solution Approach 1:
The PCRF performs preliminary actions by creating the GCS in advance before receiving handover confirmation on the Gx interface. This preliminary creation simplifies the signaling order and implementation complexity, while the deferred leg linking mechanism ensures accurate session association later when handover confirmation is received.
Solution Approach 2:
The patent introduces an intermediary mechanism (deferred leg linking indicator and timer) that mediates between the early GCS creation and the later handover confirmation. This intermediary allows the system to decouple the timing of GCS creation from handover confirmation receipt, enabling both early creation for simplicity and accurate linking for reliability.
2Reliability
If the PCRF waits for handover confirmation on Gx interface before creating GCS, then session linking accuracy is improved, but the signaling complexity and implementation difficulty increase
Solution Approach 1:
The GCS is created in advance as a preliminary action before handover confirmation is received. This preliminary creation avoids the need for complex waiting logic and signaling sequences, while the deferred leg linking ensures accurate session association when confirmation is eventually received.
Solution Approach 2:
The leg linking operation is made dynamic by deferring it until the appropriate moment when handover confirmation is received on the Gx interface. This dynamic timing resolution allows the system to maintain simple signaling flow while achieving accurate session linking when the timing is right.
3Difficulty of detecting and measuring
If a timer is started to determine handover state, then the ability to detect handover is improved, but the time required for session establishment increases
Solution Approach 1:
The GCS is created in advance as a preliminary action before the timer expires or handover is confirmed. This preliminary creation eliminates waiting time during session establishment, while the timer continues to run in the background to detect handover state for accurate leg linking.
Solution Approach 2:
The timer operation continues continuously in the background without interrupting the GCS creation and session establishment process. This continuous operation maintains handover detection capability while allowing session establishment to proceed without delay, as the timer works independently parallel to the session setup.
Data Source
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AI summary
The present invention relates to a solution for handling deferred leg linking in policy and charging rules function in a telecommunications network in relation to handover between two different access technologies. The solution is provided as a nodes, system and a method for handling handover of a user equipment, i.e. UE, (101) in a telecommunications network (100) from one access technology to another access technology, comprising the steps of detecting (203) in a target access gateway, i.e. AGW, (102) that a handover state of the UE is unknown, sending (204) from the target access gateway a gateway control session, i.e. GCS, establishment message to a policy and charging rules function node (105), wherein the message comprise an indication that leg linking of a session is to be deferred until reception of corresponding control signalling from a packet data network gateway (104).