Correlation ID for Local IP Access in Femtocells
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Solution Overview
Problem
Current Local IP Access (LIPA) solutions face challenges in defining optimal routing information, operating behind Network Address Translation (NAT) devices, assisting lawful intercept, and optimizing paging mechanisms, particularly in femtocell scenarios, where the distinction between uplink and downlink packets and gateway selection are unclear, leading to inefficiencies and errors.
Innovation Solution
The implementation of a direct path enablement method in a home cellular base station (HeNB) using a collocated Local PDN Gateway (L-GW) function, which signals S5 PGW TEID or S5 PGW GRE parameters for optimal routing, secures the backhaul with IPsec tunnels, and enhances user subscription records to associate APNs with Closed Subscriber Group (CSG) IDs for accurate gateway selection, thereby addressing the issues of optimal routing, NAT operation, lawful intercept, and paging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If LIPA solutions use local PDN connection with femtocell, then local network access is enabled, but routing information definition and gateway selection become unclear
Solution Approach 1:
The patent introduces a correlation ID as an intermediary element that links the UE context in the core network with the local PDN connection at the femtocell. This correlation ID acts as a mediator that carries routing information through the network, enabling clear gateway selection and packet routing without requiring complex local routing definitions at the femtocell side.
Solution Approach 2:
The patent performs preliminary actions by establishing the correlation ID during the PDN connection setup phase, before actual data transmission begins. The MME pre-configures the correlation ID in the UE context and ensures it is available for subsequent packet routing, eliminating the need for complex real-time routing decisions during data transmission.
2Adaptability or versatility
If LIPA operates behind NAT devices, then network address translation is achieved, but packet routing and gateway selection become ambiguous
Solution Approach 1:
The correlation ID serves as an intermediary that preserves routing information through the NAT device. Since the correlation ID is carried within the packet structure and maintained by the MME and femtocell, it survives the NAT translation process, enabling the network to identify and route packets correctly even after they have passed through NAT devices that would otherwise obscure the original routing information.
3Productivity
If uplink and downlink packets are not distinguished, then packet processing is simplified, but optimal routing cannot be achieved
Solution Approach 1:
The patent applies local quality by making the packet processing approach direction-dependent. For uplink packets (UE to network), the correlation ID is used to match with the UE context and determine the appropriate local PDN gateway. For downlink packets (network to UE), the correlation ID similarly guides routing but through reverse lookup. This directional differentiation ensures optimal routing for each traffic flow while maintaining efficient processing through the unified correlation ID mechanism.
4Reliability
If paging mechanisms are not optimized, then paging coverage is maintained, but paging efficiency in femtocell scenarios deteriorates
Solution Approach 1:
The patent implements feedback mechanisms where the MME uses the correlation ID to determine whether a UE is connected to a femtocell or macrocell based on the local PDN connection information stored in the UE context. This feedback allows the network to optimize paging behavior - paging only in the femtocell when appropriate, rather than broadcasting across the entire network, thereby maintaining reliable paging coverage while significantly improving paging efficiency.
Data Source
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AI summary
The invention relates to a home cellular base station (HeNB), comprising a radio interface (RI), to communicate with a user equipment (UE), a local interface (LI), to communicate with a local gateway (L-GW) providing access to a local IP network, a user plane interface (S1-U), to communicate with a serving gateway (SGW), and a control plane interface (S1-MME), to communicate with a control node (MME). The home cellular base station (HeNB) further comprises a selection module (SelMod) set to obtain a first correlation ID for enabling a direct user plane path between the home cellular base station (HeNB) and the local gateway (L-GW), the first correlation ID being obtained via the control plane interface (S1-MME) upon each establishment of a bearer providing access to the local IP network. The invention also relates to a control node (MME), to a home subscriber server (HSS), to a direct path enablement method, and to a PDN management method.