Heikki Lindholm , Lirim Osmani , Sasu Tarkoma , Hannu Flinck*, Ashwin Rao  State Space Analysis to Refactor the Mobile Core  University of Helsinki *Nokia Networks

Home Subscriber Server (HSS) Serving Gateway (SGW) Evolved Node B (eNodeB) Network Functions in LTE Networks Policy Control & Charging Function (PCRF) Mobility Management Entity (MME) User Equipment (UE) Internet Mobile Network Radio Access Network Mobile Core Packet Data Network Gateway (PGW) 2 / 12

Shortcomings of current architecture – Signaling Storm – Stateful gateways Demands from network operators – Reduce costs – Move functionality close to radio access network Motivation for Refactoring Serving Gateway (SGW) Evolved Node B (eNodeB) Packet Data Network Gateway (PGW) 3 / 12 With virtualization at our disposal, can we simplify the architecture?

Forwarding Element Forwarding Element A Desirable Architecture Policy Manager User Equipment (UE) Internet Mobile Network Radio Access Network Mobile Core Forwarding Element Control Plane User Plane Logically Centralized Controller Forwarding rules govern where packets are forwarded Program forwarding elements to comply with the policy 4 / 12 How do we refactor the mobile core?

Device ID Radio State Location Control-plane State User-plane State Grouping of State Variables Abstracting usage of state variables 5 / 12

Initial Attach Idle Wake-up Mobility Service Request … many more Procedures using State Variables Paper 6 / 12

Network FunctionDevice IDLocationRadio State Control- plane State User-plane State eNodeB ✔✔✔✔✔ MME ✔✔✗✔✔ SGW ✔✔✗✔✔ PGW ✔✔✗✔✔ HSS ✔✗✗✔✔ PCRF ✔✔✗✗✔ State Variables after Attach Network Functions replicate state variables 7 / 12

Network FunctionLocationControl-plane StateUser-plane State eNodeBP-PCPC MMEPCPCPC SGW-CPCPC PGW-CPCPC HSS---CP- PCRF-C--PC How are State Variables Replicated? P : Producer C : Consumer Can we group the Producers? Can we move Consumers close to the Producers?  Take decisions at Producers? 8 / 12

Module for managing each variable group – Multiple variable groups modified in each procedure – Incurs additional signaling between modules Module to serve each procedure – Merge modules from network functions that serve the same procedure – Flexibility to determine physical location of modules Approaches to Refactor 9 / 12

Forwarding Element Forwarding Element Proposed Architecture Policy Manager User Equipment (UE) Internet Mobile Network Radio Access Network Mobile Core Forwarding Element Control Plane User Plane Mobile Core Control Agent Logically Centralized Mobile Core Controller Attach Idle Wake Mobility Attach Idle … … 10 / 12 Publish Subscribe SHIM for backward compatibility

Formal Analysis – Analyze dependency network of Procedures and State Variables – Essential to gather insights on the requirements from the mobile core Simulations/Emulations – Modifying LTE simulator/emulator Next Step 11 / 12

Can we leverage virtualization technologies to simplify the architecture of the mobile core? Abstract the state variables Producer/Consumer relationship between network functions Pub-sub architecture to serve the mobile core Conclusion 12 / 12

Thank You! State Space Analysis to Refactor the Mobile Core University of Helsinki Nokia Networks

Backups

Route packets Control network access Support client mobility Provide network security Manage network functions Main Functions of the LTE Core

Modularity based on Abstraction 16 / 12

Why should future network functions be based on the existing protocol interactions? 17 / 12

What do we gain from a refactored centralized control plane? 18 / 12

Could you have reached the same architecture by considering the generic functions that any mobile network will need? 19 / 12

Network Access Control Packet Routing and Transfer Mobility Management Security Network Management Main Functions of the Core

Complete List of Procedures

1) Device ID Primary keys in device/subscription lookups IMSI, GUTI, … 2) Location Cell level location information TAI, Tracking area list, ECGI, … 3) Radio Session State Radio link related information C-RNTI, DRB, AS security context, … 4) Control-plane State Identifiers for control plane connections S5/S8/… IPs and TEIDs, NAS security context, … 5) User-plane State User-plane state identifiers S1u/S5u/…, QoS, bearer info, … Grouping of State Variables

– Is this the best grouping? – Why not consider events first? – Backward compatibility issues? – What about other procedures? TODO: Backups

Serving Gateway (SGW) Evolved Node B (eNodeB) Network Functions in LTE Networks Policy Control & Charging Function (PCRF) Mobility Management Entity (MME) Home Subscriber Server (HSS) User Equipment (UE) Internet Mobile Network Radio Access Network Mobile Core Packet Data Network Gateway (PGW) Control Plane User Plane