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Topology Setup

The Two-Tier Architecture introduces a hierarchical User Plane structure, distinguishing between two kinds of UPFs:

  • Edge UPFs (acting as Uplink Classifiers or UL-CLs)
  • Centralized UPFs (acting as PDU Session Anchors or PSAs).

This architecture models a more realistic national-wide mobile network deployment where traffic can be routed locally or forwarded to a regional/central anchor.

graph LR
    UE([UE])
    gNB([gNB])
    EdgeUPF(["Edge UPF (UL-CL)"])
    PSA(["Centralized UPF (PSA)"])
    UE -- NR interface (closest) --> gNB
    gNB -- N3 interface (closest) --> EdgeUPF
    EdgeUPF -- N9 Interface (closest) --> PSA

Architecture Components

  1. Edge UPF (UL-CL): Located close to the gNBs. Aggregates traffic from multiple base stations. In this simulation, these are the "Distributed UPFs" defined in the scenario.
  2. Centralized UPF (PSA): Regional anchors. Each Edge UPF connects to the nearest Centralized UPF. These are defined by num_centralized_upfs.

Configuration

To enable this mode, update your config.toml:

config.toml
[simulation]
# ... other settings ...

# Architecture Configuration
scenario_mode = "two_tier" 
num_centralized_upfs = 5 # Number of Centralized UPFs (PSAs) to generate

Defining Scenarios

The scenario definition remains similar to the Single-Tier mode, but the "Number of UPFs" specified in the scenario now refers to the Edge UPFs.

config.toml
[countries.spain.scenarios]
# "Spain Distributed" = 52 Edge UPFs
"Spain Distributed" = 52

The simulator performs Hierarchical K-Means Clustering: 1. gNBs -> Edge UPFs: gNBs are clustered into N regions (where N is the scenario value, e.g., 52). 2. Edge UPFs -> Centralized UPFs: The locations of the Edge UPFs are then clustered into num_centralized_upfs regions (e.g., 5) to place the PSAs.

Visualization

The network graph will show two layers of UPF nodes: Edge UPFs (Black Squares) and Centralized UPFs (Purple Diamonds), connected by the N9 Interface (Purple Dashed Lines).

Topology Map Topology Map Spain

Network Graph Network Graph Spain

Topology Map Topology Map USA

Network Graph Network Graph USA