Support: SkyStation915LTE

The GRS (Ground Radio Station) uses SkyDM (SkyLine DataMux) to manage both link switching (between mediums/paths) and roaming (between multiple GRS within a medium). SkyDM is the key component that multiplexes the C2 links during a flight.

Link Switching
Link Switching chooses the primary link medium/paths (e.g., LTE vs Satcom) on the ground.
• Inputs: 1-second average of received user data on all links.
• Scope: Evaluates and switches between different link mediums/paths (e.g., LTE vs. Satcom).
• Prioritization: When the current active link becomes inactive (no data for >1 second), chooses an active link with the highest received rate (if multiple).
• Evaluation cadence: Every 1 second with double-hysteresis, consistent with muLTElink.
• Trigger: Switch occurs when a link is disqualified (0 user data, poor RSSI, or loss of connectivity).
• Behavior: Prioritizes stability with hysteresis to avoid unnecessary flapping.

Roaming (Within a Link)
Roaming chooses the lead GRS within a given link when multiple GRS are available.
• Scope: Roaming operates within a single link when multiple GRS are available.
• Inputs: Network connectivity status, RSSI strength, and reception of ARS heartbeats.
• Qualification: Each GRS is qualified using this combination of factors.
• Evaluation cadence: Every 1.5 seconds.
• Hysteresis: Single hysteresis applied to reduce unnecessary swaps.
• Selection: Chooses the lead GRS from qualified candidates; prefers strongest RSSI if all else equal.

Key Takeaway
• Primary vs. Lead distinction: Note that link switching chooses the primary link medium, while roaming chooses the lead GRS within that link.