Functional Requirements Document (FRD) – Dual SIM Support

Feature: Dual SIM Management in zWAN SDWAN CPE
Version: 0.9

1. Objective

Enable robust and intelligent management of dual SIMs (physical or eSIM), with seamless failover based on a comprehensive health scoring mechanism, user preferences, and network conditions.

2. Functional Requirements

2.1 SIM Switching Capability

FR-2.1: Allow manual SIM switching via UI/API/CLI.
FR-2.2: Display the currently active SIM, its APN, and connection status.
FR-2.3: If the modem does not support Dual SIM, then it should function with Single SIM.

2.2 Automatic Failover Based on Health Score

FR-3: Monitor each SIM’s link health using a calculated Health Score.

FR-4: Health Score must include:

• FR-4.1: Ping test results (Latency, Packet Loss)
• FR-4.2: Signal Strength (RSSI, RSRP/RSRQ)
• FR-4.3: SIM Switch History (prevent flip-flopping; next auto-switch is blocked for 1 hour, configurable)
• FR-4.4: SIM Registration/Connection Failures
• FR-4.5: Data Plan Usage
• FR-4.6: Time of Day
• FR-4.7: Day of the Week
• FR-4.8: User-defined thresholds (optional)

FR-5: If the health score falls below threshold or fails, switch to the alternate SIM.
FR-6: If both SIMs are poor, revert to the preferred SIM and notify admin.

2.3 User-Defined Preferred SIM

FR-7: Allow setting of Preferred SIM (SIM1 or SIM2) via UI/API/CLI.
FR-8: Preferred SIM will be used as fallback if both SIMs are equally poor.

2.4 Multi-SIM APN Configuration

FR-9: Each SIM must support individual APN settings:

• APN Name
• Username
• Password
• Authentication Type

FR-10: APN settings must persist and apply correctly during SIM switching.

2.5 SIM Type Support

FR-11: Support the following combinations:

• FR-11.1: Two physical SIMs
• FR-11.2: One physical + one eSIM
• FR-11.3: Two eSIMs

2.6 eSIM Profile Management

FR-12: Support eSIM provisioning (download/activation) via UI/API.
FR-13: eSIM profiles retain their unique APN and connection settings.
FR-14: Allow deletion of unused eSIM profiles.

3. Other Functional Requirements

FR-15: SIM switch latency must be < 30 seconds.
FR-16: Health score evaluation interval must be configurable (default: 60 seconds).
FR-17: Log all SIM switch events and reasons for audit/debugging.