Architecture Decision Record
ADR: Fixed Line and 5G as Monitored Site Redundancy
Decision framework for carrier-diverse fixed-line and 5G redundancy with monitoring, failover policies, testing, and explicit limitations.
Core answer
Anexum combines fixed line and 5G as redundancy only when both paths are assessed separately, monitored continuously, and tested regularly. The architecture prioritizes controlled recovery over blanket zero-downtime promises and documents dependencies on carriers, routers, IP design, and applications.
What problem is being decided?
A site needs a second access path that remains usable when the primary path fails or degrades severely. The decision covers access technology, carrier, router, SIM, IP addressing, permitted traffic, monitoring, escalation, and testing.
What decision was made?
The preferred design uses a fixed-line primary path and an LTE/5G backup path from a separate carrier where local coverage and shared upstream dependencies do not create material correlation. Both paths are inventoried and monitored as separate services.
Why is a second contract insufficient?
Two contracts can share the same wholesale network, building entry, power supply, or router. Redundancy is therefore assessed across physical, logical, commercial, and operational dependencies rather than provider names alone.
Which measurements are required?
The minimum set includes reachability, latency, jitter, packet loss, signal quality, router state, active WAN path, and the date of the last successful test. Bandwidth and data usage are added where the backup plan or application requires them.
How are failover policies defined?
Critical applications, DNS, VPN, voice, remote access, and large transfers are considered separately. The backup path can carry all traffic or only prioritized services. The decision is documented for each site.
How is the design tested?
A planned test disconnects the primary path in a controlled way and checks switching, DNS, VPN, critical applications, failback, and alerting. Results, deviations, and follow-up actions are recorded with timestamps.
Which limitations remain?
Mobile service can be affected by radio cells, buildings, power, CGNAT, plan restrictions, weather, or regional incidents. Session preservation, static IP, and uninterrupted switching are promised only when the design and application demonstrably support them.
When is the decision reviewed?
The decision is reviewed after carrier, router, or firmware changes, site construction, a new critical application, material traffic changes, repeated test failures, or relevant changes in local coverage.