The fallback is not independent

In most firms the telephony channel is the fallback for digital. If the app or online banking fails, customers can call.

In the Operational Resilience model, Telephony Service Delivery depends directly on four elements: Customer Applications, Network Infrastructure, Legacy Core Banking and Identity Management Systems. Digital Service Delivery also depends directly on Customer Applications and Identity Management Systems, and on Network Infrastructure through Customer Applications and Cloud Infrastructure.

So when Network Infrastructure fails, the fallback fails with the channel it backs up. The disruption reaches Telephony Service Delivery by two routes at once: directly from the network, and through Customer Applications.

A dependency map can record the digital channel and the telephony channel as two entries. It does not test whether one is structurally separate from the other. The upstream view does: it lists everything that can reach a service, direct and indirect.