ISO/IEC 20000-1 backs up the service levels you promise

The services covered, who receives them, which components are delivered by other parties, and the demand and capacity assumptions behind each one.

Management ownership of service performance, a service management plan, objectives with measures, and accountability retained where parts of the service lifecycle sit with suppliers.

A service catalogue and agreements with defined targets, measurement method and reporting frequency, agreed with customers rather than published at them.

Incident and service request handling with prioritisation and escalation, major incident procedure, and problem management that finds underlying causes and removes them.

Change control with assessment, approval and back-out, configuration information kept accurate, release and deployment discipline, and availability, capacity and service continuity planned and tested.

Service reporting against targets, supplier performance reviewed, internal audits and management review conducted, and improvements recorded, prioritised and closed with evidence.