An SLA is a formally negotiated agreement between two parties. It is a contract that exists between customers and their service provider, client or between service providers. It records the common understanding about services, priorities, responsibilities, guarantee, and such — collectively, the level of service. For example, it may specify the levels of availability, serviceability, performance, operation, or other attributes of the service like billing and even penalties in the case of violation of the SLA.
Service Level Agreements can contain numerous service performance metrics with corresponding service level objectives. A common case in IT Service Management is a call center or service desk. Metrics commonly agreed to in these cases include:
ABA (Abandon Rate): Percentage of calls abandoned while waiting to be answered.
ASA (Average Speed to Answer): Average time (usually in seconds) it takes for a call to be answered by the service desk.
TSF (Time Service Factor): Percentage of calls answered within a definite timeframe, e.g. 80% in 20 seconds.
FCR (First Call Resolution): Percentage of incoming calls that can be resolved without the use of a callback, or without having the caller call back the helpdesk to finish resolving the case.
TAT (Turn Around Time): Time taken to complete a certain task.
Uptime Agreements are another very common metric, often used for data services such as shared hosting, virtual private servers and dedicated servers. Common agreements include percentage of network uptime, power uptime, amount of scheduled maintenance windows etc.