by Gary Audin
The Service Level Agreement (SLA) is a contractual agreement between a service provider and customer that defines the expected level of service delivered by a service provider. The purpose of a SLA is to specify and define what the customer will receive as part of the service. SLAs do not define how the service itself is provided or delivered. The service implementations may change during the term of the SLA.
What is in a SLA?
The SLA should clearly define and delineate what services are being provided under the agreement. The SLA should define the metrics used to determine if the SLA is being satisfied. The levels of service should cover:
- Reliability and availability can be defined quantitatively. Availability can be defined as 99.XXX% uptime.The definitions should define the percentage of uptime as well as limit the downtime and time to restore service.
- Responsiveness by the provider not only covers the time it takes to respond to an outage but also the time it takes to accept requests, schedules, and meet service dates. Service dates would include service installation and termination.
- There should be well-defined procedures for reporting problems. Who is to be contacted, how will the problem to be reported (phone call, email, instant message, or certified letter). What other steps can be taken that allow the resolution to be promptly and efficiently implemented.
- The customer should be monitoring delivery of the SLA’s. The provider must have the ability to monitor the SLA’s. This is not always true. Confirm the provider can produce the SLA metrics. If the customer believes the SLA is not being met, what data needs to be collected? Can the customer access the monitoring systems and performance data of the provider?
- Assuming an SLA is not satisfied what does a customer have to do to report their dissatisfaction? How fast does the provider respond to those reports? Even though the provider may have measurements, does a customer have to show independent measurements to qualify for credits? Are they purely credits? Or can the customer receive a check? Are credits given immediately within 30 days or spread over a longer time period? If the SLA’s are not met, can the customer terminate the service without penalties?
- You need to determine if there any escape clauses or constraints to the SLA. Are there circumstances under which the SLA promises do not apply? Are their exemptions for things like a flood, fire, terrorism, pandemic, or other situations?
What to Measure?
There are four areas to measure in a SLA. The one most people think about is the availability of a service. How often is a service down and service restored? Part of that availability is how you define and quantify the degradation of service such as service is failing, but not failed. How well does the SLA cover provisioning and installation? The fourth area is important to voice and video; the quality of transmission. The remainder this blog focuses on the first area, availability.
Defining Availability
This is the availability formula:
Availability = MTBF X 100 = 99.XXX%
_________
MTBF + MTTR
where MTBF is the mean time between failures and MTTR is mean time to repair, both measured in hours. What you want is the time to restore service, not repair. Don’t forget you have to test the restored service and initialize/reboot your devices. So the actual restoration time will be longer than what the SLA specifies. BTW, the definition of mean is that 50% of the outages and restorations will longer or shorter, it is not the average time.
It is easy to report an absolute outage. But what if an outage is actually degradation or partial loss of service or application access to some but not all users? Is there a standard that can cover this? Yes, ANSI T1.231. See “Keeping Pace with the T1.231 Evaluation” http://www.eetimes.com/document.asp?doc_id=1207335
T1.231 provides the foundation for telephony and data interfaces. The objectives are to ensure the connection operation is known at both ends. The second objective is to ensure that data is only transmitted when appropriate. The third part is to provide tools to verify and resolve problems when there are hard failures or soft failures or when there is gradual or intermittent degradations. The standard also defines when interface data needed from multiple technologies (T1/DS1, Metro Ethernet Broadband, MPLS…). It provides information when multiple providers are involved. Does you provider reference ANSI T1.231?
SLA Demarcation
Where does the availability SLA start and end? The demarcation points may not include the local access connection. If multiple providers are included, does the SLA only cover only one provider? It should not matter whether the information being transmitted on-net or off-net. Availability should be measured from the customer point of view.
What is not included in the SLA? Some providers exclude fiber cuts, but do not define what a fiber cut is. Be aware of vague descriptions of exceptions to the SLA. A major cloud provider suffered an outage that lasted days. When the customers read their SLAs, they learned that under that particular set of outages, they were not covered nor given credits. There was no recourse. In another case, the provider wanted information from the customer to demonstrate the effect of the outages. The workload was so great that the cost of detailed reporting was more than the credits.
These kinds of exceptions point out that when providers discuss availability, you should be asking these questions:
- What is the definition of usable service and who determines it?
- There may be definitions in the terms of complete loss of use vs. usability. What’s in your SLA?
- Who measures and how is service availability measured?
- What are the SLA conditions (start of service, after 30 days operation…)?
- What are the credits and are they worth pursuing?
Source: TelecomReseller
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