stands for Service Level Agreement. Basically, an SLA is the minimum level of service that a carrier will deliver to you per your agreement. It is not a guarantee or an assurance that you will get that service. It means that when the service dips below that level, you can open a repair ticket. And when you collect enough of those, you can battle your way out of the service contract.
What about credits, you ask? Usually you have to catch your carrier breaking the SLA, report it to the carrier, collect a repair ticket, then submit the repair ticket for credit. How much credit? One day's billing. To put that into perspective: on a $900 per month service that is $30 per day. You will certainly spend more than one hour trying to collect that $30! I know some of you will say that it is the principle. Sure. But reality is that for your business to continue unabated, you have to look at the reward versus time.
Why get an SLA? Mostly, you want the SLA in order to get repair started in a reasonable time. Notice, I said started. The SLA for a T1 normally states a mean time to repair time of 4 hours, translated to that in most cases, the carrier will start repair efforts within 4 hours from creation of the repair ticket. That does NOT mean that it will be repaired in 4 hours - just that a tech will start looking at the problem.
As anyone with telecom experience will tell you, many times the LEC's tech will say, "It's all clear on our end. Did you check your equipment?"
This is one reason to use a telecom broker, agent or consultant (like say RAD-INFO INC). The telecom agent can help with repair escalation and managing the SLA. By "managing the SLA", I mean that the agent can collect the repair tickets and help to get the bigger issue resolved in order for you to get the service that the SLA promised or that you can get out of your contract without penalty. (If you have another carrier to move to that can provide a similar service level and offering.)
On August 31 a Service Level Agreement (SLA) for Comcast Business Class Trunks was announced. The SLA will assure current and prospective customers that service is highly available, and in the event of an outage, will be restored with priority. The SLA is mainly about credits and uptime, not repair time, latency, or any other measurement.