How to enforce a carrier SLA with proof
To claim against a carrier's SLA, the company has to show, outage by outage, what happened and when: the time, the number called, the SIP code, the Q.850 cause and the downtime, with maintenance already subtracted. An outage a customer noticed is hard to prove; one a test recorded is hard to dispute.
Summary
- The claim starts in the contract: the measurement period, what counts as unavailability, the maintenance window and who measures.
- The proof is a record made at the time, from outside the network, with the time, number called, SIP code and Q.850 cause of each test call.
- Availability is (period − maintenance − downtime) ÷ (period − maintenance) × 100; the SLA calculator does the math for any target.
- At 99.9%, the limit is 8 h 45 min 36 s of downtime per 365-day year, or 43 min 12 s per 30-day month.
- Time when the monitoring itself had no visibility is not circuit downtime and should be left out of the calculation.
How do you enforce a carrier’s SLA?
In three parts: what the contract promises, what was measured and the math between the two. Without the first, you do not know what to claim; without the second, there is nothing to show; without the third, the claim is an opinion. An SLA can only be enforced when someone measured.
What does the contract need to say?
Before accepting a target, agree in writing on:
- the measurement period (year or month) and the time zone;
- what counts as unavailability: only a call that does not connect, or also a silent call and quality below the limit;
- how maintenance is announced and the maximum window;
- who measures, and how: the carrier’s measurement, yours, or an independent one;
- which evidence counts to open a dispute, and the deadline to request the credit.
If the contract already exists and does not say this, the first claim also serves to agree on the criteria. The guide Telephony SLA: yearly and monthly calculation details each point.
What proof should you bring?
Good proof is a record made on the spot, from outside your network, that the carrier can check. For each outage:
| Field | What it is for |
|---|---|
| Start and end time, with time zone | Measures the duration and locates the failure in the carrier’s records |
| Number called and origin number | Says which circuit and which route failed |
| SIP code of each test call | Shows how the route rejected it, for example SIP 503 |
| Q.850 cause | Gives the reason, such as cause 34 |
| Call-ID | Lets the carrier find the exact call |
| What was heard | Tells silence, busy and a carrier announcement apart |
| Duration and result of the following calls | Shows when the circuit came back |
The codes and causes are explained in Failing calls: diagnosis. An outage recorded with these fields is hard to dispute; one noticed by a customer who complained is not.
How do you calculate availability?
Availability = (period − scheduled maintenance − downtime) ÷ (period − scheduled maintenance) × 100. The site’s SLA calculator does this math for any target and already accounts for maintenance windows: use the SLA calculator.
Two references for the conversation with the carrier, at 99.9%:
| Period | Downtime allowed |
|---|---|
| 365-day year | 8 h 45 min 36 s |
| 30-day month | 43 min 12 s |
Each outage enters the calculation by its measured time, and the measured time depends on how often the test runs: with a call every 15 minutes and retests every 2 minutes after a failure, the start and end of each outage are marked within a few minutes.
What stays out of the calculation?
- Scheduled maintenance, announced and within the agreed window.
- Failures caused by the customer, such as a PBX turned off at a branch, when the contract is with the carrier and the defect is not theirs.
- Time when the monitoring had no visibility because of a problem of its own. A test that could not be made says nothing about the circuit.
Putting these exceptions in the report, rather than hiding them, is what makes the number defensible: the carrier sees that the math is honest.
How do you put the claim together, step by step?
- Gather the report for the period (year or month, as the contract says) with the outages and the availability.
- List the outages in a table, one per row, with the fields above.
- Subtract the maintenance that was announced inside the window.
- Compare with the target and work out the difference in minutes.
- Open the ticket with the table and the report, and ask the carrier to check the routes at the times indicated.
- Keep the reports month by month. The last-12-months figure is the one that closes the year.
The credit, penalty or termination is whatever the contract provides; so are the way to request it and the deadline. That is a matter for your legal team, and this guide is not legal advice.
What does Monitor by 2N5 deliver?
Monitor by 2N5 calls each voice circuit from Brazil, on its own schedule, and keeps the result of each test call. Every month it emails an SLA report with the availability for the month and the last 12 months, each incident with its duration, the total downtime and the availability by circuit and by carrier. A period when the test could not be made because of a problem on 2N5’s side is left out of the calculation and shown separately. For a consumer-service obligation, see also the SAC decree and RGC.
Frequently asked questions
How do I claim against a carrier's SLA?
Open the ticket with an availability report and the list of outages: time and time zone of each failure, number called, SIP code, Q.850 cause and duration. Add up the downtime, subtract the announced maintenance and compare with the contract target. First check whether the contract defines how to dispute and the deadline to request the credit.
What proof counts in a dispute with the carrier?
What the carrier can locate in its own records: time with time zone, origin and destination numbers, SIP code, Q.850 cause and Call-ID of each attempt. A record made at the time, by test calls from outside the network, is harder to dispute than the recollection that the number was down.
How much downtime is 99.9% availability?
In a 365-day year, 8 hours, 45 minutes and 36 seconds. In a 30-day month, 43 minutes and 12 seconds. In a week, 10 minutes and 5 seconds. In a day, 1 minute and 26 seconds. The site's SLA calculator shows the value for other targets and includes maintenance windows.
Does scheduled maintenance count as an outage?
Normally not, if it was announced with the notice the contract requires and stayed within the agreed window: it comes out of the period before the calculation. What goes past the window counts as an outage from the moment the window ended. That is why the window must be recorded before it starts.
What if the carrier disputes the measurement?
Show the sequence of test calls for the period, with the result of each, and ask the carrier to check the routes at the times indicated. If the contract says who measures, use that measurement as the reference and yours as supporting evidence. Questions about how to read the contract are for your legal team.