SLA Service Level Metrics

The following are metrics and measurements typically found in a network service provider's SLA:

• Availability— Measure of the network availability for customer activity. Availability is usually measured as mean time between failures (MTBF) and mean time to repair (MTTR). For example, a MTBF of 99.5% every day means downtime cannot exceed 7.2 minutes every 24 hours.

Most implementations use a network availability formula similar to the formula shown in Equation 22-1.

Equation 22-1

.j # minutes of outage

(10,080 minutes in one week - # minutes of block time)

Availability * 100 = % Availability For each device, then averaged among themselves-

This formula is usually geared toward specific devices on the network or the availability of a trunk. Notice that the more devices that are added into the overall calculation, the more obscure the calculation becomes. One considers all the devices on the same level as the others. Furthermore, the more devices that are added into the overall average, the more hidden they become.

This calculation is accomplished for each device, then averaged as a group. Availability can also be accomplished by doing the following:

• Gathering a list of services provided on the network by priority.

• Reporting on the availability of each of the services on a monthly basis. (Use a modifier or weighting on those services that are considered more important to the organization.)

• Telling management the truth about the availability of services. This provides an avenue to correct those problems and provides better services to the end user community.

In Equation 22-2, specific services can be weighed according to the importance to the business units.

Equation 22-2

# minutes of outage * Weighting Factor {10,080 minutes in one week - # minutes of block time)

Availability * 100 = % Availability

These services include the following:

• Response time— Measures the time to complete a request for a client, group of clients, or network.

• Throughput— Measures the amount of data (or volume) sent in a given period of time. For example, videoconferencing generally requires 384 Kbps to provide satisfactory quality.

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