To ensure accurate system sizing, Cisco recommends following a methodology that is supported by actual performance test results
and that incorporates industry-standard traffic engineering models to estimate the maximum expected traffic that the system
needs to handle during normal operating conditions.
Performance Testing
Each product performs a set of functions, and each function utilizes several resources (such as CPU and memory). Cisco defines
and executes performance tests that allow us to measure resource usage accurately for each function at different usage levels.
Most systems exhibit linearity within a certain range, beyond which the system performance can become unpredictable. Cisco
sets the usage levels for each performance test to identify and confirm the linear range of the resource usage for each function.
The results for each test can be graphed using a minimal number of data points. If required, additional data points (at intermediate
load levels) are obtained to define the actual system behavior.
System Modeling
Cisco uses the performance test results to create a system model. A system model is a mathematical model that calculates the
maximum resource usage for a specified set of features, endpoints, and traffic mix, which are provided as inputs to the model.
To develop a system model for a given product, Cisco performs the following steps:
- Itemize all the functions that the product performs. Identify variations of the function that need to be tested. For example,
each type of call will potentially use a different amount of the measured resources.
- Determine the resources of interest. Generally, this includes memory and CPU. Specific products may have additional resources
that impact system sizing.
- Run the performance tests to determine the resource usage for each function.
- For each function, use the linear range to define the formula for resource usage.
We may need to repeat these steps several times because other factors (such as software release, call mix, and types of endpoints)
can impact resource usage.
The system model for the product consists of aggregating the formulas for each function supported by the product. The model
can be simple for some products, but it can be very complex for a product that supports multiple functions, multiple endpoint
types, and multiple call types.
Traffic Engineering
Cisco uses industry-standard traffic engineering models to estimate the dynamic load on the system.
Traffic engineering provides mathematical models that calculate the maximum traffic level expected for a set of users. The
models also determine the amount of a shared resource (such as PSTN trunks) that is required to support a given traffic load.
The following sections describe traffic engineering considerations for different types of traffic:
- Voice Traffic
- Contact Center Traffic
- Video Traffic
- Conferencing and Collaboration Traffic
For planning information, refer to the Cisco Hosted Collaboration Solution End-to-End Planning Guide and the Cisco Hosted Collaboration Solution Reference Network Design Guide.