How do I get the count of user sessions?

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We are accessing answer pages hosted on the customer portal through mobile devices via the browser and would like to understand how usage with direct access to answer pages affects the session count which is taken into account for billing.

From what we understand the session for web page views is managed by cookies in the browser (and cookies are enabled in our case, both in the browser and the CP configuration) and the session timeout is 15 minutes. We tried to validate this by monitoring the 'cp_session' cookie on the device between page views and the value for that cookie changes with each page view - so this doesn't seem to be a session identifier alone and seems to be tracking more info.