Data Collection API, August 2012
How to track visitors and visitor sessions.
If you use Webtrends Analytics reporting, identifying visitors and tracking visitor sessions is relatively simple. When a user initiates a session with your application session, you can pass visitor identifying data to the WT.co_f parameter. If your application already provides a unique identifier for the visitor, you can pass this information directly to WT.co_f. If your application does not provide an identifier, you can request a visitor ID from the Webtrends data collection server using the Get Visitor Identifier method. When you use this method, the data collection server returns a unique ID based on the IP address of the device and a time stamp. You can then pass this ID in the wt.co_f parameter in the next request, when you use the Post Event Data method.
If you use a Webtrends-provided visitor ID, you can persist this information by storing it in a cookie or INI file, or using another method. Requests with no value for wt.co_f will use IP address and user agent information to identify visitors. This is a weak method of visitor identification, and is not recommended.
If you use Visitor Data Mart, you need to provide more information to effectively track visitor sessions. Visitor Data Mart requires both a visitor ID, such as WT.vtid or WT.co_f, and a session ID, WT.vtvs. The visitor identifier can be obtained using the Get Visitor Identifier method described above. The WT.vtvs parameter specifies a time stamp expressed in UTC or "epoch" time, which is equal to the number of milliseconds since January 1, 1970.