Information about the utmLinker and the __utma, __utmb and __utmc cookies? (posted: 8/8/2008)

Rating: +0

The __utmb and __utmc cookies are used to track a user's session as follows:

__utmb

* Hashcode
* Changes to identify each unique session
* Non-persistent cookie
* Works with __utmc to determine when a session ends
* Dies when a browser is closed
* If it disappears a new visitor session is started

__utmc

* Session based cookie
* Destroyed after 30 minutes of inactivity
* Can be set higher
* Works with __utmb to determine when session ends
* If it disappears, a new visitor session starts
* Visitor timeout set in __utm.js. Default is 1800 seconds
* 30 minutes is appropriate. Some websites and their visitor traffic may require a different timeout value

When using the utmLinker() function, __utmb and __utmc are assigned a value of 1 by the uDomain() function but only if the _udn variable is set to "none". How can Google Analytics track the beginning and end of a session if both values are set to 1? The beginning and end of a session are calculated and stored in values within the __utma cookie, and not in the __utmb or __utmc cookies.

The __utma cookie is formatted as follows:
__utma = domainhash.unique.ftime.ltime.stime.sessioncount;
where:
domainhash = hash of the domain name of the website
unique = a randomly generated 31 bit integer
ftime = UTC timestamp of first visitor session
ltime = UTC timestamp of last visitor session
stime = UTC timestamp of current visitor session
sessioncount = number of sessions; always incremented for each new session