If I were to use iframes, what is the best way to track banner impressions?

I am trying to create a simple banner exchange system based on impressions sent and impressions received.

Is this related to http://www.webmaster-talk.com/php-fo...need-help.html

Yep but I am figuring out two things at once. I am asking in this thread about iframes and figuring out an efficient way of tracking impressions of a banner that would be displayed inside an iframe whereas this post:

http://www.webmaster-talk.com/php-fo...need-help.html

is about implementing the ratio into the system.

Assign the banner a unique URL through a parsed script. For example, banner.php?banner_id=XX and then have the PHP script log the hit in a table. Then, you can fairly easily summarize the total number of hits for the banner and do any necessary processing. If you expect the site to be fairly busy, you may want to create the log and have that table duplicated on a remote server for doing processing and then update a primary table to simply hold the number of hits so that that number may be displayed without having to calculate it.