Count unique visits in PHP/MySQL

I am making a PHP/MySQL traffic report page from a table that records some user activity using PHP referrer information. I have a table with three rows: IP, page_name, and timestamp. The IP row records the user's IP address, page_name records the name of the page that the user loaded, and the timestamp row records in Unix timestamp format the time of day that the user requested the page. I want to be able to count unique visits per IP according to Internet Advertising Bureau standards, which count a "Unique Visit" as a log in by the same IP once every thirty minutes. IAB verbatim definition: "Visit – One or more text and/or graphics downloads from a site qualifying as at least one page, without 30 consecutive minutes of inactivity, which can be reasonably attributed to a single browser for a single session. A browser must “pull” text or graphics content to be considered a visit." So I need to make a MySQL query that will count how many times an IP logged a timestamp within a given time period. For example, the publisher checking traffic could request a date between May 1 and May 31, and I'd like to be able to return a page that counted unique users (count distinct IP), pages viewed (list distinct pages) and how many times they visited in that period. I have the first two down, but not the unique visits. Any ideas?