what is the ai= parameter in click url?

[yangya...@hotmail.com]

we  are an advertiser, and bought ads on google adwords, and enabled "Display Network", so it went to doubleclick. 

from our weblog, we see that the user came to our site (landing url) through an url:

http://googleads.g.doubleclick.net/aclk?sa=L&ai=THIS_IS_A_LONG_LONG_STRING&num=3&sig=SOMETHING&client=ca-pub-A_LONG_NUMBER&adurl=http://losangeles.citysearch.com/profile/101409/west_hollywood_ca/panini_on_sunset.html?

while in some other cases I see urls like 

http://googleads.g.doubleclick.net/pagead/ads?client=ca-pub-LONG_NUMBER&output=html&h=50&slotname=LONG_NUMBER&w=320&lmt=LONG_NUMBER&ea=0&flash=0&url=http%3A%2F%2Fakron.cityvoter.com%2Fcoccia-house-pizza%2Fbiz%2F58703&dt=LONG_NUMBER&bpp=32&shv=r20130430&cbv=r20130206&correlator=LONG_NUMBER&frm=20&adk=LONG_NUMBER&ga_vid=FLOAT_NUMBER&ga_sid=LONG_NUMBER&ga_hid=LONG_NUMBER&ga_fc=0&u_tz=-240&u_his=1&u_java=0&u_h=480&u_w=320&u_ah=460&u_aw=320&u_cd=32&u_nplug=1&u_nmime=34&dff=arial&dfs=0&adx=0&ady=41&biw=320&bih=372&eid=LONG_NUMBER&oid=3&ref=https%3A%2F%2Fm.facebook.com&fu=0&ifi=1&dtd=NUMBER

in the latter form, I can see url= param which tells me where the user came from. this is very useful in analyzing the performance of our ad. but in the first form, I guess this info is encoded in the ai= parameter. is that supposed to be hidden from us? if not, how can I decode it? also more importantly , why are there 2 different forms of landing url being used?

another question of mine is : if the doubleclick click server sends a 302 to the user, the user's browser is supposed to retain the referrer url (like http://akron.cityvoter.com in the second url above), instead of telling us that the referrer is doubleclick.net, right? but why are we seeing doubleclick as the referrer? it does not seem to be rare behavior of a few browsers, most of the referrers we see are doubleclick

thanks

Yang

[Vincent Tsao (DFP API Team)]

Hi Yang:

This is more of a GPT related question than a DFP API question. I would post this to the DFP product forums as they will be able to better assist you:

http://productforums.google.com/forum/#!forum/dfp

Thanks,

Vincent Tsao, DFP API Team