iphone - AdMob not showing ads in iOS simulator -

i trying use admob on app (built ios 4.0)

i've added sample code available in tutorial http://code.google.com/mobile/ads/docs/ios/fundamentals.html following (i've changed adunitid):

// create view of standard size @ bottom of screen. bannerview_ = [[gadbannerview alloc]                initwithframe:cgrectmake(0.0,                                         self.view.frame.size.height -                                         gad_size_320x50.height,                                         gad_size_320x50.width,                                         gad_size_320x50.height)];  // specify ad's "unit identifier." admob publisher id. bannerview_.adunitid = @"xyz";  // let runtime know uiviewcontroller restore after taking // user wherever ad goes , add view hierarchy. bannerview_.rootviewcontroller = self; [self.view addsubview:bannerview_]; [self.view bringsubviewtofront:bannerview_];  gadrequest * request = [gadrequest request];  // initiate generic request load ad. [bannerview_ loadrequest:request]; 

doing nothing happens, no ad shown , number of requests in admob app page increase erratically (i.e.: can't seem notice pattern), important no ad shown.

if add following code:

gadrequest * request = [gadrequest request];  request.testdevices = [nsarray arraywithobjects:                        gad_simulator_id,                               // simulator                        nil];  // initiate generic request load ad. [bannerview_ loadrequest:request]; 

i "success! ready travel through app galaxy" default banner, one.

so questions are:

• aren't sample code enough show ads? why never see ad sample code?
• as far understood, requests mean number of times app asked ad shown. understood not every request replied ad (otherwise fill rate 100%), still, never saw ad, doing wrong?

thanks in advance.

  gadbannerview *bannerview = [[gadbannerview alloc]               initwithframe:cgrectmake(0.0,                                        self.view.frame.size.height -                                        gad_size_320x50.height,                                        gad_size_320x50.width,                                        gad_size_320x50.height)];//set position    bannerview.adunitid = @"12331255421245";//call id  // let runtime know uiviewcontroller restore after taking // user wherever ad goes , add view hierarchy.   bannerview.rootviewcontroller = self;  [self.view addsubview:bannerview];//your attempt add bannerview   // initiate generic request load ad.  [bannerview loadrequest:[gadrequest request]];