NSURLRequest在3G上失败

Question

我有以下方法来执行NSURLRequest，但是当我通过3G连接时经常会失败

NSURLRequest *theRequest =
[NSURLRequest requestWithURL:[NSURL URLWithString:downloadServer]
                 cachePolicy:NSURLRequestReloadIgnoringLocalCacheData
             timeoutInterval:15.0];


theConnection=[[NSURLConnection alloc] initWithRequest:theRequest delegate:self];
timer = [NSTimer scheduledTimerWithTimeInterval:15.0 target:self selector:@selector(downloadsUp) userInfo:nil repeats:NO];
self.downloadStartTime = [NSString stringWithFormat:@"%ld", (long)[[NSDate date] timeIntervalSince1970]];

if (theConnection) {

    self.receivedData = [[NSMutableData data] retain];

} else {

}

与WIFI连接，它就像一个魅力，但在3G上它失败了！