Учитывая, что ASI мертва, мне недавно пришлось сделать это на старом проекте.Если кому-то нужна помощь:
-(void)request:(ASIHTTPRequest *)request didReceiveBytes:(long long)bytes
{
if (!lastBytesReceived)
lastBytesReceived = [NSDate date];
NSTimeInterval interval = [[NSDate date] timeIntervalSinceDate:lastBytesReceived];
float KB = (bytes / 1024);
float kbPerSec = KB * (1.0/interval); //KB * (1 second / interval (less than one second))
NSLog(@"%llu bytes received in %f seconds @ %0.01fKB/s",bytes,interval, kbPerSec);
lastBytesReceived = [NSDate date];
}