Suppose we dial HDFC Bank then till the call gets through to the Main Telephone no SS7 is used . Howver after that we hear Prompts like ” For English Dial -1, for Hindi dial 2″ , “For Credit Card Dial 1 , For Loans Dial 3” etc . Now in all these prompts what is the porotocol we are using – definitely not SS7 . Please clear this doubt