ling stream. Improved call monitoring. Using a feature called mobile reported interference (MRI), the base station can interrogate the mobile for the forward channel signal strength and the bit error rate (BER) of the signaling stream. Short message service (SMS) and paging. Messages up to 14 characters long can be sent on the forward channel in a messaging or paging mode. Voice-mail notification. The system has the ability to activate a message-waiting light on the mobile telephone to tell a subscriber that voice mail is waiting. 6.5 AMPS Call Setup AMPS calls are set up by the mobile telephone. The mobile subscriber may initiate a call by pressing the SEND button, or the mobile telephone may detect a page for an in- coming call. However, it is the mobile telephone that selects the cell based on its radio measurements. As we will see in the next section, it is the cellular system that handles handoffs. A mobile telephone has to register with the system. It may be in its home area or it may be roaming, but it must register and establish its identity before it can make or receive calls. Once identified, the mobile telephone stays tuned to the paging stream in case there is an incoming call. In the case of an incoming call, the system makes two attempts to page the mobile telephone. If those pages fail, then the call attempt fails. A call starts when the subscriber presses the SEND key or a page comes in for an in- coming call. The mobile telephone searches all 21 access channels to find the strongest signal. If all the access channels are set to the same transmit power level, then this should be the cell with the highest path gain (least path loss), but Rayleigh fading and measurement error have a hand in the cell-selection process. Given that the mobile telephone has been monitoring the paging channel successfully, it is highly unlikely not to find a suitable access channel, but it could fail to find one at this point. A mobile page response or call initiation is called a seizure message. The forward ac- cess cha