TELEPHONE INTERFACE MODULE (TIM)

14.1.1 SUPERVISION

The TIM can be seized from either landside or internal. Landside seizure occurs by Direct Inward Dial (DID) or Two-Way Start (2WY). Internal seizure comes from the Intra-Terminal Data Bus (IDB) as a request for outgoing service on the telephone line (see Figure 14-15).

Once seizure has occurred, connection supervision takes place. Incoming calls are connected by Immediate Start or Wink Start. Immediate Start requires the ability to accept digits in less than 70 milliseconds before digits are sent. Wink Start sends digits after a short battery reversal and back to normal Battery before digits are received. Two-Way Incoming indicates readiness to accept "end-to-end" DTMF digits by outputting a "proceed" tone.

Outgoing calls have three ways to determine when to send digits:

1.Immediate Start

Waits 70 milliseconds before digits are sent.

2.Dial Tone Delay

Waits until 100 milliseconds of dial tone is received before digits are sent

3.Wink Delay

Waits for battery reversal and back to normal battery before digits are sent.

14.1.2 SIGNALING

Once connection supervision has occurred, the digit signaling is done. There are two ways to send and receive digits:

1.Dial Pulse

Counts the "breaks and makes" of loop current.

2.DTMF

Determines the tone pair of a set of frequencies.

The TIM sends or receives the appropriate signaling depending on the direction of the call. The TIM is capable of sending and receiving "end-to- end" signaling where the call is completed and normal voice communication takes place, or numeric information can be sent or received via DTMF. Dial pulse information cannot pass through the telephone company's Central Office (CO) to make it back and forth to the units.

14.1.3 CALL SUPERVISION

Once the signaling of the digits has occurred, call status is determined for answer and disconnect.

Answer supervision is an indication of when the called party answers the telephone. The preferred method is by reverse battery answer, where the CO reverses the battery connection, therefore, current flow reverses when the called party answers. The other method is mobile speech activity that detects the presence of mobile speech for a certain length of time. If the telephone line cannot recognize reverse battery answer, none is sent toward the CO, and no real answer supervision exits. However, the mobile speech activity can be used for answer detection.

Disconnect supervision detects when the called party hangs-up (disconnects) and a message is sent to the TIM to disconnect from the telephone line. The preferred method is from reverse battery answer, where the battery returns to normal when the called party disconnects. The next method is to wait for the mobile disconnect message. If the mobile does not hang up properly, the message is not sent and the call continues. Fail-safe alternatives watch for loss of mobile speech or detect the return of dial tone. This ensures call disconnect allowing another call to be placed. The TIM then informs the Call Processor that it has disconnected from the telephone line.

14.1.4 INTRA-TERMINAL COMMUNICATION

The TIM communicates to the Call Processor through the Intra-Terminal Data Bus (IDB) and sends activity information to the Call Processor. The Call Processor sends messages to the TIM to request service, informs the TIM to disconnect, and any other necessary control information.

14-2