Exercise 2-1. External Call Answering and Termination EXERCISE OBJECTIVE

Exercise 2-1 External Call Answering and Termination EXERCISE OBJECTIVE When you have completed this exercise, you will be able to describe and explain the complete sequence of events that occurs in the Lab-Volt PABX when an external call is answered. Similarly, you will be able to describe and explain the sequence of events that takes place in the Lab-Volt PABX when an external call is terminated. DISCUSSION External Call Answering In the Lab-Volt PABX, each call from the outside (i.e. each incoming call received via the PABX analog trunk) is directed to the attendant's telephone set. Although this may seem a simple operation, a long sequence of events is triggered whenever an external call is received via the PABX analog trunk. This sequence of events is described below. 1. The Lab-Volt CO applies the ringing voltage across the PABX analog trunk. 2. The RING AND TRUNK STATUS DETECTOR in the ANALOG TRUNK INTERFACE of the Lab-Volt PABX detects the ringing voltage. Its output signal passes from logic state 0 to logic state 1. This signal, which indicates the trunk status, is time-division multiplexed to line TKS2 for transmission to the TRUNK STATUS DEMULTIPLEXING AND STORAGE CIRCUIT. This circuit stores in a memory the status of each PABX analog trunk. 3. The PABX CALL PROCESSOR, which cyclically reads the contents of the memory in the TRUNK STATUS DEMULTIPLEXING AND STORAGE CIRCUIT, detects that the status of the PABX analog trunk passed from 0 to 1 and interprets this as an incoming call from the outside. The PABX CALL PROCESSOR thus considers that this analog trunk is busy and performs the following two actions: Connects (in reception only) one circuit in the bank of analog trunk service circuits (ANALOG TRUNK SERVICE CIRCUIT 1) to the ANALOG TRUNK INTERFACE via the SPACE-DIVISION SWITCH, as shown in Figure 2-7. This makes the PABX ready for the reception of the caller ID data (FSK signal) from the CO. Sends a SETUP message to the attendant's telephone set to make it ring. 2-9

PABX TX0 TX1 SPACE-DIVISION SWITCH RX0 RX1 FSK SIGNAL BEARING CALLER ID DATA TX2 RX2 RX2 TX3 TX4 TX5 RX3 RX4 RX5 TX2 TKS2 ANALOG TRUNK INTERFACE T R PABX ANALOG TRUNK TO AND FROM CO BANK OF ANALOG TRUNK SERVICE CIRCUITS ANALOG TRUNK SERVICE CIRCUIT 1 TX3 RX3 DIGITIZED FSK SIGNAL BEARING CALLER ID DATA Figure 2-7. Path through which caller ID data from the CO is received in the Lab-Volt PABX. 4. The attendant's telephone set returns an ALERTING (ALERT) message to the PABX CALL PROCESSOR. 5. After the first burst of ringing, the CO sends an FSK signal, bearing caller ID data, to the PABX via the analog trunk. This FSK signal is routed to ANALOG TRUNK SERVICE CIRCUIT 1 via the ANALOG TRUNK INTERFACE and the SPACE-DIVISION SWITCH, as shown in Figure 2-7. The CALLER IDENTIFI- CATION CIRCUIT in ANALOG TRUNK SERVICE CIRCUIT 1 converts the FSK signal into the corresponding caller ID data and sends this data to the PABX CALL PROCESSOR. 6. Once the caller ID data has been received, the PABX CALL PROCESSOR performs the following two actions: Disconnects ANALOG TRUNK SERVICE CIRCUIT 1 from to the ANALOG TRUNK INTERFACE. Sends an INFO message to the attendant's telephone set that includes a Display IE containing the caller ID data. This information is displayed on the attendant's telephone set. 7. When the attendant answers the call, its digital telephone set sends a CONNECT (CONN) message to the PABX. 2-10

1 2 3 4 5 6 7 8 9 * 0 # External Call Answering and Termination 8. The PABX CALL PROCESSOR promptly reacts to this CONN message by performing the actions that follow to establish a bidirectional connection between the ANALOG TRUNK INTERFACE and the DUAL DIGITAL LINE INTERFACE associated with the attendant's telephone set. Sends data to TSAC 1 in the ANALOG TRUNK INTERFACE to make the ANSWER RELAY close. This causes DC current to flow in the PABX analog trunk. This is detected by the CO which immediately ceases to apply the ringing voltage to the PABX analog trunk. This current is also detected by the RING AND TRUNK STATUS DETECTOR which thus sets its output to logic state 1. This logic 1 is written in the memory of the TRUNK STATUS DEMULTIPLEXING AND STORAGE CIRCUIT. Connects (in both transmission and reception) the B channel of the DUAL DIGITAL LINE INTERFACE associated with the attendant's telephone set to the ANALOG TRUNK INTERFACE via the SPACE-DIVISION SWITCH. Figure 2-8 illustrates the connections established when the attendant's telephone set is associated with DUAL DIGITAL LINE INTERFACE A of the PABX. Sends a CONNECT ACKNOWLEDGE (CONACK) message to the attendant's telephone set. PABX ATTENDANT'S TELEPHONE SET DIGITIZED VOICE SIGNALS DUAL DIGITAL LINE INTERFACE A TX0 RX0 TX0 TX1 TX2 SPACE-DIVISION SWITCH RX0 RX1 RX2 RX2 DIGITIZED VOICE SIGNALS ANALOG VOICE SIGNALS DIGITIZED VOICE SIGNALS TX3 TX4 TX5 RX3 RX4 RX5 TX2 TKS2 ANALOG TRUNK INTERFACE T R PABX ANALOG TRUNK TO AND FROM CO Figure 2-8. Connection of the ANALOG TRUNK INTERFACE to the DUAL DIGITAL LINE INTERFACE associated with the attendant's telephone set. The calling party is now in communication with the attendant. The system remains in this state as long as the call is not held, transferred, included in a conference, or terminated. 2-11

External Call Termination The sequence of events that follows describes what happens in the Lab-Volt PABX whenever an external call is terminated. 1. The user involved in the external call replaces the handset of the digital telephone set on the cradle. This causes the user's telephone set to send a DISCONNECT (DISC) message to the PABX CALL PROCESSOR. 2. The PABX CALL PROCESSOR reacts to this message by performing the following actions to terminate the call: Disconnects the B channel of the DUAL DIGITAL LINE INTERFACE associated with the user's telephone set from the ANALOG TRUNK INTERFACE. Sends data to TSAC 1 in the ANALOG TRUNK INTERFACE to make the ANSWER RELAY open. This makes the DC current flowing in the PABX analog trunk decrease to zero. This is detected by the RING AND TRUNK STATUS DETECTOR whose output passes to logic state 0. This logic 0 is written in the memory of the TRUNK STATUS DEMULTIPLEXING AND STORAGE CIRCUIT. Marks the PABX analog trunk as available. Sends a RELEASE (RLSE) message to the user's digital telephone set. 3. The user's digital telephone set replies to the PABX CALL PROCESSOR with a RELEASE COMPLETE (RLCOM) message to complete call termination. Procedure Summary In the first part of the exercise, you will set up an analog trunk between a Lab-Volt PABX and a Lab-Volt Central Office. In the second part of the exercise, you will make a call to the Lab-Volt PABX and observe what happens to the data stored in the TRUNK STATUS BUFFER MEMORY. This will allow you to determine the function of the TRUNK STATUS DEMULTIPLEXING AND STORAGE CIRCUIT. In the third part of the exercise, you will initiate a call to the Lab-Volt PABX and determine how the caller ID FSK signal sent by the Lab-Volt Central Office, via the PABX analog trunk, is routed to an analog trunk service circuit in the signaling circuit of the Lab-Volt PABX. In the last part of the exercise, you will study the sequence of events that occur in the Lab-Volt PABX when an incoming call to the Lab-Volt PABX is received, answered, and terminated. The Call Processor Log of the Lab-Volt PABX will assist you in analyzing this sequence. 2-12

EQUIPMENT REQUIRED Refer to Appendix A of this manual to obtain the list of equipment required to perform this exercise. PROCEDURE Setting Up an Analog Trunk Between a Lab-Volt PABX and a Lab-Volt Central Office Note: In this exercise, it is assumed that a single host computer is used to download the PABX and CO programs to two Reconfigurable Training Modules, Model 9431. This host computer is used to monitor the Lab-Volt PABX. * 1. Make sure that two Reconfigurable Training Modules, Model 9431, are connected to the TTS Power Supply, Model 9408. Make sure that there is a network connection between each Reconfigurable Training Module and the host computer. Install the Dual Analog Line Interface, Model 9475, into one of the two analog/digital (A/D) slots of a Reconfigurable Training Module. This module will be used as a central office (CO). Connect an analog telephone set to the Dual Analog Line Interface. Make sure that the tone dialing mode is selected on this telephone set. CAUTION! Do not connect or disconnect the analog telephone set when the Reconfigurable Training Module is turned on. High voltages are present on the standard telephone connectors of the Dual Analog Line Interface. Connect the AC/DC power converter supplied with the analog telephone set to one of the AC power outlets on the TTS Power Supply. Connect the DC power output jack of the AC/DC power converter to the DC power input connector on the analog telephone set. * 2. Install the Digital Telephone Interface, Model 9476, into the digital (D) slot or one of the two analog/digital (A/D) slots of the other Reconfigurable Training Module. This module will be used as a PABX. Connect two digital (ISDN) telephone sets provided with the Lab-Volt PABX to the left and right connectors of interface A of the Digital Telephone Interface. These telephone sets will be referred to as digital telephone sets A-left (AL) and A-right (AR), respectively, throughout the exercise. 2-13

CAUTION! Do not connect or disconnect the digital telephone sets when the Reconfigurable Training Module is turned on. High voltages are present on the RJ-45 connectors of the Digital Telephone Interface. Finally, install the PABX Analog Trunk Interface, Model 9477, into one of the two analog/digital (A/D) slots of the Reconfigurable Training Module used as a PABX. Using the analog trunk line provided with the PABX Analog Trunk Interface (two-wire cable terminated with standard [RJ-11] male telephone connectors), connect the RJ-11 female connector on the PABX Analog Trunk Interface installed in the Reconfigurable Training Module used as a PABX to the remaining RJ-11 female connector on the Dual Analog Line Interface installed in the Reconfigurable Training Module used as a CO. * 3. Turn on the host computer. Turn on the TTS Power Supply, then turn on the Reconfigurable Training Modules. * 4. On the host computer, start the Telephony Training System software, then download the PABX program to the Reconfigurable Training Module used as a PABX. Note: If the host computer is unable to download the PABX program to the Reconfigurable Training Module used as a PABX, make sure that the proper IP address is used to communicate with this Reconfigurable Training Module. * 5. Lift off the handset of each digital telephone set connected to the Lab-Volt PABX while observing the Lab-Volt PABX diagram in the LVTTS software window. When the handset of a digital telephone set is lifted off, an icon representing this telephone set should appear connected to the corresponding DUAL DIGITAL LINE INTERFACE in the Lab-Volt PABX diagram. If so, this indicates that this telephone set is properly programmed to be operational with the Lab-Volt PABX. Otherwise, this means that this telephone set is not properly programmed to be operational with the Lab-Volt PABX. Note: An icon representing the digital telephone set may already be displayed in the Lab-Volt PABX diagram before you lift off the handset of this telephone set. This occurs because each digital telephone set automatically begins communication with the Lab-Volt PABX a certain time after it is powered up in order to identify itself to the Lab-Volt PABX. This indicates that this digital telephone set is properly programmed to be operational with the Lab-Volt PABX. 2-14

If a digital telephone set does not seem to be properly programmed, refer to Section 4 of the Telephony Training System User Guide (part number 32964-E0), entitled "Familiarization with the Lab-Volt PABX", to know how to properly program the digital telephone sets connected to the Lab-Volt PABX. Hang up the handset of each digital telephone set. * 6. On the host computer, designate digital telephone set AL of the Lab-Volt PABX as the attendant's telephone set. Make sure that no external call restriction is applied to digital telephone sets AL and AR. Set the DTMF dialing tone duration to 1 s. * 7. On the host computer, download the CO program to the Reconfigurable Training Module used as a CO. Note: If the host computer is unable to download the CO program to the Reconfigurable Training Module used as a CO, make sure that the proper IP address is used to communicate with this Reconfigurable Training Module. Once the CO program has been downloaded, a box representing the Lab-Volt CO will appear connected to the PABX, via an analog trunk, in the Lab-Volt PABX diagram displayed on the host computer screen. Record below the telephone numbers associated with ANALOG LINE INTER- FACEs A and B of the Lab-Volt CO. ANALOG LINE INTERFACE A (ALI A): ANALOG LINE INTERFACE B (ALI B): Note: If you use two separate host computers to download the PABX and CO programs to the two Reconfigurable Training Modules used in this exercise, no box representing the Lab-Volt CO will appear in the Lab-Volt PABX diagram once the CO program has been downloaded. In that case, you can access the LVTTS Options dialog box (or the Call Processor Settings dialog box) on the host computer that monitors the Lab-Volt CO to know the telephone numbers associated with each analog line interface. For the rest of this exercise, however, the term host computer always refers to the computer monitoring the Lab-Volt PABX. * 8. On the host computer, set the external call number length in the Lab-Volt PABX so that it matches the length of the telephone numbers associated with the analog line interfaces used in the Lab-Volt CO. Make sure the address of TSAC 2 in the PABX ANALOG TRUNK INTERFACE is set to 1. 2-15

Trunk Status Demultiplexing and Storage * 9. On the host computer, zoom in on the SIGNALING CIRCUIT of the Lab-Volt PABX, then zoom in on the TRUNK STATUS DEMULTIPLEXING AND STORAGE CIRCUIT. Observe that a trunk status line (line TKS2) enters the DEMULTIPLEXING (DEMUX) CONTROLLER. This line provides the DEMUX CONTROLLER with a time-division multiplexed signal that can indicate the status (busy/idle) of up to 30 PABX analog trunks grouped in the same bank (bank TKS2). The status of each trunk is stored in the TRUNK STATUS BUFFER MEMORY. * 10. Display the contents of the TRUNK STATUS BUFFER MEMORY. Which bank of analog trunk interfaces is column D0 of this memory associated with? Which time slots are memory addresses 01 to 15 and 17 to 31 associated with? * 11. Using the Pan command, observe that line TKS2 of the DEMUX CON- TROLLER is connected to the output of the RING AND TRUNK STATUS DETECTOR in the ANALOG TRUNK INTERFACE, through the tri-state buffer controlled by TSAC 2 in this interface. Consequently, line TKS2 provides the DEMUX CONTROLLER with information on the status of the analog trunk associated with the ANALOG TRUNK INTERFACE, during the time slot assigned to this interface for the transmission of the trunk status signal. * 12. Connect Oscilloscope Probes 1, 2, 3, and 4 to TP1 (DC COUPLED LINE MONITOR output), TP14 (RING AND TRUNK STATUS DETECTOR output), TP13 (TKS2 line), and TP15 (FRAME SYNC. signal) of the ANALOG TRUNK INTERFACE, respectively. 2-16

* 13. Start the Oscilloscope. Make the following settings on the Oscilloscope: Channel 1 Mode....................................... Normal Sensitivity.................................. 50 V/div Input Coupling................................... AC Channel 2 Mode....................................... Normal Sensitivity................................... 5 V/div Input Coupling................................... DC Channel 3 Mode....................................... Normal Sensitivity................................... 5 V/div Input Coupling................................... DC Channel 4 Mode....................................... Normal Sensitivity................................... 5 V/div Input Coupling................................... DC Time Base..................................... 5 ms/div Trigger Source........................................ Ch 1 Level.......................................... 1 V Slope.................................... Positive (+) Display Refresh............................... Continuous Display Mode.................................... Square Note: Set the time base to 2 ms/div if the AC ringing voltage of the Lab-Volt CO is set for a UK ringing cadence and/or a frequency of 50 Hz. * 14. Adjust the view in order to be able to simultaneously observe the contents of the TRUNK STATUS BUFFER MEMORY and the signals on the Oscilloscope screen. * 15. Using the analog telephone set connected to the Lab-Volt CO, make a call to the Lab-Volt PABX. Let digital telephone set AL (PABX attendant's telephone set) ring. On the Oscilloscope screen, observe that the signal at the RING AND TRUNK STATUS DETECTOR output (TP14) of the ANALOG TRUNK INTERFACE alternates between logic states 0 and 1 at the cadence of the AC ringing voltage applied across the analog trunk (TP1 of the ANALOG TRUNK INTERFACE). * 16. On the Oscilloscope, set the channel-1 sensitivity to 5 V/div and the trigger source to channel 4. 2-17

Decrease the Oscilloscope time base by steps until it is equal to 20 µs/div. While doing this, observe the signals at TP14 (RING AND TRUNK STATUS DETECTOR output) and TP13 (TKS2 line) of the ANALOG TRUNK INTERFACE. Is the signal at the RING AND TRUNK STATUS DETECTOR output multiplexed to line TKS2 during time slot 1? Explain. * 17. While digital telephone set AL is ringing, observe the status of the bits in column D0 of the TRUNK STATUS BUFFER MEMORY. Does a relationship exist between the logic state of bit D0 at memory address 01 and the cadence of the AC ringing voltage applied across the analog trunk? Why? Explain by referring to the signals at TP1, TP14, and TP13 of the ANALOG TRUNK INTERFACE. Hang up the handset of the analog telephone set. * 18. From your observations, what is the function of the TRUNK STATUS DEMULTIPLEXING AND STORAGE CIRCUIT? * 19. Select the manual display refresh mode on the Oscilloscope. * 20. Change the address of TSAC 2 in the ANALOG TRUNK INTERFACE to 6. 2-18

* 21. Select the continuous display refresh mode on the Oscilloscope. Using the analog telephone set connected to the Lab-Volt CO, make a call to the Lab-Volt PABX. Let digital telephone set AL (PABX attendant's telephone set) ring, while observing the signals on the Oscilloscope screen and the status of the bits in column D0 of the TRUNK STATUS BUFFER MEM- ORY. What is the memory address of the bit in column D0 of the TRUNK STATUS BUFFER MEMORY that now alternates between logic states 0 and 1 at the cadence of the AC ringing voltage applied across the analog trunk? Is this address still 01? Why? Hang up the handset of the analog telephone set. On the host computer, close the Trunk Status Buffer Memory window. * 22. Select the manual display refresh mode on the Oscilloscope. * 23. If desired and if time permits, the operation of the Lab-Volt PABX TRUNK STATUS DEMULTIPLEXING AND STORAGE CIRCUIT may be studied in detail by performing the manipulations found in Exercise 1-1 of the Telephony Training System Student Manual entitled "Central Office Operation" (part number 33646-00), under the following PROCEDURE parts: "Internal Circuitry of the DEMULTIPLEXING (DEMUX) CONTROL- LER" and "Operation of the HOOK STATUS DEMULTIPLEXING AND STORAGE CIRCUIT". Since these manipulations are used to study the operation of the HOOK STATUS DEMULTIPLEXING AND STORAGE CIRCUIT in the Lab-Volt CO, minor modifications will have to be made to their text in order to adapt them to the study of the TRUNK STATUS DEMULTIPLEXING AND STORAGE CIRCUIT in the Lab-Volt PABX, as the test point numbers and the name of certain inputs and outputs may differ. 2-19

Routing of the Caller ID Data from the CO to the PABX CALL PROCESSOR * 24. Make sure the manual display refresh mode is selected on the Oscilloscope. Disconnect all the Oscilloscope Probes. Connect Oscilloscope Probes 1, 2, and 3 to TP1 (DC COUPLED LINE MONITOR output), TP6 (CODEC analog input), and TP8 (TX2 line) of the ANALOG TRUNK INTERFACE, respectively. * 25. Go to ANALOG TRUNK SERVICE CIRCUIT 1 in the SIGNALING CIRCUIT of the Lab-Volt PABX. Observe that this circuit uses a transmit line, labeled TX3, and a receive line, labeled RX3, that are used for transmission and reception of multiplexed digitized signals, respectively, via the SPACE- DIVISION SWITCH. Connect Oscilloscope Probe 4 to TP19 (CODEC analog output) of ANALOG TRUNK SERVICE CIRCUIT 1. * 26. Make sure the Oscilloscope is set as follows: Channel 1 Sensitivity................................... 50 V/div Input Coupling................................... AC Channel 2 Sensitivity.................................... 2 V/div Input Coupling................................... DC Channel 3 Sensitivity.................................... 5 V/div Input Coupling................................... DC Channel 4 Sensitivity.................................... 2 V/div Input Coupling................................... DC Time Base.................................... 10 ms/div Trigger Source....................................... Ch 2 Level........................................ 0.1 V Slope................................... Positive (+) Display Refresh.............................. Continuous Display Mode................................... Square * 27. Using the analog telephone set, make a call to the Lab-Volt PABX. On the Oscilloscope screen, observe the analog caller ID FSK signal appearing at TP6 (CODEC analog input) of the ANALOG TRUNK INTERFACE just after the first burst of ringing. Hang up the handset of the analog telephone set. Repeat the above manipulations a few times in order to be able to answer the questions below. 2-20

When the analog caller ID FSK signal appears at TP6 of the ANALOG TRUNK INTERFACE, do PCM codes (representing the digitized caller ID FSK signal) appear on line TX2 (TP8) of this interface? * Yes * No When the analog caller ID FSK signal appears at TP6 of the ANALOG TRUNK INTERFACE, does an identical signal simultaneously appear at the CODEC analog output (TP19) of ANALOG TRUNK SERVICE CIRCUIT 1? * Yes * No * 28. On the Oscilloscope, select the manual refresh display mode. On the host computer, adjust the view in order to be able to simultaneously observe the TIME SLOT NUMBER displays of the ANALOG TRUNK INTERFACE and ANALOG TRUNK SERVICE CIRCUIT 1, the SPACE- DIVISION SWITCH and TIME SLOT SELECTOR of the SWITCHING CIRCUIT, and the signals on the Oscilloscope screen. Set the TIME SLOT SELECTOR of the SWITCHING CIRCUIT to 5. This will enable display of the connections made by the SPACE-DIVISION SWITCH during time slot 5. On the Oscilloscope, select the continuous refresh display mode. * 29. Using the analog telephone set, make a call to the Lab-Volt PABX to make digital telephone set AL ring. Just after the first burst of ringing, observe the TSAC-1 TX TIME SLOT NUMBER display of the ANALOG TRUNK INTERFACE, the connection made by the SPACE-DIVISION SWITCH of the SWITCHING CIRCUIT, and the TSAC RX TIME SLOT NUMBER display of ANALOG TRUNK SERVICE CIRCUIT 1. Hang up the handset of the analog telephone set. Repeat the above manipulations a few times in order to be able to answer the questions below. Which time slot is momentarily assigned to the CODEC of the ANALOG TRUNK INTERFACE, just after the first burst of ringing, for the transmission of the digitized caller ID FSK signal from this interface? Explain. 2-21

What connection is momentarily made by the SPACE-DIVISION SWITCH during time slot 5, just after the first burst of ringing? Explain. Which time slot is momentarily assigned to the CODEC of ANALOG TRUNK SERVICE CIRCUIT 1 in the SIGNALING CIRCUIT for the reception of the digitized caller ID FSK signal? Explain. * 30. From your observations, explain how the caller ID FSK signal sent by the Lab-Volt CO, via the analog trunk, is routed to the CODEC analog output (TP19) of ANALOG TRUNK SERVICE CIRCUIT 1, and what happens to this signal. * 31. Select the manual display refresh mode on the Oscilloscope. Receiving, Answering, and Terminating an Incoming Call to the PABX * 32. Disconnect Oscilloscope Probes 2 and 3 and connect them to TP14 (RING AND TRUNK STATUS DETECTOR output) and TP13 (TKS2 line) of the ANALOG TRUNK INTERFACE, respectively. 2-22

Make the following settings on the Oscilloscope: Channel-2 Sensitivity.............................. 5 V/div Trigger Source..................................... Ch 4 * 33. Make the following settings on the host computer: Display the contents of the TRUNK STATUS BUFFER MEMORY. Display the Control Register of the SPACE-DIVISION SWITCH (SDS Control Register). Display the Call Processor Log window. In this window, display the Detailed folder. Make sure the CALL PROCESSOR actions are included with the call-control messages that will be recorded in this folder. Adjust the view in order to be able to simultaneously observe the TRUNK STATUS BUFFER MEMORY, the SDS Control Register, and the signals on the Oscilloscope screen. On the Oscilloscope, select the continuous display refresh mode. Call Reception * 34. Prepare yourself to perform the next step by reading the sequence of events described in it a few times. When you are ready, proceed to this step and repeat it as many times as necessary in order to be able to observe all the events in the described sequence. (Hang up and clear the contents of the CALL PROCESSOR Log each time before repeating this step). * 35. Start recording the Lab-Volt PABX call-control messages and CALL PROCESSOR actions. Using the analog telephone set, make a call to the Lab-Volt PABX to make the attendant's telephone set (digital telephone set AL) ring and observe the sequence of events described below. The Lab-Volt CO applies the AC ringing voltage across the analog trunk, as can be seen at TP1 of the ANALOG TRUNK INTERFACE. This causes the RING AND TRUNK STATUS DETECTOR output signal (TP14) to go to logic state 1, which in turn causes the signal on the TKS2 line (TP13) to go to logic state 1 during time slot 6. Because of this, bit D0 at memory address 06 in the TRUNK STATUS BUFFER MEMORY goes to logic state 1. The SPACE-DIVISION SWITCH connects line TX2 to line RX3 during time slot 5, as can be observed in the SDS Control Register. This connects ANALOG TRUNK SERVICE CIRCUIT 1 to the ANALOG 2-23

TRUNK INTERFACE in reception only, making the PABX ready to receive the caller ID data. The Lab-Volt PABX sends a SETUP message to digital telephone set AL, which starts to ring and replies with an ALERTING (ALERT) message. The Lab-Volt CO sends an analog caller ID FSK signal, via the PABX analog trunk, that is recovered at the CODEC analog output (TP19) of ANALOG TRUNK SERVICE CIRCUIT 1 and converted into data that is sent to the PABX CALL PROCESSOR. The SPACE-DIVISION SWITCH releases the TX2-to-RX3 connection during time slot 5, as can be observed in the SDS Control Register. This releases the connection used to send the caller ID data to the PABX. The Lab-Volt PABX sends an INFORMATION (INFO) message to digital telephone set AL. Stop recording the Lab-Volt PABX call-control messages and the CALL PROCESSOR actions. Hang up the handset of the analog telephone set. * 36. Select the manual display refresh mode on the Oscilloscope, then minimize the Oscilloscope window. Close the TRUNK STATUS BUFFER MEMORY and SDS Control Register windows. Display the contents of each call-control message (IE's) recorded in the Detailed folder of the Call Processor Log window, as well as the contents of each IE (IE components). Also, display the additional information about each CALL PROCESSOR action recorded in this folder. Readjust the view so that the circuitry of the DUAL DIGITAL LINE INTERFACEs, SWITCHING CIRCUIT, SIGNALING CIRCUIT, CALL PROCESSOR, and ANALOG TRUNK INTERFACE of the Lab-Volt PABX can be observed at the same time. * 37. In the CALL PROCESSOR Log, locate the CALL PROCESSOR action External Service Request. Using the Playback function of the Call Processor Log, play back this action. 2-24

What is the meaning of the following information: received from TKS2, 06? Explain. What is the meaning of the following information: mark ATI TKS2, 06 as busy? Explain. * 38. In the CALL PROCESSOR Log, locate the CALL PROCESSOR action Caller ID Data Receive Path Setup. What is the purpose of this action? Using the Playback function of the Call Processor Log, display the sequence of events through which the PABX CALL PROCESSOR performs the action Caller ID Data Receive Path Setup. How does the PABX CALL PROCESSOR perform this action? 2-25

* 39. Once the PABX CALL PROCESSOR has determined that the attendant's telephone set (digital telephone set AL) is available, why does it send a SETUP message to this telephone set? After sending this message, does the PABX CALL PROCESSOR continue to monitor the trunk status signal related to the ANALOG TRUNK INTERFACE? Explain. In the SETUP message, examine the contents of the Channel Identification IE. Which B channel of the DUAL DIGITAL LINE INTERFACE (DDLI) associated with telephone set AL (DDLI A) will be used to convey voice data? Explain. In the SETUP message, what information conveyed by the codeset 5 Display IE can be displayed to the user at digital telephone set AL? * 40. What does the ALERTING (ALERT) message sent by digital telephone set AL to the Lab-Volt PABX indicate? * 41. According to the CALL PROCESSOR Log, what two actions are performed by the PABX CALL PROCESSOR, upon reception of the ALERTING (ALERT) message from digital telephone set AL? * 42. Play back the CALL PROCESSOR action Caller ID Data Reception recorded in the CALL PROCESSOR Log and observe that the message segment, expressed in hexadecimal numbers, of the caller ID data sent by 2-26

the Lab-Volt CO appears in the upper section of the PABX CALL PROCES- SOR. Record the message segment below. Decode the message segment in order to recover the following information: Telephone number of the calling party: Name of the calling party: * 43. How does the PABX CALL PROCESSOR perform the action Caller ID Data Receive Path Release? * 44. Why does the Lab-Volt PABX send an INFORMATION (INFO) message to the attendant's telephone set (digital telephone set AL) once it has received the caller ID data from the Lab-Volt CO? (Explain by referring to the IE's included in this message). * 45. Clear the contents of the CALL PROCESSOR Log. Call Answering * 46. Disconnect Oscilloscope Probe 4 and connect it to TP12 (TSAC-1 ANS output) of the ANALOG TRUNK INTERFACE. On the Oscilloscope, set the sensitivity of channel 4 to 5 V/div. 2-27

* 47. Make the following settings on the host computer: Display the contents of the TRUNK STATUS BUFFER MEMORY. Display the SDS Control Register. Adjust the view in order to be able to simultaneously observe the TRUNK STATUS BUFFER MEMORY, the SDS Control Register, and the signals on the Oscilloscope screen. On the Oscilloscope, select the continuous display refresh mode. * 48. Prepare yourself to perform the next step by reading the sequence of events described in it a few times. When you are ready, proceed to this step and repeat it as many times as necessary in order to be able to observe all the events in the described sequence. (Clear the contents of the CALL PROCESSOR Log each time before repeating this step). * 49. Start recording the Lab-Volt PABX call-control messages and CALL PROCESSOR actions. Using the analog telephone set, make a call to the Lab-Volt PABX. Lift off the handset of the attendant's telephone set (digital telephone set AL) to answer the call and observe the sequence of events described below. Digital telephone set AL sends a CONNECT (CONN) message to the Lab-Volt PABX. The TSAC-1 ANS output signal at TP12 of the ANALOG TRUNK INTERFACE goes to logic state 1, making the ANSWER RELAY in this interface close. This causes DC current to start flowing through the analog trunk loop. Upon detection of this current, the Lab-Volt CO stops applying the ringing voltage across the analog trunk (as can be seen at TP1 of the ANALOG TRUNK INTERFACE), while the RING AND TRUNK STATUS DETECTOR keeps its output signal (TP14) to logic state 1. Because of this, the signal at TP13 (TKS2 line) stays at logic state 1 during time slot 6, causing bit D0 at memory address 6 in the TRUNK STATUS BUFFER MEMORY (bit associated with the ANALOG TRUNK INTERFACE) to stay at logic state 1. The SPACE-DIVISION SWITCH connects line TX2 to line RX0, and line TX0 to line RX2 during time slot 5, as can be observed in the SDS Control Register. This permits connection of the selected B channel in the DDLI associated with digital telephone set AL to the ANALOG TRUNK INTERFACE, in both transmission and reception. The Lab-Volt PABX sends a CONNECT ACKNOWLEDGE (CONACK) message to digital telephone set AL. 2-28

A normal conversation can take place between the analog telephone set and digital telephone set AL. Thus, when talking into the handset of each telephone set, the corresponding analog voice signal appears at TP1 of the ANALOG TRUNK INTERFACE. (On the Oscilloscope, readjust the sensitivity of channel 1 to 1 V/div to observe this). Stop recording the Lab-Volt PABX call-control messages and the CALL PROCESSOR actions. Hang up the handset of digital telephone set AL and the analog telephone set. * 50. Select the manual display refresh mode on the Oscilloscope, then minimize the Oscilloscope window. Close the TRUNK STATUS BUFFER MEMORY and SDS Control Register windows. Display the contents of each call-control message (IE's) recorded in the Detailed folder of the Call Processor Log window, as well as the contents of each IE (IE components). Also, display the additional information about each CALL PROCESSOR action recorded in this folder. Readjust the view so that the circuitry of the DUAL DIGITAL LINE INTERFACEs, SWITCHING CIRCUIT, SIGNALING CIRCUIT, CALL PROCESSOR, and ANALOG TRUNK INTERFACE of the Lab-Volt PABX can be observed at the same time. * 51. In the CALL PROCESSOR Log, locate the CALL PROCESSOR action External Call Answer. What causes the PABX CALL PROCESSOR to perform this action? What is the purpose of this action? Play back the action External Call Answer. How does the PABX CALL PROCESSOR perform this action? Explain. 2-29

What happens to bit D0 at memory address 06 in the TRUNK STATUS BUFFER MEMORY when the PABX CALL PROCESSOR performs the action External Call Answer? Explain. * 52. In the CALL PROCESSOR Log, locate the CALL PROCESSOR action External Call Setup. What is the purpose of this action? Play back the action External Call Setup. How does the PABX CALL PROCESSOR perform this action? 2-30

* 53. Why does the Lab-Volt PABX send a CONNECT ACKNOWLEDGE (CONACK) message to digital telephone set AL? Does it continue to monitor the trunk status signal related to the ANALOG TRUNK INTER- FACE after sending this message? In the CONACK message, examine the contents of the Signal IE. What does this IE indicate? Explain. In the CONACK message, what information conveyed by the codeset 5 Display IE can be displayed to the user at digital telephone set AL? * 54. Clear the contents of the CALL PROCESSOR Log. Call Termination * 55. Make the following settings on the host computer: Display the contents of the TRUNK STATUS BUFFER MEMORY. Display the SDS Control Register. Adjust the view in order to be able to simultaneously observe the TRUNK STATUS BUFFER MEMORY, the SDS Control Register, and the signals on the Oscilloscope screen. Select the continuous display refresh mode on the Oscilloscope. * 56. Prepare yourself to perform the next step by reading the sequence of events described in it a few times. When you are ready, proceed to this step and repeat it as many times as necessary in order to be able to observe all the events in the described sequence. (Clear the contents of the CALL PROCESSOR Log each time before repeating this step). 2-31

* 57. Start recording the Lab-Volt PABX call-control messages and CALL PROCESSOR actions. Using the analog telephone set, make a call to the Lab-Volt PABX. Lift off the handset of the attendant's telephone set (digital telephone set AL) to answer the call, and have a normal telephone conversation. Hang up the handset of the analog telephone set. Hang up the handset of digital telephone set AL to terminate the call and observe the sequence of events described below. Digital telephone set AL sends a DISCONNECT (DISC) message to the Lab-Volt PABX. The SPACE-DIVISION SWITCH releases the TX2-to-RX0 and TX0-to- RX2 connections made during time slot 5, as can be observed in the SDS Control Register. This disconnects the selected B channel of the DDLI associated with digital telephone set AL from the ANALOG TRUNK INTERFACE. The TSAC-1 ANS output signal at TP12 of the ANALOG TRUNK INTERFACE goes to logic state 0, making the ANSWER RELAY in this interface open. This causes the DC current flowing through the analog trunk loop to drop to zero. This is detected by the RING AND TRUNK STATUS DETECTOR whose output signal (TP14) goes to logic state 0. Because of this, the signal at TP13 (TKS2 line) goes to logic state 0 during time slot 6, causing bit D0 at memory address 06 in the TRUNK STATUS BUFFER MEMORY to go to logic state 0. The Lab-Volt PABX sends a RELEASE (RLSE) message to digital telephone set AL, which replies with a RELEASE COMPLETE (RLCOM) message. Stop recording the Lab-Volt PABX call-control messages and the CALL PROCESSOR actions. * 58. Select the manual display refresh mode on the Oscilloscope, then minimize the Oscilloscope window. Close the TRUNK STATUS BUFFER MEMORY and SDS Control Register windows. Display the contents of each call-control message (IE's) recorded in the Detailed folder of the Call Processor Log window, as well as the contents of each IE (IE components). Also, display the additional information about each CALL PROCESSOR action recorded in this folder. Readjust the view so that the circuitry of the DUAL DIGITAL LINE INTERFACEs, SWITCHING CIRCUIT, SIGNALING CIRCUIT, CALL PROCESSOR, and ANALOG TRUNK INTERFACE of the Lab-Volt PABX can be observed at the same time. 2-32

* 59. Print the contents of the Signaling Sequence and Detailed folders of the Call Processor Log. Note: If a printer is not available, save the CALL PROCESSOR Log to an LVTTS file. This will allow this log to be compared to other logs you will record in the next exercises. * 60. In the CALL PROCESSOR Log, locate the CALL PROCESSOR action External Call Termination. What causes the PABX CALL PROCESSOR to perform this action? How does the PABX CALL PROCESSOR release the connection between the ANALOG TRUNK INTERFACE (ATI TKS2, 6) and the selected B channel of the DDLI associated with digital telephone set AL (channel B1 of DDLI A)? What is the meaning of the following information: open answer relay in ATI TKS2, 6? Why and how does the PABX CALL PROCESSOR achieve this? (Answer by playing back this information). 2-33

What is the meaning of the following information: mark ATI TKS2, 6 as available? Explain. * 61. Once it has performed the action External Call Termination, why does the Lab-Volt PABX send a RELEASE (RLSE) message to digital telephone set AL? Why does this telephone set reply with a RELEASE COMPLETE (RLCOM) message? * 62. As a review of what you have learned in this part of the exercise, use the Playback function of the Call Processor Log to display the sequence of events illustrating what happens in the Lab-Volt PABX when an incoming call to the Lab-Volt PABX is received, answered, and terminated. * 63. Clear the contents of the CALL PROCESSOR Log. 2-34 * 64. On the host computer, close the Telephony Training System software. Turn off the TTS Power Supply, as well as the host computer (if it is no longer required). Disconnect the AC/DC power converter from the TTS Power Supply and the analog telephone set. Remove the analog trunk line (two-wire cable terminated with standard [RJ-11] male connectors) connecting the PABX Analog Trunk Interface installed in the Reconfigurable Training Module used as a PABX to the Dual Analog Line Interface installed in the Reconfigurable Training Module used as a CO. Disconnect the digital telephone sets from the Digital Telephone Interface installed in the Reconfigurable Training Module used as a PABX. Remove

the Digital Telephone Interface and the PABX Analog Trunk Interface from this module. Disconnect the analog telephone set from the Dual Analog Line Interface installed in the Reconfigurable Training Module used as a CO. Remove the Dual Analog Line Interface from this module. CONCLUSION In this exercise, you familiarized yourself with the interpreting circuitry in the signaling circuit of the Lab-Volt PABX. You learned that the function of the interpreting circuit is to convert the signaling information carried over an analog trunk into signaling data that is meaningful to the PABX CALL PROCESSOR. You learned that the interpreting circuit consists of a TRUNK STATUS DEMULTI- PLEXING AND STORAGE CIRCUIT and a bank of analog trunk service circuits. You saw that the function of the TRUNK STATUS DEMULTIPLEXING AND STORAGE CIRCUIT is to demultiplex the analog trunk status information it receives from the TKS2 line and to store the corresponding data in a memory accessible to the PABX CALL PROCESSOR. You observed that the memory location where the status (logic state) of the analog trunk associated with a specific analog trunk interface is stored is determined by the number of the bank containing this interface and by the address assigned to TSAC 2 in this interface for the transmission of the trunk status. You made a call to the Lab-Volt PABX and saw that the caller ID FSK signal sent by the Lab-Volt CO, via the analog trunk, is received by the ANALOG TRUNK INTERFACE, digitized and time-division multiplexed to line TX2, and routed to ANALOG TRUNK SERVICE CIRCUIT 1 via the switching circuit of the Lab-Volt PABX. There the digitized caller ID FSK signal is demultiplexed, converted back into its original form, and decoded by a CALLER IDENTIFICATION CIRCUIT which sends corresponding data to the PABX CALL PROCESSOR. Finally, you learned that when an incoming call to the Lab-Volt PABX is received, answered, and terminated, a complex sequence of events occurs in the Lab-Volt PABX, which is summarized below. The PABX CALL PROCESSOR detects that an incoming call from the outside is occurring on the PABX analog trunk, based on a change in the analog trunk status stored in memory. This causes the PABX CALL PROCESSOR to mark the analog trunk as busy in its memory, establish a connection to make the PABX ready for the reception of the caller ID data from the Lab-Volt CO, and exchange messages with the attendant's telephone set to make it ring and send the caller ID data to it. When the PABX CALL PROCESSOR receives a message from the attendant's telephone set indicating that the call has been answered, it makes the ANSWER RELAY in the ANALOG TRUNK INTERFACE close in order for DC current to flow through the analog trunk loop. The PABX CALL PROCES- SOR then establishes a bidirectional connection between the ANALOG TRUNK INTERFACE and the selected B channel of the DDLI associated with the 2-35

attendant's telephone set in order for a normal conversation to occur between the users at the analog telephone set and the attendant's telephone set. It also sends a message to the attendant's telephone set indicating that the connection with the analog telephone set is established. When the PABX CALL PROCESSOR receives a message from the attendant's telephone set requesting that the connection be released, it releases the bidirectional connection between the selected B channel of the DDLI associated with the attendant's telephone set and the ANALOG TRUNK INTERFACE, makes the ANSWER RELAY in this interface open in order for the DC current through the analog trunk loop to drop to zero, marks the PABX analog trunk as available in its memory, and exchanges messages with the attendant's telephone set to complete call termination. REVIEW QUESTIONS 1. Compare the signaling protocol used to receive external calls via a PABX analog trunk to that used to receive external calls via an analog telephone line, and explain. 2. What does the interpreting circuit in the signaling circuit of the Lab-Volt PABX consist of? What is the function of this circuit? Explain. 2-36

3. Briefly describe the path through which the caller ID data received from the CO, via the analog trunk, is routed to the Lab-Volt PABX CALL PROCESSOR. 4. What does trunk status demultiplexing and storage consist in? 5. Briefly describe the sequence of events that occur in the Lab-Volt PABX when an incoming call is received and answered. 2-37