CJ = Combined Junctor LI2 = (Digital) Line Circuit

A subscriber lifts his handset to make a call. This is detected by the subscriber’s line circuit, which is scanned continuously by a device processor on the line circuit board (See Figure 2.5.4). The EMRP scans all device processors at regular intervals to see if something has happened, so the EMRP is informed about the lifting of the handset and sends in its turn a signal to the central software of the LI2 block. LI2 sends a signal to the CJ block (Combined Junctor), which co-ordinates the activities performed within the SSS subsystem. CJ asks the JT block (Junctor Terminal) to reserve a channel to the group switch for our call. If the subscriber stage is detached (i.e. remote), then a block RT (Remote Terminal) will be used instead of JT.

C
A = Charging Analysis KRC = Keyset code Reception Circuit

The next thing to do is to see if the A-subscriber has been assigned any facilities. (He may, for instance, have the facility “non-dialled connection” - also called “hot line” - which means that he need not dial any digits). Furthermore, the switching equipment must know whether the subscriber has a keyset telephone or not, and this information is stored in the SC block (Subscriber Categories). If the subscriber has a keyset telephone, a keyset code receiver (KRC) must be connected. CJ orders KR2 to select a free KRC, and when KR2 has found such a device it orders the Time Switch (TS) to set-up a connection between the subscriber’s LIC and the selected KRC.

C
A = Charging Analysis KRC = Keyset code Reception Circuit

An RE individual is now to be reserved to handle the set-up of our call. (An RE individual is a data area in the RE block which stores information about this particular call). To make the reservation, CJ sends a signal to RE, and this signal passes via SC to fetch more categories. These are then stored in RE and will be used later on during the set-up phase. When an RE individual has been selected, the exchange is ready to receive digits. RE informs CJ to that effect, and CJ passes the information on to KR2, which activates the function for sending of dial tone to the A-subscriber.

C
A = Charging Analysis KRC = Keyset code Reception Circuit

The subscriber’s dialling of the first digit is detected by the KRC. The KR2 block sends the digit to CJ, which sends it on to RE. RE stores the digit and sends it to DA (Digit Analysis) for analysis. The information contained in DA is in the form of tables and is to a great extent dependent on the configuration of the network in which the exchange is included.

The result of the analysis is sent to RE, which takes different kinds of action depending on what the result indicates.

The following are examples of analysis results:

• 
  Number length.
  
• 
  Charging case. This information is used for further analysis in CA (Charging Analysis).
  

C
A = Charging Analysis KRC = Keyset code Reception Circuit

RE receives a routing case as analysis result from DA and sends it direct to the RA block (Route Analysis) for further analysis.

RA responds by indicating the outgoing route to be used and the number of digits to be sent to the next exchange. RE treats the charging case indicated by DA as analysis result in the same manner, but sends it to CA (Charging Analysis) instead. CA responds by indicating how the call is to be charged.

BT = Bothway Trunk JT/RT = Junctor Terminal/Remote Terminal

C
A = Charging Analysis KRC = Keyset code Reception Circuit

CCS = Common Channel Signalling Subsystem KR2 = (Digital) Keyset code Receiver

CHS = Charging Subsystem LIC = Line Interface Circuit

CJ = Combined Junctor LI2 = (Digital) Line Circuit

CL = Call supervision PD = Pulse Distribution

C7LABT = CCITT No. 7 Label Translation RA = Route Analysis

C7DR = CCITT No. 7 Distribution and Routing RE = Register functions

C7ST = CCITT No. 7 Signal Terminal SC = Subscriber Categories

DA = Digit Analysis SSS = Subscriber Switching Subsystem

EMTS = Extension Module Time Switch ST-7 = Signalling Terminal for CCITT No.7

ETC = Exchange Terminal Circuit TCS = Traffic Control Subsystem

GS = Group Switch TS = Time Switch

GSS = Group Switching Subsystem TSS = Trunk and Signalling Subsystem
Figure 2.9.7

Selection of an Outgoing Line

The information about the route to be used enables RE to ask the BT block (Bothway Trunk) to select a free outgoing line in the route. If BT does not find any free line, RE will ask the RA block (Route Analysis) to provide an alternative route. (Here we assume that BT finds a free line).

BT answers RE by telling it which line has been selected, and RE can now ask the GS block (Group Switch) to reserve (just reserve - not set-up) a path from the JT/RT channel to the BT channel.

BT = Bothway Trunk JT/RT = Junctor Terminal/Remote Terminal

C
A = Charging Analysis KRC = Keyset code Reception Circuit

CCS = Common Channel Signalling Subsystem KR2 = (Digital) Keyset code Receiver

CHS = Charging Subsystem LIC = Line Interface Circuit

CJ = Combined Junctor LI2 = (Digital) Line Circuit

CL = Call supervision PD = Pulse Distribution

C7LABT = CCITT No. 7 Label Translation RA = Route Analysis

C7DR = CCITT No. 7 Distribution and Routing RE = Register functions

C7ST = CCITT No. 7 Signal Terminal SC = Subscriber Categories

DA = Digit Analysis SSS = Subscriber Switching Subsystem

EMTS = Extension Module Time Switch ST-7 = Signalling Terminal for CCITT No.7

ETC = Exchange Terminal Circuit TCS = Traffic Control Subsystem

GS = Group Switch TS = Time Switch

GSS = Group Switching Subsystem TSS = Trunk and Signalling Subsystem
Figure 2.9.8

The Digits are sent to the next Exchange

At this point all preparations have been made for sending the digits to the other exchange.

The information received from RA (Route Analysis) tells RE how many digits are to be sent. The digits are sent to BT, which forwards them - together with information about their destination - to the C7DR block (CCITT No. 7, Distribution and Routing). After examining the destination data, C7DR selects the proper signalling terminal for sending the message. The signalling terminals are administered by the C7ST block (CCITT No. 7 Signalling Terminal).

B
T = Bothway Trunk JT/RT = Junctor Terminal/Remote Terminal

CA = Charging Analysis KRC = Keyset code Reception Circuit

CCS = Common Channel Signalling Subsystem KR2 = (Digital) Keyset code Receiver

CHS = Charging Subsystem LIC = Line Interface Circuit

CJ = Combined Junctor LI2 = (Digital) Line Circuit

CL = Call supervision PD = Pulse Distribution

C7LABT = CCITT No. 7 Label Translation RA = Route Analysis

C7DR = CCITT No. 7 Distribution and Routing RE = Register functions

C7ST = CCITT No. 7 Signal Terminal SC = Subscriber Categories

DA = Digit Analysis SSS = Subscriber Switching Subsystem

EMTS = Extension Module Time Switch ST-7 = Signalling Terminal for CCITT No.7

ETC = Exchange Terminal Circuit TCS = Traffic Control Subsystem

GS = Group Switch TS = Time Switch

GSS = Group Switching Subsystem TSS = Trunk and Signalling Subsystem

Figure 2.9.9

Receiving a Signal from the B-Subscriber’s Exchange

After the other exchange has received the digits, one of its tasks will be to see if the B-subscriber is free. If this is the case and if set-up is permitted, the B-subscriber’s exchange informs our exchange to that effect by sending a CCITT No. 7 signal. The signal is received by the signalling terminal and sent to C7DR (CCITT No.7 Distribution and Routing) to see if the message is addressed to “our” exchange. If so, the message is sent to C7LABT (CCITT No.7 Label Transition) for translation of the coded number into the identity of the BT line (channel) required. The message is sent to the proper RE individual by BT.

C
A = Charging Analysis KRC = Keyset code Reception Circuit

When this “end-of-selection signal” arrives, RE will take the following action:

1. 
   Order selection of a PD individual for charging of the call (PD = Pulse Distribution).
   
2. 
   Order GS (Group Switch) to set-up the path reserved in Figure 2.9.7.
   
3. 
   Order CJ to set-up the call through the subscriber stage. CJ orders (1) KR2 to disconnect the KRC and (2) TS to set-up a connection between the subscriber’s LIC and the reserved JT/RT channel.
   

B
T = Bothway Trunk JT/RT = Junctor Terminal/Remote Terminal

When the B-subscriber answers, the two parties can start conversing. Charging is carried out by the PD block (Pulse Distribution), which has reserved a PD individual (data area) for our call.

The clearing operation is to start when the A-subscriber replaces his handset. The LI2 block (Line Interface) detects the replacement event and forwards information about this to CL via CJ.

A
ppendix 2