Dss «Kvant-e». Subscriber access subsystem. Algorithm of outgoing call in slu-128.
2.2 Algorithm of connection set up
Diagram of the voice transmission path between two subscribers is shown in the figure 2.5.
Subscriber A uses a phone with the number of 7-00-32. Customer unit is connected to a TSS with the help of TC-0 of T-2.
Subscriber module of subscriber A uses trunk 0 to access SCU of HE. The 16th time channel of the trunk 0 carries signalling information. Subscriber traffic goes in the TC-7 of T-18 towards SCU.
The SCU uses signalling information obtained from SCM to establish connection between TC-7 of T-18 and TC-5 of T-13 that is assigned to the subscriber module of subscriber B.
The number of subscriber B is 7-70-96. Customer unit of subscriber B is connected to a TSS with the help of TC-0 of T-4.
Figure 2.5 – Diagram of the voice transmission path between subscribers of Kvant-E
Typical algorithm of a call set up includes 11 steps given below.
Step 0. Subscriber A requests a connection
Subscriber A picks up his handset which results in “off-hook” state. CU-A identifies “off-hook” state with the help of a scan point. Information about the “off-hook” state goes to a controller (CS-8-a) of SM-A.
A testing unit performs all the necessary testing procedures.
The controller checks available information about the “off-hook” subscriber (his number and type of a dial pulser).
Step 1. Dial tone sending
The controller identifies a TC and trunk (TC-0 of T-2) that the CU-A uses to access the TSS.
The controller of subscriber module (CS-8A) establishes connection between TC-0 of T-7 and TC-0 of T-2 in order to connect a DGTS with a subscriber line of subscriber A.
DGTS generates the dial tone that is converted to analogue signal by CU-A. Thus, subscriber A hears the dial tone and starts dialing.
Step 2. Pulse dialing
Subscriber A dials five digits of the number of subscriber B (7-70-96). CUA receives loop pulses produced by the dial pulser. CU-A uses the scan point in order to identify pulses.
The controller of the subscriber module (CS-8A) switches off the DGTS if the first digit is dialed.
Controller scans the scan point inside CU-A and writes the dialed number to its RAM.
Step 3. The controller of SM-A operates SM-A equipment in order to establish connection
The controller selects available TC of the trunk number 0, which is the time channel number 7.
The controller generates an ISSC signalling packet that carries the number of subscriber B (7-70-96) and a number of selected TC-7 within the trunk towards SCU (TC-7 of T-18).
This packet is carried to SCM of SCU over the 16-th time channel of trunk number 0. It reaches SCM within a TC-18 (which corresponds to the number of the trunk). SCM transmits obtained signalling data to the controller of SCU (CD).
CD uses signalling data obtained from SCM in order to identify required path towards subscriber B.
Step 4. CD controls connection setup process within SCU
According to the signalling data obtained from SCM the CD of SCU selects available TC-5 of T-13 in order to reach SM of subscriber B.
The CD of SCU generates an ISSC signalling packet that carries information including the digits of the number of subscriber B and the number of TC-8 of T-13 selected to carry voice information between subscribers.
The CD of SCU sends the ISSC signalling packet to the SCM. The SCM puts ISSC signalling packet to the 16-th time channel of the 13-th trunk in order to perform signalling exchange with the controller of SM-B.