Patent GB-957052-A (GB)
Title: Improvements in or relating to communication line concentration systems
IPC: H04Q3/52
Filed: 1960-10-05
Abstract: 957,052. Automatic exchange systems. WESTERN ELECTRIC CO. Inc. Oct. 5, 1960 [Oct. 26, 1959 (2)], No. 34137/60. Heading H4K. A two-stage concentrator system includes a main exchange, a plurality of subscriber lines connectible by a primary concentrator to a smaller plurality of links, and a secondary concentrator for connecting the links to a still smaller plurality of trunks to the main exchange, means being provided at the primary concentrator for scanning the lines and the links for cyclically determining the service condition thereof and for supplying indications thereof to the main exchange, and means being provided at the main exchange controlled by the scanning means for controlling the concentrators to establish connections between the lines, the links and the trunks, and to disconnect established connections. In the embodiment described the primary stage includes a full access switch for connecting 58 subscribers to 10 links which join the primary concentrator to the secondary concentrator, at which a partial access switch connects 200 links to 100 trunks to the main exchange, similarly numbered links from each primary concentrator having access to a particular 10 of the 100 trunks. The switches at the concentrators are single stage one-wire PNPN transistor matrices with transformers to convert from two-wire to one-wire transmission. Talking battery is supplied at the primary concentrator and crosspoint holding power locally. A connection is set up by selecting an -idle path through both stages, the numbers of the link and trunk selected being transmitted to the concentrators with a " mark " order. The line number concerned is available from a line counter in both the primary concentrator and the main exchange so that both ends of each switching stage are specified. The concentrator switches are released from the link side of the primary concentrator and the trunk side of the secondary, complete records of each connection being stored in a temporary route memory at the exchange, so that the numbers of the link and trunk to be disconnected are readily available. Closures and releases of the concentrator switches, as well as failures thereof, are reported to the exchange. Both lines and links are scanned for detection of changes of state. Since the links are scanned faster than the lines, disconnections are detected by the link scanner in order that detection may take place earlier. The transmission routes for control and supervisory signals are chosen in dependence upon the speed of the signals concerned. High rate information, such as the advance pulses sent to the concentrator scanners, is transmitted over metallic trunks reserved for control signals in order to minimize crosstalk; low rate signals, such as service requests, answer and hang up indications, are transmitted on phantom circuits over speech trunks; and medium rate signals, such as primary identification numbers on phantom circuits over the control signal trunks. In transmitting information from the exchange concerning a particular primary concentrator the information is sent to the secondary concentrator concerned over the control signal trunks or a phantom circuit thereon. Thence the information is broadcast over metallic control links to all the primary concentrators associated with that secondary, a single " execute " signal being sent on a phantom over speech trunks and links to the particularly primary concentrator which is to act on, or respond to, the information. The " execute " signal for a secondary concentrator is sent over a phantom circuit on speech trunks. General description, Fig. 25.-Substations such as 25-22 are connected to primary concentrators (primaries) 25-32, 25-36, which are in turn connected to secondary concentrators (secondaries) 25-37, 25-33 over links such as 25-11. Trunks 25-12 extend directly to the distribution switching network 25-35 of the exchange. In Fig. 25 all the equipment on the right of the chain line 25-30 is within the exchange, that between the lines 25-30 and 25-31 constituting the remote concentrator control (RCC). The lines of all primaries are scanned synchronously under control of counters (not shown) at the primaries driven by trains of negative advance pulses sent from the exchange, a master line number counter 25-13 at the exchange being stepped at the same time so that the identity of a calling line can be determined from the setting of the line number counter 25-13 when a service request is signalled by a primary. A nominal time of 2 ms. is allowed for the transmission of a pulse to a primary and the transmission of a consequent signal back to the exchange. The common control system of the exchange may have a basic repetition rate of 2.5 Ás. so that the stepping of the concentrator scanners at 2 ms. intervals represents merely an occasional occurrence. In the absence of service requests or other supervisory signals the sequence control 25-15 continues to step all the counters and the lines are scanned continuously. Subscriber 25-22 goes off-hook.-When this occurs the line scanner (not shown) in primary 25-32 will observe the service request when the counter reaches the line number n, and a pulse will be sent to the primary control 25-16 where it sets a flip-flop (bi-stable state circuit). This in turn produces a so-called " flag " indication to common control via sequence control 25-15, at the same time causing the latter circuit to discontinue the train of counter advance pulses, so that all local activity in RCC ceases. After an average time of 2 to 3 ms. the common control will observe the flag and consults its programme as to the procedure to follow. As a result it directs the office scanner 25-21 to determine the condition which caused the flag. The scanner first examines points which indicate equipment failures, and finding no signals, it proceeds to the supervisory points relating to the primary controls. It looks first for hangups, then for answers, and finally for service requests. If it detects a hangup, common control will deal with this and then proceed to its other activities and will have no opportunity to learn of the service request until it returns to RCC after about 5 ms. However, if no other condition obtains, the office scanner 25-21 will read a service request on primary 00 (25-32) in consequence of the operated flip-flop in primary control 0 (25-16). The primary number inferentially provides that of the secondary and common control obtains the line number from the line number counter 25-13. It then consults a barrier grid memory to examine the records for primary 25-32 to determine if the service request is a new one or merely a malfunctioning of the equipment. This is necessary because each of the control signals from a primary is two-valued, e.g. the service request signal may also indicate cross-point failure and is termed SR/CPF. Assuming the service request is found to be a new one, common control by reference to a memory selects an appropriate route to connect the caller to the exchange, for example that including link 25-11 and trunk 25-12, and delivers this information to the remote network control 25-18 after recording it in the memory. It then instructs the control selector 25-20 to energize network control 25-18 to send the necessary control impulses to effect the connection. Network control 25-18 then transmits the appropriate information to the primary 25-32 and the secondary 25-37 through the respective controls 25-16 and 25-17. It is unnecessary to signal the line number since the counter in primary 25-32 conditioned aline selector (not shown) to provide a connection to the line when the service request was detected. The only information required is a one-out-of-ten indication for the links and a one-out-of-ten indication for the trunks since if, say, link 9 were selected then trunks 90 to 99 are those available for its extension. The control selector also resets the flip-flop in primary control 25-16 which indicated the service request, but the network control 25-18 prevents sequence control 25- 15 from recommencing scanning until it has completed transmission of the path information. The flag is also inhibited while network control 25-18 is operative. After about 15 ms. the scanning is resumed providing no other flag-producing conditions exist. Common control actuates the exchange distribution network 25-35 to connect trunk 25-12 to a free alternating-current dial pulse receiver 25-36 which reverts dial tone. The keyed number is transferred from receiver 25-36 to common control which, by reference to its programme, determines the equipment number of the wanted line e.g. that of subscriber 25-23. Establishing connection to wanted line.-Common control now has the secondary number, the primary number and the line number of the called line. It gates into the line match register the line number which is a six-bit binary number corresponding to link k and the line number counter 25-13 is then caused by the control selector 25-20 to stop when it registers this number. Thus, after a waiting time of about 60 ms., line number match 25-14 delivers an output to sequence control 25-15 which gives a flag indication to common control. The office scanner 25-21 again determines the cause of the flag and informs common control that a line number match has been effected. From its memory common control finds that the equipment number of substation 25-23 is stored, and from the switching memory it determines whether that station is recorded as a working number for any other connection, viz. whether the line is busy. If this busy test is positive, busy tone is reverted, the match condition is cleared and the call is disregarded. If the line is not listed as busy it is presumed to be idle, but just before the connection is established the office scanner 25-21 is directed to examine the service request output of the pr