Patent GB-1287590-A (GB)
Title: Communications switching office
Inventor: FUNK CHARLES JOHN
IPC: H04Q3/545
Filed: 1969-12-16
Abstract: 1287590 Automatic exchange systems WESTERN ELECTRIC CO Inc 16 Dec 1969 [18 Dec 1968] 61117/69 Heading H4K A large tall switching centre incorporates a plurality of concurrently operative markers that select an outgoing trunk and a path thereto in response to rudimentary translation data provided, in response to incoming dialled digits, by a stored programme control. The latter includes memory in which is stored sufficient detail of each call being handled by the different markers as to permit of alternative translation data being supplied to a marker in the event that it cannot set up a connection. The data may be sent to an alternative marker for example in the event that the original marker cannot set up the connection because it is faulty. Provision is made for both-way trunks by providing them with appearances on the incoming and the outgoing sides of the switching network. Particular description. Three digit call.-A calling signal at a trunk circuit, e.g. 114 causes a start signal to be applied to a sender link frame 117 associated with the trunk. The sender-link is then connected to a preferred link controller 118 (each of which controls up to 32 such frames) whereupon one of the calling trunks in a selected one of the trunk groups is selected and a test for a free path through the frame to a free one of the 40  register-senders 119 is made. With the test complete, the controller demands service from central control by changing the state of a particular ferrod in peripheral scanner 131. Control, during a normal monitoring programme, notes the request, switches to a suitable processing programme and accepts the identities of the trunk, the controller, the sender, the senderlink and the path through the frame into its temporary memory 122 via the ferrod matrix in the scanner. Various tables in the processor are used successively to fully determine the identities since these are all given in terms of related equipments i.e. the sender and trunk only have appearances on a particular sender link frame so that the latter partly identifies the sender and the trunk. Central control, via central pulse distributer 124 and CPD applique 130 (essentially an electronic to electromechanical converter using flip-flops and relays), issues commands to the controller to switch through the selected path (after checking for a possible double connection) and to withdraw its request for service. Response or not to the latter command acts as a check on system operation. A proceed-to-send signal is reverted by the sender over the incoming trunk. Incoming digits in multifrequency form are converted to D.C. and stored in relay registers in the sender. When sufficient digits have been received, the sender joins a queue for accessing a free decoder channel 126 and eventually is electrically connected to one via a relay connector. The circuitry in the decoder channel for responding to deliverately false information is inhibited. Two ferrods-one for a translation request and one indicating that this is the first such request on this call-are energized in the peripheral scanner PS. The processor, or detecting the request, notes that this is not a test call, that as previous request has occurred (using a last look memory), switches to a suitable programme and identifies the particular scanner from its appearance on the decoder connector (not shown) so that it can look-up the call details already stored in respect of the sender (appropriate energization of ferrods in P, S again provides the means for passing identification data from the sender and decoder channel to the processor). The origination and class of service of the by-now identified trunk are looked-up and the fact that normal translation is required and not connection to a recorder, as overload announcement machine no acceptance of fault details is noted. Information of this nature and also a requirement for AMA is conveyed between peripherals and the processor utilizing a single lead and ferrod, more complex data is transmitted in n-out-of-m code. In the present instance the sender is aware that the first three digits represent an office code and not an area code (as required for national or international routing) and indicates this to the processor by energizing an appropriate ferrod. The processor provides the appropriate translation using the tables (mentioned above) and tests the groups of trunks 127 having access in the required direction. One group having a free trunk is selected and its identity together with the signalling mode necessary thereon is passed to the channel decoder 126 via distributer register 128 and function translator 129. Naturally overflow trunks are used and overload statistical metering is effected in the event that a normal free trunk cannot be located. The decoder channel selects a suitable marker 105 the various types of which are each formed in a priority chain) and connects the distributer register thereto via marker connector 133 so that relevant data may be transferred thereto. Thereafter the marker is connected to the sender via decoder connector 132. Reorder &c. commands are issued to the marker if necessary at this time by the processor. The marker informs the processor that the decoder channel and the distributer register may be released, selects a relevant free trunk in the group of 40 trunks whose identity it has been supplied with and then selects and switches through a path from the incoming trunk to the just-selected outgoing trunk. The marker conveys the routing instructions i.e. 0-6 figure initial code digits which were derived by translating the original incoming 3 digit code and also the code form (model) in which the digits are to be transmitted, whereupon the marker releases and control of the call resides in the sender until all the digits have been sent. If the marker fails to find an outgoing trunk it reapplies to the processor which supplies it with alternative routing data. Initial hold routing.-It may happen that the processor cannot pretest trunk groups, e.g. due to the non-provision of group busy relays (e.g. circuits 127). It must therefore inform the decoder channel not to release until the marker has found a free trunk or that all trunks are busy. The processor additionally provides the marker with the final preferred route i.e. trunk group and keeps a record of the situation so that if the marker reapplies, a first alternative trunk group i.e. not an alternative route, can be supplied. This process repeats until either a free trunk is found or all trunks are found to be busy. At every attempt, whether alternative trunk group or alternative route, the data required for controlling digit transmission of the sender is adjusted if necessary by altering the contents of the distributer register and hence of the decoder channel and the marker. 6-digit call.-This proceeds as outlined above except that the sender informs the processor that it must take into account the D, E, F, digits in addition to the A, B, C digits. The particular translation tables viz. grid or match tables that are used with depend on the D, E, F digits. As a general rule match tables are only used when the D, E, F combination is rare since it takes a longer time to compare the received D, E, F digits and those listed in the table by running-down the list than it does to address a grid table using the D, E, F digits (the relevant grid or match table is of course decided by the A, B, C digits). Maintenance: faults.-The usual duplication of busses &c. parity checks and "all seems well" signals encountered in a No. 1 ESS control are provided. An additional feature is concerned with a "retrial" i.e. a second or even third attempt to set up a call over the same path using stored data. This occurs if the distributer register, decoder channel or marker fail to receive sufficient data, do not receive data within a determined time or are prematurely reset. Relays in the equipments coupled to ferrods in the peripheral scanner are utilized for bringing the processor's attention to the need for a retrial. Continued failure i.e. a number of retrials in excess of a predetermined threshold, will of course initiate a maintenance programme. The duplicated peripheral function translator is merely a logical interface between the processor and the peripheral codes. It passes data in binary form to the distributer registers but translates the data into addressing information so as to access required parts of the peripheral scanner under the command of the processor. In so far as maintenance is concerned, it can respond to false data deliberately inserted by the processor and can then pass the data on if necessary so as to test other equipments.