Patent GB-608466-A (GB)
Title: Improvements in or relating to class of service discrimination in telecommunication exchange systems
IPC: H04M15/08
Filed: 1946-02-25
Abstract: 608,466. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. Feb. 25, 1946, No. 5791. Convention date, March 27, 1945. [Class 40 (iv)] In an automatic exchange system the class of service to which a substation is entitled is determined for both called and calling parties. For calling lines a distinction is made between unlimited service, limited service and absentsubscriber service lines; while for called lines, first lines, intermediate and final lines of PBX groups, absent-subscriber service lines, transferred and unused lines are distinguished. Calling line class determination, Fig. 2. Point D, connected to the d wire of the subscriber, is joined to one of the terminals 1-8 to denote its class. First PBX lines, ordinary or intermediate PBX lines, and final PBX lines are connected to terminals 1, 2 and 3 or 4, 5 and 6 respectively according as their service is restricted or unlimited, while terminals 7 and 8 are associated with absent-subscriber and transferred subscriber lines. Seizure of the register brings up relay C which connects T in series with an individual current source to the d wire of the calling line over the switch train. Relay T is also connected over the bank a of the switch P to terminal 7, so that if the line is in absent-subscriber condition, T pulls up and brings up As over bank b of P. In all other cases P steps to position 1 and terminal 1 is tested, T and Rs operating if the line is a first restricted service PBX line, and P stepping on to test the terminals 2 and 3 in turn if it is not. Contact OC connects -48 volts to the d wire to mark the line busy, a rectifier in the circuit preventing cross connections via the common battery. Called line class determination, Fig. 3. With SU up and in position 4, T is connected up to test terminal 7 for connection to the d wire of the called party in the final selector bank, T and As coming up if such connection exists. Otherwise P goes to position 5, terminal 8 is tested, and if the called line belongs to a transferred subscriber, T and Tf are operated. If this test is unsuccessful, P steps on and in position 6, T tests terminals 1 and 4 simultaneously over banks a and d to determine whether the line is a first PBX line. By the same method tests are made in positions 7 and 8 to determine whether the line is an ordinary or intermediate PBX line, or a final PBX line respectively. If all these tests fail, the line is unused. PBX final selector, Fig. 4. The final selector is indicated by its driving magnet RF and its test wiper d. On reaching the first PBX line connected to terminal 1, P steps to position 6 as described above, and T operates. If this line is busy O comes up and is followed by Pb, which releases T, thus stepping P to position 7 where T tests terminal 2 connected to the intermediate lines, while T1 tests terminal 3 connected to the final line of the group. The driving magnet is operated over a back contacts of T1 and a back contact of T and a front contact of O in parallel so that rotation continues until a free line is found, whereupon T pulls up and O remains unoperated, the switch is stopped, and end-ofselection relay Fs is energized. If all the intermediate lines are busy T1 pulls up to the final line, so that operation of O is followed by that of busy relay De. Prevention of cross-connections. In order to prevent incorrect operation of the T and T1 relays of two control circuits in series, Fig. 5 (not shown), it is arranged that operation of T or T1 disconnects T1 or T respectively, (Fig. 4), or that T and T1 are fed by two different current sources connected in opposition, Fig. 6 (not shown).