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A variety of special subscriber markings may be made at the exchange so that callers to these numbers receive special printed codes. A subscriber may not wish to receive traffic for an extended period, as for example over a holiday period, and his line may have a plug inserted in such a way as to control the equipment to return the characters ABS when the number is called. Similarly, a line which is not connected will return the C.C.I.T.T. standard service code NP, indicating "not a working line." The classification facility may be employed to provide separate networks using the same switching equipment with complete or partial blocking of calls between respective groups of subscribers. For example, a network could be provided for civil or military authorities with classification such that general subscribers to the telex service could not call these outlets, although the outlets on the special network could call within their own group or to subscribers of the general telex network. Semi-automatic positions (Figure 6) have been provided at each transit centre to cater for a further range of special requirements and to handleservice difficulties, the combined facilities in one location being referred to as a Telex Service Centre. Fig. 6 Telex Service Centre — Manual assistance position 28
These semi-automatic positions provide for: • Calls to be handled through an operator for toll-ticketing reasons. Examples of this class of call are conference/ broadcast calls in which a calling subscriber may be connected to a number of other subscribers with full communication between all parties (conference) or with only the caller able to send (broadcast). The system of charging for these calls does not lend itself to fully automatic operation and for this reason semi-automatic facilities have been provided. Other calls in this category are press calls which are charged at a special concessional rate within Australia but which may be made from subscriber lines which handle full rate traffic on an automatic basis at other times. • Assistance to subscribers who experience service difficulties. Operators, where possible, will connect the call for the subscriber, or suitably advise the customer about the service difficulty if this is not possible. Genuine fault conditions are filtered from service difficulties due to subscriber maloperation or to congestion on particular routes and faults are transferred to the appropriate engineering maintenance group. Subscribers with an unduly high occurrence of service difficulties can be put on line observation through these positions, and a continuous printer record kept of their traffic in order to analyse the type of difficulty experienced. • Enquiry traffic which may concern national directory or national rate information. All international enquiry traffic is directed to the international telex exchange at Paddington, Sydney. Although semi-automatic positions are provided for these main traffic loads all subscribers are connected as automatic exchange lines. No facilities are provided for terminating manual subscriber lines on these positions since the exchange system as a whole has been based upon a transmission plan which permits fully automatic connection between any two subscribers. Regenerative repeaters can be switched-in on semi-automatically connected assistance traffic which may arise because of temporary transmission deterioration on a particular route. Inter-Operation with the International System The Australian national network connects to the international system via a single international gateway, the International Telex Centre, operated by the Overseas Telecommunications Commission (Australia) at Sydney. An Australian subscriber making an outward call semi-automatically establishes the connection in two stages. The first stage is similar to a national subscriber call except that a 3-figure number commencing with zero is sent, e.g.. 021. At this stage connection is made to the international exchange which automatically returns a printed service code identification followed by the "who are you" signal which causes the calling subscriber's "answer-back" 29
Page 1: 1 1968
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Page 6 and 7: Signalling in L M Ericsson Telex Sy
Page 8 and 9: On physical subscriber lines other
Page 10 and 11: In a new Recommendation U 11, CCITT
Page 12 and 13: Automatic Tripping of B Subscriber'
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Page 16 and 17: show the signalling both for single
Page 18 and 19: Fig. 11 gnalling for setting up a c
Page 20 and 21: In this case, after receipt of the
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Page 24 and 25: The capital cost of the telex syste
Page 26 and 27: Fig. 1 Traffic distribution by dist
Page 28 and 29: Fig-3 Charging principles Zone char
Page 30 and 31: Transmission Considerations The obj
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Page 36 and 37: References 1. C.C.T.T. Illrd Plenar
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