11 - ericssonhistory.com

More documents

Recommendations

Info

Transmission Considerations The object of the telex network is to provide economic low-error rate message or data communication with full interconnection possibilities between all subscribers and to the international network. The main problems in achieving this objective in a telex system are the effects of cumulative distortion on built-up connections and the effect of circuit aberrations such as intermittent failures to start or stop polarity of a section or sections of the overall circuit. In practice, the first mentioned problem means that the number of telex trunks which may be connected in tandem has to be limited and the network structure arranged to conform with this limitation. Routing rules must be developed to prevent successive alternate routing since this would increase the number of tandem-connected trunks. The Australian telegraph channelling network has been built up over many years and the quality of performance of equipment on different routes is not identical. Allowance has been made for this, and for the possible introduction of distortion voice frequency telegraph systems in future years, by constructing the transmission plan in terms of distortion limits per link, and these are shown in Figure 5. The term distortion used in sequential telegraph transmission is a measure of the degree of departure of the significant instants of modulation from the ideal. In start/stop transmission a receiving machine translates signals in terms of the occurrence of instants of modulation following the commencement of the 'start" pulse. Telegraph distortion is a measure of the correctness of timing of the pulse type transmission with respect to the leading edge of the release or start element. Important features shown in Figure 5 are that the subscriber path to a transit exchange (which may be through a "remote" terminal exchange) shall not produce more than 12 % of gross start/stop distortion at the output of the terminating relay set of the transit exchange, and in the reverse direction shall have a margin to gross start/stop distortion of 30%. Connections between first and final transit exchanges shall not exceed 13 % gross start/stop distortion and shall not traverse more than one other transit exchange. In order to maintain this rule alternate routing is limited to the original transit exchange. Further, alternate routing is prevented on international calls to ensure that gross start/stop distortion at the point of exit from the Australian national system, the international exchange at Sydney, does not exceed 22 %. Incoming international traffic is regenerated by the Overseas Telecommunica- Fig. 5 Transmission plan 26
tions Commission (Australia) so that the input from the international trunks at the Sydney transit exchange should not be more than 5 %. Unique Features A comparison of Figures 2 and 4 shows that while there are 44 tariff zones in the Australian automatic telex system there are exchanges in only 1 1 of these, although there are some hundreds of subscribers in the remaining tariff zones. The distribution of these is such that they cannot be economically grouped together in exchanges in their own tariff zones. The telegraph channel network, which is not exclusive to telex but is still mainly governed by private wire and public traffic system requirements, often does not provide a convenient common grouping point for an exchange within the tariff zone; in fact the transmission considerations previously mentioned tend to make this undesirable. The telegraph channel network rather tends to form a simple star pattern in each State based upon the capital city as the centre of the star. L M Ericsson offered an ingenious solution enabling these subscribers to be connected over voice frequency telegraph channels to capital city ARB 111 exchanges but automatically metered according to their remote tariff zone origin. This is arranged in the signalling system by the automatic transmission of a 5-unit start/stop tariff zone code identifying the tariff zone of the calling subscriber, and this is used in the rate setting equipment, which is part of the parent ARM exchange, with the first two (A, B) digits of the called subscriber's number to determine the appropriate metering rate. This type of subscriber has become known as the "out of tariff zone" subscriber, and the automatically transmitted tariff zone code as the "T" code. The start/stop alphabet, of course, allows a number of these tariff zones to operate from one ARM rate-setting centre. Approximately 15 % of Australian subscribers are connected in this way. A second feature of the Australian automatic system is a very flexible classification facility, enabling calls to be examined at the point of entry to the transit network, thus enabling certain classes of call to be barred from the general trunk network, or from particular trunk routes, as well as permitting calls to be examined at the terminating exchange for compatibility with the calling subscriber's individual class. In addition the calling subscriber's class may be used to modify ratesetting, enabling special rates for particular classes of customer. As for the tariff zone mark, the class mark is automatically signalled as a 5-unit start/ stop code and has become known as the "K" code. It will be observed that the total information needed for rate-setting purposes is then the T code, the K code and the A. B digits of the called subscriber's number. In a common control system such as that employed in the automatic telex network, the charging function and the routing function may be separated and although T, K, and A, B digits are examined for charging purposes, T, K, A, B, C and D may be examined for routing. Special Subscriber Facilities Group search facilities are provided at every terminal exchange, the only limitation on number allocation being that each number must be in the same 400-line ARB 111 terminal exchange block. 27
Page 1: 1 1968
Page 4 and 5: Stored Program Controlled Telephone
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'
Page 14 and 15: egister in ARM selects a new circui
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
Page 22 and 23: Similar intervvorking exists with t
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 32 and 33: A variety of special subscriber mar
Page 34 and 35: to be tripped. The calling subscrib
Page 36 and 37: References 1. C.C.T.T. Illrd Plenar
Page 38 and 39: Corrugating Machine The aim in the
Page 40 and 41: Laying The corrugated duct may have
Page 42 and 43: New Factory Opened at Ostersund L M
Page 44 and 45: Dirivox and Centrum in the Soviet U
Page 46: The Ericsson Group Associated and c

11 - ericssonhistory.com

Create successful ePaper yourself

Delete template?

Save as template?