ITU-T Q 23-1988 TECHNICAL FEATURES OF PUSH-BUTTON TELEPHONE SETS《按键话机的技术特性》.pdf
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1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 1 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU%.%2!,G0G02%#/-%.$!4)/.3G0G0/.G0G04%,%0(/.%37)4#().G0G0!.$G0G03).!,).).4%2.!4)/.!,G0G0!54/-!4)#G0G0!.$3%-)G13!54/-!4)#G0G07/2+).4%#(.)#!,G0G0b) when pressing the buttons after an international call has been s
2、et up, the signalling frequencies for push-button sets may cause interference to foreign signalling systems on the connection. However, thesubscriber can be warned of the possible disadvantages of touching the buttons in conditions differentfrom those prescribed.2 There can be no doubt that, owing t
3、o the high dialling speed which can be obtained with push-button sets,their use is bound to spread widely and rapidly and it is desirable for the signalling methods for such sets to beinternationally standardized.One factor in favour of such standardization is the advantage it offers for countries w
4、hich have to import theirequipments from various other countries. This argument, admittedly, applies to any type of telephone equipment.Other advantages of standardization are:- the possibility of using the push-button of such sets for signalling directly from one subscriber to anothersubscriber via
5、 a national and/or international connection;- the standardized allocation of signalling frequencies for push-button sets facilitates the choice ofsignalling frequencies in the frequency band of a telephone circuit for any other use (data transmission,telephone signalling system, etc.) for which prov
6、ision might have to be made. The risk of mutualinterference among the signalling systems (see Recommendation Q.25) makes it necessary to have anorderly arrangement of the spectrum of frequencies used for signalling.3 The general use of push-button sets for purposes other than telephone dialling is e
7、nvisaged by someAdministrations. However, some Administrations observe that it would seem advisable to reserve such uses for anetwork of relatively limited extent; in their view the reliability of standards for data transmission should not make anydemands on the push-button set system other than tho
8、se required for the transmission of telephone numericalinformation to the local exchange, if the design of push-button sets is to remain within economical limits compatiblewith their widespread use.However, the CCITT considered, at Mar del Plata in 1968 that, even if the transmission of data from a
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