1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 6 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU$!4!G0G0#/-5.)#!4)/.G0G0/6%2G0G04(%G0G04%,%0(/.%.%47/2+53%G0G0/ amended at Malaga-Torremolinos, 1984)Note - Acoustic coupling is a technique used to couple the output of a modem to an analoguetelecommunicatio
2、n facility using acoustic energy/power between the device and a telephone instrument. As such, itprovides for minimum complexity of attachment as well as excellent galvanic isolation. However, the technique doeslimit the data signalling rates used and does limit the functionality which can be provid
3、ed by the associated modem.Since this arrangement will generally be used to communicate with a permanently installed V Series modem at aremote station, the characteristics of the modem will, accordingly, comply with requirements defined elsewhere inthese Series V Recommendations, e.g., V.21 or V.23.
4、 As far as functionality permits, interfaces with the associatedDTE will be as defined in those Recommendations. Because of operator intervention required in manipulating thetelephone handset, automatic calling and automatic answering are not normally considered part of the functionality ofan acoust
5、ically coupled modem. However, an acoustically coupled modem can call a remote station which hasautomatic answering capability and can observe the protocol defined in Recommendation V.25, 6, “Manual datastation calling automatic answering data station“ as modified herein.The CCITT,consideringthat th
6、ere is a wide variety of telephone instruments in existence and that the acoustic path involved in the useof any coupling device cannot be accurately prescribed for all cases, and hence it will be difficult to ensure satisfactorytransmission in all situations,recommends1 that acoustic coupling of da
7、ta transmission equipment via telephone instruments to the telephonetransmission network should not be used for permanent installations.It is, however, recognized that there may be a need for a means to provide temporary connection of portabledata transmission equipment to the network in circumstanc
8、es where it may not be possible to obtain convenient accessto the subscribers line terminals.The use of acoustic coupling for temporary communications is subject to the agreement of the Administrationin charge of the telephone network to which the equipment will be connected.If an Administration dec
9、ides to permit acoustic coupling for temporary data transmission stations, the acousticcoupling equipment conforms to the following:1) The maximum power output of the subscribers equipment to the line shall not exceed 1 mW at anyfrequency.The mean permitted telephone line signal power shall not exce
10、ed -13 dBm0.2) If p is the signal power in the frequency band 0-4 kHz, the signal power outside this band shall notexceed the following values when integrated over any period of approximately 3 seconds:p - 20 dB in the band 4 to 8 kHz,p - 40 dB in the band 8 to 12 kHz,p - 60 dB in each 4-kHz band ab
11、ove 12 kHz.2 Fascicle VIII.1 - Rec. V.153) The frequencies emitted by the transducer shall be such as not to interfere with national and internationaltelephone signalling systems and pilot signals involved in the telephone connection envisaged.4) Adequate protection shall be provided in the transduc
12、er to avoid causing any dangerous electric potentialand currents to the telephone system.5) It shall not be possible to cause acoustic shock to telephone users under any normal condition or whenthe acoustic coupler develops any single fault.6) The mechanical arrangements of the transducer shall not
13、cause mechanical damage to the telephoneinstrument.7) In addition to the contents of this Recommendation, the regulations of the national Administration mustalso be complied with.2 that acoustically coupled equipment be compatible with “hard-wired counterparts“ at the remote location tothe extent th
14、at:1) The characteristics of the equivalent V Series (V.21, V.23, etc.) modem line signals are complied with(otherwise communication will be impossible).2) An equivalent V.24 interface is provided to the DTE, with the following exceptions:- circuit 108 is power ON indicator only, and cannot be used
15、to control the connection of the modemto the line;- circuit 125 is inoperative; only manual answering can be accomplished.3) Acoustically coupled modem equipment designed to operate with remote modems:- which have automatic answering capability, and- which are specifically dedicated and are adapted
16、(by means of optionally extended answer toneduration) to working with acoustically coupled calling stationsshall operate in the mode prescribed in Recommendation V.25, 6 where placement of the telephoneinstrument handset on the acoustic coupler by the operator is tantamount to depressing a data button, asspecified in 6.These modems shall also comply with the response time requirements of circuits 106 and 109 asspecified in the appropriate modem Recommendation.
