1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 5 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU4%,%2!0(G0G037)4#().).4%27/2+).G0G0“%47%.G0G0.%7G0G0).(b) that Recommendation F.201 specifies: that a validation of a called Teletex terminal is mandatory. The validation is performed either by a directvalida
2、tion call or by a data base access; that if a message delivery to a Teletex terminal fails in the case of interworking with two-stage selectionprocedure, the conversion facility should send a non-delivery notification to a telex terminal;(c) that Recommendation S.90 specifies Teletex requirements fo
3、r interworking with the telex service andRecommendations S.62 and S.70 specify control procedures and a network-independent basic transport service for aTeletex;(d) that Recommendation X.96 specifies call progress signals in a public data network,unanimously declares the following view1 ScopeThis Re
4、commendation defines service signals which are to be sent back to the telex terminal in the event ofunsuccessful validation for called Teletex terminal addresses, and service signals of the last delivery attempt to theTeletex terminal which are to be sent to the telex terminal as a part of non-deliv
5、ery notification.2 Fascicle VII.2 - Rec. U.70TABLE 1/U.70Service signals for unsuccessful validation call and non-delivery notificationAbnormal conditions Service signalsCall-progress signalsNo connection NCSelection signal transmisssion error NCLocal procedure error NCNetwork congestion NCInvalide
6、facility request NCChange number NCHNot obtainable NPAccess barred NALower PSDN and Incompatible user class of service NALevel CSDN Incompatible destination NCProtocols Out of order DERNetwork fault in local loop DERDCE power off ABSUncontrolled not ready DERControlled not ready ABSNumber busy OCCCa
7、ll information service INFRemote procedure error DERLong-term network congestion NCDTE originated DERCarrier-off NCNo response (time-out) DERCarrier off NCRing-back tone (No reply) a)ABSNo dial tone a)NCLower PSTN Busy a)OCCLevel Equipment engaged a)NCNumber unobtainable a)NPNo tone a)NPTransport Co
8、nnection Clear (TCC) receiptReason not specified DERTerminal occupied OCCTerminal out of order DERTransport Address unknown NPLayer Transport Block Reject (TBR) receiptReason not specified DERFunction not implemented DERInvalid block DERInvalid parrameter DERIllegal command/response receipt DERNo re
9、sponse DERIncorrect terminal identifierin Response Session Start Positive (RSSP) NPResponse Session Start Negative (RSSN) receiptHigher Session No specific reason stated DERLevel Layer Memory full or out of recording paper DERProtocols Explicit text message DERCommand Session Abort (CSA) receiptLoca
10、l terminal error DERUnrecoverable procedural error DERReason not defined DERIllegal command/response receipt DERNo response DERResponse Document Page Boundary Negative (RDPBN) receiptNo specific reason stated DERMemory full or out of recording paper DERDocument Sequence error DERLayerb)Local termina
11、l error DERUnrecoverable procedural error DERResponse Document General Reject (RDGR) receipt DERIllegal command/reponse receipt DERNo response DERFascicle VII.2 - Rec. U.70 3a)It is recognized that these abnormal conditions can be detected if the automatic calling procedures incoroporate detection f
12、acilites.b)Optional (if negotiation is not carried out).PSDN Packed switched data networkCSDN Circuit switched data networkPSTN Public switched telephone network2 PrinciplesThe following principles should he taken into consideration:2.1 Call progress signals arriving from the Teletex network will be
13、 converted without changing their originalmeaning as far as possible.2.2 A faulty condition between the Teletex network and the conversion facility will be regarded as a faultycondition within the network.2.3 A faulty condition between the Teletex network and the Teletex terminal will be regarded as
14、 a fault of theterminal.3 Telex service signalsIn general, telex service signals specified in Recommendation F.60 should be used. However, the telex servicesignals listed below will be used in the following circumstances:3.1 If the format of the Teletex address part is incorrect, the service signal
15、NP will be returned.3.2 If the direct validation call is unsuccessful, the conversion facility will transmit the service signals specified inTable 1/U.70 to the telex terminal.3.3 If the validation by data base access is unsuccessful, the conversion facility will transmit the service signalsspecifie
16、d in Table 2/U.70.3.4 If the message delivery to the Teletex terminal is unsuccessful, the conversion facility will transmit the servicesignals of the last delivery attempt which are specified in Table 1/U.70, as a part of non-delivery notification to thetelex terminal.TABLE 2/U.70Service signals fo
17、r unsuccessfulvalidation by data base accessNote In addition to the case “the number does not exist”, other cases, for example,“the number is being temporarily prohibited” or “the number is out of order”, might beconsidered as abnormal conditions. But at this moment such conditions and the servicesignals corresponding to them are for further study.Abnormal conditions Service signalUnsuccessful results NP
