1、INTERNATIONAL TELECOMMUNICATION UNION)45 4 8 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU-%33!% (!.$,). 3934%-3-%33!% (!.$,). 3934%-3 %.#/$%$). amended at Melbourne, 1988)The establishment in various countries of telematic services and computer-based store-and-forward messageservices in association
2、 with public data networks creates a need to produce standards to facilitate international messageexchange between subscribers to such services.The CCITT,considering(a) the need for interpersonal messaging and message transfer services;(b) the need to transfer messages of different types having a la
3、rge variety of formats;(c) that the F-series of Recommendations defines telematic services;(d) that the T-series of Recommendations defines terminal equipment and control procedures for telematicservices;(e) that the V-series of Recommendations provides the means for data communication over the tele
4、phonenetwork;(f) that Recommendation X.200 defines the reference model of open systems interconnection for CCITTapplications;(g) that a set of Recommendations describes various aspects of message handling X.400, X.402, X.403,X.407, X.408, X.411, X.413, X.419 and X.420;(h) that the CCITT and ISO have
5、 drawn up a suitable set of conversion rules;(i) that, for specific user applications, some variations may be developed and applied by bilateralagreement,unanimously declares the view(1) that the purpose and scope of this Recommendation are described in 1;(2) that general aspects of the rules for co
6、nverting between encoded information types are described in 2;(3) that conversion rules for particular encoded information types are defined in subsequent sections.TABLE OF CONTENTS1 Purpose and scope2 General aspects of conversion2.1 Encoded information types2.2 Two aspects of conversion2.3 Loss of
7、 information2.4 Encoded information types properties2 Fascicle VIII.7 - Rec. X.4083 Conversion from TLX3.1 Conversion from TLX to IA5Text3.2 Conversion from TLX to TTX3.3 Conversion from TLX to G3Fax3.4 Conversion from TLX to G4Class13.5 Conversion from TLX to Videotex3.6 Conversion from TLX to voic
8、e3.7 Conversion from TLX to mixedmode4 Conversion from IA5Text4.1 Conversion from IA5Text to TLX4.2 Conversion from IA5Text to TTX4.3 Conversion from IA5Text to G3Fax4.4 Conversion from IA5Text to G4Class14.5 Conversion from IA5Text to Videotex4.6 Conversion from IA5Text to voice4.7 Conversion from
9、IA5Text to mixedmode5 Conversion from TTX5.1 Conversion from TTX to TLX5.2 Conversion from TTX to IA5Text5.3 Conversion from TTX to TTX5.4 Conversion from TTX to G3Fax5.5 Conversion from TTX to G4Class15.6 Conversion from TTX to Videotex5.7 Conversion from TTX to voice5.8 Conversion from TTX to mixe
10、dmode6 Conversion from G3Fax6.1 Conversion from G3Fax to G3Fax6.2 Conversion from G3Fax to G4Class16.3 Conversion from G3Fax to mixedmode7 Conversion from G4Class17.1 Conversion from G4Class1 to G3Fax7.2 Conversion from G4Class1 to G4Class17.3 Conversion from G4Class1 to mixedmode8 Conversion from V
11、ideotex8.1 Conversion from Videotex to TLX8.2 Conversion from Videotex to IA5Text8.3 Conversion from Videotex to TTX8.4 Conversion from Videotex to G3Fax8.5 Conversion from Videotex to G4Class18.6 Conversion from Videotex to Videotex8.7 Conversion from Videotex to voice8.8 Conversion from Videotex t
12、o mixedmode9 Conversion from Voice9.1 Conversion from voice to voice.Fascicle VIII.7 - Rec. X.408 310 Conversion from Mixedmode10.1 Conversion from mixedmode to TLX10.2 Conversion from mixedmode to IA5Text10.3 Conversion from mixedmode to TTX10.4 Conversion from mixedmode to G3Fax10.5 Conversion fro
13、m mixedmode to G4Class110.6 Conversion from mixedmode to Videotex10.7 Conversion from mixedmode to voice10.8 Conversion from mixedmode to mixedmodeAnnex A - Code conversion tablesAnnex B - Abbreviations1 Purpose and scopeThis is one of a set of Recommendations for Message Handling. The entire set pr
14、ovides a comprehensivespecification for Message Handling comprising any number of cooperating open systems.This Recommendation specifies the algorithms the MHS uses when converting between different types ofencoded information.Other aspects of Message Handling are defined in other Recommendations. T
15、he overall system and services ofMessage Handling is specified in Recommendation X.400. The overall architecture of the MHS is defined inRecommendation X.402. The conformance testing of MHS components is described in Recommendation X.403. Theconventions used in the definition of the abstract service
16、s provided by MHS components are defined inRecommendation X.407. The abstract service the MTS provides and the procedures that govern its distributedoperation are defined in Recommendation X.411. The abstract service the MS provides is defined in RecommendationX.413. The application protocols that g
17、overn the interaction of MHS components are specified in RecommendationX.419. The interpersonal Messaging System, an application of Message Handling, is specified in Recommendation.X.420.Paragraph 2 of this Recommendation describes the general aspects of conversion for the MHS. In 3 to 10,particular
18、 conversion rules are defined. Annex A provides code conversion tables. Annex B lists the abbreviationsused.2 General aspects of conversionAmong the data elements subject to conversion are the subject and body of a message. The conversion has twoaspects, format and code. The aspect of control is des
19、cribed elsewhere in the relevant Recommendations.2.1 Encoded information typesThis Recommendation defines the conversion rules for eight types of encoded information utilized in theMHS. In order to refer to each types, the following terms are used:TLX The code is defined in Recommendation F.1. The f
20、ormat is defined in Recommendation S 5.IA5Text The code is defined in Recommendation T.50.TTX The format is defined in Recommendations F.200 and T.60, and the code is defined inRecommendation T.61.G3Fax The encoding scheme is defined in Recommendation T.4, and the signalling of the encoding scheme i
21、sdefined in Recommendation T.30.G4Class1The format and encoding scheme are defined in Recommendations T.6, T.503 and T.563.Videotex The format and encoding scheme are defined in Recommendations T.101, T.504 and T.541.4 Fascicle VIII.7 - Rec. X.408Voice The encoding scheme is for further study.Mixedm
22、ode The format and encoding scheme are defined in Recommendations T.501 and T.561.Note - TLX: Telex, TTX: Teletex.The TTX and G3Fax types have two subtypes: basic and optional. The G4Class1 type and the mixedmodetype have two subtypes: basic and non-basic.Table 1/X.408 depicts all conceivable conver
23、sions between the above types and subtypes. It characterizes eachas: (-) No conversion, (a) possible without loss of information, (b) possible but loss of information may occur, or (c)impractical. This Recommendation defines the rules for format and code conversion for conversions in the second andt
24、hird categories.Fascicle VIII.7 - Rec. X.408 5TABLE 1/X.408Encoded information type conversions- No conversiona Possible without loss of informationb Possible but loss of information may occurc ImpracticalFS For further study1)Specified in the relevant Recommendations.2)No information is lost if the
25、 originating and recipient terminals have the same optional functions.3)Information may be lost if the originating terminal uses optional functions that the recipient terminal lacks.4)The WHO ARE YOU character is assumed to be a protocol element used for communicating with the Telex terminal and not
26、 part of the messages content.5)It may be possible with loss of information, if the recipient terminal has the capability of the photographic type of information.6)When converting videotex, color information may be lost.7)In the case when IA5 Text has less than 69 characters available in a line, for
27、mat information may be lost.ToTLX IA5TTX G3 Fax G4 Class 1Videotex VoiceMixed modeFromTextbasic optional 1)basic optional 1)basic non basic 1)basic non basic1)TLX4)-b7)aaaaaa bFSa aIA5 Text b - b b b b b b b FS b bTTXbasicoptional 1)bbbb-bab2), 3)ababababaaFSFSaaab2), 3)G3 Faxbasicoptional1)cccccccc
28、-bab2), 3)ababc5)c5)ccababG4 Class 1basicnon basic 1)ccccccccbbbb-bab2), 3)c5)c5)ccabab2), 3)Videotex b b b b b6)b6)b6)b6)bFSFS FSVoice c c c c c c c c c FS c cMixed modebasicnon basic1)bbbbbbbb2), 3)bbbbabab2), 3)bbFSFS-bab2), 3)6 Fascicle VIII.7 - Rec. X.4082.2 Two aspects of conversionThe convers
29、ion rules have two aspects:1) the format aspect;2) the code aspect.The conversion rules for encoded information types which have logical structures are for further study.2.2.1 Ground rulesIf there is an existing standard on the conversion between different types, it should be referred to without any
30、modifications unless required. If there is not, the following ground rules are specified:1) If there are standards on the subject and object types, the conversion rules should be defined such that theintersecting part of the standards is preserved. The creation of new rules for non-intersecting part
31、s shouldbe based on clear requirements, otherwise they should not be created.2) When either the subject or object type has no standard, the conversion rules should be defined such thatstandard types can be accommodated as much as possible for both directions of the conversion.3) When neither type ha
32、s a standard, the definition of the rules is for further study.2.2.2 Format aspectThe format aspect represents the dimensional attributes of the presentation space of user messages.The two-dimensional (X and Y) aspect of the conversion is to be specified for a message being transferred.Following are
33、 the parameters to be defined for this aspect. Whether voice should be considered in the same context is forfurther study.a) The X-direction of the presentation space is defined by means of either:1) the size of a character and the number of characters to be presented;2) length.If the object type ha
34、s a smaller size of the X-direction than the subject type, a mechanism for adjustment ofline length, such as the insertion of a CR/LF pair, should be defined as the format conversion rule.b) The Y-direction of the presentation space is defined by means of either:1) the number of lines per presentati
35、on space or per unit length;2) length.If the object type has a smaller page size of the Y-direction than the subject type, a mechanism for changeof page format, such as the insertion of a CR/FF pair, should be defined as the format conversion rule. Ifthe object type has no length limitation of Y-dir
36、ection and the subject type is paginated, some formatconversion rule, such as the insertion of one or more blank lines, should be defined to represent the pageboundary.When converting characters to G3Fax or G4Class1, the rules for imaging should be applied according toRecommendation T.351.2.2.3 Code
37、 aspectWith respect to the code aspect, Annex A specifies the conversion between different types. Further notes can befound in each subsection if necessary.Fascicle VIII.7 - Rec. X.408 72.3 Loss of information2.3.1 Initial assumption on loss of informationWhen considering conversion between differen
38、t encoded information types some initial assumptions weretaken into account. Changes to the character font, character size or paper type, etc. are not regarded as loss ofinformation.2.3.2 Format loss of informationThe format conversions take two different forms; line length and number of lines. The
39、following definitionsapply:1) Line length (number of characters)a) originators line length less than, or equal to recipients line length: no loss of information;b) originators line length more than recipients line length: loss of information.2) Page length (number of lines)a) originators page length
40、 less than, or equal to recipients page length: no loss of information.However, in the recipients pages, a clean field should be inserted between the originators pages;b) originators page length more than recipients page: no loss of information, provided the originatorspage is mapped onto an integer
41、 number of destination pages.Note - Information may also be lost due to differences between the printable and reproducible areas in facsimile.2.3.3 Code loss of informationIf a graphic character is reproduced identically on both systems then there is no loss of information. However, ifthere is a cha
42、nge between italic, bold, underlined, normal or coloured (as in the case of Videotex) this could beconsidered to be a loss of information (e.g., one type of rendition could mean a positive financial result and the other anegative result!). This requires further study.A conversion to a similar charac
43、ter, but not identical, in the second system is loss of information. A conversionfrom one character to many characters (e.g., $ to dollar) is also loss of information.2.4 Encoded information type propertiesFollowings are the properties of encoded information types assumed for this Recommendation.2.4
44、.1 TLX encoded information typeThe TLX encoded information type is not paginated. A TLX text line contains maximum 69 graphic charactersas defined in Recommendation S.5. The end of a line is also represented by an ITA2 CR-LF pair.2.4.2 IA5Text encoded information typeThe IA5Text encoded information
45、type is paginated. An IA5Text line contains maximum N1graphic characters.The end of a line is also represented by an IA5 CR-LF pair. An IA5Text page contains maximum M1lines. The end of apage is also represented by an IA5 CR-FF pair.Note - Any value to N1or M1are not assumed in this Recommendation u
46、nless explicitly specified in therelevant sections. A common value to N1is 80.2.4.3 TTX encoded information typeThe TTX encoded information type is paginated. The format of a TTX page is as defined by following “defaultcondition of basic Teletex“:8 Fascicle VIII.7 - Rec. X.408- paper size and orient
47、ation: vertical basic page format;- character spacing: 2.54 mm;- line feed spacing: 4.23 mm;- rendition: default rendition.This implies that the maximum number of characters per line is 77 and the maximum number of lines per pageis 55. The end of a TTX line is represented by a TTX CR-LF pair. The en
48、d of a TTX page is represented by a TTX CR-FF pair.Note - When converting from Teletex, each Teletex line shall be preceded by 5 spaces reduced by the number ofbackspaces (BS) found in the beginning of each Teletex line (refer to Recommendation F.200, 7.6.9.1 ).2.4.4 G3Fax encoded information typeTh
49、e G3Fax encoded information type is paginated. The format of a G3Fax is described in Recommendation T.4.2.4.5 G4Class1 encoded information typeThe G4Class1 encoded information type is paginated. The format of a G4Class1 is described inRecommendation T.563.2.4.6 Videotex encoded information typeThe Videotex encoded information type is paginated. A Videotex line contains maximum N2graphic characters.The end of a line is represented by a Videotex APD-APR pair. A Videotex page contains maximum M2lines in thedefined-display area. The end of a page is represented by a Vide
