1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 8 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU05“,)#G0G0$!4!G0G0.%47/2+342!.3-)33)/. G0G03).!,).G0G0!.$G0G037)4#().-%4(/$G0G0/(b) Recommendation X.2 defines the international user facilities in public data networks;(c) Recommendations X.21 and X.21 bis d
2、efine the interface between data terminal equipment (DTE) anddata circuit-terminating equipment (DCE) for synchronous operation;(d) Recommendations X.50 and X.51 define the multiplexing scheme for the international interface betweensynchronous data networks;(e) Recommendations X.60, X.61 and X.71 de
3、fine the signalling system on international circuits betweensynchronous data networks;(f) some circuits implementing synchronous data networks also will connect to those networks DTEsoperating in user classes of service 1 and 2;unanimously declares the following view:1 Scope1.1 In the case where two
4、 synchronous data networks offer service for DTEs in user classes of service 1 and 2,the transfer of the anisochronous signals between the networks shall be performed using a synchronous user channel of600 bit/s in the standardized multiplexing schemes given in Recommendations X.50 and X.51 if one o
5、r both of thenetworks nationally use the synchronous user channel of 600 bit/s.1.2 In the case where two synchronous data networks offer service for DTEs in user classes of service 1 and 2but do not provide the 600-bit/s rate, the transfer of the anisochronous signals between those two networks shal
6、l beperformed using a synchronous user channel of 2400 bit/s in the standardized multiplexing schemes given inRecommendations X.50 and X.51.1.3 The method of encoding signals from DTEs in user classes of service 1 and 2 into the synchronous bearershall be independent of the multiplexing scheme used.
7、1.4 The method of encoding shall be as defined in this Recommendation.2 Encoding methodThe encoding method implies that characters generated by DTEs in user classes of service 1 and 2 inaccordance with Recommendation X.1 are transferred on international links as characters on a synchronous userchann
8、el, i.e. the transfer of characters on a synchronous user channel shall include the start signal as well as the stopsignal with the following convention:start polarity = binary zero;_1)This Recommendation is only valid for interworking between synchronous data networks. For the interworking betweena
9、nisochronous data networks the Series R Recommendations will apply.2 Fascicle VIII.3 - Rec. X.52stop polarity = binary one.Between any two characters on synchronous user channel the value of the bits shall be binary one.The encoder and decoder shall be implemented in such a way that continuous start
10、 polarity (as well ascontinuous stop polarity) generated by a DTE can be transferred.On the multiplexed link there need not be any relation between characters and envelopes.The encoder shall be implemented in such a way that the time delay between the reception of a character atnominal speed and the
11、 start of sending the character on a synchronous user channel is less than 1 bit at the datasignalling rate of the synchronous user channel used.ANNEX A(to Recommendation X.52)Location of the encoderThe location of the encoder, e.g. in the DCE in question or at a control point in the network, is a n
12、ationalmatter. The location however will have no impact on the method described in this Recommendation.When discussing the location of the encoder for harmonization reasons one should bear in mind that:- in the case of a DCE located encoder, no special features for handling asynchronous signals are
13、neededin network components such as concentrators and multiplexers and that all maintenance functions,subscriber line signalling scheme, local network modems, etc. implemented for the synchronous userclasses of service can be used without any changes;- if the encoder is placed at a central point, th
14、e data signalling rate on the local loop can be kept at thelowest possible rate allowing the use of a simple 2-wire modem and the sharing of conversion equipmentat the central point by a number of subscribers.ANNEX B(to Recommendation X.52)Higher data signalling ratesIn the case where asynchronous D
15、TEs operating at higher data signalling rates than given in RecommendationX.1 are connected to synchronous data networks, the same principle for encoding as given in the text of thisRecommendation could be used and the relationship between data signalling rate and bearer channel rate shall be asshown in Table B-1/X.52.Fascicle VIII.3 - Rec. X.52 3TABLE B-1/X.52Data signalling rate Bearer channel rate600 bit/s1200 bit/s2400 bit/s4800 bit/s2400 bit/s2400 bit/s4800 bit/s9600 bit/s
