ITU-T X 20-1988 INTERFACE BETWEEN DATA TERMINAL EQUIPMENT (DTE) AND DATA CIRCUIT-TERMINATING EQUIPMENT (DCE) FOR START-STOP TRANSMISSION SERVICES ON PUBLIC DATA NETWORKS《公用数据网上起止式传.pdf
《ITU-T X 20-1988 INTERFACE BETWEEN DATA TERMINAL EQUIPMENT (DTE) AND DATA CIRCUIT-TERMINATING EQUIPMENT (DCE) FOR START-STOP TRANSMISSION SERVICES ON PUBLIC DATA NETWORKS《公用数据网上起止式传.pdf》由会员分享,可在线阅读,更多相关《ITU-T X 20-1988 INTERFACE BETWEEN DATA TERMINAL EQUIPMENT (DTE) AND DATA CIRCUIT-TERMINATING EQUIPMENT (DCE) FOR START-STOP TRANSMISSION SERVICES ON PUBLIC DATA NETWORKS《公用数据网上起止式传.pdf(30页珍藏版)》请在麦多课文档分享上搜索。
1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 8 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU05“,)#G0G0$!4!G0G0.%47/2+3).4%2 amended at Geneva, 1976 and 1980,Malaga-Torremolinos, 1984 and Melbourne, 1988)The CCITT,considering(a) that Recommendations X.1 and X.2 define the services and facilities to b
2、e provided by a public datanetwork;(b) that Recommendation X.92 defines the hypothetical reference connections for public synchronous datanetworks;(c) that Recommendation X.96 defines call progress signals;(d) that the necessary elements for an interface Recommendation should be defined in architect
3、ural levels;(e) that it is desirable for characteristics of the interface between the DTE and DCE of a public data networkto be standardized,unanimously recommendsthat the interface between the DTE and DCE in public data networks for user classes of service employingstart-stop transmission should be
4、 as defined in this Recommendation.1 Scope1.1 This Recommendation defines the physical characteristics and call control procedures for a general purposeinterface between DTE and DCE for user classes of service, as defined in Recommendation X.1, employing start-stoptransmission.1.2 The formats and pr
5、ocedures for selection, call progress and DCE provided information are included in thisRecommendation.1.3 The provision for duplex operation is covered.2 DTE/DCE physical interface elements2.1 Interchange circuitsA list of the interchange circuits concerned is presented in Table 1/X.20. Definitions
6、of these interchangecircuits are given in Recommendation X.24.2 Fascicle VIII.2 - Rec. X.20TABLE 1/X.20Interchange circuit Interchange circuit Directionnameto DCE from DCEG(see Note)GaGbTRSignal ground orcommon returnDTE common returnDCE common returnTransmitReceiveXXXXNote - This conductor may be u
7、sed to reduce environmental signal interference at the interface. Incase of shielded interconnecting cable, the additional connection considerations are part ofRecommendations X.24 and ISO 4903.2.2 Electrical characteristicsThe electrical characteristics of the interchange circuits at the DCE side o
8、f the interface will comply withRecommendation X.26.The electrical characteristics at the DTE side of the interface may be applied according toRecommendations X.26, X.27 (without cable termination in the load), or Recommendation V.28.For interworking between a V.28-DTE and a X.26-DCE refer to Recomm
9、endation X.26 and ISO 4903.2.3 Mechanical characteristicsRefer to ISO 4903 (15-pole DTE/DCE interface connector and contact number assignments) for mechanicalarrangements.2.4 Fault conditions of interchange circuitsFor the association of the receiver circuit-failure detection to particular interchan
10、ge circuits in accordance withthe type of failure detection, see Recommendation X.26, 11 and Recommendation X.27, 9.2.4.1 Circuit R in failure stateThe DTE should interpret a fault condition on circuit R as r = 0, using failure detection type 2. When theelectrical characteristics are applied accordi
11、ng to Recommendation V.28, the DTE should interpret generator in power-off condition or open-circuited interconnecting cable as a binary 0.2.4.2 Circuit T in failure stateThe DCE will interpret a fault condition on circuit T as t = 0, using failure detection type 2.3 Call control characters and erro
12、r checkingAll characters for call control purposes are selected from International Alphabet No. 5 according toRecommendation T.50.Even parity according to Recommendation X.4 applies for IA5 characters interchanged for call controlpurposes.Fascicle VIII.2 - Rec. X.20 34 Elements of the call control p
13、hase for circuit switched serviceThe state diagram provided in Figure A-1/X.20 shows the relationship between the various call control phasestates as defined below, together with the recognized transactions between these states under normal operatingconditions. Illustrated examples of the time seque
14、nce relationships between these states and associated time-outoperation are provided in Figure B-1/X.20.The call control phase can be terminated by either the DTE or the DCE by clearing as defined in 6 below.4.1 Events of the call control procedures(See Figure A-1/X.20.)4.1.1 Ready (state 1)Circuits
15、 T and R show binary 0.4.1.2 Call request (state 2)The calling DTE shall indicate a request for a call by signalling steady binary condition t = 1 provided that itwas previously signalling DTE ready (t = 0).4.1.3 Proceed-to-select (state 3)When the network is prepared to receive selection informatio
16、n, the DCE will signal steady binary conditionr = 1.The proceed-to-select signal will start within 6 seconds of the call request being sent.4.1.4 Selection signal sequence (state 4)The selection signal sequence shall be transmitted by the DTE on circuit T.The format of selection signal sequence is d
17、efined in 4.6.1 below.The information content and coding of the selection signal sequence is contained in Annex G andRecommendation X.121.The selection signal sequence shall start within 6 seconds of the proceed-to-select being received and shall becompleted within 36 seconds.The maximum permissible
18、 interval between individual selection characters is 6 seconds.4.1.5 DTE waiting (state 5)During DTE waiting, the DTE signals steady binary condition t = 1.4.1.6 Incoming call (state 8)The DCE will indicate an incoming call by signalling steady binary condition r = 1.4.1.7 Call accepted (state 9)The
19、 DTE shall accept the incoming call not later than 600 ms by signalling the steady state binary conditiont = 1.10-100 ms thereafter, the DTE transmits the call control character 0/6 (ACK).4 Fascicle VIII.2 - Rec. X.204.1.8 Call not accepted (state 18)If the DTE does not wish to accept the incoming c
20、all it shall signal this not later than 600 ms by changingcircuit T to steady binary condition 1.10-100 ms thereafter, the DTE shall transmit the call control character 1/5 (NAK) followed by DTE clearrequest (state 13).4.1.9 Call progress signal sequence (state 6)The call progress signal sequence wi
21、ll be transmitted by the DCE to the calling DTE on the R circuit when anappropriate condition is encountered by the network.A call progress signal sequence will consist of one or more call progress signal blocks. A call progress signalblock will consist of one or more call progress signals.The forma
22、t of the call progress signal sequence is defined in 4.6.2 below.The coding of call progress signals is provided in Annex E.The description of call progress signals is provided in Recommendation X.96.A call progress signal sequence will be transmitted by the DCE within 60 seconds of: 1) the end-of-s
23、electionsignal or 2) in case of direct call, the proceed-to-select signal being sent by the DTE. The call progress signalsequence, however, will not be sent by the DCE before the reception of the end-of-selection signal except in the case ofexpiration of time-outs described in 4.1.4 where there may
24、be a call progress signal sequence followed by the clearindication.Note - When an error is detected in a received call progress signal sequence, the DTE may choose to either ignore thesignal or attempt a new call after clearing.4.1.10 DCE provided information sequence (states 7A and 7B)The DCE provi
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