1、CCITT FASCICLE VIII.2 *f 4Bb2591 0513266 9 R Recommendation X.21 bis USE ON PUBLIC DATA NETWORK3 OF DATA TERMINAL EQUIPMENT (DTE) WHICH IS DESIGNED FOR INTERFACING TO SYNCHRONOUS V-SERIES MODEMS (Geneva, 1976; amended at Geneva, 1980, Malaga-Torremolinos, 1984 and Melbourne, 1988 ) The CCIIT, consid
2、ering that (a) the interface between Data Terminal Equipment (DTE) and Data Circuit-terminating Equipment (DCE) for synchronous operation on public data networks is specified in Recommendation X.21; (b) several Administrations are also planning to provide as an interim measure the connection to publ
3、ic data networks of synchronous DTEs which are designed for interfacing to synchronous V-Series modems, unanimously recommends (1) the connection of DTEs with V-Series-type interface o public data networks allow for: i) ii) the direct call facilify, iii) (2) this Recommendation specifies the operati
4、onal modes and the optional features which apply when the data circuit interconnects V-Series DTEs. Interworking between V-Series DTEs and X.21 DTEs is described in Annex A. the leased circuit service (point-to-point and centralized multipoint), the address call facility ; 1 The iise of V-Series DTE
5、s for leased circuit service and packet-switched service (X.25, Layer 1) 1.1 General The use of V-Series DTEs utilizing the leased circuit service in public data networks is discussed in the following. The data signalling rates are those defined in Recommendation X.l for user classes of service empl
6、oying synchronous transmission, 1.2 Use of interchange circuits The electrical characteristics of the interchange circuits at both the DCE side and the DTE side of the interface may comply either with Recommendation V.28 using the 25-pole DTE/DCE interface connector and contact number assignments st
7、andardized by IS0 2110 or with Recommendation X.26 using the 37-pole DTE/DCE interface connector and contact number assignments standardized by IS0 4902. Administrations may choose to offer only one of the interface options. Where the Administration permits interworking between V.28 equipment on one
8、 side of the interface and X.26 equipment on the other side of the interface, refer to Recommendation X.26 and IS0 4902. (The onus is on the provider of X.26 equipment to supply the adaptor needed to interwork with the V.28 equipment.) Fascicle VDLI.2 - Rec. X.21 bis 133 - 7 I CCITT FASCICLE VIII.2
9、*K W 4862571 0513267 o m V.24 . Interchange circuit No. 102 103 For applications of the data signalling rate of 48 kbit/s, the connector and electrical characteristics at both the DCE side and the DTE side of the interface are given in the IS0 standard for the assignment of the 34-pin interface conn
10、ector IS0 2593 and in Recommendation V.35 respectively. Alternatively for the data signalling rate of 48 kbitls, the connector and electrical characteristics at both the DCE side and the DTE side of the interface may use IS0 4902 and Recommendations X.26/X.27 respectively as applied for Recommendati
11、on V.36. Inter- working with IS0 2593 and Recommendation V.35 configuration is for further study. Administrations may choose to offer only one of the interface options at 48 kbit/s. Table 1/X.21 bis shows the use of interchange circuits for the leased circuit service. . TABLE WX.21 bis . Note I - Ci
12、rcuit 107 shall go OFF only in cases of DCE power-off (normally the indeterminate state is interpreted as OFF), loss of service (see 0 3.2 below) or when circuit 108/1, when implemented, is turned OFF. Note 2 - Not required for V.29, V.35 and V.36 compatible interfaces. Note 3 - The DCE interprets t
13、he ON condition on circuit 108/1, when implemented, as an indication that the is operational. If circuit 108A is not provided the DCE will consider the lack of circuit 108 the ON condition. The DCE turns circuit 107 ON while circuit 108/1, if present, is ON and the circuit connection is available. N
14、ote 4 - The DCE shall provide the DTE with transmitter and receiver signal element timings; this is donne by feeding circuits 114 and 115 with the same timing signal from the DCE. Note 5 - Not required in those networks which do not provide automatic activation of the loops. All these circuit functi
15、ons are in accordance with Recommendation V.24 and the appropriate modem Recommendations (see also 8 1.2.1 below). r 11.2 - Rec. X.21 bis I Designation Signal ground or common return Transmitted data Received data Request to send Ready for sending Data set ready (see Note 1) Connect data set to line
16、 (see Notes 2 and 3) Data channel received line signal detector Transmitter signal element timing (DCE) (see Note 4) Receiver signal element timing (DCE) (see Note 4) Loopback/maintenance test (see Note 5) Local loopback (see Note 5) Test indicator (DCE) CCITT FASCICLE VIII.2 * m Li862591 0513268 2
17、- 1.2.1 Operational requirements 1.2.1.1 Half-duplex operation In principle the data circuit provided has duplex transmission capability. However, when a remote response from circuit 105 to circuit 109 is required it may be provided on an optional basis (see also Annex A). Note - Attention is drawn
18、to the fact that, although circuit 105 can control circuit 109 at the other end, in case of the half-duplex facility, the detection of a line signal should be replaced by some other control mechanism. 1.2.1.2 Response times The response time of the OFF to ON transition of circuit 106 as a response t
19、o circuit 105 OFF to ON should provisionally be between 30 and 50 ms for the 600 bit/s user rate, and 10 to 20 ms for the higher user rate. 1.2.1.3 Clamping The following conditions apply: - In the event of line failure (e.g. channel out of service, loss of alignment) the DCE shall clamp circuit 104
20、 to steady binary 1 condition and circuit 109 to OFF condition. In all applications the DCE shall hold circuit 104 in binary 1 condition, when circuit 109 is in the OFF condition. In addition, when the half-duplex facility is provided, the DCE shall hold circuit 104 in the binary 1 condition and cir
21、cuit 109 in the OFF condition when circuit 105 is in the ON condition. - - - When circuit 105 or circuit 106 or both are OFF, the DTE shall maintain a binary 1 condition on circuit 103. 1.2.1.4 Timing arrangements Timing signals on circuits 114 and 115 should aways be maintained when the DCE is capa
22、ble of generating them, disregarding the conditions of the other circuits. Circuits 114 and 115 should be held by the DCE in the OFF condition when the DCE is unable to generate the timing information, 2 The use of V-Series DTEs for direct call and address call facilities 2.1 General The use of V-Se
23、ries DTEs utilizing the direct call or the address facility in public data networks is discussed below. The data signalling rates are those defined in Recommendation X.1 for user classes of service employing synchronous transmission. 2.2 Use of interchange circuits The electrical characteristics of
24、the interchange circuits at both the DCE side and the DTE side of the interface may comply either with Recommendation V.28 using the 25-pole DTE/DCE interface connector and contact number assignments standardized by IS0 21 10 or with Recommendation X.26 using the 37-pole DTE/DCE interface connector
25、and contact number assignments standardized by IS0 4902. Administrations may choose to offer only one of the interface options. Where the Administrations permit interworking between V.28 equipment on one side of the interface and X.26 equipment on the other side of the interface, refer to Recommenda
26、tion X.26 and IS0 4902. (The onus is on the provider of the X.26 equipment to supply the adaptor needed to interwork with the V.28 equipment.) r Fascicle VIiI.2 - Rec. X.21 bis 135 % I CCITT FASCICLE VIII.2 * 4Ab2591 05132b9 4 For applications of the data signalling rate of 48 kbit/s, the connector
27、and electrical characteristics at both the DCE side and the DTE side of the interface are given in the IS0 standard for the assignment of the 34-pin interface connector IS0 2593 and in Recommendation V.35 respectively. Aiternatively for the data signalling rate of 48 kbit/s, the connector and electr
28、ical-characteristics at both the DCE side and the DTE side of the interface may use IS0 4902 and Recommendations X.26/Xa27 respectively as applied for Recommendation V.36. Inter- working with IS0 2593 and Recornmendation V.35- configuration is for further study. Administrations may choose to offer o
29、nly one of the interface Table 2/X.21 bis shows the list of interchange circuits. 2/x.21 bis CCITT FASCICLE VIII-2 f* W 4862593 0533270 O - Circuit 107 - Data set ready This circuit is used to indicate the following operational functions. Condition of circuit 107 Function in the network (see 8 2.2.1
30、.1) ON Ready for data OFF DCE clear indication OFF DCE clear confirmation Note - In duplex transmission when no circuit 105 operation is used by the DTE, circuit 104 will be set to ON with a delay from O to 20 ms with respect to the transition of circuit 197 to ON. Circuit 108/1 - Connect data set o
31、 line This circuit is used alternatively to circuit 108/2. The following operational functions should be indicated. Condition of circuit 108/1 Function in the network (see 8 2.2.1.1) ON Call request ON Call accepted OFF DTE clear request OFF DTE clear confirmation I Note - This circuit should not be
32、 operated when the DTE is connected t9 a modem which does not terminate this circuit. Circuit 108/2 - Data terminal ready This circuit is used alternatively to circuit 108/1. The following operational functions should be indicated. Condition of circuit 108/2 Function in the network (see 4 2.2.1.1) O
33、N Call accepted OFF DTE clear request OFF DTE clear confirmation Note - This circuit should not be operated when the DTE is connected to a modem which does not terminate this circuit. Fascicle YIII.2 - Rec. X.21bis 137 7 CCITT FASCICLE VIII-2 * m 4862593 0533273 2 W I - Circuit 114 - Transmitter sig
34、nal element timing (DCE) Circuit 115 - Receiver signal element timing (DCE) The DCE shall provide the DTE with transmitter and receiver element timings. This is done by feeding circuits 114 and 115 with the same timing signal from the DCE. Circuit 125 - Calling indicator The ON condition indicates i
35、ncoming call. The circuit will be turned OFF as follows: - - - in conjunction with circuit 107 turned ON, or DCE ready is received from the network, or DCE clear indication is received from the network. Circuit 141 - Local loopback Signals on this circuit are used to control the loop 3 test conditio
36、n in the local DCE. Not required in those networks which do not provide automatic activation of the loops. Circuit 142 - Test indicator This circuit is used to indicate to the DTE the test-mode status of the DCE. 2.2.1.1 Operational requirements 2.2.1.1.1 Call request For a direct call facility the
37、DTE indicates a call request by turning circuit 108/1 ON. Circuit 10812 cannot be used for this purpose. 2.2.1.1.2 Call accepted A DTE receiving an incoming call should turn circuit 108/1 or 108/2 from OFF to ON within 500 ms to indicate call accepted, otherwise the call will be cleared. A DCE prese
38、nting an incoming call to a DTE which already has circuit 108/2 ON will regard the ON condition on circuit 108/2 as an indication of call accepted. Optionally when a DTE does not provide circuit 108/1 or 108/2, the call accepted signal to the network would be generated within the DCE as an answer to
39、 the incoming call signal received from the network. However, it may be also possible to signal to the network a DTE controlled not ready by a manual action on the DCE. 2.2.1.1.3 DCE clear indication/DTE clear confirmation DCE clear indication is signalled to the DTE by turning circuit 107 OFF. The
40、DTE clear confirmation, when implemented, should be given by the DTE turning OFF circuit 108/1 or 108/2 within 500 ms after the DCE clear indication is signalled on circuit 107. Otherwise, the DCE may consider the DTE as being uncontrolled not ready until circuit 108/1 or 108/2 is turned OFF or a re
41、ady signal is generated by a manual action on the DCE. Circuit 108/1 should always be able to give DTE clear confirmation. Optionally, when a DTE does not turn circuit 108/2 OFF for DTE clear confirmation this would be automatically generated within the DCE as an answer to the clear indication recei
42、ved from the network and the DTE will be considered in the ready condition. In the case when the DTE expects to have circuit 107 OFF only as a response to circuit 108/1 or 108/2 OFF, the DCE will not turn circuit 107 OFF as a DCE clear indication and in this case the DCE clear indication will not be
43、 signalled to the DTE across the interface. The DTE clear confirmation signal will then be automatically generated within the DCE as an answer to the clear indication signal received from the network. The DTE may be regarded as uncontrolled not ready until circuit 108/1 or 108/2 is turned OFF. Fasci
44、cle VIII.2 - Rec. X.21 bis - , . I CCITT FASCICLE VIII.2 tf 4862591 0533272 4 2.2.1.1.4 Line identijcation Calling and called line identijcation signals cannot be handled by V-Series DTEs. 2.2.1.1.5 Call progress signals Call progress signals cannot be handled by Y-Series DTEs. If automatic address
45、calling is provided in accordance with Recommendation V.25, the reception of negative call progress signals will be indicated to the DTE on circuit 205. 2.2.2 Data transfer phase The interchange circuits shown in Table 3/X.21 bis should be used in the data transfer phase. TABLE 3/X.21 bis V.24 Inter
46、change circuit No. 102 103 104 105 106 109 114 115 Designation Signal ground or common return Transmitted dafa Received data Request to send Ready for sending Data channel received line signal detector Transmitter signal element timing (DCE) (see Note) Receiver signal element timing (DCE) (see Note)
47、 Note - The DCE shall provide the DTE with transmitter and receiver element timings. This is donne by feeding circuits 114 and 115 with the same timing signal from the DCE. All the circuit functions are in accordance with Recommendation V.24 and the appropriate modem Recommendations. 2.2.2.1 Operati
48、onal requiremen fs 2.2.2.1.1 Hawduplex operation In principle the data circuit provided has duplex transmission capability. However, when a remote response from circuit 105 to circuit 109 is required it may be provided on an optional basis (see also Annex A). 2.2.2.1.2 Response times The response ti
49、me of the OFF to ON transition of circuit 106 as a response to circuit 105 OFF to ON should provisionally be between 30 and 50 ms for the 600 bit/s user rate, and 10 to 20 ms for the higher user rate. Fascicle VIII.2 - Rec. X.21 bis - i CCITT FASCICLE VIII.2 * 48b2593 0533273 b -_ 2.2.2.1.3 Clamping The following conditions shall apply: - In the event of line failure (e.g. channel out of service, loss of alignment) the DCE shall clamp circuit 104 to steady binary 1 condition and circuit 109 to OFF condition. - In all applications the DCE shall hold circuit 104 in binar
