1、INTERNATIONAL STANDARD ISO/IEC 8480 Second edition 1995-09-I 5 Information technology - Telecommunications and information exchange between systems - DTE/DCE interface back-up control operation using ITU-T Recommendation V.24 interchange circuits Technologies de /information - T - back-up of a 4-wir
2、e leased line by one GSTN line; - back-up of a 4-wire leased line by two GSTN lines; - back-up of a 2-wire/4-wire leased line by one/two lines of a private switched network; - back-up of a 2-wire leased line by one ISDN line, using a terminal adaptor ; - back-up of a 4-wire leased line by one ISDN l
3、ine, using a terminal adaptor . NOTES 1 - This list may not be exhaustive 2 - the terminal adaptor may be separate equipment or physically combined with the DCE. The variety of facilities should not be visible in the protocol used at the DTUDCE interface to exchange the interface control and status
4、information necessary for back-up control. To achieve this, a standardised approach to the required protocol is essential. The majority of applications are, however, restricted to the first two of the listed possibilities. In consequence, this International Standard describes the protocol requiremen
5、ts where only one back-up facility is provided as the alternative to data transmission on the leased line. For other arrangements of facilities, although this International Standard is not directly applicable, it nevertheless should be used as a guide to the protocol requirements. Terminal Adaptor f
6、unctions are described in ITU-T Recommendation (previously CCITT Recommendation) V.l IO, Supporf of data terminal equipments with V-series type interfaces by an integrated services digital network, and CCITT Recommendation V.120, Support by an /SDN of data terminal equipment with V-series type inter
7、faces with provision for statistical multiplexing. . . . Ill INTERNATIONAL STANDARD 0 ISO/IEC ISO/IEC 8480 : 1995 (E) Information technology - Telecommunications and information exchange between systems - DTElDCE interface back-up control operation using ITU-T Recommendation V.24 interchange circuit
8、s 1 Scope This International Standard specifies the procedures for back-up operation applicable to data transmission on a leased line when implemented through a single interface, controlling both the leased and the back-up facilities, using ITU-T Recommendation V.24 interchange circuits in conjuncti
9、on with either the 25- pole connector (IS0 2110) or the 26-pole connector (ISO/IEC 11569). The method used to switch the transmission of data automatically from the leased line to or from the back-up facility is not specified in this International Standard. This International Standard is not applica
10、ble where back-up (calling or answering) is achieved by manual means. NOTES 1 The procedures specified in this International Standard may be used at the answering end only, the calling end only, or both ends of a connection. 2 An ordinary DCE (i.e. one not implementing back-up control) may be provid
11、ed at either end of the back-up circuit and only for back-up purposes. For example, a calling station could provide one or more separate auto-dial GSTN lines to provide back-up on demand to a greater number of leased lines. 2 Normative references The following standards contain provisions which, thr
12、ough reference in this text, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agre,ements based on this international Standard are encouraged to investigate the possibility of ap
13、plying the most recent editions of the standards indicated below. Members of IEC and IS0 maintain registers of currently valid International Standards. IS0 2110:1989, information technology - Data communication - 25-pole DTGDCE interface connector and contact number assignments. ISO/IEC 11569:1993,
14、information technology - Telecommunications and information exchange between systems - 26-pole interface connector mateability dimensions and contact number assignments. IT&T Recommendation1 V.24:1993, List of definitions for interchange circuits between data terminal equipment and data circuit-tem)
15、inating equipment. 3 Definitions For the purposes of this International Standard, the following definitions apply. 3.1 answering station: the station at which the DCE switches to the back-up facility when a back-up request is received (e.g. an incoming call). 3.2 authorized mode: the mode in which s
16、witching to the back-up facility is done at the DCE initiative when the DCE is authorized by the DTE to do so. NOTE - In the event that the DTE cannot control this facility over the interface, selection of this mode within the DCE during installation is permitted. 3.3 calling station: the station at
17、 which the DCE has to send to the called station a back-up request (e.g. a call for the other end to switch to the back-up facility). 3.4 direct mode: the mode in which switching to the back-up facility is done at the DTE initiative. 4 Switching to back-up operation The state diagrams applicable to
18、back-up operation, encompassing the procedures at both the calling and the answering stations, are shown in figure 1 for direct mode, and in figure 2 for authorized mode. When interchange circuit 108 is implemented, it shall be in the ON condition. When circuit 108 is not implemented, the DCE shall
19、operate as if circuit 108 were present and in the ON condition. Previously CCITT Recommendation 1 ISO/IEC 8480 : 1995 (E) 0 ISOAEC 4.1 Answering station 4.1 .I Direct mode In this mode, after receiving an incoming call, the DTE turns ON circuit 116/l at the time that it wants to force the DCE to swi
20、tch to the back-up facility. Operation: The DCE, which is connected to the leased line, when it receives a call on the back-up line, turns ON circuit 125. The DTE, if it wishes to answer this call (see the note) turns circuit 116/l ON. The DCE turns circuit 107 OFF, until it is connected to the back
21、-up facility after which it turns ON circuit 107 and circuit 117 (if used). NOTE - It is the responsibility of the DTE to ensure there is no erroneous switching to back-up. To terminate the connection to the back-up facility, the DTE turns OFF circuit 116/l. The DCE turns OFF circuit 107 and circuit
22、 117 (if used) until it is connected to the leased line after which it turns ON circuit 107. When automatic disconnection is allowed on the GSTN, and occurs, the DCE turns OFF circuit 107 and circuit 117 (if used) and waits for the DTE to turn circuit 116/l to the OFF condition before connecting to
23、the leased line. 4.1.2 Authorized mode In this mode, the DTE authorizes the DCE to switch to the back-up facility when necessary by turning circuit 11612 to the ON condition. When circuit 116/2 is not implemented on the DTUDCE interface, an internal option of the DCE, set at installation time, may e
24、nable the back-up facility. In authorized mode, where it is required by the DCE to inform the DTE of the line status, circuit 117 should be implemented. Operation: The DCE, which is connected onto the leased line, receives a call on its connection to the back-up line while circuit 116/2 is ON (see t
25、he note). Having validated the need to switch to back-up, the DCE turns OFF circuit 107 until it is connected to the back-up facility after which it turns ON circuit 107 and circuit 117. NOTE - Since there is a risk of an incoming call appearing by accident on the back-up line, it is the DCE respons
26、ibility to provide protection against erroneous switching to back- up, by checking that communication via the leased line has failed. Criteria for this may include monitoring the flow of data, in either direction as appropriate. Having validated the need to switch back to the leased line, the DCE di
27、sconnects from the back-up line and turns OFF circuit 117 and circuit 107. When the DCE is connected to the leased line, it turns ON circuit 107. The DTE may also terminate the connection onto the back-up facility, by turning OFF circuit 116/2. The DCE turns OFF circuit 117 and circuit 107 until it
28、is connected to the leased line after which it turns ON circuit 107. 4.2 Calling station 4.2.1 Direct mode In this mode, the DTE turns ON circuit 116/l at the time it wants to force the DCE to initiate a request towards the Answering Station in order to switch to the back-up facility. Operation: Whe
29、n the DTE turns ON circuit 116/l, the DCE, which is connected to the leased line, turns OFF circuit 107 (see note 1) and issues on the back- up line a call (see note 2) to the Answering Station. After the connection is established on the back-up facility with the Answering Station, the DCE turns ON
30、circuit 107 and circuit 117 (if used). NOTES 1 In order to facilitate validation of the back-up request at the Answering Station, the DCE at the Calling station should ensure that the carrier on the leased line is switched off as it turns OFF circuit 107. 2 This call may be either a predefined call
31、or a call initiated directly. To terminate the connection to the back-up facility, the DTE turns OFF circuit 116/l. The DCE turns OFF circuit 107 and circuit 117 (if used) until it is connected to the leased line after which it turns ON circuit 107. When automatic disconnection is allowed on the GST
32、N and occurs, the DCE turns OFF circuit 107 and circuit 117 (if used) and waits for the DTE to turn circuit 116/l to the OFF condition before connecting to the leased line. Where the call address information is not contained either in the DCE or the exchange the use of automatic calling procedures i
33、n accordance with CCITT Recommendation V.25bis2 for call establishment is permitted. (These procedures do not form part of this International Standard). In the case of a predefined call, it may be performed by an automatic dialler included in the DCE. It may also be issued in a so-called “hot line”
34、environment where seizure of the line by the DCE causes the exchange to establish a specific connection. * CCITT Recommendation V.25bis, Automatic calling and/or answering equipment on the General Switched Telephone Network (GSTN) using the lOO-series interchange circuits. 2 0 ISOAEC ISOIIEC 8480 :
35、1995 (E) In the case of a call initiated directly, the use of the Direct Initiated Call Procedure described in CCITT Recommendation V.25bis is permitted. (These procedures do not form part of this International Standard). line and turns OFF circuit 117 and circuit 107. When the DCE is connected to t
36、he leased line, it turns ON circuit 107. The DTE may also terminate the connection to the back-up facility, by turning OFF circuit 116/2. The 4.2.2 Authorized mode DCE turns OFF circuit 117 and circuit 107 until it is In this mode, the DTE authorizes the DCE to switch from leased line to back-up fac
37、ility as necessary, by means of a call (see note 2 to 4.2.1) to the Answering Station. When circuit 116/2 is not implemented on the DTE/DCE interface, an internal option of the DCE, set at installation time, may enable the back-up facility. In authorized mode, where it is required by the DCE to info
38、rm the DTE of the line status, circuit I I7 should be implemented. Operation: The DTE, accepting that a back-up call be issued under DCE control, turns ON circuit 116/2. When the DCE, which is connected onto the leased line, decides to issue the automatic call, it turns OFF circuit 107 (see note 1 t
39、o 4.2.1) and establishes the back-up connection with the Answering Station after which it turns ON circuit 107 and circuit 117. Having validated the need to switch back to the leased line, the DCE disconnects from the back-up connected to the leased line after which it turns ON circuit 107. Where th
40、e call address information for the predefined call is contained in the DCE, the use of the call address programming procedure described in CCITT Recommendation V.25bis is permitted. (These procedures do not form part of this International Standard). 5 Contact number assignment The following contact
41、number assignments apply to both the 25pole connector, IS0 2110, and the 26 pole connector, ISO/IEC 11569: - Interchange circuit 116: contact number 14 - Interchange circuit 117: contact number 16. NOTE - Some equipment exists in the field which uses nationaily assigned contact numbers for these cir
42、cuits. 3 ISOAEC 8480 : 1995 (E) 0 ISOAEC .eased hne ooeranon I 1 I L OFF ON OFF L v. A DCE / to lea&d line 1 DTE / DCE / DCE “-I 1 GSTN owetion ON ON OFF Figure 1 - Back-up Switching in “Direct Mode” 4 0 ISOAEC ISOAEC 8480 : 1995 (E) 1 Leasad he ooeratton BDck-up not Qermtted OFF ON OFF 4 GSTN oceratton ON ON ON . DCE disconnects from Leased he poor to automatic calling l * DCE dnconnects horn Loa& Llm on rtcomtng call Figure 2 - Back-up Switching in “Authorized Mode” 5
