1、I N T E R N AT IO N A L STANDARD I NTER N AT10 N A L 0 RG AN IZAT ION FOR STAN DAR DlZATl 0 N ORGANISATION INTERNATIONALE DE NORMALISATION MEXAYHAPOAHAR OPTAH M3AL(MR no CTAHAAPTM3AL publication anticipated in due course. IS0 9160 : 1988 (E) Physical layer Data communication DTE DCE DCE/DTE Interfac
2、e Call establishment Data transfer Test loops Serial transmission Asynchronous transmission Start Stop transmission Start signal Stop singal Synchronous transmission Duplex transmission Half duplex transmision 3.2 This International Standard makes use of the following terms drawn from the respective
3、 International Standards. Service Data Unit (SDU) Physical connection Ciphertext Plaintext Initializing Value (IV) Starting Variable (SV) (IS0 7498) (IS0 7498) (IS0 749812) (IS0 749812) (IS0 8372) (IS0 8372) 4 Applicable interfaces Where an interface exists between the DEE and the DTE, DCE, or with
4、both, this interface may be one of those recommended by CCllT such as V.24, X.20, X.20bis, X.21 or X.2lbis. This International Standard refers to the call establishment of a physical layer connection which is signalled in a different manner across these different interfaces. Control signals not affe
5、cting, nor affected by, DEE operation shall be passed through or re - driien at the DEE. A DEE presenting a standard DCHDTE Interface needs to delay some control signals such, as Ready for Sending, Data Set Ready, or the Ready for Data indications, when relaying them to the DTE, as required to compl
6、ete its own ope rations . The delay caused by the DEE, together with the delay caused by the DCE, shall fit into the time-out requirements determined by the DTE. The DTE shall not commence data transmission prior to having received the appropriate control signal as mentioned above. 4.1 V.24 Interfac
7、es For interchange circuits to Recommendation V.24, circuit 108 (Data Terminal Ready / Connect Data Set to Line) from the DTE to the DCE, if used by the DCE, circuit I07 (Data Set Ready) from the DCE to the DTE, and circuit 109 (Data Channel Received Line Signal Detector) from the DCE to the DTE are
8、 always passed through or redriven with minimal delay by the DEE. However, it is recommended that the DEE delays the ON condition on circuit 109 to the DTE until such time as the DEE is in a position to deliver data to the DTE on circuit 104 (Received Data). The DEE shall not signal the ON condition
9、 on circuit 109 to the DTE until after the ON condition on circuit 107 has been signalled to the DTE. Inserting a DEE into a DTEIDCE Interface introduces inherent delays in control signals and should consider the time - out provisions of existing equipment. The time - outs depend, among other things
10、, on duplex transmission and half duplex transmission. The appropriate modem recommendation should be consulted. 4.1.1 Duplex Transmission Call establishment of a physical connection is indicated by reception by theDEE of the ON condition on circuit 107 from the DCE. In leased line operation, circui
11、t 107 is permanently ON. Both the transmit and receive data channels are active at the time circuit 109 and circuit 106 are ON. The DEE shall not signal the ON condition on circuit 106 to the DTE until such time as all of the following conditions are met: a) Circuit 107 is switched ON from the DCE t
12、o the DEE and passed through by the DEE to the DTE b) Circuit 105 from the DTE, if required by the DCE, is switched ON and passed through to the DCE. c) Circuit 106 from the DCE is ON and the initiating DEE operations are completed. A physical connection can be cleared by: a) the DCE, indicated by t
13、he transition to the OFF condition of circuit 107, as a national option; or by b) the DTE, indicated by the transition to the OFF condition of circuit 108; or by c) the DEE, indicated by the transition to the OFF condition of circuit 1U8 to the DCE and of circuit 107 to the DIE. When this happens it
14、 indicates a fault condition in the DEE. 4.1.2 Half - Duplex TranSmissiOn Call establishment of a physical connection is indicated by reception of the ON condition on circuit 107 from the WE. In leased line operation circuit 107 is permanently ON. Depending on the condition of the Request to Send (c
15、ircuit lE), either the transmit or receive data channel is active at a time. The ready for sending state, circuit 106 ON, is indicated by the DCE after the DTE and the DEE switched circuit 105 ON. The ready for receiving state is indicated by the ON condition of circuit 109 from the DCE. Circuit 105
16、 is used such that the transition to the ON condition is always passed through or re-driven with minimal delay by the DEE. The transition to the OFF condition to the DCE is delayed by the DEE until the last data bit is transmitted on Transmitted Data (circuit 103). Circuit 106 ON from the DEE to the
17、 DTE is indicated after initiating DEE operations are completed. A physical connection can be cleared by: a) the DCE, indicated by the transition to the OFF condition of circuit 107, as a national option: or by b) the DTE, indicated by the transition to the OFF condition of circuit 108; or by c) the
18、 DEE, indicated by the transition to the OFF condition of circuit 108 to the DCE and of circuit 107 to the 2 IS0 9160 : 1988 (E) DTE. When this happens it indicates a fault condition in the DEE. NOTE - To avoid false DEE decipherment starts, caused by false signals on circuit 104 which can occur sho
19、rtly after the ON to OFF transition on circuit 105 and the following OFF to ON transition on circuit 109 in the DCE, the DEE should be used with a DCE which uses the clamping option of V.24, clause 4.3, together with the longer OFF to ON response time of circuit 106 as specified in the relevant DCE
20、recommendation. 4.2 X.2obis or X2lbis Interfaces For interchange circuits to CCllT Recommendations X.2Obis and X.21bis consult the applicable V.24 operation for duplex transmission as described above. 4.3 x.20 Interfaces For interchange circuits to CCllT Recornmendation X.20, Call establishment of a
21、 physical connection provides for start-stop and duplex transmission. It is indicated by reception of the call control character ACK on the Receive interchange circuit R. In leased circuit service, data can be transmitted and received at any time. In circuit switched service, reception of data (read
22、y for receiving state) may take place immediately after reception of ACK. This state is called Connected. Transmission of data (ready for sending state) may take place not earlier than 20 ms after ACK. This later is called Ready for Data. The Connected state from the DEE to the DTE is indicated by A
23、CK after the initiating DEE operations are completed. Clearing of a physical connection is indicated by the DCE clear confirmation at the clearing DTE or the DTE clear confirmation at the cleared DTE, both indicated by the transmission of continuous binary zeros on circuit R, Le. r=0, which persists
24、 for at least 210 ms. Clearing may be initiated either by DTE clear request from the DTE, DCE clear indication from the DCE, or by the DEE indicating DTE clear request to !he DCE and DCE clear indication to the DTE. The DEE initiated disconnect indicates a fault condition in the DEE. 4.4 X.21 Interf
25、aces For interchange circuits to CCllT Recommendation X.21, call establishment of a physical connection provides for synchronous and duplex transmission. It requires the Transmit interchange circuit T from the DTE to the DCE in ON condition. Call establishment is indicated by the Ready for Data stat
26、e, which is the transition to ON on the Indication interchange circuit I from the DCE. In leased circuit service, circuit I goes ON as a response to circuit T switched ON. Circuit T from the DTE to the DCE is always passed through or re-driven with minimal delay by the DEE. The transmission and rece
27、ption of data (ready for sending state and ready for receiving state) may take place not earlier than 16 bit times after i=ON. The Ready for Data state, Le., i=ON, from the DEE to the DTE is indicated after the initiating DEE operations are completed. Clearing of a physical connection is indicated b
28、y the DCE clear confirmation at the clearing DTE or the DTE clear confirmation at the cleared DTE, both indicated by a transition to OFF on circuit I from the DCE together with binary zeros on circuit R, Le., r=O, i=OFF. Clearing may be initiated either by DTE clear request from the DTE, DCE clear i
29、ndication from the DCE, or by the DEE indicating DTE clear request to the DCE and DCE clear indication to the DTE. The DEE initiated disconnect indicates a fault condition in the DEE. 4.5 Transmitted and Received Data Interchange Circuits The term transmitted data interchange circuit in this Interna
30、tional Standard refers, in the case of a V.24, X.2Obis or X.2lbis interface, to circuit 103 and in the case of an X.20 or X.21 interface to circuit T. The term received data interchange circuit in this International Standard refers, in the case of a V.24, X.20bis or X.2lbis interface, to circuit 104
31、, and in the cas8 of an X.20 or X.21 interface to circuit R. 5 General requirements When employing this International Standard for interworking between DEEs, the following conditions are required in all DEEs of an interworking group: a. The same cipher algorithm. b. c. The same IV length, IV structu
32、re, and IV bit The same cryptographic key value. transmission order. This International Standard does not specify a particular cipher algorithm but does require any algorithm used to be applicable on a single bit or single character at a time basis, as appropriate to the physical layer service provi
33、ded. NOTES 1. The use of a block cipher algorithm in the 1 -bit cipher feedback (CFB- 1) mode of operation specified in Is0 8372 meets the requirements of this International Standard. 2. Annex B contains the IV requirements when the DEA (ANSI X3.92 - 1981) algorithm is used for encipherment. If ther
34、e is Ioss of synchronization between DEEs and this condition is detected, resynchronization can be forced by the DEE or DTE, by clearing the physical connection, followed by the re - establishment of the physical connection using procedures appropriate to the type of interface as specified in clause
35、 4. The DEE shall not initiate connection re -establishment. 3 IS0 9160 : 1988 (E) 6 Synchronous encipherment operation 6.1 IV The IV length and IV structure may be chosen according to the application. There shall be prior agreement concerning IV length and IV structure among all the DEEs in an inte
36、rworking group. 6.2 Transmission Upon call establishment of a physical connection and indication of the ready for sending state, the transmitted data interchange circuit is in a MARK condition. The IV is sent at this point in time, preceded by a single binary zero bit to delimit the IV. Encipherment
37、 continues until clearing of the physical connection or data channel turn - around in half duplex transmission. The transmission of the first enciphered data bit of the SDU shall follow the transmission of the IV according to one of the following alternatives. 63.1 Alternative A: Immediate The first
38、 enciphered data bit follows immediately after transmission of the IV. 6.2.2 Alternative B: Delayed Immediately following transmission of the IV, an indeterminate number of binary one bits (MARK condition) may be transmitted. However, if this alternative is used this delay condition shall be maintai
39、ned for a minimum of 10 ms, up to a maximum of 50 ms. The binary one bits are followed by a single binary zero bit to delimit the data. followed by the first enciphered data bit. 6.3 Upon call establishment of a physical connection and indication of the ready for receiving state, the received data i
40、nterchange circuit is in a MARK condition. The IV is received immediately following the first binary zero bit. In Alternative A, all subsequent received bits are then deciphered. In Alternative 6, the receiving DEE shall be capable of recognising the delimiting binary zero bit and deciphering incomi
41、ng data within 10 ms. In both Alternative A and Alternative B, decipherment continues until clearing of the physical connection or data channel turn-around in half duplex transmission. Figure 1 shows the operation of the V.24 interchange circuits for duplex transmission. Figures 2 and 3 illustrate t
42、he V.24 half duplex transmission signalling sequences for synchronous encipherment Alternative A and B respect- ively. 7 Asynchronous encipherment operation NOTE - The use of a physical connection capable of duplex transmission is recommended in order to improve the efficiency of operation. 7.1 Tran
43、smission 7.1.1 IV Upon the establishment of a physical layer connection and indication of the ready for sending state, the transmitted data interchange circuit is in a MARK condition. The IV shall be sent subdivided into units equal to the size of the characters about to be enciphered and transmitte
44、d. The IV length and IV structure may be chosen according to the application. There shall be prior agreement between transmitting and receiving DEE on IV length, IV structure, and framing of the IV in transmitted characters. 7.1.2 Starting Encipherment Characters of the SDU (corresponding to charact
45、ers on the transmitted data interchange circuit). framed within start and stop signals, are transmitted enciphered following the last IV character. Start and stop framing signals are not enciphered. Encipherment continues, except for BREAK (described below), until clearing of the physical connection
46、 or data channel turn - around in half duplex transmission. Figure 4 illustrates the start of asynchronous encipher- ment as well as the Class A BREAK operation described below. 7.1.3 BREAK BREAK is signalled by a SPACE condition existing for one character time or longer. The action of the DEE on a
47、BREAK shall be according to one of the following alternatives. 7.1.3.1 Class A The first binary zero bit of the BREAK is treated as a start signal. The next n binary zero bits are enciphered, where n is the normal character length in bits without the start signal snd stop signal. The stop signal (MA
48、RK condition) is not output by the DEE. Subsequent binary zero bits in the BREAK are not enciphered and the DEE continues to output the binary zero state. Figure 4 illustrates this action on the right hand side. The transition to the MARK condition at the DEE input produces a corresponding transitio
49、n at the DEE output. Subsequently, the DEE resumes its normal operation. 7.1.3.2 Class B The DEE normally does not output any character until the stop signal has been received. BREAK is detected by the absence of the expected stop signal. Having detected a BREAK the DEE outputs an identical BREAK, suspending encipherment. The end of the BREAK is output after a suitable delay, following which normal operation is resumed. figure 5 illustrates Class E3 break operation. 7.2 Receptian 7.2.1 Starting Deciphennerrt Upon call establishme
