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.8.1.4 Frame abortReceipt of seven or more contiguous 1 bits shall be interpreted as an abort and the error control function shall ignore the frame currently being received.8.1.5 Interframe time fillInterframe time fill is accomplished by transmitting contiguous flags between frames, i.e.multiple eight-bit flag sequences (see 8.1.1.2).8.2 LAPM elements of procedures and field formatsThe elements of procedures define the commands and responses that are used on an LAPM error-corrected connection.Procedures, which are derived from these elements of procedures, are described in subsequent subclauses.8.2.1 Address field formatThe format of the address field is shown in Figure 8.The address field contains the data link connection identifier (DLCI), the C/R bit, and the address field extension (EA) bit.87654321OctetDLCIC/REA2DLCIEA2AFigure 8/V.42 - Address field format8.2.1.1 Data link connection identifierWithin the scope of this Recommendation, two DLCI values are defined.One DLCI value is used to transfer information exchanged between V.24 interfaces.The other value, which is optional, is used as a control function-to-control function information connection; it is described in clause 11.The value for each DLCI is described in 9.2.7.When using the optional two-octet address field (see 8.2.1.3), the DLCI also includes bits 8 through 2 of octet 2A.8.2.1.2 Command/response (C/R) bit fieldThe C/R (command/response) bit identifies the frame as either a command or a response.In conformance with HDLC rules, a command frame contains the "address" of the error-correcting entity to which it is transmitted while a response frame contains the "address" of the error-correcting entity transmitting the frame.For a given error-corrected connec­tion, the DLCI value of the address field remains the same but the C/R bit changes, as shown in Table 6.Table 6/V.42 - Command/response bit usageCommand/responseDirectionC/R valueCommandOriginator____!Answerer1Answerer____!OriginatorResponseOriginator____!AnswererAnswerer____!Originator18.2.1.3 Address field extension (EA) bitAccording to the rules of HDLC, the range of the address field may be extended by reserving the first transmitted bit of each octet of this field to indicate whether the octet is the last one of the field.Within the scope of this Recommendation, the address field is limited to a maximum of two octets.When the EA bit is set to 1 in an octet, it signifies that this octet is the last octet of the address field.When the EA bit is set to 0, it signifies that another octet of the address field follows.8.2.2 Control field formatThe control field identifies the type of frame, which will be a command or response.The control field will contain sequence numbers, where applicable.Three types of control field formats are specified: numbered information transfer (I format), supervisory functions (S format), and unnumbered information transfers and control functions (U format).The control field formats are shown in Table 7.Table 7/V [ Pobierz caÅ‚ość w formacie PDF ]