| Nosaukums | <p>This International Standard specifies the frame structures, the elements of procedures, the classes of procedures, the content</p>
<p>and format of the general purpose Exchange Identification (XID) frame, and a means for resolution/negotiation of a data link</p>
<p>layer address in switched environments for data communication systems using bit-oriented high-level data link control</p>
<p>(HDLC) procedures.</p>
<p>NOTE The use of the phrase "bit-oriented", referring to the HDLC control procedures, pertains to the allocation of a non-integral number</p>
<p>of bits to various subfields used for HDLC control purposes. However, the frame as an entirety may be constructed from octet-oriented units</p>
<p>(e.g., start-stop mode) for transmission purposes.</p>
<p>The frame structure portion defines the relative positions of the various components of the basic frame format and the nonbasic</p>
<p>frame format. The mechanisms used to achieve bit pattern independence (transparency), where and when required, within</p>
<p>the frame are also defined. In addition, three frame checking sequences (FCS) are specified; the rules for address field</p>
<p>extension are defined; and the addressing conventions available are described.</p>
<p>The elements of procedures portion specifies elements of data link control procedures for synchronous or start/stop, codetransparent</p>
<p>data transmission using independent frame numbering in both directions.</p>
<p>These HDLC elements of procedures are defined specifically in terms of the actions that occur on receipt of commands at a</p>
<p>secondary station, a tributary station, a peer station, or a combined station.</p>
<p>This International Standard is intended to cover a wide range of applications; for example one-way, two-way alternate or twoway</p>
<p>simultaneous data communication between data stations which are usually buffered, including operations on different</p>
<p>types of data circuits; for example multipoint/point-to-point, duplex/half-duplex, switched/non-switched, synchronous/startstop,</p>
<p>etc.</p>
<p>The defined elements of procedures are to be considered as a common basis for establishing different types of data link control</p>
<p>procedures. This International Standard does not define any single system and should not be regarded as a specification for a</p>
<p>data communication system. Not all of the commands or responses are required for any particular system implementation.</p>
<p>The classes of procedures portion describes the HDLC unbalanced classes of procedures, the HDLC balanced class of</p>
<p>procedures, and the HDLC connectionless classes of procedures for synchronous or start/stop data transmission.</p>
<p>For the unbalanced classes, the data link consists of a primary station plus one or more secondary stations and operates in</p>
<p>either the normal response mode or the asynchronous response mode in a point-to-point or multipoint configuration. For the</p>
<p>balanced class, the data link consists of two combined stations and operates in the asynchronous balanced mode in a point-topoint</p>
<p>configuration. For the unbalanced connectionless class, the data link consists of a control station plus one or more</p>
<p>tributary stations and operates in the unbalanced connectionless-mode in a point-to-point or multipoint configuration. For the</p>
<p>balanced connectionless class, the data link consists of two peer stations and operates in the balanced connectionless-mode in a</p>
<p>point-to-point configuration. In each class, a basic repertoire of commands and responses is defined, but the capability of the</p>
<p>data link may be modified by the use of optional functions.</p>
<p>Balanced operation is intended for use in circumstances which require equal control at either end of the data link. Operational</p>
<p>requirements are covered in accordance with the overall HDLC architecture.</p>
<p>The content and format of the Exchange Identification (XID) frame portion builds on the fact that the principal use of the XID</p>
<p>frame is to exchange data link information between two or more HDLC stations. For the purpose of this International Standard,</p>
<p><b>ISO/IEC 13239:2002(E)</b></p>
<p><b>2 </b>© ISO/IEC 2002 ? All rights reserved</p>
<p>data link information shall include any and all essential operational characteristics such as identification, authentication and/or</p>
<p>selection of optional functions and facilities concerning each station. This International Standard defines a single-exchange</p>
<p>negotiation procedure for establishing operational characteristics when either one or more stations are capable of providing</p>
<p>multiple selections.</p>
<p>This International Standard provides a means for exchanging the necessary information to establish, at a minimum, a data link</p>
<p>connection between two correspondents wishing to communicate. It describes a general purpose XID frame information field</p>
<p>content and format for that purpose.</p>
<p>It defines encoding for information related to the basic HDLC standards only. Mechanisms are provided to permit the general</p>
<p>purpose XID frame information field to be used to negotiate private parameters in a single XID exchange simultaneously with</p>
<p>negotiation of the defined basic parameters.</p>
<p>This International Standard does not limit or restrict the use of the XID frame information field from defining other standard</p>
<p>formats for use in specific applications.</p>
<p>The following are examples of potential uses of the XID command/response frame interchange:</p>
<p>a) Identification of the calling and called stations when using circuit switched networks (including switched network backup</p>
<p>applications).</p>
<p>b) Identification of stations operating on non-switched networks requiring identification at start-up.</p>
<p>c) The XID command frame with an individual, group or all-station address may be used to solicit XID response frame(s)</p>
<p>from other station(s) on the data link, prior to or following data link establishment.</p>
<p>d) Negotiation of the Frame Check Sequence (FCS) to be used for subsequent information interchange, by stations that</p>
<p>support both 16-bit FCS and 32-bit FCS capabilities.</p>
<p>e) Convey higher layer information that may be required prior to data link establishment.</p>
<p>f) Transmission of an XID response frame at any respond opportunity to request an XID exchange to modify some of the</p>
<p>operational parameters (for example, window size) following data link establishment.</p>
<p>g) Negotiation of the number of protected bits in the frame when an Unnumbered Information with Header check (UIH)</p>
<p>frame is used.</p>
<p>The means for resolution/negotiation of a data link layer address in switched environments portion is applicable to data stations</p>
<p>employing HDLC balanced classes of procedures which provide the XID command/response capability with the two specific</p>
<p>parameter fields, identified below. It is used to select a pair of operational link addresses when preassigned, system designated</p>
<p>addresses are not known on an a priori basis; e.g., switched circuited data links. Additional XID frame functions (including the</p>
<p>exchange of operational parameters, command/response support, higher layer information, etc.) may be accomplished in</p>
<p>conjunction with data link layer address determination or following address determination, with additional XID frame</p>
<p>exchanges.</p>
<p>NOTE Address resolution procedures for situations where the remote DTE does not support XID frames, the "all-station"</p>
<p>address, or complete address support capabilities as defined in clause 8 below are not within the scope of this International</p>
<p>Standard.</p> |
|---|
| Darbības sfēra | <p>This International Standard specifies the frame structures, the elements of procedures, the classes of procedures, the content</p>
<p>and format of the general purpose Exchange Identification (XID) frame, and a means for resolution/negotiation of a data link</p>
<p>layer address in switched environments for data communication systems using bit-oriented high-level data link control</p>
<p>(HDLC) procedures.</p>
<p>NOTE The use of the phrase "bit-oriented", referring to the HDLC control procedures, pertains to the allocation of a non-integral number</p>
<p>of bits to various subfields used for HDLC control purposes. However, the frame as an entirety may be constructed from octet-oriented units</p>
<p>(e.g., start-stop mode) for transmission purposes.</p>
<p>The frame structure portion defines the relative positions of the various components of the basic frame format and the nonbasic</p>
<p>frame format. The mechanisms used to achieve bit pattern independence (transparency), where and when required, within</p>
<p>the frame are also defined. In addition, three frame checking sequences (FCS) are specified; the rules for address field</p>
<p>extension are defined; and the addressing conventions available are described.</p>
<p>The elements of procedures portion specifies elements of data link control procedures for synchronous or start/stop, codetransparent</p>
<p>data transmission using independent frame numbering in both directions.</p>
<p>These HDLC elements of procedures are defined specifically in terms of the actions that occur on receipt of commands at a</p>
<p>secondary station, a tributary station, a peer station, or a combined station.</p>
<p>This International Standard is intended to cover a wide range of applications; for example one-way, two-way alternate or twoway</p>
<p>simultaneous data communication between data stations which are usually buffered, including operations on different</p>
<p>types of data circuits; for example multipoint/point-to-point, duplex/half-duplex, switched/non-switched, synchronous/startstop,</p>
<p>etc.</p>
<p>The defined elements of procedures are to be considered as a common basis for establishing different types of data link control</p>
<p>procedures. This International Standard does not define any single system and should not be regarded as a specification for a</p>
<p>data communication system. Not all of the commands or responses are required for any particular system implementation.</p>
<p>The classes of procedures portion describes the HDLC unbalanced classes of procedures, the HDLC balanced class of</p>
<p>procedures, and the HDLC connectionless classes of procedures for synchronous or start/stop data transmission.</p>
<p>For the unbalanced classes, the data link consists of a primary station plus one or more secondary stations and operates in</p>
<p>either the normal response mode or the asynchronous response mode in a point-to-point or multipoint configuration. For the</p>
<p>balanced class, the data link consists of two combined stations and operates in the asynchronous balanced mode in a point-topoint</p>
<p>configuration. For the unbalanced connectionless class, the data link consists of a control station plus one or more</p>
<p>tributary stations and operates in the unbalanced connectionless-mode in a point-to-point or multipoint configuration. For the</p>
<p>balanced connectionless class, the data link consists of two peer stations and operates in the balanced connectionless-mode in a</p>
<p>point-to-point configuration. In each class, a basic repertoire of commands and responses is defined, but the capability of the</p>
<p>data link may be modified by the use of optional functions.</p>
<p>Balanced operation is intended for use in circumstances which require equal control at either end of the data link. Operational</p>
<p>requirements are covered in accordance with the overall HDLC architecture.</p>
<p>The content and format of the Exchange Identification (XID) frame portion builds on the fact that the principal use of the XID</p>
<p>frame is to exchange data link information between two or more HDLC stations. For the purpose of this International Standard,</p>
<p><b>ISO/IEC 13239:2002(E)</b></p>
<p><b>2 </b>© ISO/IEC 2002 ? All rights reserved</p>
<p>data link information shall include any and all essential operational characteristics such as identification, authentication and/or</p>
<p>selection of optional functions and facilities concerning each station. This International Standard defines a single-exchange</p>
<p>negotiation procedure for establishing operational characteristics when either one or more stations are capable of providing</p>
<p>multiple selections.</p>
<p>This International Standard provides a means for exchanging the necessary information to establish, at a minimum, a data link</p>
<p>connection between two correspondents wishing to communicate. It describes a general purpose XID frame information field</p>
<p>content and format for that purpose.</p>
<p>It defines encoding for information related to the basic HDLC standards only. Mechanisms are provided to permit the general</p>
<p>purpose XID frame information field to be used to negotiate private parameters in a single XID exchange simultaneously with</p>
<p>negotiation of the defined basic parameters.</p>
<p>This International Standard does not limit or restrict the use of the XID frame information field from defining other standard</p>
<p>formats for use in specific applications.</p>
<p>The following are examples of potential uses of the XID command/response frame interchange:</p>
<p>a) Identification of the calling and called stations when using circuit switched networks (including switched network backup</p>
<p>applications).</p>
<p>b) Identification of stations operating on non-switched networks requiring identification at start-up.</p>
<p>c) The XID command frame with an individual, group or all-station address may be used to solicit XID response frame(s)</p>
<p>from other station(s) on the data link, prior to or following data link establishment.</p>
<p>d) Negotiation of the Frame Check Sequence (FCS) to be used for subsequent information interchange, by stations that</p>
<p>support both 16-bit FCS and 32-bit FCS capabilities.</p>
<p>e) Convey higher layer information that may be required prior to data link establishment.</p>
<p>f) Transmission of an XID response frame at any respond opportunity to request an XID exchange to modify some of the</p>
<p>operational parameters (for example, window size) following data link establishment.</p>
<p>g) Negotiation of the number of protected bits in the frame when an Unnumbered Information with Header check (UIH)</p>
<p>frame is used.</p>
<p>The means for resolution/negotiation of a data link layer address in switched environments portion is applicable to data stations</p>
<p>employing HDLC balanced classes of procedures which provide the XID command/response capability with the two specific</p>
<p>parameter fields, identified below. It is used to select a pair of operational link addresses when preassigned, system designated</p>
<p>addresses are not known on an a priori basis; e.g., switched circuited data links. Additional XID frame functions (including the</p>
<p>exchange of operational parameters, command/response support, higher layer information, etc.) may be accomplished in</p>
<p>conjunction with data link layer address determination or following address determination, with additional XID frame</p>
<p>exchanges.</p>
<p>NOTE Address resolution procedures for situations where the remote DTE does not support XID frames, the "all-station"</p>
<p>address, or complete address support capabilities as defined in clause 8 below are not within the scope of this International</p>
<p>Standard.</p> |
|---|
