本国际标准规定了框架结构、程序要素、程序类别、内容 和通用交换标识(XID)帧的格式，以及用于解析/协商数据链路的装置 使用面向位的高级数据链路控制的数据通信系统的交换环境中的层地址 （HDLC）程序。 笔记？短语“面向位”的使用涉及HDLC控制过程，涉及非整数的分配 用于HDLC控制目的的各种子字段。然而，作为整体的帧可以由面向八位字节的单元来构造 (例如，启停模式)用于传输目的。 帧结构部分定义基本帧格式和非基本帧格式的各种分量的相对位置 帧格式。用于在需要的地方和时间内实现位模式独立性（透明度）的机制 还定义了框架。此外，规定了三个帧校验序列(FCS)；地址字段的规则 定义了扩展；并且描述了可用的寻址约定。 过程的要素部分指定用于同步或启动/停止、代码透明的数据链路控制过程的要素 在两个方向上使用独立帧编号的数据传输。 过程的这些HDLC元素是根据在 次级站、支流站、对等站或组合站。 本国际标准旨在涵盖广泛的应用；例如单向、双向交替或双向 通常被缓冲的数据站之间的同时数据通信，包括对不同的 数据电路的类型；例如多点/点对点、双工/半双工、交换/非交换、同步/启停， 等等。 所定义的程序要素应被视为建立不同类型数据链路控制的共同基础 程序。本国际标准没有定义任何单一系统，也不应被视为 数据通信系统。并非所有命令或响应对于任何特定系统实现都是必需的。 程序类别部分描述了HDLC不平衡程序类别、HDLC平衡程序类别 过程，以及用于同步或启动/停止数据传输的HDLC无连接类过程。对于不平衡类，数据链路由一个主站加上一个或多个辅助站组成，并在 点对点或多点配置中的正常响应模式或异步响应模式。对于 平衡类，数据链路由两个组合站组成，以点对点的异步平衡模式运行 配置。对于非平衡无连接类，数据链路由一个控制站加上一个或多个 支流站，并在点对点或多点配置中以不平衡无连接模式运行。对于 平衡无连接类，数据链路由两个对等站组成，并在平衡无连接模式下运行 点对点配置。在每个类中，都定义了命令和响应的基本库，但是 可以通过使用可选功能来修改数据链路。 平衡操作旨在用于需要对数据链路两端进行同等控制的情况。操作 根据整个HDLC架构涵盖需求。 交换标识(XID)帧部分的内容和格式建立在XID的主要用途 帧用于在两个或多个HDLC站之间交换数据链路信息。就本国际标准而言， ISO/IEC 13239:2002(E) 2？ISO/IEC 2002？版权所有 数据链路信息应包括任何和所有必要的操作特征，如识别、认证和/或 与每个站相关的可选功能和设施的选择。本国际标准定义了单-交换 当一个或多个站能够提供 多项选择。 本国际标准提供了交换必要信息的手段，以至少建立数据链路 两个希望通信的通信者之间的连接。它描述了通用XID帧信息字段 为此目的的内容和格式。 它仅定义了与基本HDLC标准相关的信息的编码。提供了允许一般 目的XID帧信息字段用于同时协商单个XID交换中的私有参数 定义的基本参数的协商。 本国际标准不限制或限制XID帧信息字段的使用来定义其他标准 特定应用中使用的格式。 以下是XID命令/响应帧交换的潜在用途的示例: a)使用电路交换网络（包括交换网络备份）时主叫站和被叫站的识别 应用）。 b)在启动时需要识别的非交换网络上运行的站的识别。 c)具有个体、组或全站地址的XID命令帧可用于请求XID响应帧 在数据链路建立之前或之后，从数据链路上的其他站发送。 d)由以下站协商要用于后续信息交换的帧校验序列(FCS): 同时支持16位FCS和32位FCS功能。 e)传送在数据链路建立之前可能需要的更高层信息。f)在任何响应机会处发送XID响应帧以请求XID交换以修改所述XID中的一些。 数据链路建立后的操作参数（例如，窗口大小）。 g)当具有报头检查的未编号信息(UIH)时，协商帧中受保护比特的数量 使用框架。 用于在交换环境中解析/协商数据链路层地址的装置部分适用于数据站 采用HDLC平衡类的过程，这些过程提供XID命令/响应能力，具有两个特定的 参数字段，如下所示。它用于在预先分配、系统指定时选择一对操作链路地址 地址在先验基础上是未知的；例如，交换电路数据链路。其他XID帧功能（包括 操作参数、命令/响应支持、更高层信息等的交换）可以在 结合数据链路层地址确定或随后的地址确定，具有附加XID帧 交换。 笔记？远程DTE不支持XID帧的情况下的地址解析过程，即“全站” 地址，或下文第8条中定义的完整地址支持能力不在本国际 标准的。

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