A critical analysis of the X.400 model of message handling systems

The CCITT X.400 model of store and forward Message Handling Systems (MHS) serves as a common basis for the definition of electronic mail services and protocols both within CCITT and ISO. This paper presents an analysis of this model and its related recommendations from two perspectives. First the concepts of service, protocol and interface are discussed together with their application to this model; second the positioning within ISO's reference model for Open Systems Interconnection (OSI) is commented on.     

An interpreter for LOTOS,a specification language for distributed systems

LOTOS is an executable specification language for distributed systems currently being standardized within ISO as a tool for the formal specification of open systems interconnection protocols and services. It is based on an extended version of Milner's calculus of communicating systems (CCS) and on ACT ONE abstract data type (ADT) formalism. A brief introduction to LOTOS is given, along with a discussion of LOTOS operational semantics, and of the executability of LOTOS specifications. Further, an account of a prototype LOTOS interpreter is given, which includes an interactive system that allows the user to direct the execution of a specification (for example, for testing purposes). The interpreter was implemented in YACC/LEX, C and Prolog. The following topics are discussed: syntax and static semantics analysis; translation from LOTOS external format to internal representation; evaluation of ADT value expressions and extended CCS behaviour expressions. It is shown that the interpreter can be used in a variety of ways: to recognize whether a given sequence of interactions is allowed by the specification; to generate randomly chosen sequences of interactions; in a user-guided generation mode, etc.     

协议形式化开发环境的规范语言

LOTOS（languageoftemporalorderingspecification）是一种基于进程代数CCS的协议规范语言，面向协议验证，但它不能描述协议的某些性质．本文提出了一种LOTOS的扩充语言ELOTOS（extendedLOTOS），它在LOTOS的基础上引入了异步通讯机制、时间描述、事件发生的随机性描述．     

异构网络环境下X.400电子邮件系统的实现

当前电子邮件发展的特点是标准化，ＣＣＩＴＴ和ＩＳＯ联合公布的ＣＣＩＴＴＸ．４００／ＩＳＯ１００２１电子邮件标准为电子邮件的标准化奠定了基础。而Ｘ．４００标准是按照ＯＳＩ参考模型制定的，由于当前ＯＳＩ参考模型推广还不够广泛，因此需要在异构网络环境下实现Ｘ．４００电子邮件系统。本文提出了解决网络异构问题的集成开发平台应其有的特点，结合应用环境介绍了在ＴＣＰ／ＩＰ、ＤＥＣＮＥＴ、ＯＳＩ运输层之上实现集成     

Rapid prototyping of protocols from LOTOS specifications

A new tool for generating implementation prototypes of communication protocols and concurrent systems specified using the ISO LOTOS language is presented in this paper. A brief introduction to LOTOS and a discussion of the main problems related to the efficient execution of specifications written in LOTOS are presented first. The design and implementation of the tool are then considered: LOTOS specifications are analysed and translated into C functions which are executed by co-operating processes in the Unix environment. The set of LOTOS process definitions is first translated into a suitable number of extended finite-state machines (EFSMs). The method proposed allows the problem of deriving unbounded EFSMs to be circumvented and a sort of control on the process number/size trade-off to be obtained at the same time. The problem of implementing the LOTOS multi-way rendezvous mechanism for process synchronization is solved by using an algorithm based on message-passing techniques. An example of prototype derivation is also described, showing the form of C code generated by translating a simple specification. Finally, some performance figures are presented.     

映射ELOTOS到基于FSM的性能估价模型

ELOTOS是协议描述规范语言LOTOS的扩展．本文用标号转换系统LTS（labeledtransitionsystem）给出了ELOTOS的语义．然后，通过对LTS进行踪迹等价住分析，将ELOTOS映射到基于有穷状态机FSM（finitestatemachine）的性能估价模型．     

Using binary decision diagrams for representation and analysis of communication protocols

A symbolic representation of a state/transition system based on binary decision diagrams (BDDs) is generally more compact than an explicit representation like a state/transition table. This is due to regular and repetitive patterns occurring in state/transition systems. By exploiting this property, huge state spaces can be represented, and the resulting BDDs can be profitably used for activities such as symbolic model checking and sequential circuit synthesis. This paper shows how such techniques can be applied to communication protocols by presenting a systematic method to build BDD representations from protocol specifications expressed in the ISO standard protocol specification language LOTOS. The method exploits the compositionality of the process algebra of LOTOS to avoid the enumeration of all the states and transitions, takes also data into account, enables building the BDDs in the more convenient disjunctive partitioned form, and can handle any LOTOS specification characterized by a finite LTS. The method consists in partitioning the set of process definitions according to their mutual recursion relationships, building an LTS for each set of mutually recursive process definitions, encoding these LTSs as BDDs which in turn are combined together, according to the process algebraic operators, to obtain the overall BDD representation. An example is used throughout the paper to illustrate the method.     

通信协议的形式描述及自动实现技术

在通信协议工程的主要开发作业中，形式描述和自动实现扮演着重要的角色。本文主要研讨通信协议的形式描述及自动实现技术。文中论述了协议的典型形式描述技术，主要包括半形式描述技术；ＡＳＮ．１和ＴＴＣＮ．标准形式描述技术：Ｅｓｔｅｌｌｅ，ＬＯＴＯＳ和ＳＤＬ。     

分布实现完全LOTOS规范的转换方法

基于LOTOS规范语言,文章从系统功能规范出发,结合实际系统的分布特性,推导出符合实际系统结构的模块化规范的转换方法.用标注的完全LOTOS语言规范表达复杂的系统分布特性,研究了使用广播通信方式进行协同的、直接处理多模块划分的规范分解算法.     

Composition and synthesis with a formal interactor model

This paper discusses the formal specification of interactors, which are primitive abstractions of user interface software, and focuses on the formal aspects of their composition. The composition of interactors is discussed formally in the framework of the Abstraction-Display-Controller (ADC) interactor model. The ADC model has been defined as a LOTOS specification template tailored for specifying user interface software. LOTOS behaviour expressions combining instances of this template specify the composition of interactors to model complex user interfaces. Synthesis is defined as a transformation of these behaviour expressions which supports the generic structure of the ADC model while preserving the meaning of the specified behaviour. Further, the notion of abstract views of interactors is introduced. It is shown how abstract views are themselves primitives for specifying complex interface architectures.     

Incremental requirements specification withLotos

The importance of formally and incrementally specifying requirements is discussed. An approach based on LOTOS (Language Of Temporal Ordering Specification) is proposed that exploits desirable characteristics of the constraint-oriented style. The nature of constraint-oriented specification is discussed at some length, and guidelines for how to use it effectively with LOTOS are presented. Small introductory examples lead to the incremental specification of a file access system using the approach in the paper. It is shown how the requirements for the file access system can be gradually formalised, leading to a complete system specification.     

Standardizing the user side of the X.25 interface

CCITT Recommendation X.25 describes the interface to a public data network operating in the packet mode. However, it describes this interface almost entirely from the network's viewpoint. Investigations within ANSI X3S3 in 1980 showed that X.25 leaves open many issues regarding DTE operation. As a result, ISO/TC97/SC6, at ANSI's request, undertook an activity to define DTE operation for both DTE-to-DCE (network) operation as well as direct DTE-to-DTE operation. In June 1981, ISO/TC97/SC6 approved for balloting among its member countries a draft proposal of an X.25 LAPB-compatible DTE link layer standard. The results of this balloting were favourable; the DP was then forwarded to ISO/TC97 for further processing as a draft international standard. A proposed X.25 DTE packet layer standard has been submitted to ISO for further consideration within TC97/SC6. The purpose of this paper is to briefly trace the history of this activity and to provide insight into the proposed ISO DTE standards.     

基于LOTOS形式规范的目标实现

LOTOS形式规范的目标实现是协议设计中必不可少的阶段之一。该文对基于LOTOS的形式描述规范的实现方法进行了研究,包括目标实现环境的特点、实现中的空白因素、抽象模型到实现模型的转换、规范的最终目标实现,并对如何将LOTOS规范转换为C、C 语言实现进行了探讨。     

A Formal Definition of Time in LOTOS

Enhanced Timed-LOTOS, denoted ET-LOTOS, is an extension of LOTOS that allows the modelling of real-time behaviours. It covers all the aspects of full LOTOS, including data types, it supports both a dense and a discrete time domain and can manipulate time values as any other data values. A tutorial on ET-LOTOS, showing many application examples, has already been published [LéL97]. The present paper adds to it by providing an in-depth presentation of its theoretical aspects. The complete semantics is given and explained, and its properties are studied. In particular, we prove that the semantics is consistent and that strong bisimulation is a congruence. This requires to deal carefully with the presence of negative premises in the operational semantics, which are necessary to express urgency. ET-LOTOS is also shown to be a conservative extension of LOTOS for guarded processes, and is the basis of the timed extension of LOTOS currently developed by ISO [ISO98]. To our knowledge, this is the first in-depth study of a language that combines data types and real-time behaviours. Received May 1997 / Accepted in revised form October 1998     

测试集自动生成工具TUGEN的设计与实现

测试集自动生成工具的研究是协议一致性测试领域中比较活跃的一个分支，本文在对目前已有的各种测试集生成方法进行分析的基础上，提出了一种新的测试集自动生成方法并对它的实现ＴＵＧＥＮ作了介绍．ＴＵＧＥＮ基于一种称为ＥＢＥ的形式模型，ＥＢＥ模型只对协议的外部行为进行描述，而且可以从协议的Ｅｓｔｅｌｌｅ或ＬＯＴＯＳ描述中转化得到．ＴＵＧＥＮ以协议的ＥＢＥ－ＮＦ描述作为输入，使用我们新提出的一套测试事例生成策略，最后产生出ＴＴＣＮ．ＭＰ格式的测试集．我们用Ｘ．２５ＬＡＰＢ协议的ＥＢＥ－ＮＦ描述作为例子，对ＴＵＧＥＮ