通信软件可维护性的一种计算方法

软件可维护性的量化和波动效应的示踪是软件维护工程中的两大难题，本文基于ＣＣＩＴＴ推荐的ＳＤＬ语言和关于波动效应分析理论的研究成果，构造了一个量化通信软件系统可维护性的计算模型，并实现了一个相应的自动工具。     

进程创建顺序的行为波动效应分析

波动效应是导致大型软件系统维护费用昂贵的一个重要原因。本文基于CCITT推荐,并已在电信领域广泛应用的SDL语言研究了一种修改进程创建顺序而引起的行为波动效应现象。文中提出了进程创建式,进程创建顺序约束断言等概念。然后严格构造了一个称之为X的公理系统。从而使波动效应的分析归结为该公理系统中的演绎推理。最后给出一个例子。     

SDL形式语义定义现状及其改进

ＳＤＬ语言自身的形工化描述对该语言的不断发展,完善将发挥重要的核心,而ＳＤＬ－９２的形式语义已无法分满足应用需要,本文分析了现有形式语义定义的基本方法,指出其存在的主要不足,并针对ＳＤＬ形式语义的定义方法提出一种基于ＳＤＬ未来发展方向的语义义框架。     

SDL的静态语义定义框架

Ｓ Ｄ Ｌ 语言自身的形式化描述对于该语言的不断发展、完善将发挥重要的核心作用。 Ｓ Ｄ Ｌ－ ９２的形式语义已无法充分满足应用需要,本文对 Ｓ Ｄ Ｌ 现有的静态语义定义方法进行了深入的分析,提出了一种基于抽象语法树和谓词演算的 Ｓ Ｄ Ｌ 静态语义定义方法。     

基于SDL协议的QoS实现方案

简单数据链路协议（SDL）作为一种新型的IP over技术，其简单性和低开销更能适应高速传输链路的要求，并提供下一代光分组交换网所需要的操作维护管理功能，如何提供服务质量保证（QoS）是IP传输中的核心技术之一，文章介绍了IETF提出的两种实现QoS的业务模型；集成业务模型和差分业务模型，以及SDL；提出了一种基于SDL链路协议上的Diffserv over MPLS的QoS实现方案。     

An Idea Turns Into Reality--CCITT Activities on the way to ISDN

This paper traces, in broad terms, how the idea of integration of telecommunication services into one network has evolved in the CCITT. A brief overview of existing telecommunication networks is followed by a review of CCITT activities from 1968 to 1980. It had become evident by 1968 that digital technology would not be restricted to transmission only, but would also intrude into switching, signaling, and the terminal field. The CCITT acknowledged this tendency by setting up a Special Study Group entrusted with the study of all questions related to PCM and the coordination of work going on in other Study Groups in the digital field. By 1980 the first ISDN Recommendation (G. 705) was agreed upon, and activities during 1980-1984, when the ISDN took shape, are related in some detail. The structure of the I-Series Recommendations, all relevant to ISDN matters, is described.     

有源像素传感器恒星探测极限计算方法

恒星探测极限是星跟踪器的一个关键参数，在导航星库的建立和星图识别过程中起着重要作用。根据恒星辐射模型和CMOS有源像素传感器的噪声计算模型，提出了一种在给定信噪比和有源像素传感器噪声条件下，计算星跟踪器恒星探测极限的方法。该方法利用单位时间内、单位面积上有源像素传感器对0星等恒星的响应来求取恒星探测极限。最后，在信噪比为8的条件下，结合星跟踪器的有关参数给出了一个计算恒星探测极限的具体实例。     

Measurement of data compression in advanced group 4 facsimile systems

The CCITT (Consultative Committee for International Telephone and Telegraph) has defined Group 4 facsimile apparatus as that which transmits an ISO A4 (210 × 297 mm) document over public data networks including Packet Switched Data Networks (PSDN) and Circuit Switched Data Networks (CSDN). Data compression is employed in Group 4 systems to minimize the number of bits required for transmission of a message. CCITT Recommendation T.6 defines the basic Group 4 coding scheme to be a variation of the modified READ code (MRC II) which is the Group 3 coding option. This paper measures the compression of the MRC II algorithm for three different documents at resolutions of 200, 240, 300, 400, and 480 picture elements per inch. The compression measurement was accomplished by means of computer simulation. It was determined that the bits per page measure increases linearly with resolution. Results are presented and conclusions drawn. The Group 4 CCITT Recommendations include a mode of operation known as Mixed Mode where a page is divided into two parts: character-coded information and facsimile-coded information. This paper describes four alternative mixed-mode algorithms and measures the compression of each coding technique for CCITT document number 1. The compression measurements were performed by means of computer simulation. Conclusions are drawn regarding the relative advantages of the four algorithms.     

A dynamic synchronization method to realize soft defect localization applied on digital and mixed-mode analog ICs in failure analysis

Failure analysis on advanced logic and mixed-mode analog ICs more and more has to deal with so called ‘soft defects’. In this paper, a dynamic synchronization method is proposed to perform soft defect localization (SDL) technique by Optical Beam Induced Resistance Change (OBIRCH). It is a new and low-cost way to achieve SDL technique by OBIRCH equipment if there is no normal SDL equipment on hand. It extends the application of OBIRCH equipment to a more advanced failure analysis realm. The methodology and system configuration are presented. The experimental results show this dynamic synchronization method is accurate enough to locate a soft defect. Two real cases are studied on a digital IC and a mixed-mode analog IC respectively using this method.     

基于SDL的通信协议开发平台

SDL当前已经普遍应用在通信协议开发中,介绍了一个基于SDL的通信协议开发平台框架和平台中对SDL关键元素的实现方法,通过这个平台提高了通信协议开发中从SDL描述到代码开发的效率和代码的可维护性。     

CCITT work in teletraffic engineering

The advantages and drawbacks of standardization in TTE (teletraffic engineering) are examined. It is pointed out that the TTE recommendations of CCITT are intended to be international standards. Unlike signaling systems, interfaces, or protocols, the necessity for standardization in this area is not self-evident. However, standardization of grade of service (GOS) definitions, values, and relevant reference conditions seems to be necessary. Support for engineering methods also offers advantages. TTE-related activities in different CCITT study groups try to satisfy many often contradictory demands. Trends in telecommunications strongly support the view that concentration of TTE studies in CCITT would be desirable     

Progressive Transmission of Two-Tone Images

A technique is proposed for transmitting two-tone images in a progression of stages. In the first stage, information is transmitted to allow a crude reproduction of the picture. In the following stages, the quality of the received picture is improved until a copy identical to the original is obtained. The proposed technique uses a modification of the two-dimensional code recommended by the CCITT for transmission of facsimile. The main features of the coding scheme are as follows. 1) A crude version of the image is obtained after approximately 10-20 percent of the total transmission time. A good version, with half the resolution in both the horizontal and vertical directions, is obtained after 50 percent of the total transmission time. 2) Compatibility with the CCITT codes for transmission of facsimile. 3) Total transmission time is only about 20 percent larger than the time required for nonprogressive transmission using the CCITT codes.     

一个SDL集成环境IES

随着SDL的日趋完善,对SDL集成环境的需求更加迫切。本文先就国外在此方面的研究作一概述,然后着重介绍我们建立的SDL集成环境IES的原理和实现方法,并描述了SDL的应用前景。     

Compression and error sensitivity of two-dimensional facsimile coding techniques

Seven proposals were submitted to the International Telegraph and Telephone Consultative Committee (CCITT) for selection of a standard two-dimensional code as an extension of the current CCITT standard one-dimensional code. The CCITT specified the use of particular parameters and procedures to compare the candidate techniques on a quantitative basis. The compression ratio and error sensitivity of all seven coding techniques were measured for a wide range of operational conditions. For example, tests are performed with small K-factors for application to error-prone transmission over switched circuits, and also at infinite K-factor to simulate packet switching networks possessing error control. Particular attention is paid to the error detection/correction procedure to insure that the error sensitivity parameter is as realistic as possible. The essential differences between the seven proposed coding techniques are presented, and the measurement parameters and procedures are reviewed.     

PLL soft functional failure analysis in advanced logic product using fault based analogue simulation and soft defect localization

Soft defect localization (SDL) is an analysis technique where changes in the pass/fail condition of a test are monitored while a laser is scanned across the device under test (DUT). This technique has proven its usefulness for quickly locating defects that are temperature, frequency, and/or voltage dependant, for example, scan logic soft fault. However, due to high sensibility at analogue circuits SDL meets great challenges. This work gives a new flow to analyze soft functional failure in advanced logic products using fault based analogue simulation and SDL. The paper will present one case study illustrating the application of analogue simulation based soft defect localization flow as an effective means to achieve fault isolation.