UNIT 7 MAINTENANCE OF DIGITAL SWITCHING SYSTEMS 9/23/2016

Scope This chapter introduces typical interfaces that are utilized in maintaining central offices both remotely and locally. Topics essential to CO maintenance such as fault reports, software patches, and the software and hardware upgrade process, including firmware, are also covered. 9/23/2016

Software Maintenance - Supplier-initiated software maintenance Software maintenance by site owners 9/23/2016

Interfaces of a Typical Digital Switching System Central Office 9/23/2016

These other departments interact with a digital switch: Engineering support Billing center Security Special translation support Trunk and line assignment 9/23/2016

System Outage and Its Impact Digital Switching System Reliability Digital switch outages represent the most visible measure of switching system reliability and affect maintainability. The Various studies' have been conducted to better understand the causes of digital switch outages. Traditionally, the causes of outages have been classified into four categories: - Software deficiencies. This includes software "bugs" that cause memory errors or program loops that can be cleared only by major initialization. - Hardware failure. This relates to simplex and/or duplex hardware fail- ures in the system which result in a system outage. 9/23/2016

Impact of Software Patches Patches are a "quick fix" or program modification without recompilation of the entire generic release. Embedded Patcher Concept Embedded patcher programs that operate as software maintenance programs and reside in digital switches have alleviated some of these problems. 9/23/2016

Growth of Digital Switching System Central Offices Most digital switching systems need to be upgraded or "grown" during their lifetimes. This process represents a major effort for maintenance organizations such as SCCs and ESACs. 9/23/2016

Generic Program Upgrade At least the following points need to be covered in the method of procedure (MOP) along with other detailed items that are specific to a digital switch and a CO: - Time line for the entire upgrade process - Availability of the switch during that period a Dumping of existing data tables that need to be repackaged with the new release - Verification of old tables with new tables to ensure that all old functionalities are supported in the new release - The synchronization of hardware availability and software upgrade if hardware upgrade is included along with software upgrade 9/23/2016

A Methodology for Reporting and Correction of Field Problems 9/23/2016

Diagnostic Capabilities for Proper Maintenance of Digital Switching Systems Effective diagnostic programs and well-thought-out maintenance strategies play a very important role in the proper maintenance of digital switching systems with reduced maintenance cost. It is imperative in the overall evaluation of a digital switch that the diagnostic capability of a switch be considered an item of high importance. 9/23/2016

Effect of Firmware Deployment on Digital Switching Systems The recent trend toward distributed processing in digital switching systems has resulted in increased use of firmware. The impact of firmware on digital switching system reliability and maintainability can be substantial. The updating process for firmware can have a significant impact on the operational reliability of a switching system, particularly if firmware changes are frequent. 9/23/2016

Firmware-Software Coupling The basic notion of "coupling" between firmware and software evolved slowly in the telecommunications industry. The need to change significant numbers of firmware packs as part of generic updates has created a number of problems, including these: - Increased simplex times for switches during the firmware update process - Increased switch downtimes due to system faults while in simplex mode, required initializations for firmware changes, insertion of defective firmware circuit packs, and damaged circuit packs due to electro- static discharge (ESD) 9/23/2016

A strategy for improving software quality 9/23/2016

Software Processes The software processes shown in before slide relate to the software metrics discussed below. These include 1. Software development process 2. Software testing process 3. Software deployment process 4. Software maintenance process 9/23/2016

Defect Analysis The defect analysis is a base process for this strategy. It drives the continuous-improvement program. There are some well- defined methodologies for defect analysis a software problem may have originated from - Central processor software - Network processor software - Interface controller software - Peripheral software (lines, trunks, etc.) The next step is to identify the software subsystem that may have caused the problem: - Operating system - Recovery software - Switching software - Application software (features, etc.) 9/23/2016