Time Synchronization Solutions Guide
10 October 1997

Introduction
Basic Concepts
Time Synchronization Solutions
Server Scheduling Solutions

Introduction

The following document provides details of some manufacturers and suppliers of hardware and software for maintaining client and NetWare server time. Please note that inclusion in this list does not constitute certification or recommendation of any of these products. The list is sorted in alphabetical order of supplier name.

As from 27 Sep 94, this guide also includes a separate section which lists software for scheduling NetWare server NLM and NCF file execution.

For further information on the subject of Time and Time Synchronization, please see the Novell Application Notes of November 1993 and January 1994. For information on Novell Application Notes, please see the file APPNOT.LST in the CompuServe NWGENFILES forum library or call +1 303 297 2725.

Any 'forum libraries' referred to in this list may be accessed via the following means :

CompuServe Internet anonymous FTP to ftp.novell.com Internet anonymous FTP to ftp.novell.de Internet World Wide Web on http://www.novell.com

Basic Concepts

The following information is taken from the Novell Application Note "Time in the NetWare Environment", January 1994, written by Marcus Williamson and published by Novell Research

"The Intel-based DOS PC requires a correct system time primarily for use by the file system. When a file is changed, the date and time stamps in the directory associated with that file are also changed.

For the NetWare server, maintaining the correct date and time is important not just to the file system but also for access security and auditing, and, in the case of NetWare 4.x, directory synchronization.

PC Hardware Time

Looking closely at the system board of any AT-class PC will reveal a chip labelled Real-Time Clock (RTC), Motorola MC146818, Dallas DS or similar. It is this device which is responsible for the PC's 'hardware' clock. A Programmable Timer/Counter chip, running at 1.19318 Mhz, generates a signal approximately 18.2065 times a second, which is used to update the RTC. Backup of the clock in all machines equipped with an RTC is by CMOS memory and a battery.

The specification for the early PCs did not include a real-time clock and required the user to enter the date and time when the PC was powered on. Later models included a card, the forerunner of today's RTC devices, which would keep the workstation clock running even when the PC had been switched off. A battery on the card would back up the clock and allow the clock to continue running for as long as the battery lasted.

An RTC chip can be addressed by placing a command in I/O port 70h, then reading back the result from I/O port 71h. A simple BASIC program in Appendix A shows how it is possible to read the current time from the RTC. The PC BIOS and DOS define interrupt calls to access the time and date information held by the RTC. Most high level languages also provide functions to get and set the clock from within a program."

Thus, the basic PC hardware provides a clock, which is read by the Novell NetWare server when it starts up. Following this, it is NetWare's responsibility to maintain a software-based clock within the NetWare server. In some conditions, such as frequent switches into 'real mode', the internal software clock may drift.

The November 1993 AppNote 'Time Synchronization in NetWare 4.x' dealt with the subject of synchronizing time within the NetWare 4.x environment and mentioned one available external device.

There are many instances where it may be necessary to synchronize a single PC or a NetWare 2.x, 3.x or 4.x server to an external time source for other reasons. These might include employee time logging, airline check-in applications or source code control systems, as possible examples.

Time sources are available via the Internet, modem or radio links. Of these, modem and radio sources are most commonly used to synchronize the clocks on PC workstations and NetWare servers.

Modem Time Sources

National Institute of Standards and Technology (NIST), is an example of a US-based system providing dial in at 300 and 1200 baud on modem number +1 303 494 4774. Systems such as that at the NIST provide a continuous stream of characters indicating time in ASCII format. This accurate time source can then be used to set the date and time on a PC workstation or NetWare server.

Radio Time Sources

Radio time sources used by PC based time synchronization systems include WWVB (Colorado, USA), MSF (Rugby, UK) and DCF77 (Mainflingen, Germany). Each of these broadcasts a time signal on one or more known frequencies which can be received by suitable PC-based adapter cards."

The following key indicates the type of time source used as follows :

Modem                - Uses dial up modem
Radio                - Uses radio receiver 
Satellite            - Uses Global Positioning System (GPS) satellite receiver
External Clock       - Uses high-accuracy external clock device
Internet             - Uses Internet (TCP/IP) based time protocols
Other Server         - Obtains time from another file server
Other Workstation    - Obtains time from a workstation

The Info Check field (if present) indicates the last date that the information provided was verified.