APPENDIX 4 – TIME SYNCHRONISATION, AND WEB BROWSER CACHE - INSTRUCTIONS
The contents of this appendix are also available in Technical Instruction Sheet 051 (TIS051), dated November 10,
2006.
Overview
The instructions in TIS051, intended for maintenance technicians and for end-users, address a built-in web server
synchronization and browser cache issue where web pages of a unit may contain information that does not seem
to match the expected content, especially after a firmware upgrade.
The following paragraphs detail the cause of the problem and steps to prevent the problem.
Likely Cause
Most web browsers store the pages they display in a browser cache, so that the next time the same page is dis-
played, the browser does not have to download it all over again from the server. The browser instead displays the
version of the page that was previously stored in the cache.
This process relies on a combination of factors to establish whether a page can be retrieved from the cache or
must be freshly downloaded from the server. Typically, they are:
♦
The IP address of the server
♦
The time and date the page was last updated on the server.
Unless your unit was configured to pick up and maintain time-of-day (section 4.7.3.10), its time and date restarts
from the same point (typically, 1970-01-01 00:00:00*) after each reset or power-up. In this condition, the
timestamp applied to web pages during a firmware upgrade might predate the timestamp of the pages already in
the browser's cache. When next accessing the pages in question, the browser will pickup the cached version, as it
appears to be newer than that of the freshly upgraded unit.
* Encoded system time using the number of one-second ticks elapsed since the start of the “epoch”
set at 1970-01-01 00:00:00 Z.
Problem Prevention
In order to avoid picking up stale data, it is strongly recommended that you empty the browser's cache before
starting to browse the web content of a unit, following a software update, and when going from one unit to an-
other.
Enabling time-of-day synchronization
(on units that support it)
will also help prevent this problem.
Cache Clearing
If using Internet Explorer v6.0, select “Tools” in the menu bar, select “Internet Options”, select the “General” tab
and click on the “Delete Files” button in the “Temporary Internet files” pane; click on the “OK’ button to confirm
the deletion and on the OK button to exit.
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