User's Manual

©2006 Nordic ID Oy
Nordic ID PL3000 user manual, v. 2.6, October 2006 78
6.5.34 Simple Network Time Protocol (SNTP) Service
Introduction
Many software applications require that the handheld device clock is set correctly. For instance Wireless
LAN network credential certifi cates have a specifi c validity timeframe, which means at least the current
year and month needs to be correct. Applications requiring greater precision are numerous; most
inventory applications record some form of timestamp information that is later used to determine the
most recent data. The SNTP protocol is as its name says, an easy way to acquire the correct time from a
remote server over the network. The SNTP protocol does not attempt to correct for the data transmission
lag time over the network. This means that the time data, when arriving and being applied in the handheld
terminal is already some milliseconds too old. How much depends on the network transmission delays
involved. In almost all cases, the time value acquired using STNP can be assumed to be correct to the
second, but perhaps not to the tenth of a second and certainly not into the millisecond range. SNTP lag
can roughly be estimated by pinging the NTP server and dividing the result by two, since ping usually
reports round trip time and the time lag is only introduced by the return transmission in SNTP.
The SNTP implementation in the PL3000 consists of
three applications. There is the SNTP service which,
when enabled, is running in the background and
periodically updates the time. There is an application
called AskTime which can be confi gured to query the
user for the correct time in case the SNTP request
does not succeed. There is the SNTP Control Panel
applet which is used to confi gure both the SNTP
service and the AskTime application.