Nanometrics Data Formats Reference Guide

Chapter 2
NMX Alert Format
2.1 Overview
Nanometrics Janus, Europa, and Libra family instruments can be enabled to send Alert
frames to notify users of certain important state changes. These frames are send via
either unicast or multicast UDP to an alert handler which forwards appropriate messages
to a list of subscribers via email or other transport. Currently, the only alert handler
which has been implemented by Nanometrics is AlertMailer, which forwards alert
messages via email. For further information, see the AlertMailer reference manual.
Each Alert frame is issued in response to an important state change on the instrument,
such as loss of contact with a VSat remote instrument, or supply voltage leaving the
acceptable range. A corresponding message is issued when the condition is corrected.
Alert frames are sent via UDP to the alert destination address and port defined in the
internet section of the instrument configuration. These packets are not acknowledged
by the alert receiver, and there is no mechanism for requesting retransmission of an
Alert frame.
2.2 Alert frame format
Each message contains information identifying the message source, error class and
severity, and time of occurrence. It also contains a format string and a string of arguments
describing the error condition in detail. The arguments and format string are sent
separately to allow reformatting of the message by the alert forwarding software.
Details of this argument replacement method are provided below.
The frame format is as follows:
4 byte int packet identifier = 0x7ABCDE0F
4 byte int message type = 320
4 byte int message content length = 20 + sum of string lengths
4 byte int Message severity
8 byte int Message time (UT, milliseconds)
String sourceID = name of the module which generated the alert
String classID = type name of the alert message
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