4
Structure of forwarded messages
The WB169-RFG communication gateway receives radio messages from the WB169 series modules (terminal de-
vices), which are in the Wireless M-Bus communication protocol format (hereinafter WMBUS) and forwards them
via the Internet to a remote data collection application server (AMR) in IP/UDP data packets.
In the reverse direction, the gateway receives IP/UDP data packets via the Internet with setting messages for
individual terminal devices, stores them in a ”queue” for sending, and when establishing communication with the
individual device, the message is sent to the device in the return channel time window.
The gateway receives RF-messages in WMBUS format, checks their checksum (WMBUS CRC), and if the CRC is
OK, deletes the CRC and sends it wrapped in a UDP packet to the address of the target application. The message
is decoded only by the target application. Similarly, in the opposite direction, the gateway receives completed setup
messages in WMBUS format from AMR, adds WMBUS CRCs to them and takes care of sending them via the
RF-interface at the right time (ie at the time of opening the message recipient’s return channel).
4.1
Structure of UDP-packet
The structure of a message sent over the Internet is shown in figure
. It is a standard IP/UDP packet, containing
the IP header, UDP header and the transmitted data itself. The UDP header is described at the bottom of the
figure. The packet is addressed to the target application (see the description of the IP address settings of the target
application below).
Figure 10: UDP packet structure
4.1.1
Setting of target application IP-address
The target application is the application that the gateway should send data. The setting of target application IP
address is dynamic, using a mechanism of ”zero” packets. The target application sends a packet with zero length of
its data content to each subordinate gateway at regular intervals (for example, every 30 seconds). After receiving
such a packet, the gateway stores the source IP address of that packet as the IP address of the target application,
to which it then sends all messages. This IP address is valid for three minutes, until then the information must be
restored with another zero packet. If no valid IP address is set by using the zero packet mechanism, the module
forwards the messages to the ”default” IP address preset by using the ”nepserver” and ”nepport” commands (see
paragraph
This system allows easy redirection of traffic to another server, easy change of IP address, or temporary redirection
of traffic from the gateway to the analyzer (or other diagnostic tool) for diagnostic purposes.
The communication gateway can simultaneously send data to 4 different servers. Communication with servers can
be encrypted.
4.2
UDP message data content
The data content of the message is encoded using SOFTLINK’s proprietary ”NEP” encoding system, where each
type of variable has its own designation ”OID” (Object ID), which determines the meaning, character, and data
type of the variable. For variables that can be used multiple times (several inputs, temperatures, voltages ...), the
order number of the variable (
”
Index”) is also mandatory. The ”NEP” coding table is maintained centrally by
SOFTLINK and is available at the public WEB address
A preview of the ”NEP” table for encoding variables within the wacoSystem product family is shown in figure
WB169-RFG
27