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R
EADER
F
UNDAMENTALS
C
HAPTER
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EADER
I
NTERFACE
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OC
. C
ONTROL
# 8101938-000 R
EV
05
10
Serial Interrogation
One of the simplest methods to find out the reader’s IP address is to connect via
the RS-232 port and type the command
get IPaddress
. The reader
responds with the IP address currently in use.
However, this requires a physical connection between a host computer and the
reader—a connection that in many cases is simply not practical to set up.
Additionally, as noted previously, the ALR-9800 and ALR-9770 readers do not
provide a serial command interface at this time.
Network Heartbeats
Another way to find out a reader’s IP address is to listen for its heartbeat
messages over the network.
After a reader has booted successfully onto a network it periodically broadcasts a
heartbeat message over the network. This heartbeat can be intercepted by
network applications, and provides enough information about the reader to locate
it on the network and begin communication with it.
In network parlance, the heartbeat message is sent via UDP (Universal
Datagram Protocol) packets to all network addresses on the reader’s subnet.
There are three relevant configuration options available via the reader’s
command line to affect this heartbeat:
set | get HeartbeatTime:
This command specifies the time interval
separating successive heartbeat messages sent out over the network.
The time is specified in seconds, with a value of zero turning off the
heartbeats. The default value is 30 seconds, i.e. send out a heartbeat
message every 30 seconds.
set | get HeartbeatPort.
This command specifies the port number that
the UDP heartbeat messages are addressed to. This is the port number
that must be listened to by interested parties on the network. The default
value for this setting is 3988, i.e. send out a heartbeat message to UDP
port 3988 of every machine on the subnet.
set | get HeartbeatAddress.
This command specifies a particular IP
Address that the UDP heartbeat messages are addressed to. The default
value is 255.255.255.255, which is a special "multicast" addressed which
allows any machine on the subnet to receive the heartbeats. Any other
HeartbeatAddress results in the heartbeats going only to the machine at
that address.
set | get HeartbeatCount.
This command is implemented only on the
ALR-9800, and allows you to specify the total number of heartbeat
messages to send. This allows for the immediate discovery of readers as
they come online, but doesn't continuously load the network with
unnecessary traffic.
The format of the heartbeat is a small XML text-based message, containing
information about the reader (name and type), the reader’s network connection
(IP address and command port) and the length of time until the next heartbeat
will be sent out.
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