Issue
Sometimes when software (such as ION Enterprise or ION Setup) or a device (such as a PLC, RTU, etc.) cannot connect to a given meter, it may be that the meter already has all of its available connections used up by established connections to other software and/or devices.

Product Line
ION meter with Telnet communication capabilities
ION8800, ION8650, ION8600, ION8500, ION8400, ION8300
ION7650, ION7550, ION7600, ION7500
ION73xx, ION770/Xpress Card, ACM3720,
PM8000, PM5000, ION9000

Environment
Telnet command window

Cause
When all available connections are used by established connections and cause the meter to be unresponsive to new connection requests.

Resolution
To troubleshoot these kinds of issues, it can be useful to telnet to the device on the default telnet port (i.e. port 23) using the command "telnet <IP_address>" at the command line (see screenshot below for example)

If you can connect, the meter will respond with something like this:
-------------------------------------------
Power Measurement Ltd. 7650 ION 7650V310
Serial#: PJ-0408A009-00
login:
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The login varies from meter to meter but is commonly the model number of the meter as a username (e.g. "7300", "7500", "7600") with the password usually being "0", if it has not been changed from its default. Once logged into the meter, issue the command 1<Enter> twice to get a table showing which IP addresses the meter has connections from like this:
---------------------------------------------
Current settings programmed and in use:

IP address in use 10.168.68.5
Subnet Mask in use 255.255.248.0 Programmed 255.255.248.0
Gateway address in use None Programmed None
HW address 00607800c238
Firmware revision 7650V310

Current connections
CMM Physical Protocol To Host
CMM1 RS232 ION
CMM2 RS485 EtherGate
CMM3 IRDA ION
ETH1 Ethernet ION 10.168.67.7
ETH1 Ethernet ION 10.168.66.129
ETH1 Ethernet Telnet 10.168.67.7
ETH1 Ethernet Not in use
------------------------------------------------

Depending on the ION meter type, the meter may be able to maintain up to 4 independent TCP connections simultaneously

NOTE: more simultaneous connections are available in recent ION firmware releases - see FA221577 . Also FA212335 gives a summary of Ethernet port availability on ION meters.

If there are already four connections listed then there is a good chance that one of these connections needs to be removed. Note that some ION meters can only maintain one TCP connection at a time so pay close attention to the table in FA212335 . Make sure to inspect the list of connections to ensure that nothing is connected to the meter that should not be. The general rule is, if you can connect to the meter using telnet then ION Enterprise, ION Setup, or other software or devices should be able to make a connection.

Note that using telnet to connect to an ION meter in this way when the meter already has a full complement of connections established to it (4 TCP connections in the majority of cases for ION meters) then one of the connections that is already established will be displaced to allow for the telnet connection to be established. The connection that is thus displaced is the last connection to have been established to the meter (last in, first out - LIFO). Note that this process of displacing an existing established connection to make a place for a new connection only applies to requests for connections using telnet. Connection requests on TCP port numbers other than the default telnet port number (i.e. 23) will be rejected by the meter if the meter already has all of its connections used up.