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Section 8: Serial Remotes Can't Connect to Master

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Troubleshooting a problem serial connection between a remote site and the NOC is not too different from troubleshooting a local serial connection, as described in Section 4, "How to Test RS-232 Connections with a Screwdriver or Paper Clip."

Note: you need two techs for this: one at the NOC and another at the remote site.

  1. First, verify that the device at the remote site is OK. At the remote site, unplug the serial cable to the NOC and loop the port's TX pin to its RX pin with a paper clip or screwdriver.
  2. Make a Telnet or proxy connection to the problem device.
  3. Perform a loopback test: Type any character. You should see the character echoed on the screen. Now remove the paper clip from the port and type a character. Without the loopback, you should not see the character echoed.
  4. If the loopback test is successful, the port is physically OK. If the loopback test fails, the port may be defective.
  5. If the remote site port is OK, next test the connection between the remote site and the NOC. At the NOC, unplug the serial cable from the remote site and loop the cable's TX pin to the RX pin with a paper clip or screwdriver.
  6. At the remote site, perform a loopback test from your Telnet connection to the problem device.
  7. If this loopback test fails, there's a problem with the serial connection between the sites.
  8. If the long-distance connection is OK, the problem might be on the master port. To make sure, loop the master port's TX pin to its RX pin, make a Telnet connection to the master and perform a loopback test there.
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