MC74xx Modem Double Attach


Using Linux SDK for PDN connection, and I had network registration preference (netReg) set to “Automatic registration”. When I perform PDN connection, the test equipment receives 2 attach messages even though there is only 1 PDN successful connection (i.e. no drop of connection then reconnect). Unfortunately the test set doen’t capture RRC messages to see the details of what’s going on, and I’m a little confused why there are 2 attach requests with what looked like to be the same registration information. Anybody has an idea why?



Are you using the Sierra Wireless SDK or the open source one, if the Sierra one what API are you using and paramter?




I use Sierra SDK SLQSStartStopDataSession to start the data session, and with network attach preference set to automatic. The connection is clean from SDK perspective, no errors, no disconnect/reconnect, but the test equipment displays 2 attaches every time for the one connection. It’s not doing any harm, just unexpected signaling behavior causing some confusion.


If you take a log file from the unit we can see what is going on with the unit from its side?

The logging port on the MC is /dev/ttyUSB0, you can take a log file using the dmcapture script which is contained in the SDK zip file under /tools/logging/dmcapture, there is a help file in the showing you how to take a log file