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Getting +CEREG: 5,"FFFE","FFFFFFFF" while disconnected from the network

Lukáš

Hi,

In one of our private issues where we asked how to detect a lost cell, a Nordic engineer told us that: 

You can detect if the cell is lost from +CEREG but would not be able to detect it if this actually is about cell reselection. If +CEREG where <stat> is something else than 2 or 5 then it means the device is not in service at that moment.

However, we noticed that when we lose the signal/cell, then we receive CEREG notification with stat 5 (registered, roaming). Particularly:

+CEREG: 5,"FFFE","FFFFFFFF",9,,,"11100000","00101000"

So what is the correct procedure to detect when the modem is not attached to the network and it is not connected to any cell? Sometimes we also receive this CEREG: 4 with FFFE, so it is confusing.

 

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  • 0

    Hi 

    How do you know that the signal to the cell tower is lost?

    How long after you lose the connection do you get the +CEREG notification?

    An alternative way to detect if you are connected or not is to use the +CESQ command, as documented here. 

    If you are unable to figure out the issue it would be helpful to get a modem trace and the serial log output when the issue occurs, so we can investigate more closely what is going on. 

    Best regards
    Torbjørn

  • 0 in reply to ovrebekk

    Hi Torbjørn,

    ovrebekk said:

    How do you know that the signal to the cell tower is lost?

    Well, the +CEREG: 5,"FFFE","FFFFFFFF" doesn't seem like a valid cell. Besides that, we also receive this:

    [00:00:36.594,451] modem_at_handler: Processing notification: +CSCON: 0
[00:00:37.215,637] modem_at_handler: Processing notification: %CESQ: 255,0,255,0
[00:00:37.216,766] modem_at_handler: Processing notification: +CEREG: 5,"FFFE","FFFFFFFF",9,,,"11100000","00101000"

    So I am almost sure, that we have lost the cell. However, I don't get why we are still on CEREG 5, which is also contrary to what your colleague said in another ticket.

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  • 0 in reply to ovrebekk

    Hi Torbjørn,

    ovrebekk said:

    How do you know that the signal to the cell tower is lost?

    Well, the +CEREG: 5,"FFFE","FFFFFFFF" doesn't seem like a valid cell. Besides that, we also receive this:

    [00:00:36.594,451] modem_at_handler: Processing notification: +CSCON: 0
[00:00:37.215,637] modem_at_handler: Processing notification: %CESQ: 255,0,255,0
[00:00:37.216,766] modem_at_handler: Processing notification: +CEREG: 5,"FFFE","FFFFFFFF",9,,,"11100000","00101000"

    So I am almost sure, that we have lost the cell. However, I don't get why we are still on CEREG 5, which is also contrary to what your colleague said in another ticket.

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