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Question regarding connection and Fallback

Giannis Anastasopoulos

Dear All,

In my application I need to switch on and off the modem using AT+CFUN=0 and AT+CFUN=4 respectivelly.

My question is the following. Let's assume that the device cannot find the preferred type of network and uses the fallback one. Then the modem is switched off. What will happen once the modem is back on again?

Will it try first to connect to the preffered network and then try the fallback, or will it try to connect to the previously working network first?

Thank you very much for your response

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    Hi Giannis,

    The modem takes care of this automatically.

    e.g. Regarding the cell search done after cell lost (i.e. nrf91 moves out of range or does not find cell after startup),

    • The modem will periodically try to find a cell after a cell is lost.
    • No actions required from the application (i.e. no need for new AT+CFUN=1)
    • If there is a cell available, it will eventually be found, but depending on the current search periods it may take some time.
    • The modem does not just continuously search until the cell is found, it takes breaks in between searches.

    Also, the search itself takes the benefit of a large number of parameters gathered earlier in order to find a cell efficiently.

    • The current Data Profile affects the search periods (set with AT%XDATAPRFL): 4 (= High performance) means searching more often (and aggressively) than 0 (= Ultra low power).
    • In this aspect, the Data profile is not about connection reliability vs power consumption, it is about how fast the device finds a cell (after cell lost) vs power consumption. So when on cell, Data profile does not affect to connection reliability.

    Note: The modem indicates the state of service using AT+CEREG. Unsolicited indications can be subscribed to or the current status can be read with "AT+CEREG?".

    A sidenote, please notice that you do not need to manually send AT+CFUN=1 or 4 when using the LTE Link Controller library.
    If you look into the function lte_lc_init_and_connect() it will send the AT command inside the function. (normal = at+cfun=1)

    Best regards,

    Martin L.

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  • 0

    Hi Giannis,

    The modem takes care of this automatically.

    e.g. Regarding the cell search done after cell lost (i.e. nrf91 moves out of range or does not find cell after startup),

    • The modem will periodically try to find a cell after a cell is lost.
    • No actions required from the application (i.e. no need for new AT+CFUN=1)
    • If there is a cell available, it will eventually be found, but depending on the current search periods it may take some time.
    • The modem does not just continuously search until the cell is found, it takes breaks in between searches.

    Also, the search itself takes the benefit of a large number of parameters gathered earlier in order to find a cell efficiently.

    • The current Data Profile affects the search periods (set with AT%XDATAPRFL): 4 (= High performance) means searching more often (and aggressively) than 0 (= Ultra low power).
    • In this aspect, the Data profile is not about connection reliability vs power consumption, it is about how fast the device finds a cell (after cell lost) vs power consumption. So when on cell, Data profile does not affect to connection reliability.

    Note: The modem indicates the state of service using AT+CEREG. Unsolicited indications can be subscribed to or the current status can be read with "AT+CEREG?".

    A sidenote, please notice that you do not need to manually send AT+CFUN=1 or 4 when using the LTE Link Controller library.
    If you look into the function lte_lc_init_and_connect() it will send the AT command inside the function. (normal = at+cfun=1)

    Best regards,

    Martin L.

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