Cannot establish an MQTT connection from Thailand about ubxlib HOT 9 OPEN

HI Alex. The command sequence looks fine, seems to just be getting no MQTT broker connection within the time given.

For your module type (SARA-R412M-02B-01 I believe) uMqttConnect() (the AT+UMQTTC=1 in the log) allows 15 seconds for the broker connection (see here). You could maybe try increasing that value 60000, as an experiment, to see if it just needs longer for some reason?

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Hi @alexmaron81: how did this go in the end?

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Hi Rob, I haven't been able to test any further yet. I was on holiday last week. Friday I have another meeting with thailand.

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Can i ping an ip address?

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The cellular module does support a command called AT+UPING but it is not something we have so far been asked to implement in ubxlib. If you wanted to add it yourself you could paste something like this into the end of u_cell_net.c:

int32_t uCellNetPing(uDeviceHandle_t cellHandle, const char *pDestination)
{
    int32_t errorCode = (int32_t) U_ERROR_COMMON_INVALID_PARAMETER;
    uCellPrivateInstance_t *pInstance;
    uAtClientHandle_t atHandle;

    if (gUCellPrivateMutex != NULL) {

        U_PORT_MUTEX_LOCK(gUCellPrivateMutex);

        pInstance = pUCellPrivateGetInstance(cellHandle);
        if ((pInstance != NULL) && (pDestination != NULL)) {
            atHandle = pInstance->atHandle;

            uAtClientLock(atHandle);
            uAtClientCommandStart(atHandle, "AT+UPING=");
            // Write destination
            uAtClientWriteString(atHandle, pDestination, true);
            uAtClientCommandStopReadResponse(atHandle);
            errorCode = uAtClientUnlock(atHandle);
        }

        U_PORT_MUTEX_UNLOCK(gUCellPrivateMutex);
    }

    return errorCode;
}

...adding a header for it as follows in u_cell_net.h:

/** Ping an address.
 *
 * @param cellHandle       the handle of the cellular instance.
 * @param[in] pDestination the destination IP address or domain; cannot be NULL.
 * @return                 zero on success or negative error code on
 *                         failure.
 */
int32_t uCellNetPing(uDeviceHandle_t cellHandle, const char *pDestination);

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Hi Rob, I'm getting an error

AT+UPING="10.65.66.157"

ERROR
CONNECT-BoxAT+UMQTT=3,"10.65.66.157"

is it true what is written in the following link?

https://portal.u-blox.com/s/question/0D52p00008qiQNOCA2/sarar41002b-with-ublox-nbiot-module-atuping-gives-error-even-though-device-is-attached-and-udp-data-transfer-works

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Gah, yes, re-checking the SARA-R4 AT manual:

Sorry, no ping on SARA-R412M.

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can i do it in a different way?

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Not that I can think of I'm afraid. In theory you could connect at PPP-level and use the native ESP-IDF IP stack to do the ping but we have never tried making a PPP connection on a SARA-R412 and it would be a major change to the way your SW works to build and use PPP.

If what you would like to do is to check connectivity with a specific server or servers, what I would do is run a UDP echo client on a known/open port of that server, then you could send UDP packets to that server on that port and check for the echoed response coming back. Of course you would need access to the server-side to do this. Mind you, you might need access to the server-side in any case to be sure that it is configured to respond to ping.

Alternatively, beneath the MQTT protocol which I guess you are trying to test lies TCP, so if you opened a TCP connection on whatever your MQTT port is and that connection was successfully opened at TCP level then you have proved that there is connectivity, assuming that is your aim, you don't need to do any MQTT stuff at all. So you could just follow the pattern of the TLS sockets example (assuming you have TLS security) or otherwise the sockets example (if you don't have TLS security) to the IP address and port number of your MQTT broker.

But that is, of course, a more complicated arrangement than a UDP echo arrangement or ping.

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