PPP AT commands

This page describes AT commands related to the Point-to-Point Protocol (PPP).

Note

To use the nRF91 Series SiP as a standalone modem in Zephyr, see nRF91 Series as a Zephyr-compatible modem.

PPP is enabled in SLM by compiling it with the appropriate configuration files, depending on your use case (with or without CMUX). See the Configuration files section for more information.

Note

If CMUX is enabled, PPP is usable only through a CMUX channel. In that case, the CMUX link should be set up before PPP is started.

Control PPP #XPPP

Set command

The set command allows you to start and stop PPP.

Note

PPP is automatically started and stopped by SLM when the default PDN connection is established and lost, respectively. This happens even if PPP has previously been stopped or started with this command.

Syntax

#XPPP=<op>

  • The <op> parameter can be the following:

    • 0 - Stop PPP.

    • 1 - Start PPP.

Unsolicited notification

#XPPP: <running>,<peer_connected>

  • The <running> parameter is an integer that indicates whether PPP is running. It is 1 for running or 0 for stopped.

  • The <peer_connected> parameter is an integer that indicates whether a peer is connected to PPP. It is 1 for connected or 0 for not connected.

Example

AT+CFUN=1

OK

// PPP is automatically started when the modem is registered to the network.
#XPPP: 1,0

// Stop PPP.
AT#XPPP=0

OK

#XPPP: 0,0

// Start PPP.
AT#XPPP=1

OK

#XPPP: 1,0

// Have the peer connect to SLM's PPP.
#XPPP: 1,1

// Peer disconnects.
#XPPP: 1,0

// SLM restarts PPP automatically when peer disconnects.
#XPPP: 0,0

#XPPP: 1,0

AT+CFUN=4

OK

#XPPP: 0,0

Read command

The read command allows you to get the status of PPP.

Syntax

AT#XPPP?

Response syntax

#XPPP: <running>,<peer_connected>

  • The <running> parameter is an integer that indicates whether PPP is running. It is 1 for running or 0 for stopped.

  • The <peer_connected> parameter is an integer that indicates whether a peer is connected to PPP. It is 1 for connected or 0 for not connected.

Testing on Linux

You can test SLM’s PPP on Linux by using the pppd command, though SLM must be compiled without CMUX because there is no widely available utility that allows multiplexing a device file on Linux.

Note

If you have a utility that allows multiplexing a device file on Linux, you can use SLM’s PPP with the pppd command through CMUX. To do this, you must first set up the CMUX link. Then, make sure to replace the device file argument in the pppd command with that of SLM’s PPP channel, which will have been created by the CMUX utility. See CMUX AT commands for more information on SLM’s CMUX.

For the process described here, SLM’s UARTs must be connected to the Linux host.

  1. Get PPP running on SLM. To do this, start SLM and issue an AT+CFUN=1 command.

  2. Wait for #XPPP: 1,0, which is sent when the network registration succeeds and PPP has started successfully.

  3. Run the following command on the Linux host:

    $ sudo pppd -detach <PPP_UART_dev> <baud_rate> noauth crtscts novj nodeflate nobsdcomp debug +ipv6 usepeerdns noipdefault defaultroute defaultroute6 ipv6cp-restart 5 ipcp-restart 5

    Replace <PPP_UART_dev> by the device file assigned to the PPP UART and <baud_rate> by the baud rate of the UART that PPP is using (which is set in the overlay-ppp-without-cmux.overlay file). Typically, when uart1 is assigned to be the PPP UART (in the devicetree overlay), the device file assigned to it is /dev/ttyACM2 for an nRF9160 DK, and /dev/ttyACM1 for the other nRF91 Series DKs.

  4. After the PPP link negotiation has completed successfully, a new network interface will be available, typically ppp0. This network interface will allow sending and receiving IP traffic through the modem of the nRF91 Series SiP running SLM.

Note

You might encounter some issues with DNS resolution. Edit the /etc/resolv.conf file to work around these issues. You can add DNS servers that are reachable with your current network configuration. These added servers can even be the DNS servers that SLM’s PPP sends as part of the PPP link negotiation, which are the DNS servers of the default PDN connection obtained from the modem.