Connecting to the Internet over USB GSM Modem

Owned by Natalia Sofronova
Last updated: Jun 27, 2024Version comment
5 min read

This application note explains how to connect to the Internet from the NXP i.MX RT1170 EVK running Linux using a USB GSM modem.

The Linux PPP daemon and its shell scripts are used to initiate the connection, receive the networking parameters from the cell (IP, routing, DNS etc) and configure the system networking according to the received parameters. The pppd package integrated by Emcraft into the NXP i.MX RT1170 EVK BSP was obtained from http://www.uclinux.org/pub/uClinux/dist, release 20140504.

The functionality described below is available from the rootfs.uImage project provided by Emcraft for NXP i.MX RT1170 EVK. The generic Linux kernel device driver driver for the USB Modems (CONFIG_USB_ACM) is used in this configuration. Emcraft tested the functionality documented below using the MTD-H5-2.0 HSPA+ USB Cellular Modem from MultiTech Systems.

1. Cellular Network Configuration

For starting and terminating the PPP connection, the standard scripts from the PPP Daemon package are provided in the rootfs projects. The scripts as follows:

  • pon <provider> - starts the PPP daemon with a specified configurations in /etc/ppp/peers/. Without arguments, the /etc/ppp/peers/provider configuration is used.

  • poff - stops the PPP daemon and terminates the connection.

The following PPP configuration files are provided with the rootfs project:

  • /etc/ppp/peers/provider - contains the default PPP daemon configuration.

  • /etc/ppp/options-mobile - contains the general PPP daemon configuration options (see man pppd). Among others, there are two options enabled for debugging (dump and logfile /dev/console).

  • /etc/ppp/chatscripts/mobile-modem.chat - contains modem commands to establish connection with the network.

  • /etc/ppp/chatscripts/apn - contains the modem command to configure the Access Point Name specific to the provider.

  • /etc/ppp/chatscripts/pin - contains the modem command to configure the SIM-card PIN code, if required. Preconfigured for no PIN in the project.

For a US GSM network operator (AT&T, T-Mobile, Rogers, Bell, Telus, see in http://www.multitech.com/datasheets/86002162.pdf), the current configuration should work, after setting up an appropriate Access Point Name in /etc/ppp/chatscripts/apn and cell account information in /etc/ppp/peers/provider.

For a US CDMA network operator (Verizon, Sprint, Aeris), the modem model Multitech MTD-EV3 should be used. The project provides sample configurations /etc/ppp/peers/verizon and /etc/ppp/chatscripts/verizon.chat, which supposedly should work with Verizon.

To reconfigure the rootfs project for your SIM operator typically you will need:

2. TCP/IP Connectivity Over PPP

  1. Plug-in a USB GSM Modem device to the USB1 or USB2 port of NXP i.MX RT1170 EVK. The system will print the appropriate messages to console about the hardware detected:

    usb 1-1: not running at top speed; connect to a high speed hub cdc_acm 1-1:1.0: ttyACM0: USB ACM device cdc_acm 1-1:1.2: ttyACM1: USB ACM device cdc_acm 1-1:1.4: ttyACM2: USB ACM device cdc_acm 1-1:1.6: ttyACM3: USB ACM device cdc_acm 1-1:1.8: ttyACM4: USB ACM device cdc_acm 1-1:1.10: ttyACM5: USB ACM device

  2. Shutdown the eth0 network interface:

    / # ifconfig eth0 down

  3. Initiate connection with the cellular network:

    / # pon / # pppd options in effect: debug # (from /etc/ppp/options-mobile) holdoff 10 # (from /etc/ppp/options-mobile) persist # (from /etc/ppp/options-mobile) logfile /dev/console # (from /etc/ppp/options-mobile) maxfail 0 # (from /etc/ppp/options-mobile) dump # (from /etc/ppp/options-mobile) noauth # (from /etc/ppp/options-mobile) user gdata # (from /etc/ppp/peers/provider) password ?????? # (from /etc/ppp/peers/provider) /dev/ttyACM0 # (from /etc/ppp/options-mobile) 115200 # (from /etc/ppp/options-mobile) lock # (from /etc/ppp/options-mobile) connect /usr/sbin/chat -v -t15 -f /etc/ppp/chatscripts/mobile-modem.chat # (from /etc/ppp/peers/provider) crtscts # (from /etc/ppp/options-mobile) modem # (from /etc/ppp/options-mobile) passive # (from /etc/ppp/options-mobile) hide-password # (from /etc/ppp/options-mobile) novj # (from /etc/ppp/options-mobile) noipdefault # (from /etc/ppp/options-mobile) defaultroute # (from /etc/ppp/options-mobile) usepeerdns # (from /etc/ppp/options-mobile) Serial connection established. using channel 1 Using interface ppp0 Connect: ppp0 <--> /dev/ttyACM0 rcvd [LCP ConfReq id=0x1 <asyncmap 0x0> <auth pap> <magic 0x96a24aa4> <pcomp> <accomp>] sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x7f6a34ec> <pcomp> <accomp>] sent [LCP ConfAck id=0x1 <asyncmap 0x0> <auth pap> <magic 0x96a24aa4> <pcomp> <accomp>] rcvd [LCP ConfAck id=0x1 <asyncmap 0x0> <magic 0x7f6a34ec> <pcomp> <accomp>] sent [PAP AuthReq id=0x1 user="gdata" password=<hidden>] rcvd [PAP AuthAck id=0x1 ""] PAP authentication succeeded sent [CCP ConfReq id=0x1 <deflate 15> <deflate(old#) 15> <bsd v1 15>] sent [IPCP ConfReq id=0x1 <addr 0.0.0.0> <ms-dns1 0.0.0.0> <ms-dns2 0.0.0.0>] rcvd [LCP ProtRej id=0x2 80 fd 01 01 00 0f 1a 04 78 00 18 04 78 00 15] Protocol-Reject for 'Compression Control Protocol' (0x80fd) received sent [IPCP ConfReq id=0x1 <addr 0.0.0.0> <ms-dns1 0.0.0.0> <ms-dns2 0.0.0.0>] sent [IPCP ConfReq id=0x1 <addr 0.0.0.0> <ms-dns1 0.0.0.0> <ms-dns2 0.0.0.0>] sent [IPCP ConfReq id=0x1 <addr 0.0.0.0> <ms-dns10.0.0.0> <ms-dns2 0.0.0.0>] rcvd [IPCP ConfReq id=0x1] sent [IPCP ConfNak id=0x1 <addr 0.0.0.0>] rcvd [IPCP ConfNak id=0x1 <addr 10.145.22.97> <ms-dns1 10.152.222.141> <ms-dns2 10.152.222.132>] sent [IPCP ConfReq id=0x2 <addr 10.145.22.97> <ms-dns1 10.152.222.141> <ms-dns2 10.152.222.132>] rcvd [IPCP ConfReq id=0x2 <addr 10.145.22.97>] sent [IPCP ConfAck id=0x2 <addr 10.145.22.97>] rcvd [IPCP ConfAck id=0x2 <addr 10.145.22.97> <ms-dns1 10.152.222.141> <ms-dns2 10.152.222.132>] ioctl(SIOCDELRT): No such process(3) local IP address 10.145.22.97 remote IP address 10.145.22.97 primary DNS address 10.152.222.141 secondary DNS address 10.152.222.132 Script /etc/ppp/ip-up started (pid 101) Script /etc/ppp/ip-up finished (pid 101), status = 0x0

  4. Verify that the connection is established (depending on the cellular network, the link may take up to 10 seconds to get established):

  5. Check that the TCP/IP connection to the Internet over PPP has been configured:

  6. Ping a remote host to check that network is set up correctly:

  7. Download a file from a remote host:

  8. Close the TCP/IP connection: