How to Use GSM/3G/4G in Embedded Linux Systems

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How to Use GSM/3G/4G in Embedded Linux Systems

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• Introduction
• Embedded devices connected to the internet are
  growing every day. In many cases, these devices
  will be installed somewhere without a wire or
  wireless network connection. A good way to

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keep the devices connected to the internet in
these situations is by seeking mobile network
coverage. Therefore, this blog post will present
the necessary configurations to connect a device
running Linux to the internet through the PPP
(Point-to-Point Protocol) link.and optimize cost.
In simple terms, modularity means that a system
can be built by assembling many small units.
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• Hardware Specification
• In this article we will be using the Colibri
  iMX6S with the base board called Colibri
  Evaluation Board, both of which, are from
  Toradex. The Colibri Evaluation Board is
  recommended specifically for project evaluation
  and development. This product comes with a great
  number of interfaces like USB, Ethernet, I2C,
  SPI, RS242, RS485, CAN and many others. We can
  also find some multimedia interfaces like HDMI,
  LVDS, VGA and LCD already supported on the
  Evaluation Board.
• To follow this tutorial, you can use any USB or
  Serial modem to connect to the internet.

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• You just have to adapt the interface created at
  /dev/ and check the AT commands supported and
  implemented for your modem because each modem has
  specific AT commands. In this case, we have used
  for this tutorial a Huawei E173s 3G modem with a
  compatible SIM Card with data plan activated.
• Kernel Preparing
• To use the 3G USB modem through the PPP protocol,
  it is necessary to select some features in the
  kernel configurations and then compile the
  Kernel. To understand how to compile the kernel,
  I suggest following the link below.
• http//developer.toradex.com/software-resources/ar
  m-family/linux/board-support-package/build-u-boot-
  and-linux-kernel-from-source-code

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• Basically, the process to compile the Kernel can
  be summarized in the following steps
• Toolchain configuration
• Download the kernel from the correct repository
  and branch
• Configure the standard processor features
• Change the features for your application
• Compile

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• When you are configuring the kernel features, go
  into menuconfig and be sure to enable the
  following options
• CONFIG_PPP
• PPP (Point to Point Protocol) is a newer and
  better SLIP. It serves the same purpose sending
  Internet traffic over telephone (and other
  serial) lines. Ask your access provider if they
  support it, because otherwise you can't use it
  most Internet access providers these days support
  PPP rather than SLIP.
• Device Drivers ---gt
• Network device support ---gt
• PPP (point-to-point protocol) support
• PPP BSD-Compress compression
• PPP Deflate compression

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• PPP filtering
• PPP MPPE compression (encryption)
• PPP multilink support
• PPP over Ethernet
• PPP support for async serial ports
• PPP support for sync tty ports
• CONFIG_USB_ACM
• This driver supports USB modems and ISDN adapters
  which support the
• Communication Device Class Abstract Control Model
  interface.
• Please read ltfileDocumentation/usb/acm.txtgt for
  details.
• Device Drivers ---gt
• USB support ---gt
• USB Modem (CDC ACM) support

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• Necessary Software Packages
• To configure and connect the 3G modem to the
  internet, Linux uses, in addition to the kernel
  drivers, a software which manages the connection.
  This software is PPP. Usually Toradex images
  already have the PPP software installed by
  default.
• In case you do not have PPP installed, just add
  the following to your local.conf file for build
  environments based on Yocto/OpenEmbedded

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Testing Communication with the Modem After all
the necessary drivers and software are installed,
it is possible to check if the module recognizes
the 3G modem. The modem interface should appear
in /dev. Basically the driver simulates a USB
connection as many serial connections.
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Execute the following command to search for the
interfaces /dev/ttyUSB
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If the files ttyUSB0, ttyUSB1 e ttyUSB2 were
found, the modem was succesfully recognized by
the system. In case you want to conduct in-depth
testing, it is possible to use a serial terminal
like minicom to start communicating with the
modem and check if it is working well. In my case
the modem had a baudrate of 115200.
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Configuring the PPP Files After validating the
communication with the modem, it is time to
create the configuration files responsible for
connecting to the internet. You should be able to
find a folder inside /etc/ called ppp. Some files
need to be created inside this folder. First we
create the PPP options file
vi /etc/ppp/options ____________________________
_________ auth crtscts lock hide-password modem mr
u 296
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• mtu 296
• lcp-echo-interval 30
• lcp-echo-failure 4
• noipx
• persist
• asyncmap 0xa0000
• mru 1500
• refuse-chap
• ipcp-max-failure 30
• logfile /home/root/ppp

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In my case we use the PAP authentication file
(may vary depending on Network Provider).
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The next step is to create one more file inside
/etc/ppp/peer In this file we have configurations
for our network provider and the path for the
chat file
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Now we create the file responsible for sending
the AT commands to the modem so it can connect to
the internet. This file varies according to modem
models/brands.
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Connecting to the Internet Next we run ppp and
analyze the log files. In the log files we can
see when each AT command has been executed.
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After running ppp, we open the log file
In my case, I received the following output
tail -f ppp.log Sent 3940 bytes, received 2843
bytes. restoring old default route to eth0
192.168.10.1 restore default route
ioctl(SIOCADDRT) Network is unreachable(101)
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• Script /etc/ppp/ip-down started (pid 778)
• sent LCP TermReq id0x2 "User request"
• rcvd LCP TermAck id0x2
• Connection terminated.
• Script /etc/ppp/ip-down finished (pid 778),
  status 0x0
• ATZ
• OK
• ATCGDCONT1,"IP","zap.vivo.com.br"
• OK
• ATDT99
• CONNECT
• Script chat -v -f /etc/ppp/chat/vivo-3g.chat
  finished (pid 795), status 0x0
• Serial connection established.
• using channel 2
• Using interface ppp0
• Connect ppp0 /dev/ttyACM0

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• rcvd LCP ConfReq id0x1
• sent LCP ConfReq id0x1
• sent LCP ConfAck id0x1
• rcvd LCP ConfAck id0x1
• sent LCP EchoReq id0x0 magic0xa068db01
• sent PAP AuthReq id0x1 user"vivo" password
• rcvd LCP EchoRep id0x0 magic0x96baf40f
• rcvd PAP AuthAck id0x1 ""
• PAP authentication succeeded
• sent CCP ConfReq id0x1
• sent IPCP ConfReq id0x1
• rcvd LCP ProtRej id0x2 80 fd 01 01 00 0f 1a 04
  78 00 18 04 78 00 15
• Protocol-Reject for 'Compression Control
  Protocol' (0x80fd) received
• rcvd IPCP ConfNak id0x1
• sent IPCP ConfReq id0x2
• rcvd IPCP ConfNak id0x2

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• sent IPCP ConfReq id0x3
• rcvd IPCP ConfNak id0x3
• sent IPCP ConfReq id0x4
• rcvd IPCP ConfNak id0x4
• sent IPCP ConfReq id0x5
• rcvd IPCP ConfNak id0x5
• sent IPCP ConfReq id0x6
• rcvd IPCP ConfReq id0x1
• sent IPCP ConfNak id0x1
• rcvd IPCP ConfRej id0x6
• sent IPCP ConfReq id0x7
• rcvd IPCP ConfReq id0x2
• sent IPCP ConfAck id0x2
• rcvd IPCP ConfNak id0x7
• sent IPCP ConfReq id0x8
• rcvd IPCP ConfAck id0x8

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• local IP address 179.133.47.109
• remote IP address 179.133.47.109
• primary DNS address 187.100.246.254
• secondary DNS address 187.100.246.251
• Script /etc/ppp/ip-up started (pid 805)
• Script /etc/ppp/ip-up finished (pid 805), status
  0x0

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As seen in the log file, the chat script is
executed step-by-step until we get the following
You can validate the necessary command sequence
to get connected using the serial terminal. Once
it is validated, you can create your own
customized chat script. After checking for an IP
address from the network provider, look for
whether the ppp0 network interface is active
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Testing the Connection To test if the connection
has been successfully established, ping an
external ip address
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To configure DNS, we can use the following
command and then ping a URL, for example
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Image 1 A running web browser using 3G
connection.
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• We can avoid the file being rewritten when system
  is restarted with the following command

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Now it is possible to connect using SSH from an
external computer
Configuring a Host Name for our IP
Address Another thing we can do is to associate
our IP address to a host name. For this purpose,
we used the NoIP services (www.noip.com). We then
created a free account and added a Host. In our
case, we chose toradex.noip.me.
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Image 2 NoIP Add Host page.
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After the Host name is created we can again
connect to the module using SSH
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In our case, when the 3G modem connection is
restarted, we always receive a new IP adress. If
we try to reconnect to the module, we no longer
have access. A workaround was to use a method
called Dynamic DNS(Dynamic Domain Name System).
NoIP also offers Dynamic DNS services. Further
information for using this method can be found
here. Basically we send an http request to NoIP
with information like IP, hostname, username and
password. To accomplish this request, a small
Python program was made. It gets executed when we
start the 3G modem connection and follows the
sequence as listed below
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Image 3 Python Application Fluxogram.
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• !/usr/bin/python
• import sys
• import requests
• import netifaces as ni
• user 'xxxxxxx'
• pswd 'xxxxxxx'
• ni.ifaddresses('ppp0')
• ip ni.ifaddresses('ppp0')20'addr'
• myhostname 'toradex.noip.me'
• payload 'hostname' myhostname , 'myip' ip
• r requests.get("http//dynupdate.no-ip.com/nic/u
  pdate", paramspayload, auth(user,pswd))

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• print " "
• if "good" in r.text
• print "Hello", user, "!"
• print "Your IP was successfully updated to", ip
• print myhostname, "is up and running!"
• if "nochg" in r.text
• print "Hello", user, "!"
• print "Your IP", ip, "is still active, no change
  needed"
• if "nohost" in r.text
• print "The given Host name", myhostname, "does
  not exist under specified account"
• print "Please review your Host name and try
  again"
• if "badauth" in r.text
• print "Login and/or Username incorrect"
• print "Please correct your credentials and try
  again"
• if "911" in r.text

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• print "Sorry for the incovenience but we are
  experiencing some problems right now"
• print "Please try again later"
• print "noip.com says", r.text
• print " "

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After creating the Python program and making it
executable with chmod x, we can move it to
/etc/ppp/ip-up.d/, which is a folder where
scripts are executed after ppp connection or
create a small script which calls our Python
program. Inside /etc/ppp/ we have the files that
we created at the beginning of the article as
well as other files like ip-down, ip-up,
ppp_on_boot. Feel free to explore each one of
these files. ip-up is the script which calls
another script or program found inside ip-up.d
folder. In this case, we created a small script
inside ip-up.d
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Note the script is not terminated with .sh Note
that all the print commands inside our Python
program can be seen in the log file
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If everything is configured correctly, when we
receive a new IP from our network provider, the
system automatically updates our host created at
NoIP, so it will be possible to connect to the
module despite the IP address being
changed. Based on all the information provided
in this article, it is possible to achieve many
other network activities. One of them is to share
the 3G modem network with another computer via
Ethernet. For this we configured a basic LAN
network between two machines and ran the
following command
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Apart from internet sharing, it is also possible
to conduct port forwarding and many other network
features. Final Thoughts As seen in this
article, a Linux system has many network
functionalities. We just need to properly
configure them and have access to ppp0 network.
Another important point, is that regardless of
the used interface, the programming method
remains the same. The task of choosing the
interface to use is made automatically by Linux
depending on the routes. For those who require
network connection in their projects and also
need system flexibility, the use of Linux in
embedded systems is the way to go. References http
//metodiew.com/huawei-e173s-and-ubuntu/http//de
veloper.toradex.com/product-selector/colibri-imx6
http//developer.toradex.com/product-selector/coli
bri-evaluation-board
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Thank you!