Using pppd dial-up Internet access (GPRS) process on ARM+LINUX

1. Modify the 2.6.30 kernel options,
 make menuconfig
Device drivers -> Networking device support -> PPP (point to point protocol) support.
 I selected the following modules (in M mode, i.e. module mode)
PPP support for async serial ports
PPP support for sync tty ports
PPP Deflate compression
PPP BSD-Compress compression
SLIP (serial line) support.
Then compile: make && make install && make modules && make modules_install.
I got several kernel library files in ko format, copied them to the ARM target board, and loaded them dynamically in /etc/init.d/rcS:
insmod /etc/ppp/slhc.ko                                        
insmod /etc/ppp/ppp_generic.ko                                 
insmod /etc/ppp/ppp_async.ko                                   
insmod /etc/ppp/ppp_synctty.ko                                 
insmod /etc/ppp/ppp_deflate.ko                                 
insmod /etc/ppp/bsd_comp.ko                                    
insmod /etc/ppp/slip.ko
Pay attention to the loading order. I remember that slhc.ko must be loaded first.

2. Porting ppp and connecting to the network process,  
1) ppp2.4.4 source code compilation process

#./configure

#make CC=arm-linux-gcc Pay attention to specify the path of arm-linux-gcc, or specify it directly with the absolute path

The files that need to be copied to the ARM target board are:
pppd
pppdump
pppstatus
chat
2) Script preparation
There are 4 scripts that need to be prepared, one is the rule file /etc/ppp/gprs-connect-chat, one is the parameter file /etc/ppp/peers/gprs, and the authentication files: pap-secret and chap-secret. (In fact, I only use pap-secret here, and not chap-secret. Anyhow, create them all)
(1) Script #gprs-connect-chat:
TIMEOUT 15
ABORT '\nBUSY\r'
ABORT '\nNO ANSWER\r'
ABORT '\nRINGING\r\n\r\nRINGING\r'
#'' AT
#'OK-+++\c-OK' ATH0
TIMEOUT 40
'' \rAT
OK AT+FLO=0 #This is a special setting for GC864-DUAL-V2, that is, to turn off flow control
OK ATS0=0
OK ATE0V1
OK AT+CGDCONT=1,"IP","CMNET" #Connect to China Mobile cmnet
OK ATDT*99*1#
CONNECT ''
(2) Script gprsoptions
#/etc/ppp/peers/gprsoptions
# Usage: root>pppd call gprsoptions
/dev/ttyS4
115200
nocrtscts
modem
#noauth
#auth
#-pap
#+chap
lock
debug
nodetach
#hide-password
usepeerdns
noipdefault
defaultroute
user cmnet
#user smsong
0.0.0.0:0.0.0.0
ipcp-accept-local
#ipcp-accept-remote
#lcp-e cho-failure 12
#lcp-echo-interval 3 
noccp                
#novj                
#novjccomp           
persist              
connect '/etc/ppp/chat -s -v -f /etc/ppp/gprs-connect-chat'
(3) Authentication file pap-secrets Change as needed
/etc/ppp # cat pap-secrets 
# Secrets for authentication using PAP
# client server secret IP addresses
cmnet * cmnet *
(4) Authentication file chap- secrets Modify as needed. It is not used now.
/etc/ppp # cat chap-secrets 
# Secrets for authentication using CHAP
# client server secret IP addresses
'' * '' *

3) Call process
ifconfig eth0 down // Turn off the wired network card first to avoid conflict with dial-up initialization
/etc/ppp/pppd call gprs& // Start the /etc/ppp/peers/gprs script
ifconfig eth0 up // Restart the wired network card
Let's take a look at the display log content of the connection:
/etc/ppp # ./pppd call gprs&
/etc/ppp # timeout set to 15 seconds
abort on (\nBUSY\r)
abort on (\nNO ANSWER\r)
abort on (\nRINGING\r\n\r\nRINGING\r)
timeout set to 40 seconds
send (^MAT^M)
expect (OK)
AT^M^M
OK
 -- got it

send (AT+FLO=0^M)
expect (OK)
^M
AT+FLO=0^M^M
OK
 -- got it

send (ATS0=0^M)
expect (OK)
^M
ATS0=0^M^M
OK
 -- got it

send (ATE0V1^M)
expect (OK)
^M
ATE0V1^M^M
OK
 -- got it

send (AT+CGDCONT=1,"IP","CMNET"^M)
expect (OK)
^M
^M
OK
 -- got it

send (ATDT*99*1#^M)
expect (CONNECT)
^M
^M
CONNECT
 -- got it

send (^M)
Serial connection established.
using channel 1
Using interface ppp0
Connect: ppp0 <--> /dev/ttyS4
Warning - secret file /etc/ppp/pap-secrets has world and/or group access
sent [LCP ConfReq id=0x1 ]
rcvd [LCP ConfAck id=0x1 ]
rcvd [LCP ConfReq id=0x1 ]
sent [LCP ConfAck id=0x1 ]
Warning - secret file /etc/ppp/pap-secrets has world and/or group access
sent [PAP AuthReq id=0x1 user="cmnet" password=]
rcvd [PAP AuthAck id=0x1 "Welcome!"]
Remote message: Welcome!
PAP authentication succeeded
sent [IPCP ConfReq id=0x1 ]
rcvd [IPCP ConfReq id=0x1 ]
sent [IPCP ConfAck id=0x1 ]
rcvd [IPCP ConfRej id=0x1 ]
sent [IPCP ConfReq id=0x2 ]
rcvd [IPCP ConfNak id=0x2 ]
sent [IPCP ConfReq id=0x3 ]
rcvd [IPCP ConfAck id=0x3 ]
local  IP address 10.176.120.186
remote IP address 192.168.202.0
primary   DNS address 218.201.96.130
secondary DNS address 211.137.191.26

4)  查看网络设置与ping实验
/etc/ppp # ifconfig
lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

ppp0      Link encap:Point-to-Point Protocol  
          inet addr:10.176.120.186 PtP:192.168.202.0 Mask:255.255.255.255
          UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1500 Metric:1
          RX packets:4 errors:0 dropped:0 overruns:0 frame:0
          TX packets:4 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:3 
          RX bytes:64 (64.0 B) TX bytes:82 (82.0 B)
Let’s ping
/etc/ppp # ping www.163.com -c 3
PING www.163.com (221.204.240.161): 56 data bytes
64 bytes from 221.204.240.161: seq=0 ttl=46 time=466.873 ms
64 bytes from 221.204.240.161: seq=1 ttl=46 time=435.762 ms
64 bytes from 221.204.240.161: seq=2 ttl=46 time=414.000 ms

--- www.163.com ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max = 414.000/438.878/466.873 ms

3. Other issues

1) Set the DNS address
/etc/ppp to be automatically set by the dial-up A resolv.conf file is generated, but it is not the same file as /etc/resolv.conf, so DNS sometimes cannot be resolved.
A good way is to first ensure that /etc/resolv.conf exists, then create a soft link in /etc/ppp ln -s /etc/ppp/resolv.conf /etc/resolv.conf
so that after the dial-up is successful, /etc/resolv.conf will have the following content:
nameserver 218.201.96.130
nameserver 211.137.191.26
2) Only IP addresses can be pinged, but domain names cannot be pinged
There is a paragraph in the busybox command help page:
Quote:
LIBC NSS
When used with glibc, the BusyBox 'networking' applets will similarly require that you install at least some of the glibc NSS stuff (in particular, /etc/nsswitch.conf, /lib/libnss_dns*, /lib/libnss_files*, and /lib /libresolv*).
Then put libnss_dns* in the lib directory of the arm-linux tool chain, Copy libnss_files* and libresolv* to /lib of the ARM target board. You can ping the domain name 
/etc/ppp # ping www.163.com
PING www.163.com (221.204.240.161): 56 data bytes
64 bytes from 221.204.240.161: seq=0 ttl=46 time=641.269 ms
64 bytes from 221.204.240.161: seq=1 ttl=46 time=435.801 ms
64 bytes from 221.204.240.161: seq=2 ttl=46 time=446.776 ms
64 bytes from 221.204.240.161: seq=3 ttl=46 time=381 .381 ms
64 bytes from 221.204.240.161: seq=4 ttl=46 time=468.495 ms

--- www.163.com ping statistics ---
5 packets transmitted, 5 packets received, 0% packet loss
round-trip min/avg/max = 381.381/ 474.744/641.269 ms


3) How to dial up and connect to China Unicom's 3G network?
Use TELIT's UC864-E and use USB connection. Specify the serial port as ttyUSB0.
For ppp, only a few changes need to be made in the four scripts.
a. Change the options script
  to rename gprsoptions to g3options, change the line parameter /dev/ttyS4 to /dev/ttyUSB0, and
change connect '/ etc/ppp/chat -s -v -f /etc/ppp/gprs-connect-chat'
to connect '/etc/ppp/chat -s -v -f /etc/ppp/g3-connect-chat'
b . Change chat script
TIMEOUT 15
ABORT '\nBUSY\r'
ABORT '\nNO ANSWER\r'
ABORT '\nRINGING\r\n\r\nRINGING\r'
#'' AT
#'OK-+++\c-OK' ATH0
TIMEOUT 40
'' \rAT
OK AT+FLO=0
OK ATS0=0
OK ATE0V1
OK AT+CGDCONT=1,"IP","UNINET" #UNINET stands for China Unicom. #OK AT+
CGDCONT=1,"IP","CMNET"
OK ATDT*99*1#
CONNECT    
c. Change pap-secrets
# Secrets for authentication using PAP
# client server secret IP addresses
#cmnet * cmnet * #If it is China Mobile GPRS, use cmnet
uninet * uninet * #If it is China Unicom 3G, use uninet

d. Change chap-secrets
to the same as above pap-secrets