# About PPP



ppp won't occupy an USB interface descriptor. 

ppp is one way the modules to set up data call on the data link layer. Normally the modules will use the USB interface 3 (you can call it ttyPPP port, or ttyModem port, it will be shown as a modem in the devmgmt on Windows OS.) to start a ppp connection.

Point - to - Point Protocol (PPP) is a communication protocol of the data link layer that is used to transmit multiprotocol data between two directly connected (point-to-point) computers. It is a byte - oriented protocol that is widely used in broadband communications having heavy loads and high speeds. Since it is a data link layer protocol, data is transmitted in frames. It is also known as RFC 1661.

## PPP kernel configuration

You should enable the 

    CONFIG_PPP_DEFLATE=y
    CONFIG_PPP_FILTER=y
    CONFIG_PPP_MULTILINK=y
    CONFIG_PPP_ASYNC=y
    CONFIG_PPP_SYNC_TTY=y

Then please check whether /dev/ppp exists.


## How to get the PPPD
You need the pppd and the chat.

### Debian/Ubuntu OS

Debian System

	sudo apt-get install ppp
	

	
	quectel-pppd.sh
	

	copy the quectel-chat-connect quectel-chat-disconnect quectel-ppp to /etc/ppp/peers
	modify the quectel-ppp and quectel-chat-connect
	execute "pppd call quectel-ppp &"

### cross compile the pppd

follow the [http://www.linuxfromscratch.org/blfs/view/6.3/basicnet/ppp.html](http://www.linuxfromscratch.org/blfs/view/6.3/basicnet/ppp.html)

pppd
	
	https://ppp.samba.org/download.html
	http://samba.org/ftp/ppp/ppp-2.4.4.tar.gz

pppd is based on libcap.

	libpcap-0.9.6 ---> do PPP filtering
	Linux-PAM-0.99.10.0 ---> authenticate incoming calls using PAM
	Linux ATM ---> pppoatm.so 

PPP support (CONFIG_PPP), the asynchronous line discipline (CONFIG_PPP_ASYNC), the driver for your serial port device and/or the PPP over Ethernet (PPPoE) protocol driver (CONGIG_PPPOE) must be compiled into the kernel or loaded as kernel modules. Udev doesn't load the ppp_generic and pppoe modules automatically, they must be mentioned in the /etc/sysconfig/modules file. 

[reference ppp](http://www.linuxfromscratch.org/blfs/view/6.3/basicnet/ppp.html)

### wvdial

wvdial


``` 
    Exit status values.
	#define EXIT_OK			0
	#define EXIT_FATAL_ERROR	1
	#define EXIT_OPTION_ERROR	2
	#define EXIT_NOT_ROOT		3
	#define EXIT_NO_KERNEL_SUPPORT	4
	#define EXIT_USER_REQUEST	5
	#define EXIT_LOCK_FAILED	6
	#define EXIT_OPEN_FAILED	7
	#define EXIT_CONNECT_FAILED	8
	#define EXIT_PTYCMD_FAILED	9
	#define EXIT_NEGOTIATION_FAILED	10
	#define EXIT_PEER_AUTH_FAILED	11
	#define EXIT_IDLE_TIMEOUT	12
	#define EXIT_CONNECT_TIME	13
	#define EXIT_CALLBACK		14
	#define EXIT_PEER_DEAD		15
	#define EXIT_HANGUP		16
	#define EXIT_LOOPBACK		17
	#define EXIT_INIT_FAILED	18
	#define EXIT_AUTH_TOPEER_FAILED	19
	#ifdef MAXOCTETS
	#define EXIT_TRAFFIC_LIMIT	20
	#endif
	#define	 EXIT_CNID_AUTH_FAILED	21
```

[pppd.h](http://androidos.net.cn/android/9.0.0_r8/xref/external/ppp/pppd/pppd.h)


### modem hangup

It's not easy to judge the reason of exit_Hangup.

Sometime it is bug of the module.

Quectel need the modem log to analyze the root cause.

There is a application scenarios we will catch the modem hangup.

The first time the ppp dial up OK. And once we shutdown the pppd process, we can not dial up again. We need to reset the module at that time.

I conclude those attention:

	1. Kill the prorcess by "killall pppd" works fine, but "kill -9 ${PID}" will not.

	2. killall will show 

![](pppdkillall.png)

	and you'll see the ppp end up normally.
	
	3.kill -9 ${PID} you can see nothing about how the pppd process ends up.



### the difference between SIGINT,SIGTERM,SIGHUP

to be done..

waiting ...


More about PPP protocol

[Point to Point Protocol(PPP) by vkota1.@sycamores.indstate.edu](http://cs.indstate.edu/~vkota1/main.pdf)