monitor signal strength (AT+CSQ) after pppd create ppp interface
 

Hi All ~

I am trying to use USB 3G modem on my Linux laptop. When I insert my modem to USB port and load usbserial module, it creates ttyUSB0 and ttyUSB1. I am only able to use ttyUSB0 and launch my ppp scripts to connect to my HSDPA network. Once connected I am not able to use ttyUBS0 to launch minicom or other software to execute AT commands as it says ttyUSB0 file is locked by my ppp . Mainly I am interesting in finding signal strength and Bit Error Rate (AT+CSQ). I see that ttyUSB1 doesnt serve any purpose. Has anyone tried using AT commands or get signal strength info once ppp connection is already launched?Please provide your precious comment/experience to me. thanks a lot.

Ricky

As far as I know (am I am know expert)...

My experience is using a Sierra Wireless Compass 888 USB modem on Ubuntu 8.04.

My modem has (and I would image most/all mdoems) have two ports: a data port and a command port. Perhaps the locked port is the data port and the other is the command port.

You should send AT command only on the command port.

I am thinking that when you run ppp it's locking the data port.

With my setup from the terminal:
1) I run 'wvdialconfig' just to verify my two serial ports.
2) I run 'pppd call gsm885' to start the ppp daemon. gsm885 is specific for my modem. I think there is a generic gsm, but perhaps you need a modem specific one?
3) I open a new terminal and run 'minicom -s'. Mini com opens where I configure the serial port to the command port and the exit minicom configuration. The modem initialises and I can then send AT commands.

Hope this helps... ?

Hi DEF ~

Very appreciate your reply and share with your experience.
I have few questions about about your description.
Can you give me more details?

>>My modem has (and I would image most/all mdoems) have two ports: a >>data port and a command port. Perhaps the locked port is the data >>port and the other is the command port.
The Two ports are ttyUSB0 and ttyUSB1?
In my experience, the pppd will use ttyUSB0 to send AT command to modem by chat, after all command be completed, it will lock the ttyUSB0 and create ppp0 interface, whether it is possible the data and command be sent to the same port?

>>2) I run 'pppd call gsm885' to start the ppp daemon. gsm885 is >>specific for my modem. I think there is a generic gsm, but perhaps >>you need a modem specific one?
So, the function of gsm885 is the same as chat, is it right?

Ricky

Hmm, not sure whether both command and data can be sent on the same port? I would image this to be feasible it’s just the modems I have used have all used two ports. Anyhow, you modem manufacturer should be able to tell you this?

BTW: pppd only locks the port if directed to do so. This is done in your configuration file. For example if running 'pppd call chat', 'chat' is your configuration file. Look in here and the may be a command 'lock' just before the 'connect' command. Remove it and the port should not no longer get locked. Note, I am not sure it this has any adverse effects?

No 'gsm885' is not the same as 'chat'. Use 'man chat' to see description of chat. My example uses 'pppd call' and not 'chat' Using 'chat' you would also provide an additional script e.g. 'gsm_chat'.

What files do you have in '/etc/ppp/peers/' ?

Oops - on my last reply there is a mistake. IGNORE THE LAST REPLY AND READ THIS INSTEAD:

Hmm, not sure whether both command and data can be sent on the same port? I would image this to be feasible it’s just the modems I have used have all used two ports. Anyhow, you modem manufacturer should be able to tell you this?

BTW: pppd only locks the port if directed to do so. This is done in your configuration file. For example if running 'pppd call gsm', 'gsm' is your configuration file. Look in here and the may be a command 'lock' just before the 'connect' command. Remove it and the port should not no longer get locked. Note, I am not sure it this has any adverse effects?

No 'gsm885' is not the same as 'chat'. Use 'man chat' to see description of chat. My example uses 'pppd call' and not 'chat' Using 'chat' you would also provide an additional script e.g. 'gsm_chat'.

What files do you have in '/etc/ppp/peers/' ?