How to check Asterisk and pstn line connectivity

Hi everyone,
The connection between pstn line and interface should not be disconnected. I should be notified whenever the connection is detached by email or other mean. So my question is that , is there any way to monitor connectivity constantly.
How to know the connection is right ?
There may be some port or some thing to track this issues.
I am using A400P interface card to connect asterisk system.
Thank in advance !

Hello,
Please run the command : lsdahdi
and the "RED" means no pstn line connected to this port.

shown as below:

[root@localhost /]# lsdahdi
### Span 1: OPVXA1200/12 "OpenVox A1200P/A800P Board 13" (MASTER)
1 FXO FXSKS (In use) (EC: OSLEC - INACTIVE) RED
2 FXO FXSKS (In use) (EC: OSLEC - INACTIVE) RED
3 FXO FXSKS (In use) (EC: OSLEC - INACTIVE) RED
4 FXO FXSKS (In use) (EC: OSLEC - INACTIVE) RED
5 unknown Reserved
6 FXO FXSKS (In use) (EC: OSLEC - INACTIVE)
7 FXO FXSKS (In use) (EC: OSLEC - INACTIVE)
8 unknown Reserved

Thanks !
I can run isdahdi comment using crontab to check the connection. Is there any other way to use this message to run other script which notify the disconnection?

Sorry, I don't understand what you mean.

Thank for you help ..
I found the answer from stackoverflow
stackoverflow.com/questions/24749703/usi...-to-run-other-script