I’m using Ubuntu Lucia in dorm, the network always automatically disconnected  after a few minutes like:

root@VanXL:/etc/ppp/peers# plog

May 19 13:30:53 VanXL pppd[3087]: Connect: ppp3 <–> wlan0

May 19 13:30:53 VanXL pppd[3087]: Remote message: Authentication success,Welcome!

May 19 13:30:53 VanXL pppd[3087]: PAP authentication succeeded

May 19 13:30:53 VanXL pppd[3087]: peer from calling number 00:18:82:60:CA:A5 authorized

May 19 13:30:53 VanXL pppd[3087]: not replacing existing default route through ppp1

May 19 13:30:53 VanXL pppd[3087]: Cannot determine ethernet address for proxy ARP

May 19 13:30:53 VanXL pppd[3087]: local  IP address 114.230.98.44

May 19 13:30:53 VanXL pppd[3087]: remote IP address 114.230.96.1

May 19 13:30:53 VanXL pppd[3087]: primary   DNS address 61.147.37.1

May 19 13:30:53 VanXL pppd[3087]: secondary DNS address 61.177.7.1

root@VanXL:/etc/ppp/peers# plog

May 19 13:31:08 VanXL pppd[1996]: remote IP address 218.91.20.1

May 19 13:31:08 VanXL pppd[1996]: primary   DNS address 61.147.37.1

May 19 13:31:08 VanXL pppd[1996]: secondary DNS address 61.177.7.1

May 19 13:31:20 VanXL pppd[2716]: No response to 4 echo-requests

May 19 13:31:20 VanXL pppd[2716]: Serial link appears to be disconnected.

May 19 13:31:20 VanXL pppd[2716]: Connect time 3.5 minutes.

May 19 13:31:20 VanXL pppd[2716]: Sent 11128 bytes, received 10199 bytes.

May 19 13:31:27 VanXL pppd[2716]: Connection terminated.

May 19 13:31:27 VanXL pppd[2716]: Modem hangup

Network works fine when i use ChinaNet so i didn’t suppose this to be a hardware (or driver) problem.

and i noticed the “4 echo-request”. after googling, this appears to be a bug.

The other side of the PPP link probably dosen’t support LCP echo. You often see this with cellphone / cellular data card PPPoE implementations.

Put this line in the relevent ppp options file and try again:
lcp-echo-interval 0

(http://superuser.com/questions/109146/ubuntu-pppoe-connection-timeout)

Also you can completely disable this in /etc/ppp/options (search “echo”) if you find it worth nothing like me 😉

The network works perfectly now