Ubuntu频繁掉线

根本原因：网络环境比较差，需要延长echo-reply信号的次数。

版本：Ubuntu 14.04.1 LTS

1. 打开配置文件

sudo gedit /etc/ppp/options 

2. 查找到lcp-echo-failure这一行

lcp-echo-failure 4  改为 lcp-echo-failure 30 或者更大的数字

# If this option is given, pppd will send an LCP echo-request frame to t
he
# peer every n seconds. Normally the peer should respond to the echo-req
uest
# by sending an echo-reply. This option can be used with the
# lcp-echo-failure option to detect that the peer is no longer connected
.
lcp-echo-interval 30

# If this option is given, pppd will presume the peer to be dead if n
# LCP echo-requests are sent without receiving a valid LCP echo-reply.
# If this happens, pppd will terminate the connection.  Use of this
# option requires a non-zero value for the lcp-echo-interval parameter.
# This option can be used to enable pppd to terminate after the physical
# connection has been broken (e.g., the modem has hung up) in
# situations where no hardware modem control lines are available.
lcp-echo-failure 30

3. 修改原因

lcp-echo-failure次数被设为4，而lcp-echo-interval设为30秒，

即120秒钟内，没有echo-reply信号，UBuntu便会断开网络。

修改后，900s内没有echo-reply信号，UBuntu才会断开网络。