使用迅雷下载的时候openwrt老是掉线，查看ppp日志：
May 5 07:02:05 OpenWrt daemon.info pppd[23813]: No response to 5 echo-requests
May 5 07:02:05 OpenWrt daemon.notice pppd[23813]: Serial link appears to be disconnected.
May 5 07:02:05 OpenWrt daemon.info pppd[23813]: Connect time 1089.9 minutes.
May 5 07:02:05 OpenWrt daemon.info pppd[23813]: Sent 335012468 bytes, received 1671352386 bytes.
May 5 07:02:06 OpenWrt user.notice root: stopping ntpclient
May 5 07:02:12 OpenWrt daemon.notice pppd[23813]: Connection terminated.
May 5 07:02:12 OpenWrt daemon.notice pppd[23813]: Modem hangupPPPOE客户端会每隔10秒向服务器发送echo request确认在线，5次请求未回应就认为连线有问题并断开连接。
修改配置增加和ADSL服务器交互间隔：
vim /etc/ppp/options
lcp-echo-interval 30 #发送间隔秒
lcp-echo-failure 15 #15次未响应断开