[ubuntu] frequently prompt "Wired network disconnected you are now offline"

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http://ubuntuforums.org – Hello, after upgrade to the latest version yesterday(Ubuntu 12.04.2 LTS), $ uname -a Linux delta3 3.2.0-49-generic-pae #75-Ubuntu SMP Tue Jun 18 18:00:21 UTC 2013 i686 i686 i386 GNU/Linux a problem is, the "Indicator Applet Complete", that is on the right corner of Desktop, frequently prompts (about every 5 minutes) "Wired network Disconnected - you are now offline". but actually, the wired network is on. I have a ADSL network and using "pon dsl" command to dial. I can surf internet. Any ideas to fix this ? Thanks! (Hardware)