A network system comprising: a control node; a first head node, comprising a first head forward port, a first head backward port and a first head backup port, wherein the first head forward port is connected to the control node; a first ordinary node, comprising a first forward port, a first backward port and a first backup port, wherein the first forward port is connected to the first head backward port; a second ordinary node, comprising a second forward port, a second backward port and a second backup port, wherein the second forward port is connected to the first backward port; and a third ordinary node, comprising a third forward port, a third backward port and a third backup port, wherein the third forward port is connected to the second backward port, wherein the third backup port is connected to the first head backup port.