Patent ID: 8559322

Claim:
A link state detection method comprising: obtaining, by a lowest level switching element (SE), first link state information from the lowest level SE to a mid-level SE; notifying to the mid-level SE, by the lowest level SE, the first link state information; obtaining, by the mid-level SE, first accessibility information from the mid-level SE to the lowest level SE according to the first link state information and obtaining second link state information from the mid-level SE to a first level SE; notifying to the first level SE, by the mid-level SE, the second link state information and the first accessibility information; obtaining, by the first level SE, second accessibility information from the first level SE to the lowest level SE according to the second link state information and the first accessibility information sent by the mid-level SE; and wherein notifying to the mid-level SE, by the lowest level SE, the first link state information comprises: sending the first link state information from the lowest level SE to the first level SE through an internal bus between the lowest level SE and the first level SE or through an external bus between the lowest level SE and the first level SE, and sending the received first link state information from the first level SE to the mid-level SE.