Patent ID: 7266078

Claim:
A line backup method comprising the steps of: setting up a first connection as a permanent virtual connection on a line connecting between a first exchange unit and a second exchange unit; performing periodic communications between said first exchange unit and said second exchange unit using said first connection; detecting a failure of said line by monitoring said periodic communications at each of said first and second exchange units, wherein a failure is detected when a count of no-response notifications each indicating a no-response resultine from a communication attempt between the first and second exchange units exceeds a predetermined value; switching a second connection on said line, at each of said first and second exchange units, to a reserve connection not using said line, in the event that a failure of said line is detected; and analyzing at said second exchange unit the condition of an opposite-end line directed to a third exchange unit when the second connection to be switched to a reserve connection at said second exchange is a connection to be relayed from said second exchange unit to said third exchange unit along said opposite-end line, and wherein; in said switching step, the reserve connection to be switched to is determined in accordance with the result of the analysis of said opposite-end line.