Patent ID: 7248561

Claim:
A path establishment method for a communications network, wherein the network comprises a plurality of nodes interconnected by links, said links forming a plurality of shared risk link groups, the method comprising: a) defining a plurality of unreserved bandwidths respectively corresponding to said shared risk link groups and setting a maximum bandwidth of said each link to each of the defined unreserved bandwidths as an initial value; and b) subtracting the bandwidth of a requested path from each of the unreserved bandwidths and rejecting the establishment of the requested path if each of the subtracted unreserved bandwidths is smaller than a predetermined threshold value, wherein steps (a) and (b) comprise: a) when a working path is requested, a 1 ) defining a plurality of unreserved bandwidths respectively corresponding to all shared risk link groups of said network, a 2 ) setting a maximum bandwidth of said each link to each of the defined unreserved bandwidths as an initial value, a 3 ) subtracting the bandwidth of the working path from each of the unreserved bandwidths, and a 4 ) rejecting the establishment of the working path if a minimum value of the subtracted unreserved bandwidths is smaller than a predetermined threshold value b) when a protection path of “1+1” or “1:1” recovery type is requested, b 1 ) defining a plurality of unreserved bandwidths respectively corresponding to all shared risk link groups of said network, b 2 ) setting a maximum bandwidth of said each link to each of the defined unreserved bandwidths as an initial value, b 3 ) subtracting the bandwidth of the protection path from each of the unreserved bandwidths and b 4 ) rejecting the establishment of the requested path if a minimum value of the subtracted unreserved bandwidths is smaller than said predetermined threshold value; and c) when a protection path of “shared” recovery type is requested, c 1 ) defining a plurality of unreserved bandwidths respectively corresponding to the shared risk link groups to which links of a corresponding working path belong, c 2 ) setting a maximum bandwidth of said each link to each of the defined unreserved bandwidths as an initial value, c 3 ) subtracting the bandwidth of the protection path from each of the unreserved bandwidths and c 4 ) rejecting the establishment of the requested path if a minimum value of the subtracted unreserved bandwidths is smaller than said predetermined threshold value.