Path establishment method for establishing paths of different fault recovery types in a communications network

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, a1) defining a plurality of unreserved bandwidths respectively corresponding to all shared risk link groups of said network, a2) setting a maximum bandwidth of said each link to each of the defined unreserved bandwidths as an initial value, a3) subtracting the bandwidth of the working path from each of the unreserved bandwidths, and a4) 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, b1) defining a plurality of unreserved bandwidths respectively corresponding to all shared risk link groups of said network, b2) setting a maximum bandwidth of said each link to each of the defined unreserved bandwidths as an initial value, b3) subtracting the bandwidth of the protection path from each of the unreserved bandwidths and b4) 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, c1) defining a plurality of unreserved bandwidths respectively corresponding to the shared risk link groups to which links of a corresponding working path belong, c2) setting a maximum bandwidth of said each link to each of the defined unreserved bandwidths as an initial value, c3) subtracting the bandwidth of the protection path from each of the unreserved bandwidths and c4) rejecting the establishment of the requested path if a minimum value of the subtracted unreserved bandwidths is smaller than said predetermined threshold value.