Method and apparatus for conservative link selection

A backbone switch node in an ATM PNNI network comprising nodes and PNNI links connecting said nodes, the backbone switch comprising:

• (a) a processor for processing requests to connect from a first ATM device connected to the network to a second ATM device connected to the network;
• and
• (b) a memory communicating with said processor, the memory including computer-executable instructions, which, when executed by the processor, cause the processor to:
• (i) eliminate links in the network for which a required concave link metric exceeds the assigned concave link metric associated with each respective link, the eliminating resulting in a plurality of links still under consideration;
• (ii) process each of the plurality of links still under consideration, wherein the processing includes evaluating each of the plurality of links with an inflating function associated with the concave link metric and reassigning a higher value to the additive link metric of the link under evaluation, if the value calculated using the inflating function is greater than the assigned concave link;
• and
• (iii) select a path through the network which minimizes the additive link metric.

A computer-readable medium having contained thereon computer-executable instructions, which, when processed by a processor in a backbone switch cause the processor to:

• (a) eliminate links in the network for which a required concave link metric exceeds the assigned concave link metric associated with each respective link, the eliminating resulting in a plurality of links still under consideration;
• (b) process each of the plurality of links still under consideration, wherein the processing includes evaluating each of the plurality of links with an inflating function associated with the concave link metric and reassigning a higher value to the additive link metric of the link under evaluation, if the value calculated using the inflating function is greater than the assigned concave link;
• and
• (c) select a path through the network which minimizes the additive link metric.

A method of selecting a path in a communications network comprising nodes and links connecting the nodes, the links having assigned both a concave and an additive link metric, the method comprising:

• (a) eliminating links in the network for which a required concave link metric exceeds the assigned concave link metric associated with each respective link, the eliminating resulting in a plurality of links still under consideration;
• (b) processing each of the plurality of links still under consideration, wherein the processing includes evaluating each of the plurality of links with an inflating function associated with the concave link metric and reassigning a lower value to the additive link metric of the link under evaluation, if the value calculated using the inflating function is less than the assigned concave link metric;
• and
• (c) selecting a path through the network which minimizes the additive link metric.