Provision of Alternative Communications Paths in a Communications Network

A computer-implemented method of processing data for computing alternative paths in an optical communications network, the method comprising:

• generating a list of groups that comprise communication links in an optical communications network, wherein the links in a given group share a risk of being affected by a fault;
• comparing one or more groups in the list with other groups in the list to determine whether a group include the same communication links as another group;
• and
• deleting a group from the list if the communication links in the group are a subset of the communication links in another group.

A computer readable medium for a computer associated with an optical communications network having a plurality of nodes, the nodes being connected via communication links grouped into a list of one of Shared Risk Link Groups (SRLGs) and Shared Risk Groups (SRGs), wherein the SRLGs or SRGs include communication links that share a risk of being affected by the same fault, the computer readable medium having instructions stored thereon, the instructions configured to cause the computer to:

• generate a list of unexamined SRLGs or SRGs that includes all SRLGs or SRGs to be analysed;
• for each unexamined SRLGx or SRGx in the list:
• compare the unexamined SRLGx or SRGx with one or more other unexamined SRLGy or SRGy in the given list;
• if the communication links in a given SRLGy or SRGy are a subset of the communication links in the SRLGsx or SRGsx:
• delete the SRLGy or SRGy;
• and
• continue comparing the unexamined SRLGx or SRGx with one or more other SRLGy or SRGy;
• if the communication links in SRLGx or SRGx are a subset of the communication links in another SRLGy or SRGy, delete the SRLGx or SRGx;
• and
• if the SRLGx or SRGx has not been deleted as being a subset of SRLGy or SRGy, mark the non-deleted SRLGx or SRGx as having been examined and assign it to a reduced list.

A communications network comprising:

• a route controlling server configured to define communication paths for telecommunications signals between a first location in the network and a second location in the network, and having access to a first memory containing routing instructions for routing communications from the first location to the second location;
• and
• an alternative routing server configured to produce alternative communication paths from the first location to the second location, and to store alternative path data in the first memory, wherein the alternative routing server produces alternative path data by:
• generating a list of groups that comprise communication links between nodes in the communications network, wherein the links in a given group share a risk of being affected by the same fault;
• comparing one or more groups in the list with other groups in the list;
• deleting a group from the list if the communication links in the group are a subset of the communication links in another group, to create a reduced list;
• and
• defining an alternate communication paths for telecommunications signals between the first location and the second location using the reduced list;
• and
• wherein the route controlling server is further configured to respond to an indication of a fault in the defined communication path by causing telecommunications signals to be routed from the first location to the second location using the alternate communication path.