Evolution of a telecommunications network from ring to mesh structure
Ongoing growth in transport demand is served while deferring or eliminating expenditure for additional capacity by reclaiming the protection capacity and inefficiently used working capacity in existing multi-ring network. Reclamation is through re-design of the routing and restoration in the network using mesh principles within the pre-existing ring capacities. The installed working and protection capacity of existing rings is viewed as a sunk investment, an existing resource, to be “mined” and incorporated into a mesh-operated network that serves both existing and ongoing growth. A complete double or even tripling of demand could be supported with little or no additional capacity investment through the period of ring-to mesh conversion by ring-mining. An existing ring set may be converted to a target architecture of “p-cycles” instead of a span-restorable mesh, through placement of straddling span interface units to convert ring ADMs to p-cycle nodal elements.
1. A method of providing protection for a telecommunications network against failure of a span or node in the telecommunications network, in which the telecommunications network initially has protection organized in rings of connected protection links, the method comprising the steps of:
selecting ring nodes for conversion from ring node to mesh node according to a strategy that increases and optimizes demand served by the telecommunications network, wherein the strategy takes into account the cost of conversion of the selected nodes from ring node to mesh node;
breaking connections between protection links at the selected ring nodes; and
connecting the protection links into a mesh network of links of spare capacity, thereby converting each of the selected ring nodes from a ring node to a mesh node.
2. The method of claim 1 in which the mesh network is configured into cycles of connected links of spare capacity in readiness for span failure.
3. The method of claim 2 further comprising the step of adding a straddling span interface at the node for re-routing failed working channels onto the broken connection links upon failure of the working channels.
4. The method of claim 1 in which connecting the protection links into a mesh network comprises accessing an extra traffic feature of an add-drop multiplexer at a node and connecting the extra traffic feature to a mesh cross-connect at the node.
5. The method of claim 1 further comprising the step of adding capacity on a span of the telecommunications network to increase the demand served by the telecommunications network.
6. The method of claim 1 further comprising the step of re-using selected ones of plural add-drop multiplexers within the ring.
7. The method of claim 1 further comprising the step of abandoning selected segments of ring capacity in the telecommunications network.
8. The method of claim 1 in which the strategy uses an integer programming formulation to minimize an objective function that sums the cost for adding new capacity modules and the cost of converting or re-using ADMs.
9. The method of claim 8 in which the objective function is minimized according to a set of constraints selected from the group consisting of:
a) the demand served is a multiple of the original demand;
b) there is enough working capacity in the network to support the routing of all the demands;
c) the sum of restoration flows for each single span cut is equal to the working capacity to be restored;
d) there is enough spare capacity on each span to support all the restoration flows that cross the span in every span failure case;
e) the sum of mesh working and spare capacity on each span does not exceed the amount of available capacity on that span;
f) the capacity from a ring is not reclaimed on a span that is not covered by that ring; and
g) any ADM is converted (if at a degree 3+site) or re-used (if at a degree 2 site) if the capacity of the ring it belongs to is reclaimed on one of its two adjacent spans.
10. The method of claim 9 in which the objective function is minimized according to each one of constraints a) through g).