Multiplex communications – Fault recovery – Bypass an inoperative channel
Patent
1996-02-28
1998-03-31
Ton, Dang
Multiplex communications
Fault recovery
Bypass an inoperative channel
370256, H04J 116
Patent
active
057346402
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of allocating spare capacity in a fully or partly meshed communications network.
2. Related Art
It is known from the paper "Near Optimal Spare Capacity Planning in a Mesh Restorable Network", W. D. Grover et al., Proc. IEEE Global Conference on Communications, Phoenix, Ariz., USA, 1991, pp 2007-2012 to allocate spare capacity in a communications network, i.e. the disposition of the spares by a two phase method in which spares are progressively added in the first phase to achieve a desired restorability target (the Forward Synthesis phase), and the second phase removes redundant spares without violating the restorability target (Tightening phase). In the known allocation method, in the forward synthesis phase each step which adds a notional spare or spares computes the respective network restorability and designates the spare or spares which produce the greatest increase in network restorability.
SUMMARY OF THE INVENTION
According to the present invention there is provided a method of allocating spare capacity in a communications network comprising a fully or partly meshed arrangement of connected nodes, the method comprising the steps of a notional spare link to the selected span, the method being characterised by the further steps of: than one notional spare link added to the network at any one time; network restorability, choosing the respective notional spare link giving the greatest value of network restorability merit; the network; and restorability has been reached, or until step (d) fails to produce a notional spare link which increases network restorability.
The term network restorability merit as used herein means the network restorability value for money. In some embodiments of the invention, this may be expressed in the form of network restorability divided by protection network cost, i.e. the actual restorability value for a notionally added spare link divided by the total cost of the protection network (the cost of all the actual spare links of the network together with the cost of the notional spare link). In other embodiments of the invention, this may be expressed in the form of the increase in network restorability due to a notionally added spare link divided by the cost of the notionally added spare link.
Preferably there are included the modifications that in step (b) multiple-failure network restorability is calculated instead of network restorability, and that step (b) comprises the substeps of selecting groups of two or more spans, and for each group ranking the spans of a group in order of priority, notionally failing the spans of a group simultaneously, and resolving any contention for spare capacity by the spans of a group on the basis of their relative priorities.
More preferably, if step (d) fails to produce a single notional spare link which increases network restorability, modified steps (a) to (f) are performed in which the selected span and associated notional spare link are replaced by a pair of spans and respective notional spare links; on each occasion that modified step (f) designates a pair of notional spare links as actual spare links of the network, original steps (a) to (g) are performed; and on each occasions that modified step (d) fails to produce a pair of notional spare links which give an increase in network restorability, there are included the steps of (h) randomly choosing a span which is not yet fully restorable, and (i) adding, as actual spare links of the network, a sequence of spare links as a restoration route for the randomly chosen span.
The term roue as used herein means a sequence of spans between two nodes and includes both complete end-to-end paths in the network as well as partial paths.
In a method arranged to simulate failure of a plurality of spans, and being arranged to add the sequence to spare links to the network there is preferably included, before adding the sequence of spare links to the network, the step of checking that each of the sequence of s
REFERENCES:
patent: 5079760 (1992-01-01), Nemirowski et al.
patent: 5495471 (1996-02-01), Chow et al.
patent: 5581543 (1996-12-01), Natarajan
"Near Optimal Spare Capacity Planning in a Mesh Restorable Network", Grover et al., Dec. 1991, pp. 2007-2010.
British Telecommunications public limited company
Ton Dang
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