Approximating the Traffic Grooming Problem

The problem of grooming is central in studies of optical networks. In graph-theoretic terms, this can be viewed as assigning colors to the lightpaths so that at most

g

of them (

g

being the

grooming factor

) can share one edge. The cost of a coloring is the number of optical switches (ADMs); each lightpath uses two ADM’s, one at each endpoint, and in case

g

lightpaths of the same wavelength enter through the same edge to one node, they can all use the same ADM (thus saving

g

– 1 ADMs). The goal is to minimize the total number of ADMs. This problem was shown to be NP-complete for

g

= 1 and for a general

g

. Exact solutions are known for some specific cases, and approximation algorithms for certain topologies exist for

g

= 1. We present an approximation algorithm for this problem. For every value of

g

the running time of the algorithm is polynomial in the input size, and its approximation ratio for a wide variety of network topologies – including the ring topology – is shown to be 2 ln

g

+

o

(ln

g

). This is the first approximation algorithm for the grooming problem with a general grooming factor

g

.