Eﬃcient Online Algorithms for Dynamic Shared Path Protection
in WDM Optical Networks**
Tianjian Li, Bin Wang*
Department of Computer Science and Engineering, Wright State University, Dayton, OH, USA45435
Received December 30, 2003; Revised July 22, 2004; Accepted July 23, 2004
Abstract. In this work, we have proposed and studied eﬃcient online algorithms for shared path protection under dynamic traﬃc
conditions in survivable WDM optical mesh networks. Given a connection request, routing and wavelength assignment of a working
path and a protection path for the request is formulated as two integer linear programs based on shared and dedicated path protection,
respectively. The objective is to minimize the total cost of additional resources used by the working path as well as the protection path
to accommodate a new connection request. We then devise two resource eﬃcient online algorithms using pre-computed candidate
routes. The ﬁrst algorithm uses one candidate working path and one candidate protection path for each newly arrived connection
request while the second algorithm may use multiple candidate working paths and/or multiple candidate protection paths. The
selection of a pair of paths from candidate routes as well as the assignment of appropriate wavelengths to accommodate a connection
request is then jointly considered to minimize the total cost of additional resources. The solutions to the ILP formulations serve as the
baseline for evaluating the performance of the proposed algorithms.We have evaluated the eﬀectiveness of the proposed online
algorithms via extensive simulations in terms of the connection blocking probability and the revenue earnings improved over the
dedicated path protection approach. Our simulations indicate that our proposed computationally eﬃcient online algorithms are able to
provide 100% restorability against single failures with a resource eﬃciency comparable to that of the optimal shared path protection.
The results also show that a small increase in the number of candidate working paths or protection paths (from 1 to 3) provides better
performance, but a further increase does not improve the performance signiﬁcantly. Therefore, a proper balance can be struck to
achieve both satisfactory performance and eﬃcient computation.
Keywords: WDM optical mesh networks, dynamic traﬃc, route pre-computation, shared path protection, integer linear programming
The popularity of the Internet has resulted in an
exponential growth in bandwidth demands.
Wavelength division multiplexing (WDM) divides
the enormous bandwidth of an optical ﬁber into
many non-overlapping wavelength channels.
WDM optical networks are able to meet the rapid
growth of bandwidth demands and are considered
to be the most appropriate choice for future
Internet backbone. Since a ﬁber is capable of
carrying multiple wavelengths simultaneously,
each of which may operate at the rate of 10
Gigabit per second or higher, a failure in a net-
work such as a cable cut may result in a tremen-
dous loss of data. Therefore survivability is a very
important issue in WDM optical networks and has
attracted much recent research [1–7].
Various approaches to provisioning survivabil-
ity exist for both non-WDM and WDM optical
networks . These approaches can generally be
divided into protection (a.k.a. pre-designed ap-
proaches, proactive approaches) and restoration
(a.k.a. reactive approaches) . Speciﬁcally, pro-
tection refers to techniques that use preassigned
capacity to ensure survivability while techniques
**The work reported in this paper was supported in part by AFRL, the U.S. Department of Energy Early Career Award DE-FG02-
03ER25580, and a DAGSI graduate scholarship. Any opinions, ﬁndings, and conclusions or recommendations expressed in this paper
are those of the authors and do not necessarily reﬂect the views of the funding agencies.
Photonic Network Communications, 9:2, 207–222, 2005
2005 Springer ScienceþBusiness Media, Inc. Manufactured in The Netherlands.