The increasing capacity of optical transport net-
works has caused considerable attention to be paid
to the issue of protecting networks from equip-
ment and link failures. As transport network
topologies evolve from rings to meshes, traditional
protection schemes become inadequate and new
mesh restoration techniques are necessary. Mesh
restoration has been an active research area in
recent times, and several good solutions have
appeared in the recent literature.
In this Special Issue on Mesh Restoration, we
have selected six papers covering various aspects
of this topic. Similar versions of these papers were
originally published in the Opticomm 2002 con-
ference, and those papers were invited for possible
publication in this special issue. The papers
underwent a separate review process before they
were accepted to the special issue.
The ﬁrst paper (by M. Clouqueur and W. D.
Grover) presents various formulations of the
capacity design problem considering dual failures.
It shows that while complete dual-failure restor-
ability requires signiﬁcantly large capacities, con-
siderable restorability may be achieved with a
small amount of extra capacity.
The second paper (by W. D. Grover and
M. Clouqueur) focuses on the support of mul-
tiple Quality of Protection (QoP) service classes
in span-restorable mesh networks. In particular,
four classes of protection are considered,
namely, fully restorable (gold), best-eﬀort
restorable (silver), non-protected (bronze), and
pre-emptible (economy). Using results from
solving integer programs, the paper ﬁnds that a
large fraction of demands can belong to the
gold or silver classes with no extra capacity at
all, i.e., by pre-empting demands belonging to
the economy class. The paper investigates sev-
eral factors that aﬀect the trade-oﬀ between
capacity and restorability.
The third paper (by J. Doucette and W. D.
Grover) considers the concept of shared risk on
individual channels or links, called SRLGs, and
addresses several aspects of how shared-risk span
groups aﬀect the protection capacity design. It
reports that if a given percentage of all possible
dual failure combinations incident to a common
node are allowed for in the design, then nearly the
same percentage of other dual span failure com-
binations (any two spans in the network) will be
also restorable. It is also shown that the design of a
network withstanding a small number of multi-
span co-incident SRLGs will yield a signiﬁcant
improvement in overall dual-failure restorability.
The fourth paper (by A. Nucci, N. Taft, P.
Thiran, H. Zang, and C. Diot) studies the problem
of mapping logical links in the IP layer onto
physical links in the WDM layer in an IP-over-
WDM network. Two classes of traﬃc, namely,
fully protected (FP) and best-eﬀort protected
(BEP) are considered. Given the physical and
logical topologies, and the amount of FP traﬃc
between IP routers, the paper aims to provide a
solution to map the logical links onto paths in a
WDM network such that the carried BEP traﬃc
load is maximized. BEP traﬃc fairness and
capacity bandwidth overprovisioning for FP traﬃc
are considered in the problem.
The next paper (by C. V. Saradhi and C. S. R.
Murthy) proposes an eﬃcient algorithm to select
routes and wavelengths to establish dependable
connections called segmented protection paths.
Photonic Network Communications, 9:1, 5–6, 2005
2005 Springer ScienceþBusiness Media, Inc. Manufactured in The Netherlands.