Photonic Network Communications, 7:3, 239±253, 2004
# 2004 Kluwer Academic Publishers. Manufactured in The Netherlands.
Con®guring Traf®c Grooming VPlNs
High-Speed Networks Laboratory, Department of Telecommunications and Media Informatics,
Budapest University of Technology and Economics, Budapest, Hungary
Received June 2002; Revised October 2002 and Accepted February 2003
Abstract. AVPlN is an optical virtual private network (oVPN) built of wavelength paths within a multihop wavelength routing (WR) dense
wavelength division multiplexing (DWDM) network.
An ef®cient and general graph-theoretic model (the wavelength-graph (WG)) has been proposed along with an integer linear programming
(ILP) formulation of setting up VPlNs with given traf®c requirements over a given WR-DWDM network with two protection scenarios. Here,
we have exploited the advantages of traf®c grooming, i.e., numerous traf®c streams of a VPN can share a wavelength path. We have also
generalized the model for setting up VPNs over a WR-DWDM system where multiple VPNs can share a single wavelength path.
The objective of the optimization is in all cases to reduce resource usage at upper (electrical) layers (i.e., to reduce the load of the virtual
routers), subject to constrained amount of capacity of each wavelength channel and limited number of wavelengths. Here, we propose and
compare three basic methods for con®guring oVPNs and investigate various parameter settings.
Keywords: VON, optical VON, traf®c grooming, optimization, ILP, wavelength graph, survivability, disjoint paths
The employment of virtual private networks (VPNs)
increases steadily. IEEE  reports three IP VPNs by
GlobalOne, Infonet and Worldcom UUnet. The last
two are based on the MPLS technology. The employ-
ment of VPNs grows in Enterprise networks
accordingly . They report on use of managed
VPNs by Research, Insight-Research and NovaStor
and add that the use of VPNs results in signi®cant
revenue. MPLS VPNs can be used jointly with BGP to
avoid limitations of addressing plans and to ensure
security . This paper also mentions provisioning
end-to-end VPN services across multiple service
providers and carriers. Management of QoS enabled
VPNs  gives an excellent overview of technologies
enabling VPNs, QoS support for VPNs ( particularly
DiffServ) and management alternatives.
A detailed overview of MPLS based VPNs can be
found in Guichard and Pepelnjak  and Davie and
VPNs share the link bandwidth and the node
resources among each other. The idea has several
advantages. We do not have to build own private
physical networks, but only to con®gure VPNs. This
reduces costs and speeds up provisioning. Further-
more, the VPNs can be dynamically recon®gured or
redimensioned in contrast to physical networks. This
allows sharing resources between various VPNs.
A VPN-Diffserv solution is proposed in Khalil and
Braun . Our model deals with static bandwidth
demands and analyzes the protection methods, while
in Garg and Saran  dynamic relations are in scope
with capacity resizing and stochastic fair sharing, but
without protection. The resource allocation in con-
junction with the routing design has been analyzed in
Mitra et al. [9±11] over multi-service networks with
QoS constraints. Various tools are used, for example,
asymptotic approximations to reduce the complexity
of the numerical calculations, multiplexing inside a
VPN and introducing priorities between the traf®c
classes. Network dimensioning is addressed in
Anerousis  and the methodology is presented
for determining the sizes of VPNs. An algorithm
of very low complexity is presented in Kumar et al.
, however, the traf®c streams are not handled
separately ( pipe model), but an aggregate traf®c
which has source or sink in one network node are
handled jointly (hose model). The protection is not
handled at all.