Photonic Network Communications, 3:3, 197±211, 2001
# 2001 Kluwer Academic Publishers.Manufactured in The Netherlands.
Minimizing Wavelength Conversions in WDM Path Establishment*
Rami Melhem, Shu Li, Taieb Znati
Computer Science Department, University of Pittsburgh, Pittsburgh, PA 15260
Received August 3, 2000; Revised December 26, 2000
Abstract. This paper studies algorithms for connection establishment in wavelength division multiplexing networks.Although wavelength
conversion capabilities are assumed at each node in the network, the goal of this research is to minimize or impose an upper bound on the
number of wavelength conversions on the established path.Two types of schemes are investigated and compared.In the ®rst scheme, the
wavelengths are selected adaptively during path establishment on a given route, and in the second scheme, both the route and the wavelength
assignment are selected optimally based on global information about path costs and wavelength availability in the network.We present two
ef®cient algorithms for globally selecting routes and wavelengths, one ®nds the least cost route for a maximum number of wavelength
conversions, and the other selects from among the shortest routes, the one with a minimum number of wavelength conversions.The results of
comparing the two path establishment schemes show that, for dynamically changing traf®c, the adaptive selection of wavelengths on a ®xed
route during path establishment is more bene®cial than the optimal selection of the route and wavelengths prior to path establishment.
Keywords: wavelength division multiplexing, path setup, connections establishment, wavelength conversion, all-optical networks, bounded
Connection establishment in BISDN networks is
accomplished by ®rst selecting a path in the network,
and then reserving the resources along this path.
However, when the rate at which connections are
established and released is high, the resource
availability may change rapidly, and the likelihood
of establishing a connection along the selected path
decreases.This dif®culty can be avoided by
combining route selection and resource reservation
.In this paper, we deal with wavelength division
multiplexed (WDM) networks, where wavelengths
are the primary resources in the networks.
Although different types of photonic switching
networks have been reported and demonstrated,
wavelength division multiplexing of optical networks
has emerged as one of the most attractive approaches
to data transfer in interconnection networks [2±4].
Speci®cally, an all-optical path between two access
nodes can exploit the large bandwidth of optics,
without the overhead of buffering and processing at
intermediate nodes.However, it has been shown that
the ability of converting between wavelengths along
the same path increases the probability of successfully
establishing a connection [5±8].
Current technology does not allow wavelength
conversions to be performed ef®ciently and cost
effectively in the optical domain.Hence, in the near
future, the switching ®bers of many optical networks
will not be capable of performing wavelength
conversions.In such networks, semi-optical paths
may still be established if intermediate nodes are used
as relays to receive a message on one wavelength and
retransmit it on another.In Fig.1, we show an
intermediate node in a network with two wavelengths.
In this simple example, the node is connected to its
neighbors by two input links and two output links.The
optical input and output signals to the local node are
either multiplexed (Fig.1a) or demultiplexed (Fig.
1b).In either case, a message that is relayed at this
node because of a need for wavelength conversion
will suffer a relatively large delay because of
buffering, processing, and optics/electronic conver-
Thus, wavelength conversion in networks with all-
*This work was supported in part by NSF award MIP 96-33729 to the University of Pittsburgh.