Photonic Network Communications, 3:4, 335±348, 2001
# 2001 Kluwer Academic Publishers. Manufactured in The Netherlands.
Design and Performance Evaluation of Traf®c Grooming Algorithms in
WDM Multi-Ring Networks
Department of Computer Engineering, Chonbuk National University, 561-756, Korea
Research Institute of Industrial Technology, Chonbuk National University, 561-756, Korea
Received April 20, 2001; Revised June 25, 2001
Abstract. In this paper, we propose novel traf®c grooming algorithms to reduce the cost of the entire system in WDM multi-ring networks. In
order to achieve this goal, it is important to construct a virtual topology and groom the traf®c in these networks. We consider four kinds of virtual
topologies of WDM multi-ring networks according to the way in which traf®c is transmitted among rings. Accordingly, we design four kinds of
traf®c grooming (TG) algorithms depending on the considered virtual topologies: mixed (MTG), partially mixed (PMTG), separate (STG), and
independent (ITG) traf®c grooming algorithms. Each algorithm consists of a separation, a connection-ring construction, and a grooming
procedure. In the separation procedure, all traf®c connections are classi®ed into intra and inter-connections. The connection-ring construction
procedure makes full connection-rings from traf®c connections. The grooming procedure groups connection-rings onto a wavelength in order to
reduce the number of SONET add/drop multiplexers (SADMs) and wavelengths and to improve the utilization of network resources.
To analyze the performance of each algorithm, a circular multi-ring architecture with uniform traf®c is considered. The simulation results
show that ITG and PMTG are more ef®cient in terms of wavelengths. STG and PMTG require a smaller number of SADMs.
Keywords: traf®c grooming, virtual topology, SADM, WADM, ring network
The synchronous optical network (SONET) self-
healing ring is a very popular physical layer network
because of its large capacity and high reliability.
Typically, each SONET ring is comprised of ®bers to
connect SONET add/drop multiplexers (SADMs) and
uses a single wavelength. But with the growing
demands of communication capacity and the emer-
gency of WDM technology, WDM ring networks are
being deployed to support multiple level SONET
rings over a single physical ®ber optical ring [1,2].
One of the most fundamental network design
problems for WDM ring networks is to reduce the
overall network cost, which includes the cost of
electrical components (e.g., SADMs) as well as the
cost of optical components (e.g., wavelengths).
Especially, now that WDM technology is being used
and the price of optical components are getting lower,
electrical components become a more important cost
Traf®c grooming and wavelength ADMs
(WADMs) are major solutions of the cost reduction
problem in WDM ring networks. Since a WADM can
selectively drop and add any number of wavelengths
at a node, it is no longer necessary to have a SADM
for every wavelength at every node, but rather only
for those wavelengths that are used at that node. In
order to reduce the number of SADMs, traf®c
connections at each node are grouped onto some of
the wavelengths. Low-speed traf®c connections are
groomed onto a separate wavelength channel of a
WDM ring. For example, four OC-3 traf®c connec-
tions can be groomed together into an OC-12 traf®c
connection (in this case, the grooming factor g
Recently, many approaches of traf®c grooming in
WDM rings are well studied. The most of the previous
* Corresponding author.