Quality of Service in an Optical Burst Switching Ring
Vishwas S Puttasubbappa*, Harry G Perros
Computer Science Department, North Carolina State University, Box 8206, Oﬃce 460 EGRC 1010 Main Campus Drive, Raleigh, NC,
Received March 15, 2004; Revised August 3, 2004; Accepted August 14, 2004
Abstract. Several access protocols are proposed to support diﬀerent service classes in an optical burst switched ring. Their performance
is evaluated through simulation. Various performance metrics such as throughput, utilization, burst loss rate, end-to-end delay and
fairness are used to analyze the behavior of each protocol.
Keywords: Optical burst switching, MAN, access protocols, service classes
Optical Burst Switching (OBS) is a novel method
currently under study that can be used to transport
data over a Wavelength Division Multiplexing
(WDM) optical network. Battestelli and Perros 
provide a detailed survey on OBS and its varia-
tions. There is not much work done in the ﬁeld of
OBS over metropolitan-area rings. Xu et al. 
investigated access protocols for OBS rings based
on the Just Enough Time (JET) scheme and a new
scheme called the Only Destination Delay (ODD).
Jong  proposed several access protocols for
multicasting in such an environment. A new
architecture called the LightRing has been pro-
posed by Fumagalli and Krishnamoorthy  with
multi-token protocol to prevent contention among
bursts. Each node can transmit on any of the
wavelengths as long as it has the token associated
with that particular wavelength. Several Burst
Assembly and Transmission (BAT) strategies
which deal with simultaneous assembly and
scheduling of bursts are proposed. Packets from
diﬀerent ﬂows can be assembled into the same
burst so as to achieve lower latency of real-time
packets. Bouabdallah et al.  proposed a collision
avoidance MAC protocol for a metropolitan bus-
based optical access network. Analytical models
were developed to calculate the mean access delay
of each node in such a shared-medium system.
Fairness issues were also investigated.
The work done so far on OBS rings considered
traﬃc to be best eﬀort except in Fumagalli and
Krishnamoorthy , where real-time and best-ef-
fort were considered. The aim of this paper is to
investigate how an OBS ring can support diﬀerent
classes of traﬃc. In this study, we extend the OBS
ring architecture proposed in Xu et al.  in order to
consider the following three diﬀerent classes of
traﬃc. The ﬁrst class of traﬃc (class 1) is a variable
bit rate traﬃc with stringent end-to-end delay
constraints, the second class (class 2) is variable bit
rate with no delay constraints, and the third class
(Class 3) is non-real time variable bit rate best eﬀort
traﬃc. Several access protocols are proposed and
their performance evaluated through simulation.
The paper is organized as follows: Section 2
presents the system architecture including the
structure of the metro ring and the OBS nodes.
The proposed protocols are presented in Section 3,
and in Section 9 we describe the simulation model
and the arrival processes. The results of the
This work was supported by ARDA under contracts MDA904-00-C-2133 and MDA904-02-C-0482.
Photonic Network Communications, 9:3, 357–371, 2005
2005 Springer ScienceþBusiness Media, Inc. Manufactured in The Netherlands.