Photonic Network Communications (2006) 11:163–172
On burst length distribution and preemption probabilities
in OBS networks with burst segmentation
Eduardo Magaña · Javier Aracil
Received: 12 November 2004 / Revised: 3 August 2005 / Accepted 4 August 2005
© Springer Science + Business Media, Inc. 2006
Abstract Recently, preemption techniques have attracted
considerable attention as a means to provide differentiated
quality of service in optical burst switching (OBS) networks.
This paper is focused on the analysis of preemption prob-
abilities for bursts within the same priority class. As pro-
posed by Vokkarane and Jue ((2003)* IEEE J Select Areas
Commun 21(7): 1198–1209) an incoming burst will preempt
the burst in service, within the same priority class, if the
residual length of the burst in service is smaller than the
incoming burst length. For a general case with wavelength
conversion, the preemption probability of contending bursts
with a generic service distribution, not necessarily exponen-
tial, is analyzed. First, we show that the size distribution for
the preempting bursts is shifted to larger values, in compari-
son to the original burst size distribution. Second, we obtain
an upper and lower bound for the preemption probability.
Finally, the asymptotic behavior of the OBS switch is ana-
lyzed showing that preemption will always occur for a very
large number of wavelengths.
Keywords Burst segmentation · Optical burst switching ·
E. Magaña (
Dept. de Automática y Computación,
Universidad Pública de Navarra,
Dept. de Ingeniería Informática,
Universidad Autónoma de Madrid,
The foreseeable evolution of optical networks leads to transfer
modes that provide intermediate granularity between cir-
cuit and packet switching. Precisely, optical burst switching
(OBS)  is based on encapsulation of several packets in
an optical burst, which is preceded by a burst control packet
(BCP). The time offset between the BCP and optical burst al-
lows the optical switches along the path to arrange the switch-
ing matrix in order to accommodate the incoming burst. Thus,
on the one hand, resources are reserved in advance, in con-
trast to pure packet switching, and, on the other hand, the
“on-the-ﬂy” reservation scheme is unconﬁrmed, in contrast
to pure circuit switching. As a result, chances are that bursts
can be dropped due to blocking. However, if free wavelengths
along the route from source to destination are available, then
the burst is swiftly transferred without leaving the optical
OBS can be easily extended to provide differentiated QoS.
Two different schemes for burst prioritization have been pro-
posed: offset-based schemes and preemption-based schemes.
The former are based on the principle of granting larger off-
set times (between burst and BCP) to high-priority bursts.
By doing so, high-priority bursts are given more chances to
reserve wavelengths, in comparison to low-priority bursts.
In preemption-based schemes, a burst with high prior-
ity takes the wavelength from a low-priority burst that is
being transmitted. This paper is exclusively concerned with
such preemption-based schemes. Usually, preemption comes
together with burst segmentation. Instead of dropping the
entire burst in service when preemption occurs, burst seg-
mentation allows to drop part of a burst, so that the remain-
ing packets may continue transmission in subsequent hops.
Hence, the burst that losses the contention is segmented and
only the burst tail is dropped. Namely, only the burst residual