Photon Netw Commun (2010) 19:1–8
Source-ordering for improved TCP performance over
load-balanced optical burst-switched (OBS) networks
Bharat Komatireddy · Neal Charbonneau ·
Vinod M. Vokkarane
Received: 29 May 2009 / Accepted: 23 July 2009 / Published online: 29 August 2009
© Springer Science+Business Media, LLC 2009
Abstract Recent advances in optical switching technology
allow for the creation of networks in which data bursts are
switched optically at each node, offering a greater degree of
ﬂexibility suitable for handling bursty Internet trafﬁc. TCP-
based applications account for a majority of data trafﬁc in the
Internet; thus understanding and improving the performance
of TCP implementations over OBS networks are critical.
Previously, several articles show that load-balanced routing
improves loss-performance in OBS. In this paper, we iden-
tify the ill-effects of load-balanced OBS on TCP perfor-
mance caused by false time-outs and false fast-retransmits.
We propose a source-ordering mechanism that significantly
improves TCP throughput over a load-balanced OBS net-
Keywords Load-balancing · TCP · OBS
Next-generation high-speed optical Internet will be required
to support a broad range of emerging applications which may
not only require significant bandwidth, but may also have
strict requirements with respect to end-to-end delays and reli-
ability of transmitted data.
In optical burst switching (OBS), data to be transmitted
are assembled into bursts and are switched through the net-
work all optically . Each burst has an associated control
Portions of this paper were published in IEEE/OSA OFC/NFOEC
2007 and IEEE BroadNets 2007.
B. Komatireddy · N. Charbonneau · V. M. Vokkarane (
Department of Computer and Information,
University of Massachusetts, Dartmouth, MA 02747, USA
packet called the burst header packet (BHP) and the BHP is
sent ahead of time in order to conﬁgure the switches along the
bursts’ route. In OBS networks, apart from the data channels,
each link has one or more control channels to transmit BHPs.
BHPs carry information about the burst such as source, desti-
nation, burst duration, and offset time. Offset time is the time
at which the burst and BHP are separated at the source and
the subsequent intermediate nodes. The offset time allows for
the BHP to be processed at each intermediate node before the
data burst arrives. As the BHP travels from source to destina-
tion, it is processed at each intermediate node in order to con-
ﬁgure the optical switches accordingly. Then the data burst
cuts through the optical layer avoiding any further delays.
Bandwidth is reserved only for the duration of the burst, this
reservation technique is called just-enough-time (JET) .
The primary issue in the OBS core network is conten-
tion resolution, since the core does not have any buffers.
Contention occurs when two or more bursts contend for
the same output port at the same time. There are several
contention resolution techniques, such as optical buffering
, wavelength conversion [4,5], and deﬂection routing .
These contention resolution techniques are reactive in
nature, that try to resolve the contention when it occurs.
These contention resolution techniques attempt to minimize
the loss based on the local information at the node. An alter-
native to contention resolution is to avoid contention before it
Load-balanced routing is an approach to implement con-
tention avoidance in OBS . Load-balanced routing
involves two stages, route calculation and route selection.
Both route calculation and route selection can be imple-
mented in a static or a dynamic manner. In this paper, we
adopt the a load-balanced routing technique with static route-
calculation and dynamic route-selection as proposed in .
At every τ seconds, all the ingress OBS node dynamically