31-05-2013, 04:04 PM
Optimized Burst LSP Design for Absolute QoS Guarantees in GMPLS-Controlled OBS Networks
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Abstract
Over the past decade, the scientific community
has thrown itself into assessing optical burst switching (OBS)
as the switching technology for next-generation all-optical
networks. In this regard, a significant amount of work has
concentrated on providing OBS with the required carrier-class
features. During this process, however, little attention has
been paid to fundamental questions on the interoperability
and interworking issues that OBS will have to face in a heterogeneous
network scenario such as the future Internet. This
article introduces a generalized multi-protocol label switching
(GMPLS)-based control plane architecture for future OBS
networks. This GMPLS/OBS control plane solution leverages
on the GMPLS interoperability to enable seamless vertical
and horizontal OBS integration with different switching layers
under a common control plane. The burst label switched path
(b-LSP) entity has been introduced to accomplish this purpose,
as well as to guarantee end-users’ quality of service (QoS) requirements
to effectively support emerging data applications.
INTRODUCTION
The evolution toward the future Internet has moved
research efforts into the realization of multi-service
optical networks performing wavelength and sub-wavelength
switching, so as to seamlessly and efficiently support large
amounts of data from different applications presenting diverse
characteristics [1].
MOTIVATIONS TOWARD A GMPLS-CONTROLLED
OBS NETWORK
It is widely recognized that future metropolitan area
networks (MANs) will rely on any type of sub-wavelength
switching technology [17,18] in order to provide better access to
network resources (increasing available capacity), as well as to
increase flexibility to support the dynamics of end-users’ data
traffic. A strong candidate to this end is OBS technology, which
is itself a good trade-off between complexity (i.e., cost) and
performance. In this way, MAN networks around the world will
be interconnected over regional and core networks that, most
likely, will implement coarser dynamic wavelength switching
technologies, which are very efficient when serving smooth
permanent or semi-permanent aggregated traffic demands.
GMPLS/OBS NETWORK ARCHITECTURE
In the proposed GMPLS/OBS network architecture, the
extended GMPLS control plane lies on top of the actual OBS
control plane (see Fig. 1). This results in an interoperable
control plane composed of two control layers, namely, GMPLS
and OBS. However, the transparent and bufferless all-optical
OBS data plane will be controlled in a unique manner by this
GMPLS/OBS control plane.
The GMPLS may be deployed out-of-band, in/out-of-fiber,
and supported by any technology and topology. On the contrary,
in OBS networks, bursts and their related burst control
packets (BCPs) must keep a strict time relationship in order to
make one-way reservation feasible. Hence, it is mandatory that
OBS control and transport planes share the same resources
and topology. This is the reason why an in-fiber out-of-band
control plane configuration (i.e., signaling channels) has been
considered at the OBS layer—either manually or automatically
configured.
GMPLS/OBS CONTROL MODEL
Enabling Absolute QoS
Absolute QoS differentiation is committed to delivering
quantitative QoS levels for high-priority (HP) traffic classes,
even in highly loaded network scenarios. Compared to relative
QoS differentiation such as offset time-based differentiation
(OTD) [25] or preemption [26], absolute QoS guarantees are
more attractive for upper layer applications, as transport
services can be tailored to the specific performance requirements.
As shown in [27], the end-to-end burst loss probability
(BLP) can be effectively controlled by tightly dimensioning the
number of wavelengths that support the HP traffic. In this
article, we extend this idea taking advantage of the proposed
GMPLS/OBS network architecture.
GMPLS Signaling Extensions
The GMPLS framework needs to be extended to support
the particularity of the OBS network. First, the GMPLS LSP
hierarchy must be extended to incorporate a burst switching
region. For instance, the GENERALIZED_LABEL_REQUEST
object of the GMPLS signaling PATH message requires a
proper definition of the switching type and the LSP encoding
type fields. Second, the GMPLS RSVP-TE signaling protocol
requires additional features to manage the b-LSPs. Finally, the
computation of the b-LSPs requires knowledge of the global
network status and therefore extensions to the OSPF-TE
GMPLS routing protocol are also required to appropriately
disseminate OBS transport layer resource usage.
MILP DIMENSIONING OF b-LSPS
In order to guarantee a certain level of QoS in terms of
burst losses, wavelength resources have to be dimensioned
properly. In this section, we address the problem of the VT
design that concerns the establishment of explicit b-LSPs (also
referred to as paths in this section) and the allocation of
wavelengths in network links to support connections with QoS
guarantees. More specifically, we are looking for a network
routing that for a given set of (long-term) traffic demands and
end-to-end requirements on the burst loss rate minimizes the
overall number of allocated wavelengths (i.e., the wavelength
usage) in the network. To treat the problem of absolute
QoS guarantees analytically, we employ the non-reduced load
approximation [31] of a common OBS network loss model [32].
The modeling assumptions are then represented as a set of
constraints in an MILP formulation.
CONCLUSIONS
This article introduces a GMPLS-controlled OBS network
architecture that leverages on the GMPLS interoperability
to enable seamless vertical and horizontal OBS integration
with different switching layers under a common control plane.
The burst label switched path (i.e., b-LSP) entity is here
introduced as a means to provide QoS-aware burst transport
services for HP-class traffic, besides its main purpose of
providing end-to-end connectivity among different domains.
As a way to optimize the network resource usage, an MILP
formulation is presented to compute an optimal VT of the
b-LSPs over the OBS data plane, defining their routes and
capacities. In this study, a static scenario with a single QoS
level has been considered as the first attempt to validate
the b-LSP dimensioning model. Extensive simulation results
highlight the effectiveness of the proposed method, which
allows absolute BLP figures to be guaranteed, even in highly
loaded situations, compared to state-of-the-art QoS techniques.
Furthermore, the proposed dynamic GMPLS-driven b-LSP
reconfiguration mechanism yields a successful adaptation to
unexpected traffic surges, keeping the BLP of the HP traffic
below the requested maximum values.