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rations of the SDH/SONET and WDM layers for IP-
related services. The static nature of the current car-
rier network architecture left many carriers unpre-
pared for provisioning large amounts of fiber and
optical wavelengths to meet the needs of enterprise
IP networks, ISPs, VPNs, and other data-centric
services. Manual provisioning left the carriers with
a complex collage of multiplexers, OXCs, and fiber
patch panels. Customers want rapid provisioning
and flexible deployment of services, but the multi-
layer control structure of carrier networks built dur-
ing the last decade could not cope with the rapidly
growing and changing service demands. Carriers
need new methods for provisioning optical band-
widths and for automatically provisioning shared-
bandwidth across their networks. They need to sup-
port IP data traffic effectively, provide QoS guaran-
tees for customer service level agreements (SLAs),
and utilize core network bandwidth efficiently.
Much of the current carrier network architecture
lacks the ability to satisfy the needs of a growing
variety of IP applications. In order to bypass the
tradeoffs due to excessive layering in traffic control
the basic and necessary TE functions must move
directly to the OXCs and WDMs. At the end, this
results in a simpler, more cost-efficient network that
will transport a wide range of data streams and very
large volumes of traffic. Recently, an innovative TE
framework (Banerjee, A. et al., 2001) built on the
strengths of MPLS for fine grain traffic load balanc-
ing, and optical layer re-configuration has been pro-
posed. Moreover, there is an approach to the design
of control planes for optical cross-connects which
leverage existing control plane techniques developed
for MPLS TE. This approach combines recent ad-
vances in MPLS traffic engineering control plane
constructs with optical cross-connect technology to
provide a framework for real-time provisioning of
optical channels, foster development and deploy-
ment of a new class of optical cross-connects, and
allow the use of uniform semantics for network
management and operations control in networks
consisting of IP addressable and TE-capable optical
cross-connects.
4 INTEGRATING GMPLS
CONTROL PLANE IN OXCS
All of the above observations suggest, therefore, that
the GMPLS Traffic Engineering control plane would
be, with some minor extensions, very suitable as the
control plane for OXCs. This concept originated
from the observation that from the perspective of
control semantics, an OXC with an GMPLS Traffic
Engineering-enabled control plane would resemble a
Label Switching Router, subsuming and spanning
LSRs and OXCs functionalities in a single integrated
control plane, with some restriction due to the pecu-
liarity of the OXC data plane. In fact, the adaptation
of MPLS control plane ant TE concepts to OXCs,
which results in OXC-LSRs, needs to consider and
reflect the domain specific peculiarities of the OXC
data plane. From a data plane perspective, an LSR
switches packets according to the label that it car-
ries. An OXC uses a switching matrix to connect an
optical wavelength/signal from an input fiber to an
output fiber. From a control plane perspective, an
LSR bases its functionality on a table that maintains
relations between incoming label/port and outgoing
label/port. It must be pointed that in the case of the
OXC, the table that maintains the relations is not a
software entity but it is implemented in a more
straightforward way, e.g. by appropriately configur-
ing the micro-mirrors of an optical switching fabric.
There are several constraints in re-using the GMPLS
control plane. These constraints arise from the fact
that LSRs and OXCs use different data technologies.
More specifically, LSRs manipulate packets that
bear an explicit label and OXCs manipulate wave-
lengths that bear the label implicitly. That is, since
the analogue of a label in the OXC is a wavelength
or an optical channel there are no equivalent con-
cepts of label merging nor label push and pop opera-
tions in the optical domain. The transparency and
multi-protocol properties of the MPLS Control Plane
approach would allow an OXC to route optical
channel trails carrying various types of digital pay-
loads (including IP, ATM, SDH, etc) in a coherent
and uniform way. The distribution of topology state
information, establishment of optical channel trails,
all-optical network Traffic Engineering functions,
and protection and restoration capabilities would be
facilitated by the GMPLS control plane. An out-of-
band IP communications system can be used to carry
and distribute control traffic between the control
planes of different connected OXCs, perhaps
through dedicated supervisory channels, using dedi-
cated wavelengths or channels, or an independent
out-of-band IP network. An OXC that uses the
GMPLS control plane would effectively become an
IP addressable device. Thus, this proposition also
solves the problem of addressing for OXCs. In this
environment, SNMP, or some other network man-
agement technology, could be used for element
management. A reasonable architectural model for
an OXC equipped with an integrated GMPLS con-
trol plane (OXC-LSR) consists of two components:
the data forwarding plane and the GMPLS control
plane. A simple schema, consistent with IETF
GMPLS standard draft, is represented in Fig. 2 be-
low:
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