MPLS In Optical Networks
Optical MPLS And GMPLS
One of the fastest growing applications of MPLS is optical
provisioning. This has been enabled by the development of three key areas of function.
- Generalized MPLS (GMPLS),
the Generalized Signaling extensions to MPLS. These have extended the MPLS concept of a label
to include implicit values defined by the medium that is being provisioned, for example
a wavelength for a DWDM system or a timeslot for a SONET device.
- The User to
Network Interface (OIF UNI) as defined by the
Optical Internetworking Forum. This has been developed as extensions to MPLS and LMP to allow a user of
an optical network, for example an attached router, to provision a lightpath through the
core.
- The Network to Network Interface
(OIF NNI) as defined by the Optical Internetworking Forum. This
allows lightpaths to traverse multiple administrative domains with dissimilar internal
architectures. It achieves this by defining routing and signaling interfaces to be used between
domains.
In addition to the above, the ASON work in
ITU SG 14/15 is building
an overall optical control plane architecture. At the very least, this will provide additional
requirements for IETF and OIF specifications, and may generate additional protocols.
Metaswitch is heavily involved in the development
of the standards in this area and has developed a scalable, high performance,
highly available implementation of these technologies. Metaswitch's MPLS solution,
DC-MPLS, fully supports the GMPLS and OIF UNI optical extensions, and in combination with
DC-LMP, DC-OSPF, and
DC-ISIS, provides a complete optical control plane solution that can be used in a
wide variety of devices. This includes both devices that use an overlay model between Optical and Electrical domains,
and those that use a peer model, with GMPLS throughout the network.
As a result of our leading role in these technologies,
Metaswitch works with many of the leading manufacturers of optical networking equipment, including
Calient Networks, CIENA,
Fujitsu, Infinera, and many others. For a full list of those
customers we can publicize, please see our customer list.
In this model, GMPLS is used from the ingress router all the
way through the optical core and to the egress router. It might even be that GMPLS is used in the packet
networks connected to the routers. DC-MPLS can provide this GMPLS support.
In addition, LMP may well be required between the
cross-connects. DC-LMP can provide this function.
In this model, the core and edge networks are distinct
administrative domains and may use differing protocols, for example GMPLS in the core and IP or packet MPLS
at the edge. The connection between these networks occurs at the client and network facing devices (UNI-C
and UNI-N respectively). A UNI-C can use the OIF UNI protocol to request lightpaths through the core,
which terminate at a remote UNI-C. OIF UNI incorporates protocols from both GMPLS and LMP.
The overlay model means that there need not be a one-to-one
mapping between connections requested by the edge network and those in the optical core. Instead, several
lower bandwidth requests can be tunneled through a single larger bandwidth pipe in the core. See
our white paper on Optical MPLS for more details.
DC-MPLS and DC-LMP can be used to build full function UNI-C
and UNI-N devices, as well as in devices providing the core or edge networks, if required. Note that it is
also possible to implement the overlay model using GMPLS throughout.
The OIF NNI defines a standardized interface between dissimilar optical
networks. Each network uses its own internal protocols, which can be standard ones (such as GMPLS with either
OSPF or IS-IS) or proprietary ones. These protocols are mapped to the OIF NNI at network boundaries, and the
specifications provide flexibility in how those mappings are achieved. The OIF NNI can be used in conjunction with the
OIF UNI to provide full end-to-end provisioning across multiple network providers.
The OIF NNI makes use of two distinct protocol elements for routing and
signaling.
- Multi-area traffic engineered routing is used at the highest
level to calculate the optimum sequence of networks to traverse. The OIF NNI specifies a Domain to Domains
Routing Protocol (DDRP) for this purpose. A separate IGP, such as OSPF, is used to route within each
domain.
- Extensions to RSVP/GMPLS are used to signal the lightpaths
between domains.
Work is in progress to finalize and ratify the OIF NNI standard.
Metaswitch's portable protocol products, coupled with DCL's
integrated optical control plane can be used to build new devices that implement the full OIF NNI or can be used to
implement enhanced controllers that add OIF NNI functionality to existing proprietary optical switching systems.
Metaswitch successfully demonstrated
this solution in the first public OIF NNI event, held at
OFC in March 2003, in its own right and through several of its
customers who manufacture optical switching devices.
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For more information about Metaswitch's
MPLS products and expertise contact
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