GMPLS Control Plane for SONET/SDH and WDM
SONET/SDH is very widely deployed in service provider networks. It was initially deployed
to carry circuit originated traffic (such as T1 and T3 TDM) over fiber, but it quickly evolved
mapping and concatenation capabilities to also carry ATM, Frame Relay, IP and Ethernet traffic.
It was also attractive to service providers in providing deterministic and
connection oriented behavior, with OAM capabilities, guaranteed QoS, and protection
and restoration.
Subsequently, Wavelength Division Multiplexing (WDM) and Dense Wavelength Division
Multiplexing (DWDM) have become extremely popular technologies with service providers,
as they enable network capacity expansion without laying more fiber.
By using WDM / DWDM, optical amplifiers, and Optical Add-drop Multiplexers (OADMs),
service providers can support several generations of optical technology
without having to overhaul their fiber backbone networks. And they can expand the capacity
of any given link by simply upgrading the multiplexers and demultiplexers at each end.
As a result, WDM / DWDM is now commonplace in service providers' core networks.
SONET/SDH and WDM / DWDM Model
There are multiple standards bodies involved in developing control plane specifications
for SONET/SDH and WDM/DWDM network architectures.
- The IETF has defined
Generalized Multi-Protocol Label Switching (GMPLS) in RFC3473,
which are generalized signaling extensions to MPLS. These extend the MPLS concept of a label
to include implicit values defined by the medium that is being provisioned, for example
a timeslot for a SONET device, or a wavelength for a WDM or DWDM device.
- The ITU-T has defined the requirements for an Asynchronous Switched Optical Network
(ASON). ASON's vision is for a complete network architecture with automated resource
and connection management within the network, driven by dynamic signaling between the user
and ASON network components.
- The Optical Internetworking Forum (OIF) has defined an instantiation of the control plane
dictated by ASON's requirements, by specifying a User to Network Interface (OIF UNI)
and an external Network to Network Interface (OIF E-NNI). As part of this, the OIF
has specified extensions to GMPLS.
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 extensions, and in combination with DC-LMP,
DC-OSPF and
DC-ISIS, provides
a complete control plane solution that can be used on a wide variety of SONET/SDH
and WDM/DWDM devices. This includes both devices that use an overlay model
between circuit and packet domains, and those that use a peer model with GMPLS
throughout the network.
In addition, DC-MPLS provides all the tools and features necessary to build
a full-function device that realizes the OIF UNI-C, UNI-N and E-NNI interfaces.
GMPLS Peer Model
In this model, GMPLS is used from the ingress router all the way through the optical core
and to the egress router. DC-MPLS can provide this end-to-end peer GMPLS support.
In addition, the Link Management Protocol (LMP) may be used between the cross-connects.
DC-LMP provides this function.
Overlay Model
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.
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.
OIF NNI - Connecting Networks Together
The OIF E-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 E-NNI
at network boundaries, and the specifications provide flexibility in how those mappings
are achieved. The OIF E-NNI can be used in conjunction with the OIF UNI to provide
full end-to-end provisioning across multiple network providers.
The OIF E-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 specifies OIF-ENNI-OSPF-01
for this purpose. OSPF is used to route within each domain.
- Extensions to RSVP/GMPLS are used to signal the lightpaths between domains.
The OIF has ratified the E-NNI signaling 2.0 specification, and work is in progress
to finalize the E-NNI routing 2.0 specification.
Metaswitch's integrated control plane can be used both to build new devices that implement
the OIF E-NNI or can be used to implement enhanced controllers that add OIF NNI functionality
to existing proprietary optical switching systems.
Metaswitch's MPLS and IP routing software, coupled with Metaswitch's integrated
optical control plane, supports all of the key GMPLS, IP Routing and LMP functions
to provide the industry’s widest range of standards-based solutions for SONET/SDH
and WDM / DWDM networks – and it is very widely deployed on SONET/SDH and WDM / DWDM devices
today.
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