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.

Data Connection 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. Data Connection'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, Data Connection 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.

Optical Architectures

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. 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.

OIF UNI 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. 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.

OIF NNI - Connecting Networks Together

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.

Data Connection'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.

Data Connection 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.

For more information about Data Connection's MPLS products and expertise contact dcmpls@dataconnection.com.