Improving optical switching with independent control planes

Currently, many next generation optical switches or cross connects support elements of an embedded proprietary control plane, a standard GMPLS control plane to peer with other vendor's network equipment, and/or OIF UNI/NNI interfaces to interconnect domains and network boundaries. As we move forward, tomorrow's transport network will support embedded and independent control planes. Embedded control plane software operates directly on the network element. These can either be vendor-proprietary that manage a specific network element or domain, or they could be standards-based that promise the possibility of peering between disparate vendor equipment. Signaling information is typically transferred in-band on the same facilities as the transferred data payload.

Independent software-based control planes reside and operate on a system outside the network element, and utilize out-of-band signaling to communicate with the network elements. Independent control planes can peer with network domains operating a GMPLS or OIF control plane as well as provide proxy control plane capability for the legacy equipment that lack control plane capability.

Typically, the suite of products supplied by optical switch or cross-connect vendors include the switch, an Element Management System (EMS) supporting a management domain, and an embedded control plane that operates on the switch or the EMS.

Within the domain of next generation equipment, the carrier experiences the benefits of an optical control plane. These domain-specific benefits include automated service provisioning and activation, quick restoration for mesh architectures, and instant call setup and tear-down based on user signaling from customer equipment.

These benefits are achieved within a network domain using a combination of OSPF-TE for routing, RSVP-TE for bandwidth reservation, and LMP for link management. In addition, OIF NNI can be used as a common external interface to peer two equipment domains operating different control plane algorithms. The eventual adoption of IETF GMPLS and OIF UNI/NNI standards will drive interoperability among network domains within a specific carrier, as well as between carriers.

Unfortunately, a core optical network operating an embedded control plane only provides those benefits within its domain. As a result, end-to-end circuit provisioning across networks takes several steps, may require manual circuit design, and may also involve the manual operation of several EMS to achieve the end result.

The challenge for carriers is to extend the benefits of the embedded optical control plane across all elements of their transport network, even when the legacy equipment may be a simple network element unaware of its placement in the surrounding network topology. The carrier's objective is to derive the full benefit of an optical control plane across the legacy and next generation domains of their entire network.

Unified control

Independent control plane software solutions can unify control over resources and services across multiple network domains (legacy and next generation) and multiple vendors. By providing a mediation layer that brings multiple signaling types into common management, these solutions give carriers the freedom to extend the benefits of GMPLS or OIF signaling across their entire network. Unlike traditional embedded control plane approaches, that are restricted to a specific vendor or technology implementation, independent control planes enable consistent, advanced, network-wide control plane functionality within a multi-vendor network without disrupting existing operations.

One function of an independent control plane is to peer with an adjacent OIF NNI network and/or GMPLS-enabled network elements. An independent control plane can peer with an OIF-compliant network, and extend the control plane functionality (and its operational benefits) over the network elements under its control.

By definition, an independent control plane runs independently of the network elements that it manages, typically as a software application with IP connectivity to the managed network. Because it must unify the control of dissimilar network elements, an independent control plane must provide both a universal model of network resources plus a unified signaling and control mechanism.

There are a handful of network topologies that are most conducive to supporting independent control planes. These network topologies can utilize independent control plane technology within a multi-vendor environment, as well as extend this GMPLS control plane over "unintelligent" legacy equipment. Source: Elematics, Inc.

Primary motivation for adopting independent and embedded control plane architectures includes fast provisioning and restoration. Independent control planes enable carriers to accommodate the provisioning of circuits initiated horizontally (i.e. a switched connection requested from customer equipment) or vertically (i.e. a permanent connection request from a northbound OSS or management application).

Prior to implementing a provisioning request, an independent control plane must be tightly integrated with the underlying physical assets of the transport network. This tight integration creates an equipment and service inventory that is fully synchronized for the entire multi-vendor network. Reconciling the network inventory data with the overlying OSS inventory databases provides a mechanism for recovering stranded network assets and capacity.

Once the network elements are inventoried, the independent control plane inventories the logical circuits utilizing the circuit identifiers. By extracting all the active circuit identifiers and cross-connects from the network elements, the independent control plane can trace circuits end-to-end across the network. At this point, the independent control plane has identified all active and inactive circuits. By integrating the independent control plane with both the network and the overlying OSSs, the carrier experiences complete visibility and maximized allocation of their network resources, for example, equipment slots, ports, services, cross-connects, and inter-office facilities.

Once the independent control plane has provided a harmonious and accurate view of the network assets, the independent control plane can successfully provision and activate circuits on the first attempt. Provisioning requests can originate from northbound OSS applications, peer OIF NNI or GMPLS-enabled network domains, or customer equipment supporting OIF UNI. A provisioning request from either source will result in an optimized circuit on the first attempt without the need for manual intervention through multiple EMS solutions.

Selecting a path

Utilizing the route computation capabilities of the control plane, path selection can be determined using a multitude of criteria (length, hops, latency, diversity), and the control plane ensures optimal routing of the circuit. Once a path has been determined, configuration commands are sent from the independent control plane to the appropriate network elements. The independent control plane utilizes TL-1, CORBA, or SNMP as the management channel to the network element.

Independent and embedded control plane architectures enable many common provisioning and restoration functions found in next generation networks. The common advantages of both architectures include:

• -Optimal routing and bandwidth utilization. Utilizing the IETF GMPLS specification as a guideline, OSPF-TE routing and RSVP-TE bandwidth reservation schemes optimize network resources. Sophisticated traffic engineering algorithms and solutions provide high utilization of network resources.

• - Instantaneous circuit provisioning. Optical control planes have tight and real-time access to the underlying network elements, as well as an accurate view of the underlying network state. Once the optimal path is computed, a circuit can be quickly provisioned as resource availability and connection management can be implemented in real-time.

• -Fast restoration. Circuit protection and restoration is typically implemented within less than one second for mesh architectures and 50 milliseconds for SONET architectures.

• -Horizontal UNI/NNI signaling with other equipment or networks. Ability to accept signaling from other networks or customer premise equipment. Utilizing the OIF UNI/NNI interface, multiple network domains can peer with each other and provide multi-domain connection establishment and tear-down.

• The incremental benefits of the independent control plane extend beyond typical provisioning and restoration functions. Many of the functions supported by independent control planes facilitate the unification of all equipment domains and integration of the overlying OSS applications. These functions include:

• - Multi-vendor interoperability. An independent control plane operates with legacy and next generation equipment, utilizing signaling or management protocols to provide end-to-end provisioning.

• -Peering legacy equipment with next generation equipment or domains. An independent control plane can peer a domain of legacy equipment with an OIF-compliant optical network, enabling end-to-end provisioning across both the legacy and next generation portions of the network.

• -Overlay control plane functions with legacy equipment. An independent control plane can operate over legacy (non-signaled) equipment, and utilize GMPLS routing and path selection techniques to improve provisioning, restoration, and protection functions.

An independent control plane enables service providers to significantly accelerate service velocity by automating and unifying the northbound OSS applications with underlying network elements. When carriers assess next generation optical equipment with control planes, they should look beyond the selection of embedded control planes. Increasingly, they assess solutions that apply all the efficiencies of an optical control plane to their entire network.

By addressing the interoperability requirements of both legacy and next generation equipment, carriers not only ensure the success of the control plane deployment, but also improve the operational and economic efficiencies of the entire network.