CVSA

The CVSA, built on the Multiservice Switching Forum (MSF) framework, enables true multiservice switching capabilities in an open and standard way and lets the telecom industry grow in a modular and horizontal fashion. The MSF plays a key role in enabling these changes, gathering different vendors and service providers to standardize the multiservice switching framework.

In this architecture, the adaptation plane transforms services into a format that the forwarding plane can cross-connect. The control plane manages this forwarding plane, and the two planes work in tandem to create a virtual switch. Different control-plane implementations include MPLS, PNNI, and voice (through the Media Gateway Control Protocol [MGCP].) The control plane can in turn be directed by an application plane such as SS7 intelligent networks or RFC 2547 MPLS VPNs. (Future control planes, either vendor-developed or service provider-developed, will be integrated into an existing infrastructure.)

There also can be different forwarding planes, such as cell-based, frame-based, and lambda-based optical cross-connects (OXC). The key in allowing true multiservice functionality resides in the partitioning function.

The MSF architecture not only defines the partitioning and sharing of resources in a switch controlled in a standard way, but it also defines a set of open interfaces among the planes to enable interworking and interoperability. In general terms, CVSA enables the use of any and every control plane over any and every forwarding plane.

Another important consequence of the architecture decomposition is that the core transport can evolve independently of the edge services.

Cisco's architecture also enhances the network's high-availability features by separating the control plane and the forwarding plane.

Virtual Switch Interface

The Virtual Switch Interface (VSI) discussed in Chapter 2, "SCI: Virtual Switch Interface," allows all of the following:

• Multiple simultaneous controllers The controllers do not need to reside on a common platform, and they can have different locations. Each controller can be upgraded separately.

• Control plane independence Each control plane manages resources independently, and each service receives the QoS required.

• Dynamic partitioning The resources allocated to each controller can be changed dynamically. This allows planning for future events, such as adding a service to the network or modifying its resources according to the number of users. It also enables incremental provisioning.

• Quality of Service (QoS) Each partition receives a guaranteed number of resources, but it also can use a shared pool to achieve maximum use. Separate queues are assigned to different services. Each service receives native QoS support.

To provide pure separation between the control and forwarding planes, the interface between them needs to be purely messaging-based. To ensure no adverse interaction between the control and forwarding planes, no databases should be shared between them. This is one of VSI's strengths. In cases where the control and forwarding planes reside on the same card, VSI provides a clean, logical separation between the two planes.

VSI is a published and open interface that allows third parties to develop control planes to manage the switches. It also allows switches to be controlled by a Cisco-developed control plane.