Summary

VSI is an open interface between a controller and a controlled switch. It's a robust SCI implementation that has proven to be solid and versatile in deployments worldwide.

This chapter has delved into the Cisco Systems SCI implementation called the Virtual Switch Interface (VSI) and analyzed VSI master and slave functions and their relationship.

The VSI master module residing in the protocol controller discovers, controls, monitors, and resynchronizes the controlled switch. Taking instructions from the VSI master, the VSI slaves in the controlled switch translate those instructions into platform-specific directives that tell the switch to set up, manage, and teardown connections and manage queues. Because multiple VSI masters can control a single switch, we also discussed resource allocation. A switch's resources are partitioned using hard or soft allocation. Hard allocation forces each partition's resource allotment to a fixed range or value and does not allow sharing. Conversely, soft allocation provides a shared pool of resources for use by all partitions, but it still guarantees resources for every partition. We also examined dynamic partitioning, which is a platform-dependent way to allow service modules within the switch to expand and contract a partition's resource allocation on-the-fly and with minimum service impact.

The next chapter deals with the different implementations of multiservice switches and VSI in the Cisco Systems equipment.