Typically, networks operate on a best-effort delivery basis, which means that all traffic has equal priority and an equal chance of being delivered in a timely manner. When congestion occurs, all traffic has an equal chance of being dropped. L2 Switching Engine I WS-F6020 or L2 Switching Engine II WS-F6020A is intended for the Catalyst 6000 family. All network management functions occur on the active supervisor engine. If the active supervisor engine detects a major problem, it resets itself and the standby supervisor engine seamlessly becomes the active supervisor engine.