The output confirms that the switch is running Per-VLAN Spanning Tree Plus (PVST+), which is indicated by the presence of a unique Spanning Tree instance for VLAN 20. PVST+ is a Cisco enhancement of the original IEEE 802.1D Spanning Tree Protocol (STP) that provides for separate 802.1D spanning trees for each VLAN configured in the network; this allows for better load balancing. References: Implementing and Operating Cisco Service Provider Network Core Technologies (SPCOR) v1.1