What component of RSTP allows for quicker convergence by using a designated port?

PortFast is a feature of Rapid Spanning Tree Protocol (RSTP) that enables faster convergence by allowing specific ports on a switch to transition directly to the forwarding state, bypassing the listening and learning states. This rapid transition is particularly beneficial for access ports connected to end devices like computers, printers, and IP phones, where the goal is to minimize delays in communication.

In RSTP, designated ports are the ones that have the best path to the root bridge for a particular segment. When PortFast is applied to these ports, the device can quickly start forwarding frames as soon as it is connected, which is essential for maintaining network efficiency and reducing the likelihood of interruptions in service. Thus, by using PortFast with designated ports, network convergence is significantly faster compared to the standard Spanning Tree Protocol, which requires more time for port state changes.

Other features like BackboneFast and UplinkFast aim to improve the recovery time in their own ways but do not directly provide the same level of immediate port state transition that PortFast does. Bridge Protocol Data Units (BPDUs) are crucial for the operation of Spanning Tree Protocols, but they are not responsible for directly enabling quicker convergence via designated ports.