Implementing the Rapid Spanning Tree Protocol – RSTP
RSTP link types

Link type provides a categorization for each port participating in RSTP. The link type can predetermine the active role that the port plays as it stands by for immediate transition to a forwarding state, if certain parameters are met. These parameters are different for edge ports and non-edge ports. Non-edge ports are categorized into two link types. Link type is automatically determined but can be overwritten with an explicit port configuration.  – 

Edge ports, the equivalent of PortFast enabled ports, and Point-to-Point Links are candidates for rapid transition to a forwarding state. Before the link type parameter can be considered for the purpose of expedient port transition, RSTP must determine the port role.

Root ports do not use the link type parameter. Root ports are able to make a rapid transition to the forwarding state as soon as the port is in "sync."

Alternate and backup ports do not use the link type parameter in most cases.

Designated ports are those that make the most use of the link type parameter. Rapid transition to the forwarding state for the designated port occurs only if the link type parameter indicates a point-to-point link.