  Port-based teleportation (PBT) is a teleportation protocol that employs a
number of Bell pairs and a joint measurement to enact an approximate
input-output identity channel. Replacing the Bell pairs with a different
multi-qubit resource state changes the enacted channel and allows the PBT
protocol to simulate qubit channels beyond the identity. The channel resulting
from PBT using a general resource state is consequently of interest. In this
work, we fully characterise the Choi matrix of the qubit channel simulated by
the PBT protocol in terms of its resource state. We also characterise the PBT
protocol itself, by finding a description of the map from the resource state to
the Choi matrix of the channel that is simulated by using that resource state.
Finally, we exploit our expressions to show improved simulations of the
amplitude damping channel by means of PBT with a finite number of ports.
