Answer: Switching packets function.
Explanation: while the main function of a router is to forward packets to their target destination, this can be actualised by adopting a switching packet function.
Switching packet function is the process which the router uses to accept a packet from one interface and passes it to another interface. The main function the switching packet plays is to encapsulate the packets in the right data link frame type for the data link meant to be sent out.
The switching is about moving the packet to the right destination without been mistaken with the layer 2 switch function.