There are two types of Traffic in RLC AM mode. Either it can be control PDU or Data PDU.
For control pdu it has no need to go for Segmentation or Concatenation. Just add the header and send it out.
In similar way receiving side of AM-RLC-PDU receives two types of traffic.
The routing box purpose is just to check the header and verify that either it is control PDU or Traffic PDU. If it is control PDU then it will route the PDU to RLC control entity and if it is Data PDU then it will go for the Reception buffer & HARQ reordering.