A network comprising a first optical line terminal (OLT), and a second OLT in communication with the first OLT, at least one first-type optical network unit (ONU), and at least one second-type ONU. Included is an OLT configured to implement a method comprising forwarding a first downstream data from a first-type OLT to at least one first-type ONU, and transmitting a second downstream data to at least one second-type ONU. Also included is a method comprising adding at least one second-type ONU to a passive optical network (PON) comprising a first-type OLT and at least one first-type ONU without removing the first-type OLT from the PON.