Avaya Definity TN570D Expansion Interface (Refurbished)Avaya Definity TN570D Expansion Interface. More Information Provides interface between the TDM bus and packet bus, and fiber optic links interconnecting cabinets Used in a Port Network (PN) between a PN and another PN in a direct connect system, and between a PN and an SNI in a switch node carrier in a CSS connected system Provides control channel applications and time slot interchanging between the PPN and EPNs Used when ISDN BRI and or ASAI is