This read-write value identifies which SMDS Subscriber-Network Interface, SSI, interface this DXI/SNI port's traffic is being multiplexed onto, mapping the customer-facing DXI/SNI connection to its actual SMDS network-side interface. An admin sets this during provisioning to route a customer's SMDS traffic correctly onto the right internal trunk interface, and gets it wrong at the risk of misdirecting that customer's SMDS cells entirely. For example, lportSmdsSsiIf pointing to interface 3 means this DXI/SNI port's SMDS traffic is aggregated onto SSI interface 3 rather than some other SSI trunk on the shelf.