This read-write value identifies which address-screening rule set, referenced later by the individual and group address screen maps like lportSmdsIaScrnMap and lportSmdsGaScrnMap, applies to this SMDS interface, effectively selecting a security policy for which SMDS addresses this port is allowed to send to or receive from. An admin assigns different screen IDs to different customer ports to enforce closed-user-group restrictions on the shared SMDS fabric. For example, two customer ports sharing the same SSI trunk but belonging to different closed user groups would be configured with different lportSmdsScrnId values so their allowed-address bitmaps do not overlap.