This read-only DisplayString, up to 255 characters, holds the subaddress this connection originates from, returning a zero-length value when the subaddress is undefined for the media in use or simply unused. An admin checks this on media types, such as certain ISDN configurations, that support subaddressing to further route a call beyond the main number. For example, an admin troubleshooting a multi-device ISDN line that uses subaddresses to route calls to specific equipment would inspect this field to confirm the correct subaddress was used for a given connection.