A set of bits that indicate whether the S-Tags represented by the bit positions are being transported between the East and West spans of this ERPS interface. The bit positions in this string identify the S-Tag, so that the most significant bit is S-Tag 4095, the least significant bit is S-Tag 0 (unused), with the entire range in between. If the bit position is set, the S-Tag is being transported on this ERPS interface, and otherwise, it is not being transported.