This enumerated value selects the T1 framing format used within a byte-synchronous VT mapping — superframe (sf) or extended superframe (esf) — and is only applicable when sonetTributaryMappingType is byte-synchronous, otherwise it's notApplicable; the default is esf if byte-sync mapping is used. An admin cares because this framing format must match what the T1 tributary's originating equipment actually uses, and a mismatch here will cause bit errors or misaligned channel extraction even though the SONET-level signal looks fine. For example, an older T1 circuit still running superframe (sf) framing connected through a byte-sync VT mapping defaulted to esf will need this object explicitly changed to sf.