The framing format used in D4 transmission consisting of 12 consecutive frames. The 12 framing bits mark frame boundaries and contain the alignment pattern.
any structure made of multiple frames; SONET recognizes superframes at the DS–1 level (D4 and extended superframe) and at the VT (500 µs STS superframes)
12 frames are bundled in a certain format and transmitted. Used in T1 mode. Up to Top