The H.248 PCM Frame Spare Bit package provides support for spare bits Si and Sa4-Sa8, which are defined for the ITU-T Rec. G.704 2048 kbit/s basic frame structure. The PCM Frame Spare Bit
package may be applied for PCM30 and PCM31 systems.
ITU-T H.248.33-2005 history
2005ITU-T H.248.33-2005 Gateway control protocol: PCM frame spare bit package