In CCSDS constant bit rate voice may be transmitted using either the bit stream or the insert service. ATM can serve constant rate voice using AAL-1. In CCSDS the insert service is established by an ''insert zone'' in every virtual channel data unit that is transmiited on the physical channel. The insert service data units are placed in this insert zone. The CCSDS insert service data can use AAL-1. AAL-1 provides circuit emulation. CCSDS insert service data is buffered until enough data is received to fill a AAL-1 SAR-PDU payload.