Following the BCB are two bytes, called function control sequence (FCS), used by each receiver to control inbound flow. There is one bit to hold (off) or enable (on) each of the eight inbound streams and one bit to hold/enable all inbound streams. The latter bit is referred to as the “wait-a-bit”. Table 1 defines the binary representation and the meaning of bits in the FCS.

The FCS bit assignments cause the BSC protocol restriction of a maximum of eight SYSIN and SYSOUT streams concurrently in each direction.

The compressed transmission records are placed in the buffer after the FCS bytes. Each transmission buffer contains transmission records that belong to the same NJE job. NJE protocols do not allow transmission records from different streams to be placed in the same transmission buffer.

The system receiving an FCS containing Wait-a-bit that is on, should delay responding. The delay can be in the range of one or two seconds if the Wait-a-bit was sent with a null record. A delay of greater than two seconds is not recommended because a timeout will occur if the response is not received within three seconds. If the data was sent with the wait-a-bit, the system should respond immediately. The immediate response allows the system requesting the delay to continue to transmit data as fast as possible. The approach of always delaying causes transmission delays whenever a system has no data to transmit, but cannot receive data.