DSSHDR syntax
DSSHDR is the 6-byte header that contains information about the data stream structure (DSS) of terms defined by the distributed data management (DDM) architecture.
DSSHDR has the following format:
- LL
- A 2-byte specification of the length of the whole command, reply, or object, including the 6-byte DSS HEADER. The minimum possible value is 6, and the maximum is 32,767.
- DDMID
- A 1-byte Systems Network Architecture (SNA) registered General Data Stream (GDS) identifier. The DDMID field is always D0 for a DDM command.
- FORMAT ID
- A 1-byte indicator of whether the DSS is chained to the next
DSS and what to do when errors occur. The byte contains the following
bits, from 0 to 7, left to right:
- Bit 0
- Unused.
- Bit 1
- A flag. 1 indicates that the DSS structure is chained to the next structure. 0 indicates no chaining.
- Bit 2
- A flag. 1 indicates to continue when errors occur, and 0, otherwise.
- Bit 3
- A flag. 1 indicates that the next DSS has the same request correlator, and 0, otherwise. If bit 1 is 0, bit 3 is also 0.
- Bits 4 through 7
- Indicate the DSS type:
- 1: a Request DSS.
- 2: a Reply DSS.
- 3: an Object DSS.
- 4: an Encrypted Object DSS.
- RQSDRR
- A generated 2-byte field that associates a request with its request data, the replies to the request, and the data that is returned for the request.