ulpszProtocol (ULONG)
This field, like all offsets in these BIDI command structures, is relative to the beginning of the buffer; 0 (zero) indicates no string.
This field overrides any default protocol converter selection. For example, a printer may support PJL, but it can be best serviced by a protocol converter other than the PJL converter shipped with OS/2. The value pointed to by this field must match the name of an installed protocol converter in order for the port driver to be able to use a protocol converter. For example, for NPAP, the value would be 'NPAP;' for PJL, the value would be 'PJL.'