OSI/FTAM Programming Reference Manual

Conformance and Interoperability
HP NonStop OSI/FTAM Programming Reference Manual—528611-001
2-5
Presentation Encoding of FTAM PDUs and Data
For FTAM-3 files, remember that the native character sets (ASCII, EBCDIC, and so on)
might be incompatible on the sending and receiving systems. For example, NonStop
systems use the 7-bit ASCII character set, whereas some other vendors’ systems use
8-bit EBCDIC. If you decide to send or receive text characters as FTAM-3 binary data,
some conversion of the native character set might be necessary.
Presentation Encoding of FTAM PDUs and Data
As described in ISO 8823, clause 8, there are several options for encoding
presentation data for FTAM. Presentation data is encoded as SEQUENCE OF
PDV-list. Each PDV list in turn can encode data as single-ASN1-type, octet-aligned, or
arbitrary. If only a single ASN.1 data element is to be encoded, then a single PDV list
encoded as single-ASN1-type must be used. However, when multiple ASN.1 data
elements are to be encoded (as with grouped requests and most F-DATA requests),
there are several options:
•
Place the data in a single PDV list encoded as octet-aligned.
•
Place the data in multiple PDV lists, each containing one ASN.1 data element,
encoded as single-ASN1-type.
•
Place the data in multiple PDV lists, some containing multiple data elements
encoded as octet-aligned and others containing a single data element encoded as
single-ASN1-type.
Any of these three options is valid when all data elements have the same presentation
context. If different presentation contexts are used (as would be the case with FTAM-2
data using FA access context), a separate PDV list must be used for each different
presentation context.
When receiving PDUs, NonStop FTAM supports all three options. When sending
PDUs, NonStop FTAM follows these rules:
•
If single FTAM PDUs are to be sent, they are placed in a single PDV list encoded
as single-ASN1-type.
•
If multiple FTAM PDUs are to be sent (grouped requests or responses), they are
sent in a single PDV list encoded as single-ASN1-type.
•
When F-DATA requests are sent by the initiator, the method of encoding depends
on the number of data elements to be encoded. If only a single data element is
provided, it is placed in a single PDV list encoded as single-ASN1-type; when more
than one data element is provided, the data elements are placed in a single PDV
list, encoded as octet-aligned.
For FTAM-2 files, node-descriptor data elements are placed in their own PDV lists
as single-ASN1-type; consecutive file-contents data elements are placed in a
single PDV list as single-ASN1-type or octet-aligned, depending on whether one or
more consecutive data elements exist.