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Conformance and Interoperatility
OSI/FTAM Responder Manual—425199-001
2-5
Data-Transfer Considerations
Limits on Small String-Length Values With Large PDUs
When the Compaq FTAM responder receives data from a remote initiator, it decodes the
data and stores it, as a sequence of strings, in an internal buffer with a maximum size of
25 KB. According to the NIST FTAM Phase 2 agreements, P-DATA carrying encoded
FTAM PDUs or data elements cannot exceed 16 KB; however, string-header
information in the buffer can cause the data in the buffer to be much larger than the
maximum size of the encoded data. Because each string in the buffer includes a fixed
number of bytes of header information, packing small strings into a large PDU can cause
the 25 KB buffer size to be exceeded.
During data decoding, the responder checks the length of the data. If the decoded data
cannot be accommodated in the 25 KB buffer, the responder generates a provider
abort.
To avoid exceeding the buffer-size limit for writes to the Compaq responder, you can
either send a smaller number of strings per PDU or send larger strings, as described in
Section 4.
Handling of Escape Sequences
When writing data to the Guardian file system from a remote initiator, the responder
first removes any escape sequences contained in each string it receives before enforcing
the maximum-string-length limitation. When sending data to the remote initiator, it
does not check for escape sequences, but simply counts all bytes and packages them into
strings.
Use of Format Effectors
Format effectors are characters such as carriage returns and line feeds, which control
the formatting of information on character-imaging devices. To interoperate
successfully, application programmers must understand what an implementation expects
as an end-of-line symbol and how it interprets format effectors. For example, some
implementations use the FTAM-1 document type to transfer binary data as opposed to
text. Some implementations recognize carriage returns and line feeds as format
effectors and discard them if binary data, not text, is being transferred. Others see the
format effectors as data and transfer them as such.
In the Compaq FTAM responder’s virtual filestore (VFS), FTAM-1 files are treated as
documents and are implemented as Guardian EDIT files, which have a maximum record
length of 239 characters. The responder interprets carriage return-line feed
combinations (CR/LFs) as end-of-line indicators. If a file being written to the
responder’s VFS does not contain CR/LFs, the file is written in 239-character records.
Character Sets
The Compaq FTAM responder does no character-set verification. For FTAM-1 and
FTAM-2 files, to ensure that the file being transferred contains the correct character-
string type as specified in the universal-class parameter, your remote application should
verify characters as it sends or receives the data.