Recently, an interop testing partner submitted a T.38 implementation that had
yet to be fielded and asked for our assistance in shortening his testing time.
Below is an excerpt of just some of the analysis produced by the Lab. It
should give you a good idea of just how valuable the testing can be.
- v21-preamble indicator needs only be sent once. It
appears you are sending it for each detected
flag character.
Cisco sends only one indicator.
Lucent send one at start and one between
frames.
- Field length value for a data field should start with
0 for a single data octet. Thus, a field
containing 3 octets would have the length
field set to 2.
- The Cisco boxes send no-signal at the end of the
V21 sequence and appears not to work without
it.
- The v17-14400 long-training signal is sent multiple
times. It appears that you are sending the
indicator every 40 milliseconds while the
training is present. This is not required.
- Image data bits appear to be reversed.
- First packet sent should be no-signal
(Probably will not affect interoperability
but is common practice.)
- The format of the "Open type" is not correctly
interpreted. The length of the frame should
preceed the frame. For example:
++-- length of primary
VV
00 04 06 c0 01 80 00 00 c0 00 02 06 c0 01 80 00
00 ff 01 06 ^^ ^^ ^^
|| || ++-- length of first 2ndary
|| ++----- Number of redundant frames
++-------- Type of 2ndary frames (Redundant)
This problem existed in older versions of Telogy
T.38, but has since been corrected.
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