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resource. According to the EPA's analysis, you may decide to fix the
problem yourself (e.g. modify the configuration and try again) or log
the analyzed results as a file (a very comprehensive bug report), and
then send it to ZyXEL's Tech Support department.
Capturing the Protocol Data
The data captured by the EPA can be classified into three categories:
B-channel user data protocols.
D-channel signaling protocols.
DTE-DCE protocols.
The D-channel signaling protocols include layer 2 and layer 3 call
control protocols. Frames and messages exchanged via the D-
channel are all recorded for further analysis. These data messages are
essential to understanding interactive operations between an ISDN
TA and the ISDN network. They contain the compatibility
information for the TA and your Central Exchange.
The B-channel user data protocols include X.75 and V.120. Only the
layer 2 header (addresses and control bytes) and layer 3 header are
captured. Since X.75 may be used with various layer 3 protocols
(e.g. T.70, T.90, and ISO8208), only the first 8 octets of the
information field are recorded as the layer 3 header, and are displayed
in raw data form. The analysis of the protocol data will be carried out
by ZyXEL's Technical Support department.
The DTE-DCE protocols (at the R reference point according to the
ISDN nomenclature) include the AT commands/responses as well as
the CAPI internal interface. The CAPI internal interface is used with
the ZyXEL CAPI driver. The ZyXEL CAPI driver communicates
with the TA through this internal interface. It is not recommended
that users get involved in this internal interface. The AT
commands/responses, on the other hand, are in a standard user
interface. An analysis of these commands and responses might prove
very informative. All messages captured by the EPA are tagged with
a time stamp according to a free running timer that starts at the
104 Diagnostics
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