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
