NETGEAR XM128 ISDN - Manual (Page 93)

Reference Guide for the Model XM128 ISDN Digital Modem
Troubleshooting 10-5
Setting up the Embedded EPA
The EPA records and analyzes various protocols on the B channel, D channel and DTE-DCE
interface. The results are displayed with ANSI color. This professional tool is designed for
hobbyists as well as users with technical backgrounds. The EPA enables you to examine messages
exchanged between your Model XM128 modem and the Central Exchange office when making an
ISDN call. You can review the packets sent or received through the B channel (for X.75 or V.120
protocols) to or from the remote site. You can also check the AT commands issued from an
application software program. This helps you understand their causal relationship with other
events.
In addition to its tutorial purpose, the EPA is very useful for diagnostics. If you have compatibility
problems with your Central Exchange or with the TA at the remote site, the EPA is your first aid
resource. According to the analysis of the EPA, you might decide to fix the problem yourself
( modify the configuration and try again) or log the analyzed results as a file (a very
comprehensive bug report), and then send it to NETGEAR Technical Support.
Capturing the Protocol Data
The data captured by the EPA is 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 through 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 Model XM128 modem and your
Central Exchange.
The B channel user data protocols include X.75 and V.120 protocols. Only the layer 2 header
(addresses and control bytes) and layer 3 header are captured. Since the X.75 protocol can be used
with various layer 3 protocols (T.70, T.90, and ISO8208 protocols), 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 is carried out by NEGEAR Technical Support.