Specifications

4-18
Cisco AS5x00 Case Study for Basic IP Modem Services
11/24/1999
Section 4 Verifying Modem Performance
Initiating and Inspecting a V.90 Test Call
Step 14
Turn off all debug commands:
5300-NAS#undebug all
All possible debugging has been turned off
Task 2. Initiating and Inspecting a V.90 Test Call
Before you let users dial in to the NAS, initiate and inspect a V.90 test call. V.90 call performance is
heavily dependent upon the telco’s network topology. There are many variables.
Most modem manufactures have unique AT command sets. The AT commands used in the following
procedure might not be supported by your modem. For more information, see the following URLs:

http://56k.com/links/Modem_Manuals/

http://808hi.com/56k/trouble1.htm
Step 1
Locate a client PC, client modem, and an analog line. The following figure shows the network
environment for this test.
Step 2
Test your RS-232 connection to the client modem:
at
OK
Line shape:
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A line shape is the frequency-response graph of
the channel.
For this modem loopback test call, there should
be no rolloff (even at the highest frequency).
High-end rolloff is characteristic of an
analog-to-digital conversion (not good).
A flat vertical line shape is an ideal V.90 line
shape. ISDN uses a 64-kb clear channel. No
statistical roll off should exist at the low end or
the high end of the spectrum. The spectrum has
a Y and X axis.
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The Y axis (vertical) represents frequencies
from 150 Hz (top of chart) to 3750 Hz
(bottom of chart) in 150 Hz steps. A flat
spectrum plot is best, it is available for V.34,
V.90, and K56Flex.
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The X axis (horizontal) represents a normal
amplitude. The graph identifies nulls,
bandwidth, and distortion (irregular shape).
Table 4-4 Operational Parameter Descriptions for a Loopback Test Call (continued)
Parameter Description