Specifications

4-23
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 11
Enter the
+++
command to jump back to the client modem and examine client-side performance
statistics. The modem connection to the NAS is not dropped.
5300-NAS>+++
OK
at
OK
In the example, the client modem reports both “OK” messages. The
+++
modem-escape sequence is
similar to a router’s telnet-escape mode (Shift + Ctrl + 6 + x). See Figure 4-8.
Parameter #21
Signal Noise Ratio: 36 dB
The signal to noise ratio (SNR) is 36 dB. (40 dB is a
perfect SNR.
MICA measures the SNR in the signal band. The SNR
value ranges from 0 to 70 dB, and it changes in 1 dB
steps.
A 28.8 kbps connection requires a SNR of about 37 dB.
SNRs lower than 37 dB reduce the quality of the
connection.
A 33.6 kbps connection requires a SNR of about 38 to
39 dB.
Parameter 30
Characters transmitted, received:
67109, 43
67109 characters are transmitted by the NAS modem to
the client modem over the synchronous/asynchronous
connection.
Line shape:
.........................*
................................*
.................................*
.................................*
................................*
.................................*
.................................*
.................................*
................................*
................................*
................................*
................................*
................................*
................................*
................................*
A line shape is the frequency-response graph of the
channel.
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.

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.

The X axis (horizontal) represents a normal
amplitude. The graph identifies nulls, bandwidth,
and distortion (irregular shape).
Table 4-5 Show Modem Operational-Status Field Descriptions (continued)
Parameter Description