The AT#UD command was created by Microsoft as an attempt for a standard diagnostic screen. Unfortunately they did it in Hex,
and most modems now support it, but for some modems it is one of the only ways to look for noise. The keys that we want to
concentrate on are keys 10, 11, 14, and 12. Convert these numbers to decimal by using the following table:
Key 10 is the Received signal power level, in -dBm. If the value represented displays over 30, then there may be signal
problems with the phone line, however I have seen "impossible" values that are out of range from this field, so use caution
if this is the only key that shows that there may be noise. The range for this field should be between 0 and 43.
Key 11 is the Transmit signal power level, in -dBm. This value should be between 6 and 16. If it is above or below this
range there may be signal problems with the phone line.
Key 14 is the Near echo loss, in units of dB. This field indicates the transmit level that is being reflected at the
telco hybrid. A normal value is around 30. If this value is in the 200's or higher there could a line problem.
Key 12 has been difficult for me to determine. It represents the Estimated noise level, in -dBm, however after testing a
line with it a value of 50 was indicated. Lucent's Estimated noise level report would tell us that this is a very poor quality
line as you would normally be dropped when 50 is reached, however this was done on a VERY clean line. I then took a USR
and tested the line, getting an SNR of about 49.3. Thus it would be reasonable to assume that the Estimated noise level that
is represented in this command displays the Signal to Noise Ratio, but this is not necessarily a FACT, but just a
hypothesis. This may not be correct however, as what I believe was a noisy line tested with this modem showed a number between
40-50. It may or may not be SNR and requires more research. So unfortunately this modem does not seem to have very
positive/useful diagnostics at this point. If this is the case, the following table will help in determining what shape the
line is in:
SNR Range (Note: SNR = Signal to Noise Ratio)
Expected "Stable" Speed
40+
33,600 - 56,000
37-40
33,600-56,000 (a little unstable at high speeds)
34-37
31,200-33,600
31-34
28,800-31,200
29-31
26,400-28,800
28-29
24,000-26,400
25-28
16,800-24,000
23-25
14,400-16,800 (NOTE: If your SNR is around this level or lower the FCC may step in if your telco won't fix it,
this level is not required to be supported, but often is by local teclos and must be upheld if in their charter.)
21-23
12,000-14,400
18-21
9600-12,000 (NOTE: If your SNR is around this level or lower the FCC will step in if your telco won't fix it,
this level is REQUIRED, BARE MINIMUM support.)
14-18
7200-9600
13-14
4800-7200
6-13
2400-4800
1-6
300-2400 if you are lucky enough to connect.
This page was last modified on Wednesday, 18-Jul-2007 13:44:05 EDT.
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