USR Ati11 Explained
U.S. Robotics 56K FAX EXT Link Diagnostics...
Modulation V.90
Carrier Freq (Hz) None/1920
Symbol Rate 8000/3200
Trellis Code None/64S-4D
Nonlinear Encoding None/ON
Precoding None/ON
Shaping ON/ON
Preemphasis (-dB) 0/0
Recv/Xmit Level (-dBm) 0/0
Near Echo Loss (dB) 0
Far Echo Loss (dB) 0
Carrier Offset (Hz) NONE
Round Trip Delay (msec) 0
Timing Offset (ppm) 0
SNR (dB) 0
Speed Shifts Up/Down 0/0
Status : 1,2,3,4,5,6,7,8,9,10
Modulation - This field indicates the Modulation used to
establish the connection. Several values can be seen here, the most likely being V.90, X2, or V.34 and the least likely
being V.22bis, V.32/bis/terbo, VFC, or HST.
Carrier Freq - This field displays the carrier frequency
of both the receiver and transmitter.
Symbol Rate - This field displays the symbol rate (the number
of symbols or waveforms containing encoded bits) of both the receiver and transmitter. These values should not drop
below 3200 for a good connection.
Trellis Code - This is the type of mathematical "anti-noise"
operation that has been selected for transmitted data. This can vary and really has little bearing on determining noise,
though it may be possible that a value of None/None could be problematic.
Nonlinear Encoding - This displays the state of the
received signal and transmitted signal with respect to the status of Nonlinear Encoding activation upon handshake. This is
an operation that the modem can perform on the transmitted signal to improve the received signal under certain conditions.
Precoding - This displays the state of the received signal
and transmitted signal with respect to the status of Precoding activation upon handshake. This is an operation that
the modem can perform on the transmitted signal to help in reducing the effects of noise increasing in the adaptive
equalization process.
Shaping - This displays the state of the received signal and
transmitted signal with respect to the status of Shaping activation upon handshake. This is an operation that the modem
can perform on the transmitted signal to improve the received signal under certain conditions.
Preemphasis - This field indicates how much signal boosting
the modem decided was enough to compensate for a poor signal. Keep in mind that there is often something here. I do not
yet know what the values mean, but I do know that higher means more boosting had to be used.
Recv/Xmit Level - This field indicates the receive
and transmit levels. Standard levels for the US are -10, but the values are adjusted by the modem during modulation.
Ranges from -1 to -6 and -30 to -40 could indicate a poor local loop.
Near Echo Loss - 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.
Far Echo Loss - This field indicates the transmit level
that is being reflected at the remote modem's hybrid circuit. This field will usually not be high if you are dialing into
a digital server. A normal value is around 30. If this value is in the 200's or higher there could be an ISP or telco
problem.
Carrier Offset - This field indicates the dc
offset in the FM discriminator output. You should normally have "NONE" here, but sometimes there is an offset. If the
offset is greater than 1000 you will most likely see v.34 connections, and if it is far greater than 1200 you may begin to
see performance issues. This may indicated dc voltage issues on your telephone line.
Round Trip Delay - This field indicates the amount of
time that it takes for the modem to hear a reflection of it's own transmission. Since this field helps to indicate the
physical distance between the modem and the server it is not very useful, though a number greater than 10-15 would often
indicate that the modem is connecting to a "Virtual POP"/"Super POP", which is a normal practice by ISPs and should not
really affect your connection.
Timing Offset - This field indicates the difference
in synchronization between the local clock and the host clock. This field provides the local modem with a means of
synchronizing its sampling clock to that of the host. This field will normally not indicate any problems, though there may
be issues if the value is about 10,000 or lower than -10,000.
SNR - This field indicates the Signal to Noise Ratio. This is
not always a true measure of the SNR (due to digital impairments), but if a low SNR is found, it is one of the best indications
of noise issues. The following chart helps to show what SNR will often yield what stable speeds, but can vary.
| 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. |
Speed Shifts Up/Down - This field indicates the
number of times your receive rate was bumped up/down due to your connection stability. If this number is above 10 you probably
have a pretty unstable connection.
Status - This field lists information regarding the server
and phone line that the modem has detected. The fields are as follows:
Item Number 1: This item indicates the type of Codec used, U-law or
A-law. The US uses the U-law codec.
Item Number 2: This item indicates the number of sign bits and should
be 5 under normal conditions.
Item Number 3: This item indicates the the maximum transmit level of
the host. If you experience a value
of 6 or less, or 19 or higher there may be a signal or power problem. A Y in this
field indicates that the server
is not capabale of compensating for digital pads (thus providing for a worse transmit level)
and an N indicates
that the server is capable of this and the number indicated does not necessarily reflect the quality of
your line
(though if it is a poor value, then the quality may be even worse than shown).
Item Number 4: This item indicates the sliding power window, which should
be relative to item number 3.
A poor value here may also indicate poor signal or power issues.
Item Number 5: This item indicates the amount of padding used inbetween
the client and host on the telephone
circuit. A value of 0 is the best, indicating no padding, a value of -7 indicating 3db
of padding, and a value of -15
indicating 6db of padding which could cause potential problems.
Item Number 6: This item indicates the number of Robbed Bit Signal links
in the telco circuit between client
and host. You can still achieve 56k type connect speeds with RBS links, however if you
have a Y here, this
indicates a type B Codec which could mean that you are on a SLC96 (often referred to as a Slick). A
slick is
used when there are not enough twisted pairs in the area to meet customer needs. When a slick is used you
are given
extra Analog to Digital/Digital to Analog conversions, thus making v90 speeds impossible.
Item Number 7: This item usually indicates a value of 0. I do not have
a clue as to what it is supposed to be for.
Item Number 8: This item indicates SNR using another type of training.
Use the above chart to find the
meaning of your SNR value.
Item Number 9: This item indicates the Codec Distortion. A value here
that is higher than 26 could indicate
troubles. (Note that item 9 works differently on v92 USRs.)
Item Number 10(only shown on v92 USRs): I do not yet have a clue as to
what this item is supposed to be for.
This page was last modified on Saturday, 05-Feb-2011 15:13:38 EST.
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