┬┬ ┬ ┌┬──┐ ┬┬──┐ ┌┬──┐ ┌─┬┬─┐ ┌┬──┐ ┌─┬┬─┐ ┌┬──┐
││ │ ││ ││ │ ││ ││ ││ │ ││ ││ Version 4.19
││ │ └┴─┬┐ │├─┬┘ └┴─┬┐ ││ │├──┤ ││ └┴─┬┐
││ │ ││ ││ │ ││ ││ ││ │ ││ ││ 2/28/97
└┴──┘ └──┴┘ ┴┴ ┴─ └──┴┘ ┴┴ ┴┴ ┴ ┴┴ └──┴┘
Interpreting the USRSTATS Report
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Public posting of this document in its unmodified form is permitted.
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The USRSTATS report is divided into several sections, like this:
┌─────────────────────────────────┐
│ Info │
├───────────────┬─────────────────┤
│ │ │
│ Error Control │ Data Pump stats │
│ and DTE stats │ │
│ │ │
└───────────────┴─────────────────┘
┌─────────────────────────────┐
│ │
│ Channel Probe │
│ (V.34 and V.FC modes) │
│ │
└─────────────────────────────┘
┌─────────────────────────────┐
│ │
│ Current settings │
│ (optional) │
│ │
└─────────────────────────────┘
Error Control and DTE stats - This section contains information about
the Error Control and Data Compression protocols currently active.
This includes MNP, LAPM, V.42, and V.42bis. It also displays the
number of characters sent and received by the attached terminal.
Data Pump stats - This section contains information on the operation of
the Data Pump. Specifically, it provides details of the modulation
protocol that was negotiated, the impairments that are affecting the
connection, and how the modem has responded to those impairments.
Channel Probe - This section is applicable only to connections made
under V.34 and VFC modulation. It shows details of the frequency
response and bandwidth characteristics of the physical link. (Phone
line.)
Info - This field contains the USRSTATS banner, and information used
for record-keeping purposes, such as the date and time, or the name of
the system being called.
───────────────────────────────────────────────────────────────────────
Here's a sample of a V.34 connection report:
┌───────────────────────┬─────────────────┬──────────────────────────┐
│ USRSTATS Version 4.19 │ 02-28-97 11:35 │ Caller 0 │
├───────────────────────┴─────────┬───────┴──────────────────────────┤
│ Elapsed Time 00:00:18 │ Modulation V.34+ │
│ Blocks Received 15 │ Speed 31200/28800 │
│ Blers 0 │ Symbol Rate 3429/3429 │
│ Blocks sent 5 │ Carrier Frequency 1959/1959 │
│ Link Naks 0 │ Trellis Code 64S-4D/64S-4D │
│ Blocks resent 0 │ Nonlinear Encoding ON/ON │
│ Link Timeouts 0 │ Precoding OFF/ON │
│ Chars sent 0 │ Shaping ON/ON │
│ Octets sent 10 │ Preemphasis 4/6 │
│ Chars lost 0 │ Rx Lev/TX Lev/SNR 25.2/12.0/36.8 │
│ Chars Received 0 │ Echo Loss Near 17.0 Far 40.0 │
│ Octets Received 239 │ Roundtrip Delay 4 │
│ Protocol LAPM SREJ │ Retrains Request/Grant 0/0 │
│ Block Size 244 │ Fallback Enabled │
│ Window Size 15 │ HST Line Reversals 0 │
│ Compression V42BIS │ HST Equalization Long │
│ Dictionary Size 2048 │ SV: 02/25/97 DSP: 02/25/97 │
│ String Length 32 │ Reason: Online │
└─────────────────────────────────┴──────────────────────────────────┘
┌───────────────────────────────────────────────────────────────┐
│ -22 │ ∙ ∙ ∙ ∙ ∙ ∙ ▄ ▄ ▄ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ │ 0 │
│ -24 │ ∙ ∙ ∙ ▄ █ █ █ █ █ █ █ █ █ █ ▄ ▄ ▄ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ │ 2 │
│ -26 │ ∙ ∙ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ ▄ ▄ ∙ ∙ ∙ ∙ │ 4 │
│ -28 │ ∙ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ ▄ ∙ ∙ │ 6 │
│ -30 │ ∙ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ ∙ ∙ │ 8 │
│ -32 │ ∙ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ ▄ ∙ │ 10 │
│ -34 │ ∙ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ ∙ │ 12 │
│ -36 │ ∙ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ ∙ │ 14 │
│ -38 │ ▄ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ ∙ │ 16 │
│ -40 │ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ ∙ │ 18 │
│ -42 │ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ █ │ 20 │
│Level└───────────────────────────────────────────────────┘Atten│
│ 0 0 0 0 0 0 1 1 1 1 1 1 1 2 2 2 2 2 2 3 3 3 3 3 3 │
│ 1 3 4 6 7 9 0 2 3 5 6 8 9 1 2 4 5 7 8 0 1 3 4 6 7 │
│ 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 │
│ 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 │
└───────────────────────────────────────────────────────────────┘
───────────────────────────────────────────────────────────────────────
Error Control Group:
Blocks Sent/Received - The number of Blocks sent and received by the
Error Control protocol.
Blers - (Block Errors) This field is a count of errors in received
Error Control Protocol or Data blocks. These errors are caused by
noise or other impairments in the channel, and small numbers of them
are to be expected. On severely impaired lines, values in the hundreds
or thousands may be seen. This field is one of the key indicators of
the receive channel quality. This number is a count of 50 millisecond
time units during which one or more errors occurred, and is therefore
related to the elapsed time of the connection as well as the number of
blocks received.
Link Naks - This field indicates the number of times the remote modem
requested the re-send of one or more blocks of data. Since it is
possible for the request to encompass more than 1 block, this number
does not necessarily indicate the actual block count. The remote
modem requests a re-send when a data block is corrupted by impairments
in the channel.
Blocks resent - This field is a count of transmitted Error Control
protocol blocks that were re-sent at the request of the remote
receiver. The Link Naks field counts these requests, and is related
to the number of blocks resent.
Link Timeouts - This field indicates the number of times the Error
Control protocol did not receive a response from the remote modem
within the expected time frame. This is normally caused by channel
impairments, and also occurs when the remote receiver is being flow
controlled by its terminal.
Chars Sent/Received - These fields count the number of characters sent
and received through the modem's DTE interface. These fields are only
updated periodically when in the on-line state. After the modem goes
off-line, the true value is shown.
Octets sent/Received - Octets are compressed data units. The
compression ratio can be determined by dividing Characters by Octets.
Chars lost - This field indicates the number of characters lost in the
Transmit Buffer, due to buffer over-runs. This field should always be
zero. Non-zero values indicate a problem with Transmit Data flow
control in the terminal.
Protocol - This field indicates the Error Control protocol in use.
Possible values include NONE, HST, MNP, and LAPM. (LAPM is sometimes
referred to as V.42, although it is actually only one part of the V.42
spec.) USR modems will prefer LAPM over MNP, although they can be
forced into MNP mode. HST Error Control is only used in conjunction
with the proprietary HST modulation mode.
Block Size - The data frame size used in LAPM and MNP modes. Larger
block sizes result in less protocol overhead, and faster throughput.
This is a negotiated parameter, and will vary depending on the remote
modems capabilities.
Window Size - The number of LAPM or MNP data frames that may be in
transit without being accounted for at any moment in time. Larger
window sizes can improve performance under conditions of high round-
trip delay. This is a negotiated parameter, and will vary depending
on the remote modems capabilities.
Compression - This field indicates the Data Compression protocol in
use. Possible values are NONE, MNP5, or V42BIS.
Dictionary Size - The number of entries in the V42bis compression
table. Larger numbers indicate greater potential compression
performance with certain data types. This number may vary when
connecting to modems from different manufacturers. USR modems default
to a Dictionary Size of 2048 entries.
String Length - The length of each string in the V42bis compression
table. Larger numbers indicate greater potential compression
performance with certain data types. This number may vary when
connecting to modems from different manufacturers. USR modems default
to a String Length of 32 characters.
───────────────────────────────────────────────────────────────────────
Data Pump Group:
Modulation - This field indicates the modulation protocol negotiated
for this connection. Possible values are V.34, VFC, V.32/bis/terbo,
HST, V.22bis, and several others. Note that the USR Courier modems
will report V.32/bis/terbo for ANY of the V.32-type modulation schemes.
HST is USR's proprietary High-Speed protocol.
Speed - This field indicates the current bit rate of the connection, in
Bits Per Second (BPS). For normal V.32/bis/terbo AND VFC modulation, a
single speed will be displayed since those protocols require the
receive and transmit channels to always run at the same speed. This is
an important point, because it means that both channels are limited to
the speed of the LOWER of the two directions. USR's ASL feature
enhances the V.32/bis/terbo protocols by allowing the transmit and
receive channel speeds to be adjusted independently, maintaining
maximum throughput in each channel regardless of the "direction" of the
channel impairments. In this case, two speeds will be displayed, which
are the Receiver and Transmitter speeds, respectively. Other fields in
the Data Pump Group which display 2 values follow the same convention
of Receiver/Transmitter.
───────────────────────────────────────────────────────────────────────
This concept of independent channel speed is an integral part of the
V.34 protocol, and is one of the key improvements over VFC.
───────────────────────────────────────────────────────────────────────
Symbol Rate - This field indicates the Symbol Rate of the receiver and
transmitter, respectively. A Symbol is a waveform transmitted by the
modem, which contains a certain number of encoded bits of data to be
moved across the link. The receiving modem decodes this waveform,
recovers the package of bits, and re-assembles it. (The noise levels
in the channel determine how many bits are encoded in each symbol.
Lower noise levels allow a greater number of bits per symbol.) The
design of the telephone system limits how many of these symbols may be
sent across a phone line each second. Symbols cannot be sent faster
than the *bandwidth* available through the phone line. V.34 and VFC
modulation allow adjusting this symbol rate to any of six possible
values, to obtain the best match with the available bandwidth. Other
protocols only allow a single, fixed value for the symbol rate,
regardless of the bandwidth of the link. This field has a very direct
link to the overall connection speed, and under V.34 and VFC
modulation, it is directly related to the available bandwidth as
determined by the line probe.
───────────────────────────────────────────────────────────────────────
The V.34 protocol allows independent adjustment of the Symbol Rate in
the receive and transmit channels, while VFC requires both channels to
run at the same Symbol Rate, the LOWER of the two.
───────────────────────────────────────────────────────────────────────
Carrier Freq - This field indicates the Carrier Frequency (in Hz) of
the receiver and transmitter, respectively. Under V.34 and VFC
modulation, the Carrier Frequency can be one of several values,
determined during the handshake and line probe processes. Under other
modulation types, the Carrier Frequency is a single fixed value.
Trellis Code - This field indicates the type of Trellis Code in use by
the receiver and transmitter, respectively. Trellis coding improves
the system's noise immunity. The type of coding may vary when
connecting modems from different manufacturers.
Nonlinear Encoding - This field applies only under V.34 and VFC
modulation, and shows the state of the received signal and transmitted
signal, respectively. Nonlinear Encoding is an operation performed on
the transmitted signal to improve the operation of the receiver in the
presence of nonlinear distortion. The modem will automatically
negotiate this option during the handshake.
Precoding - This field applies only under V.34 and VFC modulation, and
shows the state of the received signal and transmitted signal,
respectively. Precoding is an operation performed on the transmitted
signal to reduce the effects of noise multiplication in the adaptive
equalization process. The modem will automatically negotiate this
option during the handshake.
Shaping - This field applies only under V.34 and VFC modulation, and
shows the state of the received signal and transmitted signal,
respectively. Shaping is an operation performed on the transmitted
signal to improve the operation of the receiver in the presence of
certain types of noise. The modem will automatically negotiate this
option during the handshake.
Preemphasis Index - This field applies only under V.34 and VFC
modulation, and shows the Index value for the receiver and transmitter,
respectively. Preemphasis is a way of compensating for poor phone line
bandwidth. If the line has poor bandwidth, the upper frequencies of
the transmitted signal can be boosted to compensate for the roll-off.
The modem will select 1 of 10 possible values, based on the actual
roll-off rate of the phone line. This field indicates which value has
been chosen, larger numbers mean that more preemphasis is being applied
to compensate for the line. The modem will automatically negotiate
this option during the handshake.
Rx/Tx Level - This field indicates the level (in -dB) of the receive
and transmit signals, respectively. Standard transmit level for
US/Canada modems is approximately -10 dB, although under V.34 and VFC
modulation, the levels are negotiated and adjusted by the modem during
the handshake. Receive level can vary widely, depending on the
conditions on your local phone line, the line at the remote modem, and
any long-distance or inter-office carrier facilities. *Typical*
values will range from -40 dB at the low end, to -15 dB at the high
end, with figures in the -20 to -35 range being most common. Extreme
values in either direction probably indicate a problem in your local
loop, which the phone company may be able to adjust.
SNR (Signal to Noise Ratio) - The number displayed is the ratio of the
Receive Level to the Noise Level. The Absolute Noise Level (in dBm)
can be computed from the SNR and Receive Level. In a "noiseless"
channel, the Absolute Noise Level is approximately -60 dBm. SNR is
one of the most important factors in modem performance. Lower SNR
values generally result in lower connect speeds. Note that a poor SNR
does not necessarily mean that the Noise Level is too high; it can also
mean that the RX Level is too low. Typical SNR values range from 15
to 35 dB. Larger values indicate better SNR.
Near Echo Loss - Near End echo occurs when the transmitted signal is
reflected from the local modem's hybrid circuit due to impedance
mismatch. The number displayed is the ratio of the Transmit Level to
the Near End Echo Level, or the amount of attenuation the Near End echo
has when compared to the transmitter. Under normal conditions, the
Near End echo is approximately 30 dB below the TX signal level. Larger
numbers indicate better impedance matching at the local modem.
Far Echo Loss - Far End echo occurs when the transmitted signal is
reflected from the REMOTE modem's hybrid circuit due to impedance
mismatch. This echo experiences both the forward channel and reverse
channel losses, and is usually very small in magnitude. The number
displayed is the ratio of the Receive Level (which has the reverse
channel loss embedded within) to the Far End Echo Level along with the
forward channel loss. Typical values of Far Echo Loss are
approximately 30 dB. Larger numbers indicate better impedance matching
at the remote modem.
Roundtrip Delay - This field indicates the amount of time (in
milliseconds) it takes for the modem to hear a reflection of it's own
transmitter. This is closely related to the physical length and
transmission path of the phone link, and it affects the operation of
the modem's echo canceller. This delay also affects the timing of the
modem's handshaking routines.
Retrains Requested - This field is a count of the number of times the
modem sent a request for a re-train to the remote end. This happens
when the line quality degrades to the point where the modems lose sync
with each other. Note that under some modulation types, and with
certain configuration settings, the remote modem is NOT required to
*honor* this request, it may be simply ignored. This field corresponds
with the "Retrains Granted" field of the REMOTE modem, NOT the field in
THIS report.
Retrains Granted - This field is a count of the number of times the
modem responded to a re-train request from the remote end. This field
corresponds to the "Retrains Requested" field of the REMOTE modem, NOT
the field in THIS report.
Fallback - This field indicates whether the modem has performed a speed
shift, either up or down, at any point during the connection.
"Disabled" means that there has been no speed shift, "Enabled" means
there has been a speed shift.
HST Line Reversals - This field is only meaningful for connections
using HST modulation. It then indicates the number of times the modem
switched the directions of the high-speed forward channel and the low-
speed back channel.
HST Equalization - This field indicates whether the modem is using
extra pre-emphasis on the transmitted signal. This field applies only
to HST modulation.
SV - This field indicates the revision date of the modem Supervisor
(Controller) firmware.
DSP - This field indicates the revision date of the modem DSP (Data
Pump) firmware.
Reason - This is the "Disconnect Reason" reported by the modem.
───────────────────────────────────────────────────────────────────────
Line Probe Group:
Line Probing only applies to V.34 and VFC modulation. This is a test
to determine the actual bandwidth available over the phone line.
During the handshake, the modems send a series of tones to each other,
at known levels and specific frequency points. The modem calculates
the level of the received signal at each point, and therefore can
determine the maximum bandwidth available for use. This section of the
report shows each of those frequency points, and, on the left side of
the graph, the signal level (in -dB) at that point. (Levels are
referenced from 0.) The right side of the graph shows the attenuation
at each frequency, relative to the HIGHEST level recorded. (This
corresponds to the dynamic range of the received signal.) If any of
the signal levels fall below -44 dB, the chart will include a line of
==== characters to show that threshold. Generally speaking, values
below about -40 dB become difficult for the modem to interpret,
depending on other line conditions. If the calculated noise level
falls within the range of the chart, a line of **** characters will be
included to mark that level. The effective bandwidth calculated here
directly affects the Symbol Rate, and overall connect rate. The modem
will select the fastest Symbol Rate that can be reliably handled by
this bandwidth.
───────────────────────────────────────────────────────────────────────
Info Group:
This field shows the USRSTATS banner and version number, and the date
and time that the report was created. (Not when the data was
captured!) It will also optionally show the Caller and Node number
(when used with the PCBoard PPE), the last number dialed (in stand-
alone mode), the elapsed time of the current call, or other data passed
by a "door" program on a BBS.
───────────────────────────────────────────────────────────────────────
Settings Group:
This is an optional display of the current modem settings at the time
the report data was captured.
───────────────────────────────────────────────────────────────────────
[END]