NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/dcom/modems-part1/5738

Internet Message Format | 1996-08-05 | 17.5 KB

Path: in2.uu.net!insync!usenet
From: [e-mail] (Greg Bretting)
Newsgroups: comp.dcom.modems
Subject: Re: USR Sportster 33.6 Retrain disconnect ???
Date: Wed, 14 Feb 1996 23:21:40 -0800
Organization: - not one of my strong points, really...
Message-ID: <4fufnm$[e-mail]>
References: <[e-mail]> <4fd72n$[e-mail]> <4fp1uc$[e-mail]> <4fraa6$[e-mail]>
NNTP-Posting-Host: line-204.insync.net
X-Newsreader: Forte Agent .99b.112

On 13 Feb 1996 19:27:50 -0500, [e-mail] (doug haire) wrote:

>: : Karel Vetrovsky ([e-mail]) wrote:
>: : : I am getting frequent disconnects from my internal USR Sposter 33.6 due
>: : : to "Unable to Retrain". My ISP has Cardinal modems - if it helps. Funny
>: : : thing is that my friend who uses Supra 28.8 and the same ISP does not
>: : : have this problem. I am using the unmodified .INF setup string for USR
>: : : modems (I believe it is the one updated for 33.6 modems). Any
>: : : suggestions?
>: : :
>: : : Here's the result of ATI6 after one of those disconnects:
>: : :
>: : : USRobotics Sportster 33600 Fax Link Diagnostics...
>: : :
>: : : Chars sent                 1547      Chars Received            30212
>: : : Chars lost                    0
>: : : Octets sent                1175      Octets Received           16173
>: : : Blocks sent                  74      Blocks Received             181
>: : : Blocks resent                 0
>: : :
>: : : Retrains Requested            3      Retrains Granted              0
>: : : Line Reversals                0      Blers                         6
>: : : Link Timeouts                 3      Link Naks                     0
>: : :
>: : : Data Compression       V42BIS 2048/32
>: : : Equalization           Long
>: : : Fallback               Disabled
>: : : Protocol               LAPM
>: : : Speed                  28800/28800
>: : : Last Call              00:07:55
>: : :
>: : : Disconnect Reason is Unable to Retrain
>:
>: : There were 3 requests from the Cardinal to retrain and there were 3 link
>: : timeouts. There were no requests from the Sportster to retrain. This
>: : implies that the Cardinal is seeing problems on its receive. Try your
>: : friend's Supra from your house (on your line) and see if it is more
>: : stable. An alternative test would be to bring your modem to your
>: : friend's place and try it. If it shows that only the Sportster has
>: : trouble, you will need to contact USR to return it for repair.

I wan't able to find the original article, so please forgive the nested
attributes, but...

The above interpretation of the ATI6 dump is somewhat incorrect; the
"Retrains requested" field refers to retrains requested by the local modem,
NOT the remote modem.  In the above example, it was the Sportster - not the
Cardinal at the other end - that requested three retrains.  This according
to info supplied by USR along with their USRSTATS program... here is an
excerpt from that - pay special attention to the retrains requested/granted
part:

    [BEGIN QUOTE]

    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.   In order to preserve
    modem performance, 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 is a
    mathematical operation performed on the transmitted data which 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 under
    certain channel conditions.  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 under certain channel
    conditions.  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.

    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.


    ---------------------------------------------------------------------


    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 -48 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.   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]


--
|     Greg Bretting     |"The whole problem with the world is that  |
|  [e-mail]  |fools and fanatics are always so certain of|
|     --==<< >>==--     |themselves, but wiser people are so full of|
|            |doubts." - Bertrand Russell            |