  Explanation of ATI6/ATI11 commands

     US Robotics Technical Support, 07/JUL/1995, Rev 1.01


     This document explains the results given from ATI6 and ATI11 on US 
     Robotics modems. Please note that not all USR modems have ATI11 
     available, and not all ATI6 options are applicable to all modems.

     All comments are encased in [square brackets]

     ATI6
     USRobotics Courier HST Dual Standard V.34+ Fax Link Diagnostics...

     [Standard USR modem ID]

     Chars sent                 1730      Chars Received              571 
     Chars lost                    0

     [Number of characters received, sent or lost]

     Octets sent                1483      Octets Received             487

     [Octets are units of compressed data - note that this is lower than 
     characters sent, as the compression has reduced it. If octets sent is 
     higher than Chars sent, MNP5 is probably enabled and compressed files 
     were sent - MNP5 tries to recompress the data and ends up with more 
     data.]

     Blocks sent                  85      Blocks Received              26 
     Blocks resent                 0

     [Number of blocks sent, resent and received using error correction.]

     Retrains Requested            0      Retrains Granted              0

     [Retrains are when the speed is renegotiated, either up or down. 
     Retrains requested is the number of retrains requested by your end; 
     retrains granted are the number of retrains requested by the remote 
     end.]

     Line Reversals                0      Blers                         7

     [Line reversals are for HST only; as there is a slower back channel 
     (usually 300 or 450 bps), when more data starts coming through on the 
     back channel the line is reversed so the data goes through at high 
     speed (ie, the line goes from 450/14400 to 14400/450).
     Blers are errors in the data and protocol blocks, down to line noise. 
     Note that due to the redundancy in trellis encoding, it is not always 
     necessary to resend a block.]

     Link Timeouts                 0      Link Naks                     0

     [This indicates the modem had some form of problem communicating, 
     usually down to the line being dropped momentarily.
     Link Naks are negative acklowledgements (think XModem NAK).]

     Data Compression       V42BIS 2048/32

     [This is the sort of compression used, MNP or V.42bis. The two numbers 
     following refer to V.42bis only and are the size of the compression 
     dictionary, and the maximum string length used. Note that different 
     modems have different size dictionaries and string lengths.]

     Equalisation           Long

     [HST setting; whether equalisation is short or long.]

     Fallback               Enabled

     [Whether the modems can renegotiate to a different speed; not all 
     modems can do this.]

     Protocol               LAPM 128/15

     [This is the error correction protocol (compare to Data Compression); 
     it is one of LAPM, HST, MNP, SYNC or NONE.]

     Speed                  28800/28800

     [Speed connected at - receive/transmit]

     Last Call              00:00:14

     [Length of last call.]

     Disconnect Reason is DISC Received

     [The reason the modem hung up. This will give you useful information 
     if you suddenly get hung up for no apparent reason. You can find more 
     information in the Courier V.34 manual, pp6-4 to 6-6.]

     OK

     ati11
     USRobotics Courier HST Dual Standard V.34+ Fax Link Diagnostics...

     Modulation               V.34

     [Modulation protocol used - V.34, V.32bis, etc]

     Carrier Freq (Hz)        1959/1959

     [Frequency of the carrier, receive/transmit]

     Symbol Rate              3429/3429

     [The symbol rate is the number of symbols that can be sent, similar to 
     the carrier frequency; this is, if you like, the underlying baud rate. 
     A symbol will have several different states, and thus represent more 
     than one bit of data. For example, a system with 16 symbol rates can 
     encode four bits per symbol, and transfer 9600bps over a 600 baud 
     channel.]

     Trellis Code             64S-4D/16S-4D

     [Trellis encoding is the way the data is encoded to maximise bandwidth 
     use. A full explanation is beyond the scope of this document, but 
     briefly a trellis encoding algorithm takes n data bits as input and 
     produces n+1 bits as an output. The extra bit is generated by another 
     algorithm and represents redundant data. The m+1 bits are then fed 
     into a normal QAM (quadrature
     m+1
     amplitude modulation) system with 2    states.]

     Nonlinear Encoding       ON/OFF
     Precoding                OFF/ON
     Shaping                  OFF/ON

     [The above three deal with how data is prepared to be sent down the 
     line, for example shaping will avoid certain frequencies if there is a 
     defect there.]

     Preemphasis (-dB)        4/10

     [This boosts the signal strengths if and where necessary, for example 
     if your line has a problem transmitting at a certain frequency, the 
     signal will be boosted - but only at that frequency.]

     Recv/Xmit Level (-dB)    27/18

     [This is the measured receive level, and level set for transmit, with 
     the transmit level automatically adjusted by the modem for optimal 
     performance. Please note that this is the last sample taken, and not 
     an average; if the line was hit by line noise, the value may be too 
     high. An ideal line will have both levels fairly low, and near or 
     exactly equal, for example 15/15.]

     Roundtrip Delay (msec)   11

     [This is the amount of time it takes for a block of data to go from 
     one modem to the remote and back again; it is analogous to "ping" on 
     Unix.]

     Note that you can increase the likeliehood of getting a high speed 
     connect by minimising the amount of equipment on your line. If you 
     cannot manage a full 28800 connect, try removing all extensions and 
     extension cable and plug your modem directly into the incoming line in 
     your house. In addition, standard BT lines are not guaranteed to work 
     above 2400 baud; 28800 requires a symbol rate of 3200, which is 
     significantly above the BT minimum. That said, most phone lines can 
     manage 24000 or 26400 connects nationally, and 26400 or 28800 connects 
     locally, which is still quite a tribute to BT lines.

     USRobotics UK Online Support
