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