Explanation of ATI6/ATI11 commands

Please note that not all USR modems have ATI11 available, and not all ATI6 options are applicable to all modems.
Often communication software is configured to use ATZ to reset the modem after a connection. This will also reset the ATI6 and ATI11 values. So you might want to change ATZ to AT&F1.

ati6

USRobotics Sportster 33600 Fax Link Diagnostics...

Chars sent                14760      Chars Received            34270
Chars lost                    0
Octets sent                6677      Octets Received           25925
Blocks sent                 369      Blocks Received             636
Blocks resent                 0

Retrains Requested            0      Retrains Granted              0
Line Reversals                0      Blers                         0
Link Timeouts                 0      Link Naks                     0

Data Compression       V42BIS 2048/32
Equalization           Long
Fallback               Disabled
Protocol               LAPM
Speed                  28800/26400 
Last Call              00:03:21

Disconnect Reason is DISC Received

OK

ati11
USRobotics Sportster 33600 V.34+ Fax Link Diagnostics ...

Modulation                  V.34
Carrier Freq     (Hz)       1959/1959
Symbol Rate                 3429/3429
Trellis Code                64S-4D/64S-4D
Nonlinear Encoding          ON/ON
Precoding                   OFF/ON
Shaping                     OFF/ON
Preemphasis      (-dB)      2/2
Recv/Xmit Level  (-dB)      23/16
SNR              (dB)       30
Near Echo Loss   (dB)       31
Far Echo Loss    (dB)       57
Roundtrip Delay  (msec)     3

OK

Error Control Group

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.

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.

Octets sent/Received

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.

The compression ratio can be determined by dividing Characters by Octets.

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.

Note that due to the redundancy in trellis encoding, it is not always necessary to resend a block.

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.

Data Compression

This is the sort of compression used, NONE, 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.

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.

Protocol

This field indicates the Error Control protocol in use. Possible values include NONE, HST, MNP, SYNC, 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.

Data Pump Group

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 two 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.

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.

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.

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 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

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.

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

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 canceler. This delay also affects the timing of the modem's handshaking routines.

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.

Retrains Requested

This field is a count of the number of times the modem sent a request for a re-train of the speed 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 with 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.

Explanation by USR: Whether the modems can renegotiate to a different speed. Not all modems can do this.

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.

Equalization

This field applies only to HST modulation. This field indicates whether the modem is using extra pre-emphasis on the transmitted signal.

Line Probing

Last advise

USRobotics UK Online Support:

Note that you can increase the likelihood of getting a high speed connect by minimizing 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 British Telecom 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.