Multi-Tech Systems MTA128NT - Manual (Page 39)

Troubleshooting
MTA128ST/NT 39
File transfer appears slower than it should be
• If you have a Universal Asynchronous Receiver/Transmitter (UART) that is compromising data
throughputs, we recommend replacing it with a special I/O card.
• If you are running under Windows 3.1 and have a 16550AFN UART, replace the Windows serial driver,
COMM.DRV, to take full advantage of the UART’s speed.
• Check the serial port baud rate in your communications software, and make sure it is set as high as your
UART allows.
Data is being lost
• Your UART may not be reliable at serial port speeds over 9600 bps or 19,200 bps. Reset your serial port
speed to a lower rate, or replace your serial port with a faster one.
• Check the serial port baud rate in your communications software, and make sure it is set as high as your
UART allows.
• Make sure the flow control method you selected in software matches the method selected in the
MTA128ST/NT.
Garbage characters appear on the monitor
Your computer and the remote computer may be set to different parities. Check with the remote system
and set your communications software to use the same parity as the remote system.
Making a V.120 call, caller gets a NO CARRIER message after dialing the number.
Some switches don’t support ISDN SETUP messages that contain a LLC (low layer compatibility) element.
When these switches receive an LLC in the SETUP, they immediately reject the call and a NO CARRIER
message displays. Disable LLC for V.120 calls by issuing the command AT!D0=0. To enable LLC again for
V.120 calls, issue the command AT!D0=1 (the default setting).
Making a V.110 call, caller gets a NO CARRIER message after dialing the number.
Some switches don’t support extended BC (bearer capability) information in the ISDN SETUP message,
such as the one normally sent by V.110 data protocol. When these switches receive a BC with extended
capability information in the SETUP, they immediately reject the call and a NO CARRIER message
displays. Disable sending extended BC information for V.110 calls by issuing the command AT!D1=0. To
enable sending extended BC information for V.110 calls, issue the command AT!D1=1 (the default setting).
Note: V.110 is supported on some MTA128ST models only.
When using X.75 data protocol to transfer data via the Zmodem, the Zmodem displays Intermittent bad
packet errors and data throughput drops.
This occurs in cases when the X.75 packet size is greater than 1024 bytes and the terminal adapter
sending the file has a fast serial baud rate (e.g., 115200 bps) and the terminal adapter receiving the file
has a slow serial baud rate (e.g., 19200 bps). To reduce or possibly eliminate this, reduce the X.75 packet
size (S53) to a value less than or equal to 102 bytes (e.g., ATS53=512). However, if you set the receiving
terminal adapter’s serial baud rate nearly equal to or greater than the serial baud rate of the sending
terminal adapter, then the packet size can be greater than 1024, and Zmodem transfers the data without
bad packet errors.
The MTA128ST/NT won’t accept V.120 calls from a 3Com Impact IQ terminal adapter. The Impact IQ
displays a connected status, but the MTA128ST/NT does not.
The MTA128ST/NT is looking for a SABME command from the Impact IQ to finish establishing the V.120
connection. However, the Impact IQ won’t send a SABME until it has data to send. Have the Impact IQ
send a character by pressing any key (such as the space bar) on the terminal attached to the Impact IQ.
The MTA128ST/NT responds with a CONNECT message and displays the key you pressed (e.g., a
space).
MTA128ST/NT receives garbage characters when connected to a 3Com Impact IQ terminal adapter.
Most likely, the Impact IQ has compression turned on. The compression used by the Impact IQ is
incompatible with the compression used by the MTA128ST/NT. Disconnect the data connection and give
the Impact IQ the command AT%CO and then establish the data connection again. The garbage
characters should disappear.