Avaya Partner 18 Connection Manual page 304

Appendix B: PC Serial Ports
PassageWay Solution operates at a relatively high data rate (19.2 kbps,
or 19200 baud), and it relies on Windows to manage the flow of data
through your PC's serial port. Depending upon your configuration,
Windows may have problems maintaining high data rates through
traditional serial ports. In these situations, a serial port designed for
high-speed communications can eliminate such problems while
providing a reduced load on the microprocessor (thus increasing the
performance of Windows during data transfers relative to standard serial
ports). In most cases, the price differential for such a card is quite
modest and a worthwhile investment
Many serial port cards on the market (and most built-in serial ports) use
either the 8250 or 16450 Universal Asynchronous Receiver Transmitter
(UART) as their key component. Although these UARTs can operate at
high speeds, they do not assist the PC's microprocessor in dealing with
high-speed data transfer. Under Windows, in particular, data can be
lost at high baud rates using these UARTs. If this data loss occurs,
PassageWay Solution cannot function properly.
Whenever possible, select a serial port card which uses the 16550
UART. This industry standard UART is an improved version of the
16450 with hardware support to help offload the microprocessor during
high-speed data transfers. Windows 3.1 has built-in support for the
16550, so no special software configuration is required to obtain the
benefits of the 16550's enhanced capabilities. In addition, any high-
speed peripheral can benefit from the 16550 (for example, a 9.6 kbps or
14.4 kbps data and/or fax modem), not only PassageWay Solution.
In generall, since there is no way of knowing ahead of time if your
particular PC configuration requires an enhanced serial port for
PassageWay Solution, AT&T strongly recommends that you purchase a
card based on the 16550 UART to insure trouble-free operation with
PassageWay Solution.
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