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Configuring the Modem 4-23
Confi
guring
the Modem
• Configuring The Modem for SDC Operation—configuration options that are
critical to ensure optimum network performance on an SDC connection
• SDC Sample Applications—examples of common SDC applications
SDC Pre-Operation Notes
This section contains important information for using the 326XFAST-SDC Modem in
SDC operating mode. Read this section before configuring the unit.
Operational Requirements
• 326XFAST-SDC modems require framed HDLC/SDLC-like data. NOTE: BER
tests do not operate in an SDC environment because the data is not framed.
• 326XFAST-SDC modems support an NRZ or NRZI data encoding method. Refer
to the DTE documentation for information on the data encoding method the DTE
supports. (Refer to Appendix A, Data Form [AT
* DF] option, for details on
NRZ/NRZI data encoding methods.)
Optimizing Network Performance
The 326XFAST-SDC modem provides front panel displays of RX/TX Throughput and
Link Utilization. Higher values indicate more efficient utilization; lower values indi-
cate less efficient usage. These values are affected by the attached DTE and protocol
characteristics—frame size, window size, and DTE rate selected.
(Refer to Chapter 1 of the326X Series Modem Reference Guide for a description of
how to use the RX/TX Throughput and Link Utilization displays.)
Motorola recommends the following to maximize efficiency:
• If your application is operating in a windowed protocol environment, set the win-
dow sizes to greater than 1 to improve performance. Recall that windowing
refers to the number of packets sent before an acknowledgment is required.
• To improve network performance, adjust frame sizes. The optimum frame size
for most applications is between 128 and 1024 bytes. Experiment with window
and frame sizes for maximum performance.
• If link utilization is low, raise the DTE rate. Low link utilization typically implies
that the DTE equipment is the bottleneck in data transmission.
Configuring the Modem for SDC Operation
You can configure the 326XFAST-SDC Modem for SDC in one of these ways:
• Select Option Set 2, 3, or 4Leased, discussed below
• Configure the modem as follows:
— Select one of the reliable data transfer modes (Reliable, Auto Reliable, or
Speed Auto Reliable).
— Choose an Auto-Call Unit (ACU)—AT, V.25bis, LPDA, or None—using
the ACU Select option, ACU OPT’S category.
— Select a bit-synchronous data format (depending on the ACU type).