StarTech.com SV1115IPEXT - Manual (Page 50)

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Connecting a Modem
The SV1115IPEXT will work with virtually any Hayes-compatible
modem that recognizes the standard AT command set. Some modem
manufacturers offer “enterprise” grade modem products (at a premium
price) that include technology to improve the stability of connections;
whether this type of product would be beneficial to your application
depends on whether you consider the modem connection to be
mission-critical, the quality of your telecom infrastructure, and your
budget for implementing this solution. The model of modem attached is
essentially transparent to the SV1115IPEXT.
It is important to note that modems that offer “56K” (or 56,000 bps)
connections often achieve connection speeds that are far lower
than their maximum capabilities. Given the limitations of telecom
infrastructure (many locations have yet to implement fully digital
switching technology, and still rely on older analog technology for
some segments), the maximum “upstream” transfer rate is limited to
a maximum of 33,600 bps between two modems; the “downstream”
rate is often within a similar range for a typical connection. Therefore,
speeds below 56,000 bps do not indicate a problem with the modem or
the SV1115IPEXT, but simply reflect the line conditions at the time the
connection is made.
The DTE Serial port on the front panel can be used for serial port
configuration when the modem is connected. It requires the use of a
null modem serial cable.
The DCE Serial port on the rear panel is used to connect the modem
to the SV1115IPEXT and requires the use of a straight through serial
cable.