Modem Speeds; Serial Speed; Line Speed; Modem Profiles - Lantronix SCS Reference Manual

Modems

9.2 Modem Speeds

The modem's serial speed, measured in bits per second (bps), is the rate at which the modem sends data to
a host computer or other device (such as the SCS) over its serial port. The modem's line speed, also
measured in bits per second, is the rate at which the modem sends data through a telephone line to another
modem or communications server. Although the two are related, they are not the same thing.

9.2.1 Serial Speed

The modem and the SCS must agree on the serial speed used for the connection to avoid corrupted data.
However, the SCS may speak to a remote modem at a different speed due to error correction and flow
control techniques used for the connection. In general, the serial speed should be set higher than the line
speed, and higher still if compression is used.
Commonly used serial speeds include 300, 600, 1200, 2400, 4800, 9600, 19200, 38400, 57600, 115200, and
230,400 bps. The SCS's default serial speed is 9600 bps, but can be changed with the Set/Define Ports
Speed command. When a modem profile is defined, the SCS will automatically select the highest possible
serial speed.
See your modem's documentation for more information about supported serial
Note:
speeds and configuration options.

9.2.2 Line Speed

Common line speeds include 9600, 14400, 28800, and 33600 bps. 9600 and 14400 are sometimes referred
to by the names of the modem standards that define them (v.32 and v.32bis, respectively).
Notice that the faster line speeds do not have corresponding serial speeds. If there is not matching serial
speed, the next highest serial speed should be used because faster serial speeds make the most efficient use
of the given line speed. For example, a v.32bis modem (14400 bps) should use at least a 19200 bps serial
speed.
To configure the proper serial and line speeds for a connection, see the Examples section on page 9-13.
Flow control must be used when the line speed and serial speed do not match.
Note:
For more information on flow control setup, see Flow Control on page 8-18.

9.3 Modem Profiles

The SCS interacts with a modem by sending commands to and expecting responses from the modem. This
communication consists of strings or of simple commands to enable or disable modem features.
In order to communicate properly with a particular modem (this varies from modem to modem), the SCS
consults a list of appropriate commands and responses for that modem. This compilation is called a modem
profile.
9-2
Modem Speeds