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Appendix A – Working With the IWF

CDMA 1xEV-D0 AT Commands Reference Guide (Document S000482B) 63

Pass through and Reflection

In many respects, the local modem operates as a pass through modem providing the local host device with a

radio link to the IWF modem. In many cases commands are passed through the local modem for execution

at the IWF. The IWF then reflects the command back to the local modem on the transport layer of the airlink.

Both modems are kept synchronized with respect to their configuration.

When a command is entered into the local modem (with the airlink active) the command is passed through to

the IWF without any processing locally. The IWF controls the command line echo (if enabled). There is a

noticeable delay in the echo time when the airlink is active and when it is not.

The IWF processes the command line and reflects it back to the local modem. Only if the IWF is successful

at executing the command is the command reflected back to the local modem for processing locally. If the

command fails, the ERROR result is passed back and through to the local host. This ensures the two

modems are kept synchronized.

For further details on how the command line is processed, see “Command Handling”.

Closing the Airlink

The airlink is closed whenever a call terminates through:

• Normal disconnection (ATH)

• Loss of carrier (disconnection at the remote end or break in the PSTN connection)

• Loss of cellular coverage

If the modem has an airlink established but is not in an active call, the link can be closed by the IWF if there

is no traffic (commands or replies) for the duration set with +CQD. This timer defaults to 50 seconds. The link

can be closed before this time by issuing the H command.

When the airlink is closed, the local modem reports to the host (DTE) with the NO CARRIER result code.

Modem Defaults and Configurations

To summarize the discussion above:

• Both the local modem and the IWF share common defaults.

• The user cannot save a non-standard default configuration.

• Upon initialization of the airlink, the IWF is reset to default, and then any non-default values stored at the

local modem are sent to the IWF to configure both modems to the same settings.

• When the airlink is active, all commands are executed by the IWF first.

Settings are reflected back to the local modem to keep them synchronized.

When the airlink connection is closed, the local modem retains the settings last used, while the IWF modem is

reset to defaults. When the next airlink is opened, the local modem may connect to a different modem at the

IWF, so the local modem must repeat the initialization process. The user does not need to reconfigure the local

modem for each call, although reconfiguration will be needed if the local modem is reset or power-cycled.

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Multitech CDMA Betriebsanweisung Seite 63