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Appendix A – Working With the IWF

CDMA 1xEV-D0 AT Commands Reference Guide (Document S000482B) 61

Appendix A – Working With

the IWF

Introduction

Note: The information in Appendix A applies to cellular accounts with Circuit-Switched Data service. Check

with your service provider to see which services are enabled for your account.

When operating a CDMA modem in IS 95B Circuit-Switched Cellular (CSC) service, the local modem and the

IWF modem must work as a team to perform the duties that a traditional wire line modem handles alone. To

support this teamwork, the modem has an extensive set of commands to query the PCS network and IWF for

information about the services and capabilities available. There are also commands to configure the IWF modem

as well as commands to configure the local modem.

The modem is designed to keep this dependency as transparent as possible. Commands that configure the IWF

modem are typically stored at the local modem until a connection request is made. At that time, the commands

are sent as a block to the IWF to set up the modem team for the call. Settings stored at the local modem will

report the user setting even though the command is intended for execution / implementation at the IWF.

The airlink radio connection between these two modems operates on two levels. There is the traditional link to

exchange user data between the local and remote terminal applications, and a second link to exchange

operational information between the local modem and the IWF modem. This second link is largely transparent to

the user.

The modem control information is exchanged using a transport layer of the airlink that is independent of an active

data call. The modem can open the airlink specifically to exchange command settings without having an

incoming or outgoing call on the usual data link. Normal call setup will trigger the local modem to open the airlink

for the transport of the dial command. The data aspect of the link is not opened until the IWF has established the

call through to the remote terminal.

The two modems use the transport layer of the airlink to stay synchronized. In simple operation, the user would

not be aware that there are actually two modems on the local side of the connection. The local modem and the

IWF modem co-ordinate their functions without specific user actions.

Local and Remote Commands

Some commands in this reference are noted as “(Remote)”. This indicates that the command is related to query

or configuration of the IWF modem.

There are essentially three classes of commands: Local Only, Shared, and Remote-only.

Local Only

These are commands that control or query the local modem only. There are only a very few commands like

this that are not shared. Local only commands return an ERROR result when the airlink to the IWF is active,

but return valid results when the modem is on-hook. I5 is an example.

Shared

These commands appear to execute on the local modem. In fact these commands only store settings that

are later used to configure the IWF, which must actively use the settings in establishing a call on the PSTN.

The local modem does not need to create an airlink to the IWF for these commands. When an airlink is

needed, the settings are sent to the IWF as part of the initialization of the link.

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