User's Guide

2110059 Rev 1.1 Proprietary and Confidential Page 21
4. Basic Modem Operation
4.1. Introduction
This chapter provides some fundamentals to the operation of Sierra Wireless OEM modems and
some configuration elements of the host (DTE) to modem communication. Important
considerations for wireless connections are covered here but specific techniques for setting up the
modem for various remote operations are provided in chapters on each mode of operation.
This chapter covers:
• Important terminology on modem modes and states.
• DTE / DCE communications link.
• Introduction to communication protocols and protocol stacks.
• Introduction to modem-to-modem handshaking and protocols.
4.2. Modem Modes and States
The SB320 modem supports multiple modes of operation and various states within each mode.
The other OEM modems only support CDPD mode but the states and conditions apply to them as
well.
The commands and registers used depend on the modem’s operating mode. The state of the
modem and its condition also determine how the modem will behave in any given situation.
Depending on the product, the exact options available can differ. If a mode or state is not
available on the product, commands related to those modes and states will return the ERROR
result code.
4.2.1. Modes
The SB320 supports all of these modes while the SB30x family are CDPD mode only.
• Wireline data – connected to the Public Switched Telephone Network (PSTN) using a cable
(usually with RJ-11 connectors). The TIP and RING signals service the wireline connection.
• Wireline voice – connected to the PSTN and using the MIC and SPKR signals to convey
voice instead of data.
• Circuit Switched Cellular (CSC) data – connected to a cellular network using the Advanced
Mobile Phone Service (AMPS).
• Circuit Switched Cellular (CSC) voice – using the AMPS cellular network to communicate
voice instead of data.
• Cellular Digital Packet Data (CDPD) – connected to a cellular packet switched data
network.
4.2.2. States
The modem’s state, in conjunction with its condition, will govern how the modem handles traffic
to and from the host and to and from a remote modem.
All non-voice modes support two states:
• Command – the modem exchanges data with the host (DTE) as AT commands and replies.
• Data – communication is passed between the host and remote terminal as computer data.