User's Guide

2110059 Rev 1.1 Proprietary and Confidential Page 57
6. CSC Operation
This section provides information on configuring and using the SB320 modem in Circuit Switched
Cellular (CSC) data mode if you are not using Watcher and Windows Dial-up Networking for
your connections. If you are using a standard Windows-based application then consult Section 3.3
Configuration using WirelessExpert.
The introduction provides some background on CSC communications in general.
For details on CSC Voice operation see Section 8 Voice Operation in CSC and Wireline.
6.1. Introduction
Circuit Switched Cellular is a wireless mode of communication in which the data link connection
between the SB320 modem and the remote modem is made over the circuit switched voice cellular
network. This voice cellular network is based on the Advanced Mobile Phone Service (AMPS).
Data communications are carried on over this link as if a standard landline telephone connection is
being used. Circuit Switched Cellular is perhaps the most familiar form of wireless data and voice
communications. This mode works like normal wireline communication except that the modem
link is over a cellular phone call rather than a landline phone call. Like cellular phones, cellular
modems have their own telephone number and require a dedicated channel for the duration of the
call.
6.1.1. Modem Registration
6.1.1.1. Cellular Phone Number
Using the modem over the cellular network requires that the modem be assigned a Number
Assignment Module (NAM). This is essentially the phone number associated with your modem.
This is assigned to you when you register your modem with a cellular carrier. The cellular carrier
requires the unique Electronic Serial Number (ESN) which is assigned to your modem at the
factory.
The unit is capable of retaining two NAMs, with each NAM being independently assigned to any
cellular service provider.
As with your credit card number, bank machine number, or any other private password, you
should safeguard the NAM and keep it private.
Calls made with the Sierra Wireless modem using CSC mode are not possible until the NAM has
been programmed. The NAM data consists of the cellular phone number as well as other
subscriber and cellular service provider information.
6.1.1.2. Electronic Serial Number (ESN)
The Sierra Wireless modem stores the ESN internally. You can display it through the Watcher
application by choosing Help > About from the main menu when the modem is operating in
Circuit Switched Cellular mode. You can also display the ESN by using the AT+WVESN
command. The ESN is displayed in text form for both NAMs.
6.1.2. CSC Radio Coverage
Because the cellular radio channel is an inherently noisy channel (unlike the public switched
telephone network), the remote modem to which the Sierra Wireless modem places a call should
as a minimum, support the V.42 error correction standard. This will correct the errors in data
transmission that occur over the radio channel.