User's Guide

User’s Guide CDPD Operation
2110059 Rev 1.1 Proprietary and Confidential Page 31
Directory Profile maintained for each subscriber on that CDPD network by the CDPD service
provider.
5.1.3.3. Authentication
Each NEI (network account) is mated to an EID (modem device). One NEI cannot be used with
different devices (EIDs). One device (EID) can have more than one associated NEI (account).
One of the functions performed by the CDPD network is NEI authentication and verification.
This service provides corroboration to ensure that the source of the data received from a user is as
claimed and not from a cloned CDPD subscriber device. In other words, only the authorized
owner of the NEI (the modem) is using the NEI. As a result of this authentication procedure,
once a user has registered an NEI and a modem, they cannot use that NEI for data
communication over the CDPD network on a new or different modem.
If you replace or change modems, you must contact your service provider to reset your network
credentials before you can use the new modem.
5.1.4. CDPD Radio Coverage
The subscriber should obtain information from the service provider about what CDPD service
coverage is available in the required areas.
In most cases, the subscriber will not be aware of the quality of service provided over the CDPD
airlink. Watcher does provide a feature that gives the user an indication of the airlink quality for
their Sierra Wireless modem. This quality metric is based on the strength of the signal that is
being received by the modem.
Received Signal Strength Indication (RSSI) is a measure of the strength of the RF signal received
by the modem. It is expressed either by an analogue thermometer or a logarithmic scale, in
decibels relative to one milliWatt (dBm). A strong signal level has a less negative number (i.e.,
-60 dBm) and a weak signal level has a more negative number (i.e., -100 dBm). Connections are
lost for signals below -113 dBm.
The CDPD service provider attempts to ensure that the signal level is fairly strong throughout the
coverage area (i.e., -80 dBm or stronger), but due to shielding of the signal by man-made
structures, the signal may be less than this desired value.
Examples of locations where a signal could be weaker than desired is in underground parking
garages, tunnels, buildings with all metal construction, old concrete buildings with large amounts
of steel reinforcing bars, etc. In such cases, the CDPD subscriber may be able to get a stronger
signal by locating the antenna near an opening or window. The effect of this repositioning on the
RSSI can be observed in the signal strength window of the Watcher application.
5.1.5. CDPD and the SB300 Series Modems
The role of the Sierra Wireless modem in CDPD mode is:
6. Accept commands and digital data from the end-user application equipment (DTE) through
the serial connection.
7. Assemble the data into packets.
8. Encrypt the packets.
9. Transmit the encrypted data packet to the network.
10. Receive packet data from the network.
11. Decrypt the packets.
12. Disassemble the packets to extract the application data.
13. Pass the serial data to the end-user’s application equipment.