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Cellular Modems

Toplevel Technologies is experienced in using CDMA, GSM, and Serial RF modem technologies. CDMA is a US standard developed by Qualcomm and has much coverage in the United States.

CDMA was developed mainly for the US market and is well established. Verizon is the main carrier and we have found the system very robust when it comes to data communications. We have experience with circuit switched data on CDMA, and always-on packet switched 1xRTT systems using both dynamic and static IP address modes.

One issue to watch out for is the Preferred Roaming List ( PRL ) used by CDMA. Make sure your modem can automatically update the PRL especially if using a dynamic IP address.

We have worked with GSM circuit switched data in the past. At the time, it was necessary to use a special "data number" to improve connection rates. According to some sources there were issues going across older networks. The GSM system was ultimately tied together by T-Mobile. The GPRS system is T-Mobile’s standard for consumer based packet switched data on their system. It is quite stable when using GPRS phone modems to access the Internet.

The main difference between landline and cellular RF modems is the wireless modem need to understand its own connection quality on the system. So, we are always concerned with Relative Signal Strength Indication (RSSI) and network registration. (It is possible to acquire good RSSI while not being registered on the network).

Command and control issues are similar between cellular modems and landline modems. Both have the standard command mode where you tell the modem what to do, and then there is data mode for data transfer.

Cellular modems are ideal for transmitting data over long distances, when a landline is unavailable. They are also ideal for mobile data collection like fleet management, and where one set of data must be compared to a remote set of data while in motion. There is an associated monthly service fee. Unlike cell phones you can sign up for an account and add or remove individual cellular modems as required. . The use of cellular modem applications is constantly evolving as new methods are devised for new applications.