CDPD Network Error Messages

There are a number of conditions under which a modem must attempt to find a better channel. The following channel scan triggers are possible:

Max Missing Busy - The modem started transmitting but did not see the base station and set the channel busy flag. The modem retried some number of times, with same result. This error indicates that the base station cannot "hear" the mobile at all. A particularly weak return path, or a mistuned base station can cause this error.

Max Tx Attempts - The modem started transmitting but the base station signaled that some part of the transmission burst was received with uncorrectable errors. The modem retried a number of times, with the same results. This error indicates that the base station can "hear" the mobile, but not very well. It could also be due to excessive collisions for access to the inbound channel between mobiles.

New Cell Config - The modem has received information from the base station about neighbor cells it was not aware of before. The modem should check to see if one of those new neighbors is a better channel than the current channel.

RSSI Scan Timeout - The modem is required to periodically scan the known neighbor cells for a better signal, no matter what else happens.

RSSI Upper/Lower Threshold - The modem is required to scan the neighbor cells if the signal in the current channel changes by more than a certain threshold. It indicates the mobile may be moving, and could be crossing the boundary between cells.

BLER Threshold - The signal received from the base station is being received with more than a certain threshold of uncorrectable errors.

Channel Sync Lost - There have been so many uncorrectable errors in the signal received from the base station that the modem no longer knows which bit is which. Typically happens if the base station signal is suddenly cut off -- a tunnel, for example, or voice preempt of the channel (if channel hopping).

Color Change - In a cellular system, where channels are reused on other cells, each cell broadcasts a color code. It allows the modem to distinguish whether it's listening to, say, channel 720, at the nearby cell, or channel 720 from a cell several kilometers away. If the color code changes unexpectedly, then somehow the modem is no longer listening to the cell it thought it was.

Wide Area Scan (?) - The modem has tried all it's short lists of known channels or neighbor cells without success and has resorted to a more exhaustive search of all possible cellular channels.

In actual practice, the most common scan trigger is "Rssi Scan Timeout" or "RSSI Threshold", followed by "BLER Threshold" or "MaxTxAttempts" in marginal coverage areas.

Last update: October 3, 2000 - KC
Reviewed: December 1, 2000 - DJW