Specifications

Sierra Wireless, Inc. CDPD Primer
2130006 Rev 1.0 Page 31
In most urban areas, the maximum power level allowed is 2 (600 mW) because of the high density
of cells. However, the carrier may set a lower value (a higher level number), believing that CDPD
traffic can cause noise problems on the voice channels. There is little evidence that this actually
happens, but voice-conscious carriers may arbitrarily set the maximum to a level from 3 to 5. This
may cause serious problems for CDPD operation.
For voice systems, any adjustments made to the cell transmit power or receiver sensitivity, to
improve voice system operation, are automatically compensated for by the cell site base station
algorithms that control the voice system power level. This is not true for the CDPD system: the
modem is responsible for determining its own transmit power level by using the parameters
provided by the serving MDBS.
A site may have been set up properly for voice and CDPD, but over time adjustments made for
voice issues may have caused the CDPD configuration to fall out of balance. This can happen if
the cell site transmitter (forward channel) power or receiver (reverse channel) sensitivity have
been adjusted without making compensating changes to the appropriate CDPD parameters. End
users may need to contact their carrier if CDPD service is unreliable because the M-ESs are not
being permitted to transmit at sufficient power for their local conditions.
5.7. Sleep Mode
CDPD provides a facility to allow modems to go into sleep mode when they do not have active
traffic with the network, allowing the M-ES to shut down hardware to reduce power consumption.
When the modem is waiting for data from either the host or the network, it does not need to keep
all hardware systems running. The modem can negotiate with the CDPD network during the
registration process to have the network send a periodic message advising if there is pending
traffic. Between these messages, the modem can be programmed to shut down the radio (go to
sleep). The modem will wake up at the predetermined intervals to check the network for incoming
traffic. If there is no pending traffic, then the device can go back to sleep until the next scheduled
notification message.
Sleep mode is managed using the Mobile Data Link Protocol (MDLP, see section 5.4). During the
registration process (see section 5.1), the CDPD network advises the modem of the time interval
between periodic notification messages. This is typically 60 to 90 seconds, set by the carrier.
The CDPD modem goes to sleep after a specified period of inactivity, the modem wakes up after
every interval to listen to the list of TEIs (see section 5.1.2) broadcast by the MD-IS. If one of the
broadcast TEIs corresponds to the NEI for the sleeping device, it goes back online to make the
connection. Otherwise, it returns to sleep for another interval.
The disadvantage to sleep mode is that traffic from the network will have to wait up to a full
interval before the modem can receive it. This delay in responding can be too great for some time-
critical applications.
Most CDPD networks support sleep mode, and many M-ES devices can go to sleep. Those that
do, also let the end user disable sleep mode to keep the data connection as fast as possible,
especially when the modem is plugged into a wall socket or other power source that does not
require conservation of battery power.