Rants, Raves, Reviews


CDMA Application Development Part 3

By Gary R, in , posted: 27-Mar-2006 13:43

The other week I talked about dormancy. If you use 1xRTT for telemetry applications you will notice that there a delay in receiving a reply to a data request from the CDMA device. This delay can be 5 seconds and sometimes as high as 8 seconds.
When a CDMA device is dormant its availability to reconnect (bring up radio) and respond to a data request is governed by a setting called Slot Cycle Index (SCI). Each shared network channel is divided into time slots, to conserve battery life phones/devices wake up and listen for network messages based on the phone/device assigned time slot. Generally the default SCI is to '2', which means the phone/device will wake up and check network messages every 5.12 seconds. This is the overhead and the reason why there is a delay to data requests. The good news is that the setting can be changed. Generally this can not be done by the user as it requires a software tool to change the phone/device. If you are on battery I don't recommend you change the setting at all, if you are on power (modem on mains) then there is no reason why you can not have the setting changed. For time critical data applications changing the SCI can have quite a dramatic effect. The recommended SCI settings are '0'- check network messages every 1.18 seconds or '1' - every 2.56 seconds.
Push to Talk is a example of a service that changes the SCI to suit the application. When PTT is initiated the phone changes the SCI from '2' to '0'. The reason for changing SCI is to improve response time, at SCI '2' a user would have to wait 5 seconds to reply on PTT - quite a lag.


Other related posts:
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Gary R
Wellington
New Zealand


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