SARA-R42 - Application note
UBX-20050829 - R02 PSM, eDRX and deep-sleep mode Page 27 of 58
C1-Public
The selection of the requested T3324 timer value is a trade-off between power consumption and
responsiveness. Low values save more battery life making it possible for the UE to enter PSM
deep-sleep mode more quickly. High values of T3324 give some margin to the application server (AS)
to respond to MO data sent by the UE before it enters PSM. AS responses to MO data can be both MO
data acknowledgements as well as MT data delivery as a response to MO pull messages.
As a rule of thumb, the maximum suggested T3324 is 10 times shorter than T3412 and the minimum
suggested T3324 should allow reliable paging if MT data or acknowledgements delivery is considered
in the application design. The time needed to reliably deliver paging to the UE depends on whether the
network uses discontinuous reception (DRX) and can be determined as 2*DRX cycle + 10 s (buffer
time at network side), which amounts to 16 s in case of 2.36 s long DRX cycles. In case MT data or
acknowledgements are not considered in the application design or in case the RRC inactivity timer
adopted by the network matches the paging delivery reliability application needs a 0 s T3324 timer
duration is also allowed.
Customers are advised to test out both parameters to come to a value that best fits their use case
and requirements in terms of power consumptions, MT data delay, and reliability.
8.1.2 Timer values
8.1.2.1 Encoding of timer T3412
The extended TAU timer is encoded as GPRS timer 3 IE (see TS 3GPP TS 24.008 [12]).
Bits 5 to 1 represent the binary coded timer value. Bits 6 to 8 define the timer value unit for the GPRS
timer and are encoded as follows.
BIT 8 7 6
0 0 0 value is incremented in multiples of 10 minutes
0 0 1 value is incremented in multiples of 1 hour
0 1 0 value is incremented in multiples of 10 hours
0 1 1 value is incremented in multiples of 2 seconds
1 0 0 value is incremented in multiples of 30 seconds
1 0 1 value is incremented in multiples of 1 minute
1 1 0 value is incremented in multiples of 320 hours
1 1 1 value indicates that the timer is deactivated
Example: "01000111" = 7 x 10 hours = 70 hours
☞ If the timer is not received in an integrity protected message (this can happen for example on lab
setup on network simulators), the 110 unit shall be interpreted as 1 hour.
☞ If the 111 unit is used, the T3412 extended value is considered as not included in the message.
In case the network does not grant an extended periodic TAU timer value the standard periodic TAU
timer value can be decoded using the T3324 timer table, since they share the same encoding. The
standard or extended value encoding of the periodic TAU timer is indicated by the
<Assigned_Periodic_TAU_Format_Type> parameter of the +UCPSMS AT command response.
8.1.2.2 Encoding of timer T3324
The Active Time T3324 is encoded as GPRS timer IE (see TS 3GPP TS 24.008 [12]).
Bits 5 to 1 represent the binary coded timer value. Bits 6 to 8 define the timer value unit for the GPRS
timer as follows:
BIT 8 7 6
0 0 0 value is incremented in multiples of 2 seconds
0 0 1 value is incremented in multiples of 1 minute
0 1 0 value is incremented in multiples of decihours (6 minutes)
1 1 1 value indicates that the timer is deactivated
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