Yealink SIP-T2 SERIES Administrator's Manual page 212

Administrator's Guide for SIP-T2 Series/T19(P) E2/T4 Series/CP860 IP Phones
Details of Configuration Parameters:
Parameters
local_time.summer_time
Description:
Configures Daylight Saving Time (DST) feature.
0-Disabled
1-Enabled
2-Automatic
Web User Interface:
Settings->Time & Date->Daylight Saving Time
Phone User Interface:
Menu->Settings->Basic Settings->Time & Date->SNTP Settings->Daylight Saving
local_time.dst_time_type
Description:
Configures the DST time type.
0-DST by Date
1-DST by Week
Note: It works only if the value of the parameter ―local_time.summer_time‖ is set to 1
(Enabled).
Web User Interface:
Settings->Time & Date->Fixed Type
Phone User Interface:
None
local_time.start_time
Description:
Configures the start time of the DST.
Value formats are:
Month/Day/Hour (for DST by Date)

Month/Week of Month/Day of Week/Hour of Day (for DST by Week)

If ―local_time.dst_time_type‖ is set to 0 (DST by Date), use the mapping:
Month: 1=January, 2=February,..., 12=December
Day: 1=the first day in a month,..., 31= the last day in a month
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Permitted Values
0, 1 or 2
0 or 1
Time
Default
2
0
1/1/0