of NTP absolute times when a daylight offset (expressed in seconds or using a type time) will need to be applied to the repeated start time or end time falling at or after each daylight adjustment. All these offsets are relative to the start time, they are not cumulative. NTP supports this with field z, which indicates a series of pairs whose first item is the NTP absolute time when a daylight adjustment will occur, and the second item indicates the offset to apply relative to the absolute times computed with the field r. For example, if a daylight adjustment will subtract 1 hour on 31 October 2010 at 3 am UTC (i.e. 60 days minus 7 hours after the start time on Sunday 1 August 2010 at 10am UTC), and this will be the only daylight adjustment to apply in the scheduled period which would occur between 1 August 2010 up to the 28 November 2010 at 10 am UTC (the stop time of the repeated 1-hour session which is repeated each week at the same local time, which occurs 88 days later), this can be specified as: t= r=7d 1h 0 z= -1h If the weekly 1-hour session was repeated every Sunday for one full year, i.e. from Sunday 1 August 2010 3 am UTC to Sunday 26 June 2011 4 am UTC (stop time of the last repeat, i.e. 360 days plus 1 hour later, or 31107600 seconds later), so that it would include the transition back to Summer time on Sunday 27 March 2011 at 2 am (1 hour is added again to local time so that the second daylight transition would occur 209 days after the first start time): t= r=7d 1h 0 z= -1h 0 As SDP announcements for repeated sessions should not be made to cover very long periods exceeding a few years, the number of daylight adjustments to include in the z= parameter should remain small. Sessions may be repeated irregularly over a week but scheduled the same way for all weeks in the period, by adding more tuples in the r parameter. For example, to schedule the same event also on Saturday (at the same time of the day) you would use: t= r=7d 1h 0 6d z= -1h 0 The SDP protocol does not support repeating sessions monthly and yearly schedules with such simple repeat times, because they are irregularly