They are used as identifiers and are not intended to be displayed to users. A few other attributes are also present in the example, either as a session-level attribute (such as the attribute in property form a=recvonly), or as a media-level attribute (such as the attribute in value form a=rtpmap:99 h263-1998/90000 for the video in the example). ==Time formats and repetitions== Absolute times are represented in Network Time Protocol (NTP) format (the number of seconds since 1900).
SDP was originally a component of the Session Announcement Protocol (SAP), but found other uses in conjunction with the Real-time Transport Protocol (RTP), the Real-time Streaming Protocol (RTSP), Session Initiation Protocol (SIP), and as a standalone protocol for describing multicast sessions. The IETF published the original specification as a Proposed Standard in April 1998.
Revised specifications were released in 2006 (RFC 4566), and in 2021 (RFC 8866).. ==Session description== The Session Description Protocol describes a session as a group of fields in a text-based format, one field per line.
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 1h 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 full one 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.
from Sunday 1 August 2010 3 am UTC to Sunday 26 June 2011 4 am UTC (stop time of the last repeat, i.e.
Revised specifications were released in 2006 (RFC 4566), and in 2021 (RFC 8866).. ==Session description== The Session Description Protocol describes a session as a group of fields in a text-based format, one field per line.
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