character encoding (as registered in the IANA registry) from the recommended default value (UTF-8) for standard protocol keys. These values contain a text that is intended to be displayed to a user. a=sdplang:code is used to specify the language of text. Alternate text in multiple languages may be carried in the session, and selected automatically by the user agent according to user preferences. In both cases, text fields intended to be displayed to a user are interpreted as opaque strings, but rendered to the user or application with the values indicated in the last occurrence of the fields charset and sdplang in the current media section, or otherwise their last value in the session section. The parameters v, s, and o are mandatory, must not be empty, and should be UTF-8-encoded. 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). If the stop time is 0 then the session is unbounded. If the start time is also zero then the session is considered permanent. Unbounded and permanent sessions are discouraged but not prohibited. Intervals can be represented with NTP times or in typed time: a value and time units (days: d, hours: h, minutes: m and seconds: s) sequence. Thus an hour meeting from 10 am UTC on 1 August 2010, with a single repeat time a week later at the same time can be represented as: t= r=604800 3600 0 Or using typed time: t= r=7d 1h 0 When repeat times are specified, the start time of each repetition may need to be adjusted to compensate for daylight saving time changes so that it will occur at the same local time in a specific time zone throughout the period between the start time and the stop time. Instead of specifying this time zone and having to support a database of time zones for knowing when and where daylight adjustments will be needed, the repeat times are assumed to be all defined within the same time zone, and SDP supports the indication