megaco_sdp.hrl

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%%   time zone adjustment happens and the offset from the time when
%%   the session was first scheduled.  The "z" field allows the sender
%%   to specify a list of these adjustment times and offsets from the
%%   base time.
%%
%%   An example might be:
%%
%%                      z=2882844526 -1h 2898848070 0
%%
%%   This specifies that at time 2882844526 the time base by which the
%%   session's repeat times are calculated is shifted back by 1 hour,
%%   and that at time 2898848070 the session's original time base is
%%   restored. Adjustments are always relative to the specified start
%%   time - they are not cumulative.
%%
%% o If a session is likely to last several years, it is expected that
%%   the session announcement will be modified periodically rather
%%   than transmit several years worth of adjustments in one
%%   announcement.
%% 

-record(megaco_sdp_t, {
          start,                                % integer()
          stop                                  % integer()
         }).

-record(megaco_sdp_r, {
          repeat_interval,                      % string()
          active_duration,                      % string()
	  list_of_offsets                       % [ string() ]
	 }
       ).
      
-record(megaco_sdp_z, {
	  list_of_adjustments                   % [ string() ]
	 }
       ).




%% ===================================================================
%% 
%% Encryption Keys
%% 
%% k=<method>
%% k=<method>:<encryption key>
%%
%% o The session description protocol may be used to convey encryption
%%   keys.  A key field is permitted before the first media entry (in
%%   which case it applies to all media in the session), or for each
%%   media entry as required.
%%
%% o The format of keys and their usage is outside the scope of this
%%   document, but see [3].
%%
%% o The method indicates the mechanism to be used to obtain a usable
%%   key by external means, or from the encoded encryption key given.
%%
%%   The following methods are defined:
%%
%%    k=clear:<encryption key>
%%      The encryption key (as described in [3] for  RTP  media  streams
%%      under  the  AV  profile)  is  included untransformed in this key
%%      field.
%%
%%    k=base64:<encoded encryption key>
%%      The encryption key (as described in [3] for RTP media streams
%%      under the AV profile) is included in this key field but has been
%%      base64 encoded because it includes characters that are
%%      prohibited in SDP.
%%
%%    k=uri:<URI to obtain key>
%%      A Universal Resource Identifier as used by WWW clients is
%%      included in this key field.  The URI refers to the data
%%      containing the key, and may require additional authentication
%%      before the key can be returned.  When a request is made to the
%%      given URI, the MIME content-type of the reply specifies the
%%      encoding for the key in the reply.  The key should not be
%%      obtained until the user wishes to join the session to reduce
%%      synchronisation of requests to the WWW server(s).
%%
%%    k=prompt
%%      No key is included in this SDP description, but the session or
%%      media stream referred to by this key field is encrypted.  The
%%      user should be prompted for the key when attempting to join the
%%      session, and this user-supplied key should then be used to
%%      decrypt the media streams.
%% 

-record(megaco_sdp_k, {
	  method,            % clear | base64 | uri | prompt | string()
	  encryption_key     % undefined | string()
	 }
       ).




%% ===================================================================
%% 
%% Attributes
%% 
%% a=<attribute>
%% a=<attribute>:<value>
%%
%% Attributes are the primary means for extending SDP.  Attributes may
%% be defined to be used as "session-level" attributes, "media-level"
%% attributes, or both.
%%
%% A media description may have any number of attributes ("a=" fields)
%% which are media specific.  These are referred to as "media-level"
%% attributes and add information about the media stream.  Attribute
%% fields can also be added before the first media field; these
%% "session-level" attributes convey additional information that
%% applies to the conference as a whole rather than to individual
%% media; an example might be the conference's floor control policy.
%%
%% Attribute fields may be of two forms:
%%
%% o property attributes.  A property attribute is simply of the form
%%   "a=<flag>".  These are binary attributes, and the presence of the
%%   attribute conveys that the attribute is a property of the
%%   session.  An example might be "a=recvonly".
%%
%% o value attributes.  A value attribute is of the form
%%   "a=<attribute>:<value>".  An example might be that a whiteboard
%%   could have the value attribute "a=orient:landscape"
%%
%% Attribute interpretation depends on the media tool being invoked.
%% Thus receivers of session descriptions should be configurable in
%% their interpretation of announcements in general and of attributes
%% in particular.
%%
%% Attribute names must be in the US-ASCII subset of ISO-10646/UTF-8.
%%
%% Attribute values are byte strings, and MAY use any byte value
%% except 0x00 (Nul), 0x0A (LF), and 0x0D (CR). By default, attribute
%% values are to be interpreted as in ISO-10646 character set with
%% UTF-8 encoding.  Unlike other text fields, attribute values are NOT
%% normally affected by the `charset' attribute as this would make
%% comparisons against known values problematic.  However, when an
%% attribute is defined, it can be defined to be charset-dependent, in
%% which case it's value should be interpreted in the session charset
%% rather than in ISO-10646.
%%
%% Attributes that will be commonly used can be registered with IANA
%% (see Appendix B).  Unregistered attributes should begin with "X-"
%% to prevent inadvertent collision with registered attributes.  In
%% either case, if an attribute is received that is not understood, it
%% should simply be ignored by the receiver.
%% 
%% Suggested Attributes
%% 
%% The following attributes are suggested.  Since application writers
%% may add new attributes as they are required, this list is not
%% exhaustive.
%%
%% a=cat:<category>
%%   This attribute gives the dot-separated hierarchical category of
%%   the session.  This is to enable a receiver to filter unwanted
%%   sessions by category.  It would probably have been a compulsory
%%   separate field, except for its experimental nature at this time.
%%   It is a session-level attribute, and is not dependent on charset.
%%
%% a=keywds:<keywords>
%%   Like the cat attribute, this is to assist identifying wanted
%%   sessions at the receiver.  This allows a receiver to select
%%   interesting session based on keywords describing the purpose of
%%   the session.  It is a session-level attribute. It is a charset
%%   dependent attribute, meaning that its value should be interpreted
%%   in the charset specified for the session description if one is
%%   specified, or by default in ISO 10646/UTF-8.
%%
%% a=tool:<name and version of tool>
%%   This gives the name and version number of the tool used to create
%%   the session description.  It is a session-level attribute, and is
%%   not dependent on charset.
%%
%% a=ptime:<packet time>
%%   This gives the length of time in milliseconds represented by the
%%   media in a packet. This is probably only meaningful for audio
%%   data.  It should not be necessary to know ptime to decode RTP or
%%   vat audio, and it is intended as a recommendation for the
%%   encoding/packetisation of audio.  It is a media attribute, and is
%%   not dependent on charset.
%% 
%% a=recvonly
%%   This specifies that the tools should be started in receive-only
%%   mode where applicable. It can be either a session or media
%%   attribute, and is not dependent on charset.
%%
%% a=sendrecv
%%   This specifies that the tools should be started in send and
%%   receive mode.  This is necessary for interactive conferences with
%%   tools such as wb which defaults to receive only mode. It can be
%%   either a session or media attribute, and is not dependent on
%%   charset.
%%
%% a=sendonly
%%   This specifies that the tools should be started in send-only
%%   mode.  An example may be where a different unicast address is to
%%   be used for a traffic destination than for a traffic source. In
%%   such a case, two media descriptions may be use, one sendonly and
%%   one recvonly. It can be either a session or media attribute, but
%%   would normally only be used as a media attribute, and is not
%%   dependent on charset.
%%
%% a=orient:<whiteboard orientation>
%%   Normally this is only used in a whiteboard media specification.
%%   It specifies the orientation of a the whiteboard on the screen.
%%   It is a media attribute. Permitted values are `portrait',
%%   `landscape' and `seascape' (upside down landscape). It is not
%%   dependent on charset
%%
%% a=type:<conference type>
%%   This specifies the type of the conference.  Suggested values are
%%   `broadcast', `meeting', `moderated', `test' and `H332'.
%%   `recvonly' should be the default for `type:broadcast' sessions,
%%   `type:meeting' should imply `sendrecv' and `type:moderated'
%%   should indicate the use of a floor control tool and that the
%%   media tools are started so as to "mute" new sites joining the
%%   conference.
%%
%%   Specifying the attribute type:H332 indicates that this loosely
%%   coupled session is part of a H.332 session as defined in the ITU
%%   H.332 specification [10].  Media tools should be started
%%   `recvonly'.
%%
%%   Specifying the attribute type:test is suggested as a hint that,
%%   unless explicitly requested otherwise, receivers can safely avoid
%%   displaying this session description to users.
%%   
%%   The type attribute is a session-level attribute, and is not
%%   dependent on charset.
%% 
%% a=charset:<character set>
%%   This specifies the character set to be used to display the
%%   session name and information data.  By default, the ISO-10646
%%   character set in UTF-8 encoding is used. If a more compact
%%   representation is required, other character sets may be used such
%%   as ISO-8859-1 for Northern European languages.  In particular,
%%   the ISO 8859-1 is specified with the following SDP attribute:
%%   
%%                         a=charset:ISO-8859-1
%%   
%%   This is a session-level attribute; if this attribute is present,
%%   it must be before the first media field.  The charset specified
%%   MUST be one of those registered with IANA, such as ISO-8859-1.
%%   The character set identifier is a US-ASCII string and MUST be
%%   compared against the IANA identifiers using a case-insensitive
%%   comparison.  If the identifier is not recognised or not
%%   supported, all strings that are affected by it SHOULD be regarded
%%   as byte strings.
%%   
%%   Note that a character set specified MUST still prohibit the use
%%   of bytes 0x00 (Nul), 0x0A (LF) and 0x0d (CR). Character sets
%%   requiring the use of these characters MUST define a quoting
%%   mechanism that prevents these bytes appearing within text fields.
%%
%% a=sdplang:<language tag>
%%   This can be a session level attribute or a media level attribute.
%%   As a session level attribute, it specifies the language for the
%%   session description.  As a media level attribute, it specifies
%%   the language for any media-level SDP information field associated
%%   with that media.  Multiple sdplang attributes can be provided
%%   either at session or media level if multiple languages in the
%%   session description or media use multiple languages, in which
%%   case the order of the attributes indicates the order of
%%   importance of the various languages in the session or media from
%%   most important to least important.
%%   
%%   In general, sending session descriptions consisting of multiple
%%   languages should be discouraged.  Instead, multiple descriptions
%%   should be sent describing the session, one in each language.
%%   However this is not possible with all transport mechanisms, and
%%   so multiple sdplang attributes are allowed although not
%%   recommended.
%%   
%%   The sdplang attribute value must be a single RFC 1766 language
%%   tag in US-ASCII.  It is not dependent on the charset attribute.
%%   An sdplang attribute SHOULD be specified when a session is of
%%   sufficient scope to cross geographic boundaries where the
%%   language of recipients cannot be assumed, or where the session is
%%   in a different language from the locally assumed norm.
%% 
%% a=lang:<language tag>