%% ``Licensed under the Apache License, Version 2.0 (the "License"); %% you may not use this file except in compliance with the License. %% You may obtain a copy of the License at %% %% http://www.apache.org/licenses/LICENSE-2.0 %% %% Unless required by applicable law or agreed to in writing, software %% distributed under the License is distributed on an "AS IS" BASIS, %% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. %% See the License for the specific language governing permissions and %% limitations under the License. %% %% The Initial Developer of the Original Code is Ericsson Utvecklings AB. %% Portions created by Ericsson are Copyright 1999, Ericsson Utvecklings %% AB. All Rights Reserved.'' %% %% $Id$ %% %%---------------------------------------------------------------------- %% Purpose: %%---------------------------------------------------------------------- %% %% %% Explanaition of the fields in the SDP body %% (See RFC 4566 for the complete decription) %% %% Session descriptions %% %% v protocol version %% o owner/creator and session identifier %% s session name (optional) %% i session information (optional) %% u URI of description (optional) %% e email address (optional) %% p phone number (optional) %% c connection information (optional) %% b bandwidth information (optional) %% One or more time descriptions ("t=" and "r=" lines; see below) %% z time zone adjustment (optional) %% k encryption key (optional) %% a zero or more session attribute lines (optional) %% Zero or more media descriptions %% %% Time descriptions %% %% t time the session is active %% r zero or more repeat times (optional) %% %% Media descriptions, if present %% %% m media name and transport address %% i media title (optional) %% c connection information - optional if included at session-level %% b bandwidth information (optional) %% k encryption key (optional) %% a zero or more media attribute lines (optional) %% %% %% An example SDP description is: %% %% v=0 %% o=jdoe 2890844526 2890842807 IN IP4 10.47.16.5 %% s=SDP Seminar %% i=A Seminar on the session description protocol %% u=http://www.example.com/seminars/sdp.pdf %% e=j.doe@example.com (Jane Doe) %% c=IN IP4 224.2.17.12/127 %% t=2873397496 2873404696 %% a=recvonly %% m=audio 49170 RTP/AVP 0 %% m=video 51372 RTP/AVP 99 %% a=rtpmap:99 h263-1998/90000 %% %% %%---------------------------------------------------------------------- -ifndef(megaco_sdp_). -define(megaco_sdp_, true). %% =================================================================== %% %% Protocol Version ("v=") %% %% v=0 %% %% The "v=" field gives the version of the Session Description %% Protocol. This memo defines version 0. There is no minor version %% number %% -record(megaco_sdp_v, { version % integer() } ). %% =================================================================== %% %% Origin ("o=") %% %% o= %% %% %% The "o=" field gives the originator of the session (their username %% and the address of the user's host) plus a session id and session %% version number: %% %% is the user's login on the originating host, or it is %% "-" if the originating host does not support the concept of %% user IDs. The MUST NOT contain spaces. %% %% is a numeric string such that the tuple of , %% , , and form a %% globally unique identifier for the session. The method of %% allocation is up to the creating tool, but it has %% been suggested that a Network Time Protocol (NTP) %% timestamp be used to ensure uniqueness [13]. %% %% is a version number for this announcement. Its %% usage is up to the creating tool, so long as %% is increased when a modification is made to the session data. %% Again, it is RECOMMENDED that an NTP format timestamp is used %% %% is a text string giving the type of network. %% Initially "IN" is defined to have the meaning "Internet", but %% other values MAY be registered in the future (see Section 8 %% of RFC 4566). %% %% is a text string giving the type of the address that %% follows. Initially "IP4" and "IP6" are defined, but other %% values MAY be registered in the future (see Section 8 %% of RFC 4566). %% %% is the address of the machine from which the %% session was created. For an address type of IP4, this is %% either the fully qualified domain name of the machine or the %% dotted-decimal representation of the IP version 4 address of %% the machine. For an address type of IP6, this is either the %% fully qualified domain name of the machine or the compressed %% textual representation of the IP version 6 address of the %% machine. For both IP4 and IP6, the fully qualified domain name %% is the form that SHOULD be given unless this is unavailable, %% in which case the globally unique address MAY be substituted. %% A local IP address MUST NOT be used in any context where the %% SDP description might leave the scope in which the address is %% meaningful (for example, a local address MUST NOT be included %% in an application-level referral that might leave the scope). %% %% In general, the "o=" field serves as a globally unique identifier %% for this version of this session description, and the subfields %% excepting the version taken together identify the session %% irrespective of any modifications. %% %% For privacy reasons, it is sometimes desirable to obfuscate the %% username and IP address of the session originator. If this is a %% concern, an arbitrary and private MAY be %% chosen to populate the "o=" field, provided that these are selected %% in a manner that does not affect the global uniqueness of the field. %% %% -record(megaco_sdp_o, { user_name, % string() session_id, % integer() version, % integer() network_type = in, % in | string() address_type = ip4, % ip4 | ip6 | string() address % string() } ). %% =================================================================== %% %% Session Name ("s=") %% %% s= %% %% The "s=" field is the textual session name. There MUST be one and %% only one "s=" field per session description. The "s=" field MUST %% NOT be empty and SHOULD contain ISO 10646 characters (but see also %% the "a=charset" attribute). If a session has no meaningful name, %% the value "s= " SHOULD be used (i.e., a single space as the session %% name). %% -record(megaco_sdp_s, { name % string() } ). %% =================================================================== %% %% Session and Media Information ("i=") %% %% i= %% %% The "i=" field provides textual information about the session. %% There MUST be at most one session-level "i=" field per session %% description, and at most one "i=" field per media. If the %% "a=charset" attribute is present, it specifies the character set %% used in the "i=" field. If the "a=charset" attribute is not %% present, the "i=" field MUST contain ISO 10646 characters in %% UTF-8 encoding. %% %% A single "i=" field MAY also be used for each media definition. %% In media definitions, "i=" fields are primarily intended for %% labelling media streams. As such, they are most likely to be %% useful when a single session has more than one distinct media %% stream of the same media type. An example would be two different %% whiteboards, one for slides and one for feedback and questions. %% %% The "i=" field is intended to provide a free-form human-readable %% description of the session or the purpose of a media stream. It %% is not suitable for parsing by automata. %% -record(megaco_sdp_i, { session_descriptor % string() } ). %% =================================================================== %% %% URI ("u=") %% %% u= %% %% A URI is a Uniform Resource Identifier as used by WWW clients [7]. %% The URI should be a pointer to additional information about the %% session. This field is OPTIONAL, but if it is present it MUST be %% specified before the first media field. No more than one URI field %% is allowed per session description. %% -record(megaco_sdp_u, { uri % string() } ). %% =================================================================== %% %% Email Address and Phone Number ("e=" and "p=") %% %% e= %% p= %% %% The "e=" and "p=" lines specify contact information for the person %% responsible for the conference. This is not necessarily the same %% person that created the conference announcement. %% %% Inclusion of an email address or phone number is OPTIONAL. Note %% that the previous version of SDP specified that either an email %% field or a phone field MUST be specified, but this was widely %% ignored. The change brings the specification into line with %% common usage. %% %% If an email address or phone number is present, it MUST be %% specified before the first media field. More than one email or %% phone field can be given for a session description. %% %% Phone numbers SHOULD be given in the form of an international %% public telecommunication number (see ITU-T Recommendation E.164) %% preceded by a "+". Spaces and hyphens may be used to split up a %% phone field to aid readability if desired. For example: %% %% p=+1 617 555-6011 %% %% Both email addresses and phone numbers can have an OPTIONAL free %% text string associated with them, normally giving the name of the %% person who may be contacted. This MUST be enclosed in parentheses %% if it is present. For example: %% %% e=j.doe@example.com (Jane Doe) %% %% The alternative RFC 2822 [29] name quoting convention is also %% allowed for both email addresses and phone numbers. For example: %% %% e=Jane Doe %% %% The free text string SHOULD be in the ISO-10646 character set with %% UTF-8 encoding, or alternatively in ISO-8859-1 or other encodings %% if the appropriate session-level "a=charset" attribute is set. %% -record(megaco_sdp_e, { email % string() } ). -record(megaco_sdp_p, { phone_number % string() } ). %% =================================================================== %% %% Connection Data ("c=") %% %% c= %% %% The "c=" field contains connection data. %% %% A session description MUST contain either at least one "c=" field %% in each media description or a single "c=" field at the session %% level. It MAY contain a single session-level "c=" field and %% additional "c=" field(s) per media description, in which case the %% per-media values override the session-level settings for the %% respective media. %% %% The first sub-field ("") is the network type, which is a %% text string giving the type of network. Initially, "IN" is %% defined to have the meaning "Internet", but other values MAY be %% registered in the future (see Section 8 of RFC 4566). %% %% The second sub-field ("") is the address type. This %% allows SDP to be used for sessions that are not IP based. This %% memo only defines IP4 and IP6, but other values MAY be registered %% in the future (see Section 8 of RFC 4566). %% %% The third sub-field ("") is the connection %% address. OPTIONAL sub-fields MAY be added after the connection %% address depending on the value of the field. %% %% When the is IP4 and IP6, the connection address is %% defined as follows: %% %% o If the session is multicast, the connection address will be an %% IP multicast group address. If the session is not multicast, %% then the connection address contains the unicast IP address of %% the expected data source or data relay or data sink as %% determined by additional attribute fields. It is not expected %% that unicast addresses will be given in a session description %% that is communicated by a multicast announcement, though this %% is not prohibited. %% %% o Sessions using an IPv4 multicast connection address MUST also %% have a time to live (TTL) value present in addition to the %% multicast address. The TTL and the address together define the %% scope with which multicast packets sent in this conference will %% be sent. TTL values MUST be in the range 0-255. Although the %% TTL MUST be specified, its use to scope multicast traffic is %% deprecated; applications SHOULD use an administratively scoped %% address instead. %% %% The TTL for the session is appended to the address using a slash %% as a separator. An example is: %% %% c=IN IP4 224.2.36.42/127 %% %% IPv6 multicast does not use TTL scoping, and hence the TTL value %% MUST NOT be present for IPv6 multicast. It is expected that IPv6 %% scoped addresses will be used to limit the scope of conferences. %% %% Hierarchical or layered encoding schemes are data streams where %% the encoding from a single media source is split into a number of %% layers. The receiver can choose the desired quality (and hence %% bandwidth) by only subscribing to a subset of these layers. Such %% layered encodings are normally transmitted in multiple multicast %% groups to allow multicast pruning. This technique keeps unwanted %% traffic from sites only requiring certain levels of the hierarchy. %% For applications requiring multiple multicast groups, we allow the %% following notation to be used for the connection address: %% %% [/]/ %% %% If the number of addresses is not given, it is assumed to be one. %% Multicast addresses so assigned are contiguously allocated above %% the base address, so that, for example: %% %% c=IN IP4 224.2.1.1/127/3 %% %% would state that addresses 224.2.1.1, 224.2.1.2, and 224.2.1.3 are %% to be used at a TTL of 127. This is semantically identical to %% including multiple "c=" lines in a media description: %% %% c=IN IP4 224.2.1.1/127 %% c=IN IP4 224.2.1.2/127 %% c=IN IP4 224.2.1.3/127 %% %% Similarly, an IPv6 example would be: %% %% c=IN IP6 FF15::101/3 %% %% which is semantically equivalent to: %% %% c=IN IP6 FF15::101 %% c=IN IP6 FF15::102 %% c=IN IP6 FF15::103 %% %% (remembering that the TTL field is not present in IPv6 multicast). %% %% Multiple addresses or "c=" lines MAY be specified on a per-media %% basis only if they provide multicast addresses for different layers %% in a hierarchical or layered encoding scheme. They MUST NOT be %% specified for a session-level "c=" field. %% %% The slash notation for multiple addresses described above MUST NOT %% be used for IP unicast addresses. %% -record(megaco_sdp_c, { network_type = in, % in | string() address_type = ip4, % ip4 | ip6 | string() connection_addr % string() | conn_addr() }). %% Only if address type = ip4 %% conn_addr() -> #megaco_sdp_c_conn_addr{} -record(megaco_sdp_c_conn_addr, { base, % string() ttl, % integer() num_of % undefined | integer() }). %% =================================================================== %% %% Bandwidth ("b=") %% %% b=: %% %% This OPTIONAL field denotes the proposed bandwidth to be used by %% the session or media. The is an alphanumeric modifier %% giving the meaning of the figure. Two values are %% defined in this specification, but other values MAY be registered %% in the future (see Section 8 of RFC 4566 and [21], [25]): %% %% CT If the bandwidth of a session or media in a session is %% different from the bandwidth implicit from the scope, a %% "b=CT:..." line SHOULD be supplied for the session giving the %% proposed upper limit to the bandwidth used (the "conference %% total" bandwidth). The primary purpose of this is to give an %% approximate idea as to whether two or more sessions can coexist %% simultaneously. When using the CT modifier with RTP, if %% several RTP sessions are part of the conference, the conference %% total refers to total bandwidth of all RTP sessions. %% %% AS The bandwidth is interpreted to be application specific (it %% will be the application's concept of maximum bandwidth). %% Normally, this will coincide with what is set on the %% application's "maximum bandwidth" control if applicable. For %% RTP-based applications, AS gives the RTP "session bandwidth" %% as defined in Section 6.2 of [19]. %% %% Note that CT gives a total bandwidth figure for all the media at %% all sites. AS gives a bandwidth figure for a single media at a %% single site, although there may be many sites sending %% simultaneously. %% %% A prefix "X-" is defined for names. This is intended %% for experimental purposes only. For example: %% %% b=X-YZ:128 %% %% Use of the "X-" prefix is NOT RECOMMENDED: instead new modifiers %% SHOULD be registered with IANA in the standard namespace. SDP %% parsers MUST ignore bandwidth fields with unknown modifiers. %% Modifiers MUST be alphanumeric and, although no length limit is %% given, it is recommended that they be short. %% %% The is interpreted as kilobits per second by default. %% The definition of a new modifier MAY specify that the %% bandwidth is to be interpreted in some alternative unit (the "CT" %% and "AS" modifiers defined in this memo use the default units). %% %% bwtype() -> ct | as | string() -record(megaco_sdp_b, { bwtype, % bwtype() bandwidth % integer() }). %% =================================================================== %% %% Times ("t=") %% %% t= %% %% The "t=" lines specify the start and stop times for a session. %% Multiple "t=" lines MAY be used if a session is active at %% multiple irregularly spaced times; each additional "t=" line %% specifies an additional period of time for which the session will %% be active. If the session is active at regular times, an "r=" %% line (see below) should be used in addition to, and following, a %% "t=" line -- in which case the "t=" line specifies the start and %% stop times of the repeat sequence. %% %% The first and second sub-fields give the start and stop times, %% respectively, for the session. These values are the decimal %% representation of Network Time Protocol (NTP) time values in %% seconds since 1900 [13]. To convert these values to UNIX time, %% subtract decimal 2208988800. %% %% NTP timestamps are elsewhere represented by 64-bit values, which %% wrap sometime in the year 2036. Since SDP uses an arbitrary length %% decimal representation, this should not cause an issue (SDP %% timestamps MUST continue counting seconds since 1900, NTP will use %% the value modulo the 64-bit limit). %% %% If the is set to zero, then the session is not bounded, %% though it will not become active until after the . If %% the is also zero, the session is regarded as %% permanent. %% %% User interfaces SHOULD strongly discourage the creation of %% unbounded and permanent sessions as they give no information about %% when the session is actually going to terminate, and so make %% scheduling difficult. %% %% The general assumption may be made, when displaying unbounded %% sessions that have not timed out to the user, that an unbounded %% session will only be active until half an hour from the current %% time or the session start time, whichever is the later. If %% behaviour other than this is required, an end-time SHOULD be given %% and modified as appropriate when new information becomes available %% about when the session should really end. %% %% Permanent sessions may be shown to the user as never being active %% unless there are associated repeat times that state precisely when %% the session will be active. %% -record(megaco_sdp_t, { start, % integer() stop % integer() }). %% =================================================================== %% %% Repeat Times ("r=") %% %% r= %% %% "r=" fields specify repeat times for a session. For example, if a %% session is active at 10am on Monday and 11am on Tuesday for one %% hour each week for three months, then the in the %% corresponding "t=" field would be the NTP representation of 10am %% on the first Monday, the would be 1 week, the %% would be 1 hour, and the offsets would be zero %% and 25 hours. The corresponding "t=" field stop time would be %% the NTP representation of the end of the last session three months %% later. By default, all fields are in seconds, so the "r=" and %% "t=" fields might be the following: %% %% t=3034423619 3042462419 %% r=604800 3600 0 90000 %% %% To make description more compact, times may also be given in units %% of days, hours, or minutes. The syntax for these is a number %% immediately followed by a single case-sensitive character. %% Fractional units are not allowed -- a smaller unit should be used %% instead. The following unit specification characters are allowed: %% %% d - days (86400 seconds) %% h - hours (3600 seconds) %% m - minutes (60 seconds) %% s - seconds (allowed for completeness) %% %% Thus, the above session announcement could also have been written: %% %% r=7d 1h 0 25h %% %% Monthly and yearly repeats cannot be directly specified with a %% single SDP repeat time; instead, separate "t=" fields should be %% used to explicitly list the session times. %% -record(megaco_sdp_r, { repeat_interval, % string() active_duration, % string() list_of_offsets % [ string() ] } ). %% =================================================================== %% %% Time Zones ("z=") %% %% z= .... %% %% To schedule a repeated session that spans a change from daylight %% saving time to standard time or vice versa, it is necessary to %% specify offsets from the base time. This is required because %% different time zones change time at different times of day, %% different countries change to or from daylight saving time on %% different dates, and some countries do not have daylight saving %% time at all. %% %% Thus, in order to schedule a session that is at the same time %% winter and summer, it must be possible to specify unambiguously by %% whose time zone a session is scheduled. To simplify this task for %% receivers, we allow the sender to specify the NTP time that a 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 the following: %% %% 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. Adjustments apply to all "t=" %% and "r=" lines in a session description. %% %% 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 session %% announcement. %% %% adjustment() -> #megaco_sdp_z_adjustement{} -record(megaco_sdp_z, { list_of_adjustments % [ adjustment() ] } ). -record(megaco_sdp_z_adjustement, { time, % string() offset % string() } ). %% =================================================================== %% %% Encryption Keys ("k=") %% %% k= %% k=: %% %% If transported over a secure and trusted channel, the Session %% Description Protocol MAY be used to convey encryption keys. A %% simple mechanism for key exchange is provided by the key field %% ("k="), although this is primarily supported for compatibility %% with older implementations and its use is NOT RECOMMENDED. Work %% is in progress to define new key exchange mechanisms for use with %% SDP [27] [28], and it is expected that new applications will use %% those mechanisms. 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. The format of keys and their %% usage are outside the scope of this document, and the key field %% provides no way to indicate the encryption algorithm to be used, %% key type, or other information about the key: this is assumed to %% be provided by the higher-level protocol using SDP. If there is %% a need to convey this information within SDP, the extensions %% mentioned previously SHOULD be used. Many security protocols %% require two keys: one for confidentiality, another for integrity. %% This specification does not support transfer of two keys. %% %% 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: %% %% The encryption key is included untransformed in this key %% field. This method MUST NOT be used unless it can be %% guaranteed that the SDP is conveyed over a secure channel. %% The encryption key is interpreted as text according to the %% charset attribute; use the "k=base64:" method to convey %% characters that are otherwise prohibited in SDP. %% %% k=base64: %% %% The encryption key is included in this key field but has %% been base64 encoded [12] because it includes characters %% that are prohibited in SDP. This method MUST NOT be used %% unless it can be guaranteed that the SDP is conveyed over %% a secure channel. %% %% k=uri: %% %% A Uniform Resource Identifier is included in the 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 %% reply should specify the encoding for the key. The URI is %% often an Secure Socket Layer/Transport Layer Security %% (SSL/TLS)-protected HTTP URI ("https:"), although this is %% not required. %% %% 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. The use of %% user-specified keys is NOT RECOMMENDED, since such keys tend %% to have weak security properties. %% %% The key field MUST NOT be used unless it can be guaranteed that %% the SDP is conveyed over a secure and trusted channel. An example %% of such a channel might be SDP embedded inside an S/MIME message %% or a TLS-protected HTTP session. It is important to ensure that %% the secure channel is with the party that is authorised to join the %% session, not an intermediary: if a caching proxy server is used, it %% is important to ensure that the proxy is either trusted or unable %% to access the SDP. %% %% method() -> clear | base64 | uri | prompt -record(megaco_sdp_k, { method, % method() | string() encryption_key % undefined | string() } ). %% =================================================================== %% %% Attributes ("a=") %% %% a= %% a=: %% %% 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) that 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. %% %% Attribute fields may be of two forms: %% %% o A property attribute is simply of the form "a=". 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 A value attribute is of the form "a=:". For %% example, 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 session descriptions in general and of %% attributes in particular. %% %% Attribute names MUST use the US-ASCII subset of ISO-10646/UTF-8. %% %% Attribute values are octet strings, and MAY use any octet 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 its value should be interpreted %% in the session charset rather than in ISO-10646. %% %% Attributes MUST be registered with IANA (see Section 8 of RFC %% 4566). If an attribute is received that is not understood, it %% MUST be ignored by the receiver. %% %% SDP Attributes %% %% The following attributes are defined. Since application writers %% may add new attributes as they are required, this list is not %% exhaustive. Registration procedures for new attributes are defined %% in Section 8.2.4 of RFC 4566. %% %% a=cat: %% %% This attribute gives the dot-separated hierarchical category %% of the session. This is to enable a receiver to filter %% unwanted sessions by category. There is no central registry %% of categories. It is a session-level attribute, and it is %% not dependent on charset. %% %% a=keywds: %% %% 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; there is no central registry of keywords. 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: %% %% This gives the name and version number of the tool used to %% create the session description. It is a session-level %% attribute, and it is not dependent on charset. %% %% a=ptime: %% %% This gives the length of time in milliseconds represented by %% the media in a packet. This is probably only meaningful for %% audio data, but may be used with other media types if it %% makes sense. 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-level attribute, and it is not dependent on charset. %% %% a=maxptime: %% %% This gives the maximum amount of media that can be encapsulated %% in each packet, expressed as time in milliseconds. The time %% SHALL be calculated as the sum of the time the media present in %% the packet represents. For frame-based codecs, the time SHOULD %% be an integer multiple of the frame size. This attribute is %% probably only meaningful for audio data, but may be used with %% other media types if it makes sense. It is a media-level %% attribute, and it is not dependent on charset. Note that this %% attribute was introduced after RFC 2327, and non-updated %% implementations will ignore this attribute. %% %% a=rtpmap: / [/] %% %% This attribute maps from an RTP payload type number (as used in %% an "m=" line) to an encoding name denoting the payload format %% to be used. It also provides information on the clock rate and %% encoding parameters. It is a media-level attribute that is not %% dependent on charset. %% %% Although an RTP profile may make static assignments of payload %% type numbers to payload formats, it is more common for that %% assignment to be done dynamically using "a=rtpmap:" attributes. %% As an example of a static payload type, consider u-law PCM %% coded single-channel audio sampled at 8 kHz. This is %% completely defined in the RTP Audio/Video profile as payload %% type 0, so there is no need for an "a=rtpmap:" attribute, and %% the media for such a stream sent to UDP port 49232 can be %% specified as: %% %% m=audio 49232 RTP/AVP 0 %% %% An example of a dynamic payload type is 16-bit linear encoded %% stereo audio sampled at 16 kHz. If we wish to use the dynamic %% RTP/AVP payload type 98 for this stream, additional %% information is required to decode it: %% %% m=audio 49232 RTP/AVP 98 %% a=rtpmap:98 L16/16000/2 %% %% Up to one rtpmap attribute can be defined for each media %% format specified. Thus, we might have the following: %% %% m=audio 49230 RTP/AVP 96 97 98 %% a=rtpmap:96 L8/8000 %% a=rtpmap:97 L16/8000 %% a=rtpmap:98 L16/11025/2 %% %% RTP profiles that specify the use of dynamic payload types %% MUST define the set of valid encoding names and/or a means to %% register encoding names if that profile is to be used with %% SDP. The "RTP/AVP" and "RTP/SAVP" profiles use media subtypes %% for encoding names, under the top-level media type denoted in %% the "m=" line. In the example above, the media types are %% "audio/l8" and "audio/l16". %% %% For audio streams, indicates the number %% of audio channels. This parameter is OPTIONAL and may be %% omitted if the number of channels is one, provided that no %% additional parameters are needed. %% %% For video streams, no encoding parameters are currently %% specified. %% %% Additional encoding parameters MAY be defined in the future, %% but codec-specific parameters SHOULD NOT be added. %% Parameters added to an "a=rtpmap:" attribute SHOULD only be %% those required for a session directory to make the choice of %% appropriate media to participate in a session. Codec-specific %% parameters should be added in other attributes (for example, %% "a=fmtp:"). %% %% Note: RTP audio formats typically do not include information %% about the number of samples per packet. If a non-default (as %% defined in the RTP Audio/Video Profile) packetisation is %% required, the "ptime" attribute is used as given above. %% %% a=recvonly %% %% This specifies that the tools should be started in %% receive-only mode where applicable. It can be either a %% session- or media-level attribute, and it is not dependent %% on charset. Note that recvonly applies to the media only, %% not to any associated control protocol (e.g., an RTP-based %% system in recvonly mode SHOULD still send RTCP packets). %% %% a=sendrecv %% %% This specifies that the tools should be started in send and %% receive mode. This is necessary for interactive conferences %% with tools that default to receive-only mode. It can be %% either a session or media-level attribute, and it is not %% dependent on charset. %% %% If none of the attributes "sendonly", "recvonly", "inactive", %% and "sendrecv" is present, "sendrecv" SHOULD be assumed as %% the default for sessions that are not of the conference type %% "broadcast" or "H332" (see below). %% %% 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 used, %% one sendonly and one recvonly. It can be either a session- %% or media-level attribute, but would normally only be used as %% a media attribute. It is not dependent on charset. Note %% that sendonly applies only to the media, and any associated %% control protocol (e.g., RTCP) SHOULD still be received and %% processed as normal. %% %% a=inactive %% %% This specifies that the tools should be started in inactive %% mode. This is necessary for interactive conferences where %% users can put other users on hold. No media is sent over an %% inactive media stream. Note that an RTP-based system SHOULD %% still send RTCP, even if started inactive. It can be either %% a session or media-level attribute, and it is not dependent %% on charset. %% %% a=orient: %% %% Normally this is only used for a whiteboard or presentation %% tool. It specifies the orientation of a the workspace on %% the screen. It is a media-level attribute. Permitted %% values are "portrait", "landscape", and "seascape" %% (upside-down landscape). It is not dependent on charset. %% %% a=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 an H.332 session as %% defined in the ITU H.332 specification [26]. 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 it is %% not dependent on charset. %% %% a=charset: %% %% 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. For example, the ISO 8859-1 is specified %% with the following SDP attribute: %% %% a=charset:ISO-8859-1 %% %% This is a session-level attribute and is not dependent on %% charset. 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 octet 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 from %% appearing within text fields. %% %% a=sdplang: %% %% 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 is 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 3066 %% language tag in US-ASCII [9]. 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: %% %% This can be a session-level attribute or a media-level %% attribute. As a session-level attribute, it specifies the %% default language for the session being described. As a %% media-level attribute, it specifies the language for that %% media, overriding any session-level language specified. %% Multiple lang attributes can be provided either at session %% or media level if 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. %% %% The "lang" attribute value must be a single RFC 3066 %% language tag in US-ASCII [9]. It is not dependent on the %% charset attribute. A "lang" 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=framerate: %% %% This gives the maximum video frame rate in frames/sec. %% It is intended as a recommendation for the encoding of %% video data. Decimal representations of fractional values %% using the notation "." are allowed. It %% is a media-level attribute, defined only for video media, %% and it is not dependent on charset. %% %% a=quality: %% %% This gives a suggestion for the quality of the encoding %% as an integer value. The intention of the quality %% attribute for video is to specify a non-default trade-off %% between frame-rate and still-image quality. For video, %% the value is in the range 0 to 10, with the following %% suggested meaning: %% %% 10 - the best still-image quality the compression %% scheme can give. %% 5 - the default behaviour given no quality suggestion. %% 0 - the worst still-image quality the codec designer %% thinks is still usable. %% %% It is a media-level attribute, and it is not dependent on %% charset. %% %% a=fmtp: %% %% This attribute allows parameters that are specific to a %% particular format to be conveyed in a way that SDP does %% not have to understand them. The format must be one of %% the formats specified for the media. Format-specific %% parameters may be any set of parameters required to be %% conveyed by SDP and given unchanged to the media tool that %% will use this format. At most one instance of this %% attribute is allowed for each format. %% %% It is a media-level attribute, and it is not dependent on %% charset. %% %% a= %% a=: -record(megaco_sdp_a, { attribute, % string() value % undefined | string() } ). %% a=cat: -record(megaco_sdp_a_cat, { category % string() } ). %% a=keywds: -record(megaco_sdp_a_keywds, { keywords % string() } ). %% a=tool: -record(megaco_sdp_a_tool, { name_and_version % string() } ). %% a=ptime: -record(megaco_sdp_a_ptime, { packet_time % integer() } ). %% a=maxptime: -record(megaco_sdp_a_maxptime, { maximum_packet_time % integer() } ). %% a=rtpmap: / [/] -record(megaco_sdp_a_rtpmap, { payload_type, % integer() encoding_name, % string() clock_rate, % integer() encoding_parms = [] % [ string() ] } ). %% a=orient: %% orientation() -> portrait | landscape | seascape -record(megaco_sdp_a_orient, { orientation % orientation() } ). %% a=type: -record(megaco_sdp_a_type, { conf_type % string() } ). %% a=charset: -record(megaco_sdp_a_charset, { char_set % string() } ). %% a=sdplang: -record(megaco_sdp_a_sdplang, { tag % string() } ). %% a=lang: -record(megaco_sdp_a_lang, { tag % string() } ). %% a=framerate: -record(megaco_sdp_a_framerate, { frame_rate % string() } ). %% a=quality: -record(megaco_sdp_a_quality, { quality % integer() } ). %% a=fmtp: -record(megaco_sdp_a_fmtp, { format, % string() param % string() } ). %% =================================================================== %% %% Media Announcements ("m=") %% %% m= ... %% %% A session description may contain a number of media descriptions. %% Each media description starts with an "m=" field and is terminated %% by either the next "m=" field or by the end of the session %% description. A media field has several sub-fields: %% %% is the media type. Currently defined media are "audio", %% "video", "text", "application", and "message", although this %% list may be extended in the future (see Section 8 of RFC 4566). %% %% is the transport port to which the media stream is sent. %% The meaning of the transport port depends on the network being %% used as specified in the relevant "c=" field, and on the %% transport protocol defined in the sub-field of the %% media field. Other ports used by the media application (such as %% the RTP Control Protocol (RTCP) port [19]) MAY be derived %% algorithmically from the base media port or MAY be specified in %% a separate attribute (for example, "a=rtcp:" as defined in %% [22]). %% %% If non-contiguous ports are used or if they don't follow the %% parity rule of even RTP ports and odd RTCP ports, the "a=rtcp:" %% attribute MUST be used. Applications that are requested to send %% media to a that is odd and where the "a=rtcp:" is present %% MUST NOT subtract 1 from the RTP port: that is, they MUST send %% the RTP to the port indicated in and send the RTCP to the %% port indicated in the "a=rtcp" attribute. %% %% For applications where hierarchically encoded streams are being %% sent to a unicast address, it may be necessary to specify %% multiple transport ports. This is done using a similar notation %% to that used for IP multicast addresses in the "c=" field: %% %% m= / ... %% %% In such a case, the ports used depend on the transport protocol. %% For RTP, the default is that only the even-numbered ports are %% used for data with the corresponding one-higher odd ports used %% for the RTCP belonging to the RTP session, and the %% denoting the number of RTP sessions. For %% example: %% %% m=video 49170/2 RTP/AVP 31 %% %% would specify that ports 49170 and 49171 form one RTP/RTCP pair %% and 49172 and 49173 form the second RTP/RTCP pair. RTP/AVP is %% the transport protocol and 31 is the format (see below). If %% non-contiguous ports are required, they must be signalled using %% a separate attribute (for example, "a=rtcp:" as defined in %% [22]). %% %% If multiple addresses are specified in the "c=" field and %% multiple ports are specified in the "m=" field, a one-to-one %% mapping from port to the corresponding address is implied. For %% example: %% %% c=IN IP4 224.2.1.1/127/2 %% m=video 49170/2 RTP/AVP 31 %% %% would imply that address 224.2.1.1 is used with ports 49170 %% and 49171, and address 224.2.1.2 is used with ports 49172 and %% 49173. %% %% The semantics of multiple "m=" lines using the same transport %% address are undefined. This implies that, unlike limited past %% practice, there is no implicit grouping defined by such means %% and an explicit grouping framework (for example, [18]) should %% instead be used to express the intended semantics. %% %% is the transport protocol. The meaning of the transport %% protocol is dependent on the address type field in the %% relevant "c=" field. Thus a "c=" field of IP4 indicates that %% the transport protocol runs over IP4. The following transport %% protocols are defined, but may be extended through %% registration of new protocols with IANA (see Section 8 of RFC %% 4566): %% %% * udp: denotes an unspecified protocol running over UDP. %% %% * RTP/AVP: denotes RTP [19] used under the RTP Profile for %% Audio and Video Conferences with Minimal Control [20] %% running over UDP. %% %% * RTP/SAVP: denotes the Secure Real-time Transport Protocol %% [23] running over UDP. %% %% The main reason to specify the transport protocol in addition %% to the media format is that the same standard media formats %% may be carried over different transport protocols even when %% the network protocol is the same -- a historical example is %% vat Pulse Code Modulation (PCM) audio and RTP PCM audio; %% another might be TCP/RTP PCM audio. In addition, relays and %% monitoring tools that are transport-protocol-specific but %% format-independent are possible. %% %% is a media format description. The fourth and any %% subsequent sub-fields describe the format of the media. The %% interpretation of the media format depends on the value of %% the sub-field. %% %% If the sub-field is "RTP/AVP" or "RTP/SAVP" the %% sub-fields contain RTP payload type numbers. When a list of %% payload type numbers is given, this implies that all of these %% payload formats MAY be used in the session, but the first of %% these formats SHOULD be used as the default format for the %% session. For dynamic payload type assignments the "a=rtpmap:" %% attribute (see Section 6 of RFC 4566) SHOULD be used to map %% from an RTP payload type number to a media encoding name that %% identifies the payload format. The "a=fmtp:" attribute MAY %% be used to specify format parameters (see Section 6 of RFC %% 4566). %% %% If the sub-field is "udp" the sub-fields MUST %% reference a media type describing the format under the %% "audio", "video", "text", "application", or "message" %% top-level media types. The media type registration SHOULD %% define the packet format for use with UDP transport. %% %% For media using other transport protocols, the field is %% protocol specific. Rules for interpretation of the sub- %% field MUST be defined when registering new protocols (see %% Section 8.2.2 of RFC 4566). %% %% ma_media() -> audio | video | application | data | control -record(megaco_sdp_m, { media, % ma_media() | string() port, % integer() num_ports, % undefined | integer() transport, % string() fmt_list = [] % [ string() ] }). %% =================================================================== %% %% References %% %% Normative References %% %% [1] Mockapetris, P., "Domain names - concepts and facilities", STD %% 13, RFC 1034, November 1987. %% %% [2] Mockapetris, P., "Domain names - implementation and %% specification", STD 13, RFC 1035, November 1987. %% %% [3] Bradner, S., "Key words for use in RFCs to Indicate Requirement %% Levels", BCP 14, RFC 2119, March 1997. %% %% [4] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax %% Specifications: ABNF", RFC 4234, October 2005. %% %% [5] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD %% 63, RFC 3629, November 2003. %% %% [6] Handley, M. and V. Jacobson, "SDP: Session Description %% Protocol", RFC 2327, April 1998. %% %% [7] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform %% Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, %% January 2005. %% %% [8] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA %% Considerations Section in RFCs", BCP 26, RFC 2434, October %% 1998. %% %% [9] Alvestrand, H., "Tags for the Identification of Languages", BCP %% 47, RFC 3066, January 2001. %% %% [10] Olson, S., Camarillo, G., and A. Roach, "Support for IPv6 in %% Session Description Protocol (SDP)", RFC 3266, June 2002. %% %% [11] Faltstrom, P., Hoffman, P., and A. Costello, %% "Internationalizing Domain Names in Applications (IDNA)", RFC %% 3490, March 2003. %% %% [12] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", %% RFC 3548, July 2003. %% %% %% Informative References %% %% [13] Mills, D., "Network Time Protocol (Version 3) Specification, %% Implementation", RFC 1305, March 1992. %% %% [14] Handley, M., Perkins, C., and E. Whelan, "Session Announcement %% Protocol", RFC 2974, October 2000. %% %% [15] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., %% Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: %% Session Initiation Protocol", RFC 3261, June 2002. %% %% [16] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time Streaming %% Protocol (RTSP)", RFC 2326, April 1998. %% %% [17] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with %% Session Description Protocol (SDP)", RFC 3264, June 2002. %% %% [18] Camarillo, G., Eriksson, G., Holler, J., and H. Schulzrinne, %% "Grouping of Media Lines in the Session Description Protocol %% (SDP)", RFC 3388, December 2002. %% %% [19] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, %% "RTP: A Transport Protocol for Real-Time Applications", STD 64, %% RFC 3550, July 2003. %% %% [20] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video %% Conferences with Minimal Control", STD 65, RFC 3551, July 2003. %% %% [21] Casner, S., "Session Description Protocol (SDP) Bandwidth %% Modifiers for RTP Control Protocol (RTCP) Bandwidth", RFC 3556, %% July 2003. %% %% [22] Huitema, C., "Real Time Control Protocol (RTCP) attribute in %% Session Description Protocol (SDP)", RFC 3605, October 2003. %% %% [23] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. %% Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC %% 3711, March 2004. %% %% [24] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Indicating %% User Agent Capabilities in the Session Initiation Protocol %% (SIP)", RFC 3840, August 2004. %% %% [25] Westerlund, M., "A Transport Independent Bandwidth Modifier for %% the Session Description Protocol (SDP)", RFC 3890, September %% 2004. %% %% [26] International Telecommunication Union, "H.323 extended for %% loosely coupled conferences", ITU Recommendation H.332, %% September 1998. %% %% [27] Arkko, J., Carrara, E., Lindholm, F., Naslund, M., and K. %% Norrman, "Key Management Extensions for Session Description %% Protocol (SDP) and Real Time Streaming Protocol (RTSP)", RFC %% 4567, July 2006. %% %% [28] Andreasen, F., Baugher, M., and D. Wing, "Session Description %% Protocol (SDP) Security Descriptions for Media Streams", RFC %% 4568, July 2006. %% %% [29] Resnick, P., "Internet Message Format", RFC 2822, April 2001. %% %% [30] Hinden, R. and S. Deering, "IP Version 6 Addressing %% Architecture", RFC 2373, July 1998. %% %% [31] Freed, N. and J. Klensin, "Media Type Specifications and %% Registration Procedures", BCP 13, RFC 4288, December 2005. %% -endif.