session
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... SIP) is an application-layer control
protocol that can establish, modify and terminate multimedia sessions
or calls. These multimedia sessions include multimedia conferences,
...
... control
protocol that can establish, modify and terminate multimedia sessions
or calls. These multimedia sessions include multimedia conferences,
distance learning, Internet telephony ...
... SIP can invite parties to both unicast and multicast
sessions; the initiator does not necessarily have to be a member of
the session ...
... sessions; the initiator does not necessarily have to be a member of
the session to which it is inviting. Media and participants can be
added to an existing session.
...
... the session to which it is inviting. Media and participants can be
added to an existing session.
...
...
SIP can be used to initiate sessions as well as invite members to
sessions that have been advertised and established by other means.
...
... SIP can be used to initiate sessions as well as invite members to
sessions that have been advertised and established by other means.
Sessions can be advertised using multicast ...
... sessions that have been advertised and established by other means.
Sessions can be advertised using multicast protocols such as SAP,
...
... SAP) [5] for advertising
multimedia sessions via multicast and the session description
protocol (SDP ...
... multimedia sessions via multicast and the session description
protocol (SDP) (RFC 2327(-> 4566prop) [6 ...
... SDP) (RFC 2327(-> 4566prop) [6]) for describing multimedia sessions.
However, the functionality and operation of SIP does not depend on
...
...
SIP can invite users to sessions with and without resource
reservation. SIP does not reserve resources, but can convey to the
...
... call-id (Section 6.12). Thus, if a user is, for example, invited
to the same multicast session by several people, each of these
invitations will be a unique call. A point-to-point Internet
telephony ...
... clients (and servers).
Conference: A multimedia session (see below), identified by a common
session description. A conference can have zero or more members
...
... Conference: A multimedia session (see below), identified by a common
session description. A conference can have zero or more members
and includes the cases of a multicast conference, a full-mesh
...
... Invitation: A request sent to a user (or service) requesting
participation in a session. A successful SIP invitation consists
of two transactions ...
... user agent
servers or registrars.
Session: From the SDP specification: "A multimedia session is a set
...
... Session: From the SDP specification: "A multimedia session is a set
of multimedia senders and receivers ...
... senders to receivers. A multimedia conference is an example
of a multimedia session." (RFC 2327(-> 4566prop) [6]) (A session ...
... multimedia session." (RFC 2327(-> 4566prop) [6]) (A session as defined
for SDP can comprise one or more RTP sessions ...
... session as defined
for SDP can comprise one or more RTP sessions.) As defined, a
callee can be invited several times, by different calls, to the
same session ...
... RTP sessions.) As defined, a
callee can be invited several times, by different calls, to the
same session. If SDP is used, a session is defined by the
...
...
The INVITE request typically contains a session description, for
example written in SDP (RFC 2327(-> 4566prop) ...
... 6]) format, that provides the
called party with enough information to join the session. For
multicast sessions ...
... session. For
multicast sessions, the session description enumerates the media
types and formats that are allowed to be distributed to that session ...
... multicast sessions, the session description enumerates the media
types and formats that are allowed to be distributed to that session.
...
... sessions, the session description enumerates the media
types and formats that are allowed to be distributed to that session.
For a unicast session, the session ...
... media
types and formats that are allowed to be distributed to that session.
For a unicast session, the session description enumerates the media
types and formats that the caller ...
... session.
For a unicast session, the session description enumerates the media
types and formats that the caller is willing to use and where it
...
... wishes to accept the call, it responds to the invitation by returning
a similar description listing the media it wishes to use. For a
multicast session, the callee SHOULD only return a session
description if it is unable to receive the media indicated in the
...
... a similar description listing the media it wishes to use. For a
multicast session, the callee SHOULD only return a session
description if it is unable to receive the media indicated in the
caller ...
... Changing an Existing Session ...
...
In some circumstances, it is desirable to change the parameters of an
existing session. This is done by re-issuing the INVITE, using the
same Call-ID ...
... and simultaneously sends an INVITE to the second party, with the new
multicast session description, but with the old call identifier.
...
...
A single conference session or call involves one or more SIP
request-response transactions. Proxy servers ...
... method indicates that the user or service is being invited
to participate in a session. The message body contains a description
of the session ...
... session. The message body contains a description
of the session to which the callee is being invited. For two-party
calls, the caller indicates the type of media ...
...
Not all session description formats have the ability to
indicate sending media.
...
... Call-ID or a globally unique identifier within the session
description, with a 200 (OK) response.
...
... Call-ID, it MUST check any version identifiers in the session
description or, if there are no version identifiers ...
... version identifiers, the content of
the session description to see if it has changed. It MUST also
inspect any other header fields for changes. If there is a change,
...
... state or information
generated as a result of that header. If the session description has
changed, the user agent server MUST adjust the session parameters ...
... session description has
changed, the user agent server MUST adjust the session parameters
accordingly, possibly after asking the user for confirmation.
(Versioning of the session ...
... session parameters
accordingly, possibly after asking the user for confirmation.
(Versioning of the session description can be used to accommodate the
capabilities of new arrivals to a conference, add or delete media or
...
... The ACK request MAY contain a message body with the final session
description to be used by the callee. If the ACK message body is
...
... description to be used by the callee. If the ACK message body is
empty, the callee uses the session description in the INVITE request.
...
... client to indicate to the server in
which language it would prefer to receive reason phrases, session
descriptions or status responses carried as message bodies. A proxy
...
... INVITE request. If the user is already a member of the conference and
the conference parameters contained in the session description have
not changed, a callee user agent server MAY silently accept the call,
...
... Call-ID. An invitation for an existing Call-ID or
session can change the parameters of the conference. A client
application MAY decide to simply indicate to the user that the
...
... client MAY use identifiers within
the session description to detect this duplication. For example, SDP
contains a session id ...
... session description to detect this duplication. For example, SDP
contains a session id and version number in the origin (o) field.
...
... This is intended to provide a summary, or to indicate the nature, of
the call, allowing call filtering without having to parse the session
description. (Also, the session description does not have to use the
...
... filtering without having to parse the session
description. (Also, the session description does not have to use the
same subject indication as the invitation.)
...
... This is a list of the currently-defined "warn-code"s, each with a
recommended warn-text in English, and a description of its meaning.
Note that these warnings describe failures induced by the session
description.
...
...
Warnings 300 through 329 are reserved for indicating problems with
keywords in the session description, 330 through 339 are warnings
related to basic network services requested in the session ...
... session description, 330 through 339 are warnings
related to basic network services requested in the session
description, 370 through 379 are warnings related to quantitative QoS
...
... description, 370 through 379 are warnings related to quantitative QoS
parameters requested in the session description, and 390 through 399
are miscellaneous warnings that do not fall into one of the above
categories.
...
... network protocol: One or more network protocols
contained in the session description are not available.
301 Incompatible network ...
... address formats: One or more network address
formats contained in the session description are not available.
302 Incompatible transport protocol ...
... transport protocol: One or more transport protocols
described in the session description are not available.
303 Incompatible bandwidth ...
... bandwidth units: One or more bandwidth measurement
units contained in the session description were not understood.
304 Media type ...
... Media type not available: One or more media types contained in
the session description are not available.
305 Incompatible media format ...
... media format: One or more media formats contained in
the session description are not available.
306 Attribute not understood: One or more of the media attributes in
...
...
306 Attribute not understood: One or more of the media attributes in
the session description are not supported.
307 Session ...
... session description are not supported.
307 Session description parameter not understood: A parameter other
than those listed above was not understood.
...
... 370 Insufficient bandwidth: The bandwidth specified in the session
description or defined by the media exceeds that known to be
available.
...
...
Warning: 307 isi.edu "Session parameter 'foo' not understood"
Warning: 301 isi.edu "Incompatible network address type ...
... The user's agent was contacted successfully but some aspects of the
session description such as the requested media, bandwidth, or
addressing ...
...
A 606 (Not Acceptable) response means that the user wishes to
communicate, but cannot adequately support the session described. The
606 (Not Acceptable) response MAY contain a list of reasons in a
Warning header field ...
... 606 (Not Acceptable) response MAY contain a list of reasons in a
Warning header field describing why the session described cannot be
supported. Reasons are listed in Section 6.41. It is hoped that
negotiation ...
... ACK, INVITE and OPTIONS, the message body is always a session
description. The use of message bodies for REGISTER ...
... contain advisory information about the progress of the request. 2xx
responses to INVITE requests contain session descriptions. In 3xx
responses, the message body MAY contain the description of
...
... UDP with authentication and a complex
session description, it may be possible that the size of a request or
response is larger than the MTU. To address ...
... The SIP message body MAY also contain encryption keys for the session
itself. SIP supports three complementary forms of encryption ...
...
The first example invites schooler@vlsi.cs.caltech.edu to a multicast
session. All examples use the Session Description Protocol (SDP) (RFC
...
...
The first example invites schooler@vlsi.cs.caltech.edu to a multicast
session. All examples use the Session Description Protocol (SDP) (RFC
2327(-> 4566prop) ...
...
In this case, the session description is using the Session
Description Protocol (SDP), as stated in the Content-Type ...
...
In this case, the session description is using the Session
Description Protocol (SDP), as stated in the Content-Type header ...
... header is terminated by an empty line and is followed by a
message body containing the session description.
...
... fields of the request message. The original sense of From field is
preserved (i.e., it is the session initiator).
...
...
Since the two sides have agreed on the set of media, Bell confirms
the call without enclosing another session description:
...
... at watson@h.bell-tel.com (H), as well as a permanent registration at
watson@acm.org (A). For brevity, the examples omit the session
description and Via header fields.
...
... B Usage of the Session Description Protocol (SDP) ...
...
This section describes the use of the Session Description Protocol
(SDP) (RFC 2327(-> 4566prop) ...
... media stream ("m=" line) in the caller's session description
corresponds to the nth media stream in the callee's description.
...
... port number and
address in the session description indicate where the media stream
should be sent to by the recipient of the session ...
... session description indicate where the media stream
should be sent to by the recipient of the session description, either
caller or callee. For send-only streams, the address and port ...
... caller SHOULD list all of the codecs it is capable
of supporting in the session description in an INVITE or ACK. For
...
... send-only streams, the caller SHOULD indicate only those it wishes to
send for this session. For receive-only streams, the payload type
numbers indicate the value of the payload type ...
... INVITE. The actual payload type numbers
in the callee's session description corresponding to a particular
codec MUST be the same as the caller ...
... no media formats in common for a particular
stream, the callee MUST return a session description containing the
particular "m=" line, but with the port number set to zero ...
...
The interpretation of send-only and receive-only for multicast media
sessions differs from that for unicast sessions. For multicast ...
... multicast media
sessions differs from that for unicast sessions. For multicast,
send-only means that the recipient of the session ...
... sessions. For multicast,
send-only means that the recipient of the session description (caller
or callee) SHOULD only send media streams ...
... media streams to the address and port
indicated. Receive-only means that the recipient of the session
description SHOULD only receive media on the address and port
...
... all parties use the same port numbers to receive media data. If the
session description provided by the caller is acceptable to the
callee, the callee can choose not to include a session ...
... session description provided by the caller is acceptable to the
callee, the callee can choose not to include a session description or
MAY echo the description in the response.
...
...
A callee MAY, in the response, return a session description with some
of the payload types removed ...
... occurs, a caller MAY issue an INVITE with a session description that
contains no media lines. The callee SHOULD interpret this to mean
...
... no media lines. The callee SHOULD interpret this to mean
that the caller wishes to participate in a multimedia session
described by the session description, but that the media streams ...
... caller wishes to participate in a multimedia session
described by the session description, but that the media streams are
not yet known. The callee SHOULD return a session ...
... session description, but that the media streams are
not yet known. The callee SHOULD return a session description
indicating the streams and media formats it is willing to support,
...
... however. The caller MAY update the session description either in the
ACK request or in a re-INVITE ...
... a party re-invites the other by sending an INVITE request with a
modified session description. The session description is the same as
in the original invitation (or response), but the "c" destination
addresses ...
... INVITE request with a
modified session description. The session description is the same as
in the original invitation (or response), but the "c" destination
addresses for the media streams ...
... Subject header field have different
meanings when inviting to a multicast session. The session
description line describes the subject ...
... header field have different
meanings when inviting to a multicast session. The session
description line describes the subject of the multicast session ...
... session
description line describes the subject of the multicast session,
while the SIP Subject ...
... header field describes the reason for the
invitation. The example in Section 16.2 illustrates this point. For
invitations to two-party sessions, the SDP "s=" line MAY be left
empty.
...
...
The "o=" line is not strictly necessary for two-party sessions, but
MUST be present to allow re-use of SDP-based tools ...
... Handley, M., "SAP: Session announcement protocol," Internet Draft, Internet Engineering Task Force, Nov. 1996. Work in progress ...
... Handley, M. and V. Jacobson, "SDP: session description protocol", RFC 2327(-> 4566prop), April 1998. ...