7.5 Session description types defined within the present document

24.2293GPPIP multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP)Release 18Stage 3TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

7.5.1 General

This subclause contains definitions for SDP parameters that are specific to SDP usage in the 3GPP IM CN Subsystem and therefore are not described in an RFC.

7.5.2 End-to-access-edge media plane security

7.5.2.1 General

The end-to-access-edge media security-indicator is used to indicate that a UE requests a P-CSCF to apply media plane security or to indicate that a P-CSCF has applied end-to-access-edge media security as defined in 3GPP TS 33.328 [19C].

7.5.2.2 Syntax

3GPP end-to-access-edge media security indicator is a value attribute which is encoded as a media-level SDP attribute with the ABNF syntax defined in table 7.5.1. ABNF is defined in RFC 2234 [20G].

Table 7.5.1: ABNF syntax of 3ge2ae attribute

3ge2ae-attribute = "a=3ge2ae:" indicator

indicator = "requested" / "applied" / token

"requested": the sender indicates its wish that end-to-access-edge media security is applied.

"applied": the sender indicates that it has applied end-to-access-edge media security.

This version of the specification only defines usage of the "requested" and "applied" attribute values. Other values shall be ignored.

The "3ge2ae" attribute is charset-independent.

7.5.2.3 IANA registration

NOTE: This subclause contains information to be provided to IANA for the registration of the end-to-access-edge security indicator SDP attribute.

Contact name, email address, and telephone number:

3GPP Specifications Manager

3gppContact@etsi.org

+33 (0)492944200

Attribute Name (as it will appear in SDP)

3ge2ae

Long-form Attribute Name in English:

3GPP_e2ae-security-indicator

Type of Attribute

Media level

Is Attribute Value subject to the Charset Attribute?

This Attribute is not dependent on charset.

Purpose of the attribute:

This attribute specifies the end-to-access-edge security-indicator as used for IMS media plane security

Appropriate Attribute Values for this Attribute:

The attribute is a value attribute. The values "requested" and "applied" are defined.

7.5.3 Optimal Media Routeing (OMR) attributes

7.5.3.1 General

The SDP attributes associated with OMR are used to identify and select alternative media plane paths for the purpose of bypassing unneeded media functions in the network, as described in 3GPP TS 29.079 [11D].

7.5.3.2 Semantics

The visited-realm attribute contains an IP realm identifier and transport address for a media function in the media plane that can potentially be used to bypass other allocated media functions.

The secondary-realm attribute contains an IP realm identifier and transport address for an alternate media function in the media plane that can potentially be used to bypass other allocated media functions.

The omr-s-cksum and omr-m-cksum attributes includes checksums for session level information and media level information to identify if the SDP was altered by intermediaries in such a way as to invalidate OMR information present in the SDP.

The "omr-codecs", "omr-m-att" and "omr-s-att" attributes contain codec-related SDP offer information encapsulated by a SIP-ALG in the signalling path that has modified codec related information.

The "omr-m-bw" and "omr-s-bw" attributes contain bandwidth-related SDP offer information encapsulated by a SIP-ALG in the signalling path that has modified codec related information.

Each group of zero or more versions of each of the "omr-codecs", "omr-m-att", "omr-s-att", "omr-m-bw" and "omr-s-bw" attributes for a media line with the same instance number is associated with the visited-realm instance for the modified media line and represents the version of the SDP information for the media line before modifications.

7.5.3.3 Syntax

The syntax specified in table 7.5.2 uses the augmented Backus-Naur Form as described in RFC 2234 [20G].

Table 7.5.2: Syntax OMR attributes

visited-realm = "visited-realm" ":" instance-number SP

realm SP

nettype SP ;from RFC 4566 [39]

addrtype SP ;from RFC 4566 [39]

connection-address SP ;from RFC 4566 [39]

port ;from RFC 4566 [39]

[SP rtcp-port [SP rtcp-address]]

*(SP extension-name SP extension-value)

secondary-realm = "secondary-realm" ":" instance-number SP

realm SP

nettype SP ;from RFC 4566 [39]

addrtype SP ;from RFC 4566 [39]

connection-address SP ;from RFC 4566 [39]

port ;from RFC 4566 [39]

[SP rtcp-port [SP rtcp-address]]

*(SP extension-name SP extension-value)

instance-number = 1*DIGIT

realm = non-ws-string ;from RFC 4566 [39]

rtcp-port = "rtcp-port" SP port

rtcp-address = "rtcp-address" SP connection-address

extension-name = token ;shall be different to existing tokens "previsous-fmt",

"rtcp-port" and "rtcp-address".

extension-value = non-ws-string

omr-m-cksum = "omr-m-cksum" ":" 1*HEXDIG

omr-s-cksum = "omr-s-cksum" ":" 1*HEXDIG

omr-codecs = "omr-codecs" ":" instance-number SP proto 1*(SP fmt) ;from RFC 4566 [39]

omr-m-att = "omr-m-att" ":" instance-number SP attribute ;from RFC 4566 [39]

omr-s-att = "omr-s-att" ":" instance-number SP attribute ;from RFC 4566 [39]

omr-m-bw = "omr-m-bw" ":" instance-number SP bwtype ":" bandwidth ;from RFC 4566 [39]

omr-s-bw = "omr-s-bw" ":" instance-number SP bwtype ":" bandwidth ;from RFC 4566 [39]

This grammar encodes the primary media level information about each visited-realm and secondary-realm instance: the sequence in which the realm was visited, the realm identity, its IP address and port:

<instance-number>: instance-number is a positive decimal integer which identifies the sequence in which this visited-realm was added during the forwarding of an SDP offer. If an IMS-ALG adds second-realm attribute(s), omr-codecs attribute(s), omr-m-att attribute(s), omr-s-att attribute(s), omr-m-bw attribute(s) and/or the omr-s-bw attribute(s) to an SDP offer it will assign the same instance number as assigned to the visited-realm attribute for the forwarded SDP offer. When used in the SDP answer, the instance-number, realm, nettype and addrtype uniquely identify the corresponding visited-realm or secondary-realm instance from the SDP offer.

<realm>: identifies a set of mutually reachable IP endpoints that share a common IP addressing scheme.

Effective application of OMR depends on the scope of each realm being determined by reachability and not by administrative domain. A public IPv4 or IPv6 address reachable from the open internet shall be associated with the special realm "IN". For application to OMR in IPv6 networks, a realm corresponds to an IPv6 autonomous system.

Entity operators must adhere to the following guidelines for creation of an OMR realm string to ensure the integrity of the visited-realm and secondary-realm instance information for their realm(s): 1) Realm strings must be globally unique. It is recommended that a realm string contain a hostname or domain name, following the recommendation in subclause 3.3 of RFC 7616 [286], 2) Realm strings should present a human-readable identifier that can be rendered to a user.

<nettype>, <addrtype> and <connection-address>: are taken from the connection-field (c= line) of RFC 4566 [39]. They describe the IP address associated with the visited-realm or secondary-realm instance, allowing for IPv4 addresses, IPv6 addresses and FQDNs. The connection-address can be either an IP address or an FQDN.

<port>: It is the port associated with the visited-realm or secondary-realm instance as taken from RFC 4566 [39]. Its meaning depends on the network being used for the connection-address, and on the transport protocol selected for the corresponding media line, e.g., UDP or TCP.

<rtcp-port> and <rtcp-address>: taken together are semantically equivalent to the rtcp attribute defined in RFC 3605 [37A]. They optionally encode the RTCP port and address information when the RTCP port number is not exactly one greater than the port for an RTP stream at the same address.

The previous-fmt-list may be supplied within the visited-realm if this attribute is included in an SDP offer and shall not be supplied if this attribute is included in an SDP answer.

The visited-realm and secondary-realm attributes can be extended via <extension-name> and <extension-value>. The grammar allows for new name/value pairs to be added at the end of the attribute.

<omr-m-cksum>: is a hex value calculated on the contents of the media level information per media line.

<omr-s-cksum>: is a hex value calculated on the contents of the session level information.

<omr-codecs> provides the transport format <proto> and list of media formats (e.g., payload type numbers) <fmt> supported by the visited-realm instance immediately preceding the instance identified by <instance-number>. Transport format <proto> and media format <fmt> are defined in RFC 4566 [39] for the SDP m-line.

<omr-m-att> provides a media level SDP attribute <attribute> supported by the visited-realm instance immediately preceding the instance identified by <instance-number>. Attribute <attribute> is defined in RFC 4566 [39] for the SDP a-line.

<omr-s-att> provides a session level SDP attribute <attribute> supported by the visited-realm instance immediately preceding the instance identified by <instance-number>. Attribute <attribute> is defined in RFC 4566 [39] for the SDP a-line.

<omr-m-bw> provides a media level SDP bandwidth described by <bwtype> and <bandwidth> supported by the visited-realm instance immediately preceding the instance identified by <instance-number>. <bwtype> and <bandwidth> are defined in RFC 4566 [39] for the SDP b-line.

<omr-s-bw> provides a session level SDP bandwidth described by <bwtype> and <bandwidth> supported by the visited-realm instance immediately preceding the instance identified by <instance-number>. <bwtype> and <bandwidth> are defined in RFC 4566 [39] for the SDP b-line.

The "visited-realm", "secondary-realm", "omr-m-cksum", "omr-s-cksum", "omr-codecs", "omr-m-att", "omr-s-att" "omr-m-bw" and "omr-s-bw" SDP attributes are media-level attributes.

7.5.3.4 IANA registration

7.5.3.4.1 visited-realm attribute

Contact Name:3GPP Specifications Manager, 3gppContact@etsi.org, +33 (0)492944200

Attribute Name: visited-realm

Long Form: visited-realm

Type of Attribute: media level

Charset Considerations: The attribute is not subject to the charset attribute.

Purpose: This attribute is used in networks employing OMR procedures allowing to bypass border gateways in configurations in which IP realms are re-entered when establishing an end-to-end multimedia session. This attribute is used to identify configurations in which IP realms are re-entered when establishing an end-to-end multimedia session, so that border gateways can be bypassed without compromising their role in securing access to the networks. The attribute provides a means to identify connection information for visited IP realms to help select the most optimal available path.

Appropriate Values: See table 7.5.2.

7.5.3.4.2 secondary-realm attribute

Contact Name: 3GPP Specifications Manager, 3gppContact@etsi.org, +33 (0)492944200

Attribute Name: secondary-realm

Long Form: secondary-realm

Type of Attribute: media level

Charset Considerations: The attribute is not subject to the charset attribute.

Purpose: This attribute is used in networks employing OMR procedures allowing to bypass border gateways in configurations in which IP realms are re-entered when establishing an end-to-end multimedia session. This attribute is used to identify configurations in which secondary IP realms are available to establish an end-to-end multimedia session, so that border gateways can be bypassed without compromising their role in securing access to the networks. The attribute provides a means to identify connection information for secondary IP realms to help select the most optimal available path.

Appropriate Values: See table 7.5.2.

7.5.3.4.3 omr-s-cksum attribute

Contact Name: 3GPP Specifications Manager, 3gppContact@etsi.org, +33 (0)492944200

Attribute Name: omr-s-cksum

Long Form: omr-s-cksum

Type of Attribute: media level

Charset Considerations: The attribute is not subject to the charset attribute.

Purpose: This attribute is used in networks employing OMR procedures allowing to bypass border gateways in configurations in which IP realms are re-entered when establishing an end-to-end multimedia session. This attribute is used to provide a means to verify that session level SDP information has not been modified by intermediate SIP nodes not supporting the OMR procedures. The attribute provides a checksum calculated value against the session level information. Any OMR information associated with unexpectedly modified media information will be discarded.

Appropriate Values: See table 7.5.2.

7.5.3.4.4 omr-m-cksum attribute

Contact Name: 3GPP Specifications Manager, 3gppContact@etsi.org, +33 (0)492944200

Attribute Name: omr-m-cksum

Long Form: omr-m-cksum

Type of Attribute: media level

Charset Considerations: The attribute is not subject to the charset attribute.

Purpose: This attribute is used in networks employing OMR procedures allowing to bypass border gateways in configurations in which IP realms are re-entered when establishing an end-to-end multimedia session. This attribute is used to provide a means to verify that media level SDP information has not been modified by intermediate SIP nodes not supporting the OMR procedures. The attribute provides a checksum calculated value against the media level information associated with the media stream for which the checksum is provided. Any OMR information associated with unexpectedly modified media information will be discarded.

Appropriate Values: See table 7.5.2.

7.5.3.4.5 omr-codecs attribute

Contact Name: 3GPP Specifications Manager, 3gppContact@etsi.org, +33 (0)492944200

Attribute Name: omr-codecs

Long Form: omr-codecs

Type of Attribute: media level

Charset Considerations: The attribute is not subject to the charset attribute.

Appropriate Values: See table 7.5.2.

7.5.3.4.6 omr-m-att attribute

Contact Name: 3GPP Specifications Manager, 3gppContact@etsi.org, +33 (0)492944200

Attribute Name: omr-m-att

Long Form: omr-m-att

Type of Attribute: media level

Charset Considerations: The attribute is not subject to the charset attribute.

Purpose: This attribute is used in networks employing OMR procedures allowing to bypass border gateways in configurations in which IP realms are re-entered when establishing an end-to-end multimedia session. The attribute provides means to encapsulate a media-level SDP attribute that is applicable if a particular border gateway is bypassed.

Appropriate Values: See table 7.5.2.

7.5.3.4.7 omr-s-att attribute

Contact Name: 3GPP Specifications Manager, 3gppContact@etsi.org, +33 (0)492944200

Attribute Name: omr-s-att

Long Form: omr-s-att

Type of Attribute: media level

Charset Considerations: The attribute is not subject to the charset attribute.

Purpose: This attribute is used in networks employing OMR procedures allowing to bypass border gateways in configurations in which IP realms are re-entered when establishing an end-to-end multimedia session. The attribute provides means to encapsulate a session-level SDP attribute that is applicable if a particular border gateway is bypassed.

Appropriate Values: See table 7.5.2.

7.5.3.4.8 omr-m-bw attribute

Contact Name: 3GPP Specifications Manager, 3gppContact@etsi.org, +33 (0)492944200

Attribute Name: omr-m-bw

Long Form: omr-m-bw

Type of Attribute: media level

Charset Considerations: The attribute is not subject to the charset attribute.

Purpose: This attribute is used in networks employing OMR procedures allowing to bypass border gateways in configurations in which IP realms are re-entered when establishing an end-to-end multimedia session. The attribute provides means to encapsulate a media-level SDP bandwidth that is applicable if a particular border gateway is bypassed.

Appropriate Values: See table 7.5.2.

7.5.3.4.9 omr-s-bw attribute

Contact Name: 3GPP Specifications Manager, 3gppContact@etsi.org, +33 (0)492944200

Attribute Name: omr-s-bw

Long Form: omr-s-bw

Type of Attribute: media level

Charset Considerations: The attribute is not subject to the charset attribute.

Purpose: This attribute is used in networks employing OMR procedures allowing to bypass border gateways in configurations in which IP realms are re-entered when establishing an end-to-end multimedia session. The attribute provides means to encapsulate a session-level SDP bandwidth that is applicable if a particular border gateway is bypassed.

Appropriate Values: See table 7.5.2.

7.5.4 Media plane optimization for WebRTC

7.5.4.1 General

The SDP attributes associated with media plane optimization procedures for WebRTC are used to encapsulate an SDP offer or SDP answer received from a WIC, as described in 3GPP TS 23.228 [7], annex U.2.4.

7.5.4.2 Semantics

The "tra-m-line" and "tra-att" SDP attributes contain media-related SDP information which is applicable if optimized transparent media between WICs are selected. In the SDP offer, the attributes describe the offered transparent media which can be selected. In the SDP answer, the presence of the attributes indicates that the transparent media have been selected and the attributes which have been selected.

The "tra-SCTP-association" SDP attribute indicates for a media line that the related optimized transparent media are transported in the indicated SCTP association. The optimized transparent media related to several media lines can be transported in the same SCTP association.

The "tra-bw" SDP attribute contains bandwidth-related SDP information which is applicable if the optimized transparent media between WICs are selected. In the SDP offer, the attributes describe the bandwidths the offerer wants to receive for transparent media. In the SDP answer, the attributes describe the bandwidths the answerer wants to receive for transparent media.

The "tra-contact" SDP attribute in the SDP offer encapsulate address information which is compared with the address information in contact by the receiving eP-CSCF to detect whether intermediates that do not support switching to transparent media between WICs are in the path.

The "tra-media-line-number" SDP attribute provides the total number of media lines in the SDP, excluding any media lines with port zero, which is compared with the real number of media lines in the SDP, excluding any media lines with port zero, by the receiving eP-CSCF to detect whether intermediates have removed or dissabled media lines.

7.5.4.3 Syntax

The syntax specified in table 7.5.4.3-1 uses the augmented Backus-Naur Form as described in RFC 2234 [20G].

Table 7.5.4.3-1: Syntax of media plane optimization for WebRTC related SDP attributes

tra-contact = "tra-contact" ":" nettype SP addrtype SP connection-address

; from RFC 4566 [39]

tra-m-line = "tra-m-line" ":" media SP port ["/" integer] proto 1*(SP fmt)

; from RFC 4566 [39]

tra-att = "tra-att" ":" attribute ; from RFC 4566 [39]

tra-bw = "tra-bw" ":" bwtype ":" bandwidth ; from RFC 4566 [39]

tra-SCTP-association = "tra-SCTP-association" ":" SCTP-association-number

tra-media-line-number = "media-line-number" ":" m-line-number

SCTP-association-number = integer

m-line-number = integer

This grammar encodes the media level information received in an initial SDP offer from a WIC.

<tra-contact>: It is the contact used in the outgoing SDP offer which contains encapsulated media information. It contains nettype, addrtype and connection-address. Nettype, addrtype and connection-address are defined in RFC 4566 [39].

<tra-m-line>: provides the media <media>, port <port>, transport format <proto> and list of media formats (e.g., payload type numbers) <fmt> in the received SDP offer. Media <media>, port <port>, transport format <proto> and media format <fmt> are defined in RFC 4566 [39] for the SDP m-line.

<tra- att> provides an encapsulated SDP attribute <attribute> supported by the sender of the offer. Attribute <attribute> is defined in RFC 4566 [39] for the SDP a-line.

<tra- bw> provides an SDP bandwidth described by <bwtype> and <bandwidth> supported by the sender of the offer. <bwtype> and <bandwidth> are defined in RFC 4566 [39] for the SDP b-line.

<tra-SCTP-association> provides the number <SCTP-association-number> of an SCTP association a media line relates to. If optimized media are selected, the media related to a media line with an "a= tra-SCTP-association" SDP attribute will be transported in that SCTP association, possibly together with media relating to other media lines with a= tra-SCTP-association" SDP attributes with the same <SCTP-association-number>. For a WIC terminating call, the eP-CSCF receiving an offer from the core network containg m-lines with "a= tra-SCTP-association" SDP attributes with the same <SCTP-association-number> will construct a single m-line related to that SCTP association in the offer towards the served WIC.

<tra-media-line-number> provides the total number <m-line-number> of media lines in the SDP, excluding any media lines with port zero.

The "tra-contact", "tra- att", "tra-bw", SDP attributes are session and media-level attributes.

The "tra-m-line" and "tra-SCTPassociation" SDP attributes are media level attributes.

The "tra-media-line-number" SDP attribute is a session level attribute.

7.5.4.4 IANA registration

Editor’s note: [eWebRTCi_CT, CR#5474] Subclause 7.5.4.4 forms the basis for an IANA registration of the new SDP attributes. The registration should be performed by MCC when Release 13 is declared 100% complete.

7.5.4.4.1 tra-contact

Contact Name: 3GPP Specifications Manager, 3gppContact@etsi.org, +33 (0)492944200

Attribute Name: tra-contact

Long Form: tra-contact

Type of Attribute: session and media level

Charset Considerations: The attribute is not subject to the charset attribute.

Purpose: This attribute is used in networks supporting WebRTC-IMS interworking. This attribute is used to encapsulate contact information received from gateways in the SDP offers and SDP answers when setting up a session that supports media plane optimization feature as specified in 3GPP TS 23.228 and 3GPP TS 24.371.

Appropriate Values: See table 7.5.4.3-1.

7.5.4.4.2 tra-m-line

Contact Name: 3GPP Specifications Manager, 3gppContact@etsi.org, +33 (0)492944200

Attribute Name: tra-m-line

Long Form: tra-m-line

Type of Attribute: media level

Charset Considerations: The attribute is not subject to the charset attribute.

Purpose: This attribute is used in networks supporting WebRTC-IMS interworking. This attribute is used to encapsulate an m-line received in an SDP offer or SDP answer into an attribute in an outgoing SDP offer or SDP answer when setting up a session that supports media plane optimization feature as specified in 3GPP TS 23.228 and 3GPP TS 24.371.

Appropriate Values: See table 7.5.4.3-1.

7.5.4.4.3 tra-att

Contact Name: 3GPP Specifications Manager, 3gppContact@etsi.org, +33 (0)492944200

Attribute Name: tra-att

Long Form: tra-att

Type of Attribute: session and media level

Charset Considerations: The attribute is not subject to the charset attribute.

Purpose: This attribute is used in networks supporting WebRTC-IMS interworking. This attribute is used to encapsulate an attribute received in an SDP offer or SDP answer into an attribute in an outgoing SDP offer or SDP answer when setting up a session that supports media plane optimization feature as specified in 3GPP TS 23.228 and 3GPP TS 24.371.

Appropriate Values: See table 7.5.4.3-1.

7.5.4.4.4 tra-bw

Contact Name: 3GPP Specifications Manager, 3gppContact@etsi.org, +33 (0)492944200

Attribute Name: tra-bw

Long Form: tra-bw

Type of Attribute: session and media level

Charset Considerations: The attribute is not subject to the charset attribute.

Purpose: This attribute is used in networks supporting WebRTC-IMS interworking. This attribute is used to encapsulate bandwidth information received in the SDP offers and SDP answers when setting up a session that supports media plane optimization feature as specified in 3GPP TS 23.228 and 3GPP TS 24.371.

Appropriate Values: See table 7.5.4.3-1.

7.5.4.4.5 tra-SCTP-association

Contact Name: 3GPP Specifications Manager, 3gppContact@etsi.org, +33 (0)492944200

Attribute Name: tra-SCTP-association

Long Form: tra-SCTP-association

Type of Attribute: media level

Charset Considerations: The attribute is not subject to the charset attribute.

Purpose: This attribute is used in networks supporting WebRTC-IMS interworking. This attribute is used to indicate that a media line relates to an SCTP association received in the SDP offers and SDP answers when setting up a session that supports media plane optimization feature as specified in 3GPP TS 23.228 and 3GPP TS 24.371.

Appropriate Values: See table 7.5.4.3-1.

7.5.4.4.6 tra- media-line-number

Contact Name: 3GPP Specifications Manager, 3gppContact@etsi.org, +33 (0)492944200

Attribute Name: tra-media-line-number

Long Form: tra-media-line-number

Type of Attribute: session level

Charset Considerations: The attribute is not subject to the charset attribute.

Purpose: This attribute is used in networks supporting WebRTC-IMS interworking. This attribute is used to encapsulate the total number of media lines in the SDP, excluding any media lines with port zero, to detect a removal or dissabling of media lines by intermediate nodes when setting up a session that supports media plane optimization feature as specified in 3GPP TS 23.228 and 3GPP TS 24.371.

Appropriate Values: See table 7.5.4.3-1.

7.5.5 Void

7.5.6 SDP content attribute values

7.5.6.1 General

As defined in RFC 4796 [206], the "a=content" attribute is a media level attribute in SDP.

7.5.6.2 SDP "a=content" attribute "g.3gpp.announcement-no-confirmation" value

7.5.6.2.1 General

The SDP "a=content" attribute "g.3gpp.announcement-no-confirmation" value is used only for informative purposes during an established session, to indicate an SDP media description is for the video announcement service and the operator wishes to play the announcement stream without user confirmation.

The AS may use this value, based on the operator policy, only for the video announcement which is important or needs to be seen by the user immediately.

The UE may accept to play the video announcement without user confirmation when received this value, based on UE’s local policy (e.g., local configuration on the UE).

The use of the SDP "a=content" attribute "g.3gpp.announcement-no-confirmation" value shall conform to the procedure specified in 3GPP TS 24.628 [8ZF].

7.5.6.2.2 IANA registration for values of "a=content" attribute

Editor’s note [CR#6438, WI TEI17]: IANA registration about the announcement service indication "g.3gpp.announcement-no-confirmation" needs to be done in IANA when Release 17 is completed.

IANA registration table: "content SDP Parameters" table of "Session Description Protocol (SDP) Parameters" registry.

IANA registry: A new value "g.3gpp.announcement-no-confirmation" for the SDP a=content media-level attribute defined in RFC 4796 [206].

Reference: 3GPP TS 24.229, http://www.3gpp.org/ftp/Specs/archive/24_series/24.229/.