2026-01-15 IETF Review 1 pix-x horizontal pixels 2 pix-y vertical pixels 3 dpi dots-per-inch 4 ua-media ua-media 5 paper-size paper-size 6 color color 7 size-x size-x 8 size-y size-y 9 dpi-xyratio dpi-xyratio 10 color-levels color-levels 11 color-space color-space 12 CIELAB-L-depth CIELAB-L-depth 13 CIELAB-A-depth CIELAB-A-depth 14 CIELAB-B-depth CIELAB-B-depth 15 CIELAB-L-min CIELAB-L-min 16 CIELAB-L-max CIELAB-L-max 17 CIELAB-a-min CIELAB-a-min 18 CIELAB-a-max CIELAB-a-max 19 CIELAB-b-min CIELAB-b-min 20 CIELAB-b-max CIELAB-b-max 21 image-file-structure image-file-structure 22 image-coding image-coding 23 image-coding-constraint image-coding-constraint 24 JBIG-stripe-size JBIG-stripe-size 25 image-interleave image-interleave 26 color-subsampling color-subsampling 27 MRC-mode MRC-mode 28 MRC-max-stripe-size MRC-max-stripe-size 29 color-illuminant color-illuminant 30 type type 31 charset charset 32 language language 33 unknown-character-replacement unknown-character-replacement Expert Review Paul Kyzivat Registration requests can be sent directly to iana@iana.org or submitted via IANA's general request form. IANA will forward requests to the Media Feature Tags mailing list and the IESG-designated expert(s), who will notify IANA if the request is approved. IANA does not monitor the list. 1 g.3gpp.cs-voice This feature-tag indicates that the device supports circuit switched voice when combining circuit switched calls and IM sessions. ETSI TS 124 279 2 g.3gpp.cs-video This feature-tag indicates that the device supports circuit switched video when combining circuit switched video calls and IM sessions. ETSI TS 124 279 3 g.3gpp.smsip This feature-tag indicates that the device is capable of accepting SMS messages via SIP as specified by ETSI TS 124 341. ETSI TS 124 341 4 g.3gpp.icsi-ref Each value of the Service Reference media feature-tag indicates the software applications supported by the agent. The values for this tag equal the IMS communication Service Identifier (ICSI) values supported by the agent. The Service Reference media feature tag is defined to fulfil the requirements for forking to an appropriate UE when multiple UEs are registered and dispatch to an appropriate application within the UE based upon the IMS communication Service Identifier (ICSI) values as stated in 3GPP TS 23.228. 3GPP TS 24.229 5 g.3gpp.iari-ref Each value of the Application Reference media feature-tag indicates the software applications supported by the agent. The values for this tag equal IMS Application Reference Identifier (IARI) values supported by the agent The Application Reference media feature tag is defined to fulfil the requirements for forking to an appropriate UE when multiple UEs are registered and dispatch to an appropriate application within the UE based upon and IMS Application Reference Identifier (IARI) values as stated in 3GPP TS 23.228. 3GPP TS 24.229 6 g.3gpp.ics This feature-tag when used in a SIP REGISTER request indicates that the function is ICS capability and may operate in ICS mode. This feature-tag when used is a none SIP REGISTER method indicates that the function wants to invoke ICS functionality. 3GPP TS 24.292 7 g.3gpp.accesstype This feature-tag when used in a SIP REGISTER request indicates access network technology used by the device and the particular registration flow that the device is using to register over. 3GPP TS 24.292 8 g.3gpp.pne-id This media feature-tag when used in a SIP request or a SIP response indicates the identifier of a PNE other than a UE. 3GPP TS 24.259 9 g.3gpp.iut-controller This media feature-tag when used in a SIP request or a SIP response indicates that the function sending the SIP message supports the IUT Controller functionality.This media feature tag does not imply that the controller UE capabilities are handled in the same protocol manner. 3GPP TS 24.337 10 g.3gpp.iut-focus This media feature-tag when used in a Contact header field or a Accept-Contact header field of a SIP request or a SIP response indicates that the function sending the SIP message supports anchoring a IUT session and/or the SIP message is an inter-UE transfer operation. 3GPP TS 24.337 11 g.3gpp.current-iut-controller This media feature-tag when used in a Contact header field of SIP request or SIP response indicates that the UA is the currently active IUT controller for the collaborative session or is a controllee in the collaborative. The values of the feature tag are "active" and "passive". 3GPP TS 24.337 12 g.3gpp.mid-call This feature-tag when used in a SIP request or a SIP response indicates that the function sending the SIP message supports the MSC server assisted mid-call feature. 3GPP TS 24.237 13 g.3gpp.srvcc-alerting This media feature-tag when used in a Contact header field of a SIP request or a SIP response indicates that the functional entity sending the SIP message supports SRVCC access transfer for calls in alerting phase, i.e. for calls whith early dialog. 3GPP TS 24.237 14 g.3gpp.cs2ps-srvcc-alerting This media feature-tag when used in a Contact header field of a SIP request or a SIP response indicates that the functional entity sending the SIP message supports CS to PS SRVCC access transfer for calls in alerting phase. 3GPP TS 24.237 11.10.0 15 g.3gpp.path This media feature tag when used in a Contact header field in SIP REGISTER request or SIP response to the SIP REGISTER request indicates capability of identifying the registration path and binding SRVCC related information to it. 3GPP TS 24.237 11.10.0 16 g.3gpp.cs2ps-srvcc This media feature tag when included in Contact header field indicates support of the CS to PS single radio voice call continuity as specified in 3GPP TS 24.237. 3GPP TS 24.237 11.10.0 17 g.3gpp.pstops-sti This media feature-tag when used in a Contact header field of a SIP request or a SIP response indicates that the functional entity sending the SIP message supports the use of the PS to PS STI URI. 3GPP TS 24.237 11.10.0 18 g.3gpp.ti This media feature tag when used in a Contact header field as specified in IETF RFC 3840 in SIP INVITE request or SIP response to the SIP INVITE request indicates the capability of associating a CS call with dialog created by the SIP INVITE request. 3GPP TS 24.237 11.10.0 19 g.3gpp.drvcc-alerting This media feature-tag when used in a Contact header field of a SIP request or a SIP response indicates that the functional entity sending the SIP message supports the PS to CS dual radio access transfer for calls in alerting phase. 3GPP TS 24.237 12.8.0 20 g.3gpp.dynamic-stn This media feature-tag when used in a Contact header field of a SIP request or a SIP response indicates that the functional entity sending the SIP message supports the use of dynamic STN. 3GPP TS 24.237 12.8.0 21 g.3gpp.ps2cs-drvcc-orig-pre-alerting This media feature-tag when used in a Contact header field of a SIP request or a SIP response indicates that the functional entity sending the SIP message supports the PS to CS dual radio access transfer for originating calls in pre-alerting phase. 3GPP TS 24.237 12.8.0 22 g.3gpp.ps2cs-srvcc-orig-pre-alerting This media feature tag when used in a Contact header field of a SIP request or a SIP response indicates that the functional entity sending the SIP message supports the PS to CS SRVCC for originating calls in pre-alerting phase. 3GPP TS 24.237 12.8.0 23 g.3gpp.cs2ps-drvcc-alerting This media feature-tag, when used in a Contact header field of a SIP request or a SIP response, indicates that the functional entity sending the SIP message supports the CS to PS dual radio access transfer for calls in alerting phase. 3GPP TS 24.237 v12.9.0 24 g.3gpp.cs2ps-drvcc-orig-pre-alerting This media feature-tag when used in a Contact header field of a SIP request or a SIP response indicates that the functional entity sending the SIP message supports the CS to PS dual radio access transfer for originating calls in pre-alerting phase. 3GPP TS 24.237 v12.9.0 25 g.3gpp.smsip-msisdn-less This media feature-tag when used in a Contact header field of a SIP request or a SIP response indicates that the functional entity sending the SIP message supports MSISDN less operation of SMS via SIP MESSAGE request. 3GPP TS 24.341 v12.6.0 26 g.3gpp.nw-init-ussi This feature-tag indicates support of user equipment procedures for the network initiated USSD over IMS. 3GPP TS 24.390 v12.6.0 27 g.3gpp.registration-token This media feature tag, when included in a third party SIP REGISTER request, indicates the support of using a token to identify the registration used for the request. The mediafeature tag is assigned a value that can be used by the receiving AS to later identify the used registration for initial requests from an originating user or dialog forming responses from a terminating user. 3GPP TS 24.229 v12.16.0 28 g.3gpp.mcptt This media feature tag when used in a SIP request or a SIP response indicates that the function sending the SIP message supports Mission Critical Push To Talk (MCPTT) communication. 3GPP TS 24.379 v13.5.0 29 g.3gpp.mcdata.sds This media feature tag when used in a SIP request or a SIP response indicates that the function sending the SIP message supports Mission Critical Data (MCData) communications Short Data Service (SDS). 3GPP TS 24.282 14.3.0 30 g.3gpp.mcdata.fd This media feature tag when used in a SIP request or a SIP response indicates that the function sending the SIP message supports Mission Critical Data (MCData) communications File Distribution (FD). 3GPP TS 24.282 14.3.0 31 g.3gpp.mcvideo This media feature tag when used in a SIP request or a SIP response indicates that the function sending the SIP message supports Mission Critical Video (MCVideo) communication. 3GPP TS 24.281 Rel-14 32 g.3gpp.dynamic-e-stn-drvcc This media feature-tag when used in a Contact header field of a SIP request or a SIP response indicates that the functional entity sending the SIP message supports the use of dynamic-e-stn-drvcc. 3GPP TS 24.237 33 g.3gpp.ps2cs-srvcc-mid-call-emergency This media feature-tag, when used in a Contact header field of a SIP request or a SIP response, indicates that the functional entity sending the SIP message supports the PS to CS SRVCC for emergency session in early dialog state with active speech media component when both the emergency session in early dialog state with active speech media component and a non-emergency call in confirmed dialog state with inactive speech media component exists. 3GPP TS 24.237 34 g.3gpp.ps2cs-srvcc-term-pre-alerting This media feature tag when used in a Contact header field of a SIP request or a SIP response indicates that the functional entity sending the SIP message supports the PS to CS SRVCC for terminating calls in pre-alerting phase. 3GPP TS 24.237 35 g.3gpp.ps-data-off This media feature tag when included in a Contact header field in a REGISTER request indicates the status of the 3GPP PS data off for the registration time. This media feature tag, when included in the Contact header field in a REGISTER request indicates that the UE supports the 3GPP PS data off. The g.3gpp.ps-data-off media feature tag can take a value that indicates whether the 3GPP PS data off has been activated or deactivated by the user at the UE. 3GPP TS 24.229 36 g.3gpp.mcdata.ipconn This media feature tag when used in a SIP request or a SIP response indicates that the function sending the SIP message supports Mission Critical Data (MCData) communications IP Connectivity (IPCONN). 3GPP TS 24.282 37 g.3gpp.rlos This feature-tag when used in a SIP REGISTER request indicates that the function sending the SIP message supports restricted local operator service. 3GPP TS 24.229 38 g.3gpp.dc-mux Support of multiplexing multiple IMS application data channels from different data channel applications on a single SDP media description, resulting in use of multiple a=3gpp-req-app SDP attributes with different application-id tag values. Also, support of multiplexing IMS bootstrap data channels from both local network and remote network bootstrap content sources on a single SDP media description. 3GPP TS 26.114 Unregistered (formed from uri) IETF Review 1 sip.audio This feature tag indicates that the device supports audio as a streaming media type. 2 sip.application This feature tag indicates that the device supports application as a streaming media type. This feature tag exists primarily for completeness. Since so many MIME types are underneath application, indicating the ability to support applications provides little useful information. 3 sip.data This feature tag indicates that the device supports data as a streaming media type. 4 sip.control This feature tag indicates that the device supports control as a streaming media type. 5 sip.video This feature tag indicates that the device supports video as a streaming media type. 6 sip.text This feature tag indicates that the device supports text as a streaming media type. 7 sip.automata The sip.automata feature tag is a boolean value that indicates whether the UA represents an automata (such as a voicemail server, conference server, IVR, or recording device) or a human. 8 sip.class This feature tag indicates the setting, business or personal, in which a communications device is used. 9 sip.duplex The sip.duplex media feature tag indicates whether a communications device can simultaneously send and receive media ("full"), alternate between sending and receiving ("half"), can only receive ("receive-only") or only send ("send-only"). 10 sip.mobility The sip.mobility feature tag indicates whether the device is fixed (meaning that it is associated with a fixed point of contact with the network), or mobile (meaning that it is not associated with a fixed point of contact). Note that cordless phones are fixed, not mobile, based on this definition. 11 sip.description The sip.description feature tag provides a textual description of the device. 12 sip.events Each feature tag value indicates a SIP event package supported by a SIP UA. The values for this tag equal the event package names that are registered by each event package. 13 sip.priority The sip.priority feature tag indicates the call priorities the device is willing to handle. A value of X means that the device is willing to take requests with priority X and higher. This does not imply that a phone has to reject calls of lower priority. As always, the decision on handling of such calls is a matter of local policy. 14 sip.methods Each value of the sip.methods (note the plurality) feature tag indicates a SIP method supported by this UA. In this case, "supported" means that the UA can receive requests with this method. In that sense, it has the same connotation as the Allow header field. 15 sip.extensions Each value of the sip.extensions feature tag is a SIP extension (each of which is defined by an option-tag registered with IANA) that is understood by the UA. Understood, in this context, means that the option tag would be included in a Supported header field in a request. 16 sip.schemes Each value of the sip.schemes (note the plurality) media feature tag indicates a URI scheme that is supported by a UA. Supported implies, for example, that the UA would know how to handle a URI of that scheme in the Contact header field of a redirect response. 17 sip.actor This feature tag indicates the type of entity that is available at this URI. 18 sip.isfocus This feature tag indicates that the UA is a conference server, also known as a focus, and will mix together the media for all calls to the same URI. 19 sip.byeless The feature tag is a boolean flag. When set it indicates that the device is incapable of terminating a session autonomously. 20 sip.rendering This feature tag contains one of three tokens indicating if the device is rendering any media from the current session ("yes"), none of the media from the current session ("no"), or if this status is not known to the device ("unknown"). 21 sip.message This feature tag indicates that the device supports message as a streaming media type. 22 sip.ice This feature tag indicates that the device supports Interactive Connectivity Establishment (ICE). 23 sip.instance This feature tag contains a string containing a URN that indicates a unique identifier associated with the UA instance registering the Contact. Values appropriate for use with this feature tag: String (equality relationship). The feature tag is intended primarily for use in the following applications, protocols, services, or negotiation mechanisms: This feature tag is most useful in a communications application, for describing the capabilities of a device, such as a phone or PDA. 24 sip.app-subtype This feature tag indicates the MIME application sub-types supported by the agent for purposes of streaming media. 25 sip.fax This feature tag indicates whether a communications device supports the ITU-T T.38 fax protocol ("t38") or the passthrough method of fax transmission using the ITU-T G.711 audio codec ("passthrough"). 26 sip.uui-isdn This media feature tag when used in a Contact header field of a SIP request or a SIP response indicates that the entity sending the SIP message supports the package "uui-isdn". 27 sip.src This feature tag indicates that the UA is a Session Recording Client for the purpose of an RS. 28 sip.srs This feature tag indicates that the UA is a Session Recording Server for the purpose of an RS. 29 sip.pnsreg This media feature tag, when inserted in the Contact header field of a SIP REGISTER request, conveys that the SIP UA associated with the tag is able to send binding-refresh REGISTER requests associated with the registration without being awakened by push notifications. 30 sip.clue This feature tag indicates that the device supports CLUE-controlled media. Values appropriate for use with this feature tag: Boolean. The feature tag is intended primarily for use in the following applications, protocols, services, or negotiation mechanisms: This feature tag is most useful in a communications application for describing the capabilities of a device to use the CLUE control protocol to negotiate the use of multiple media streams. Kiran Kapale mailto:kiran.kapale&samsung.com 2023-02-27 Dongwook Kim mailto:dongwook.kim&etsi.org 2026-01-15