This document updates the registration guidance provided in Section 4.2 of RFC 5031, which allows the registration of service URNs with the 'sos' service type only for emergency services "that are offered widely and in different countries". This document updates those instructions to allow such registrations when, at the time of registration, those services are offered in only one country.

This document specifies how the UDP Transport Layer (UDPTL) protocol, the predominant transport protocol for T.38 fax, can be transported over the Datagram Transport Layer Security (DTLS) protocol, how the usage of UDPTL over DTLS is indicated in the Session Description Protocol (SDP), and how UDPTL over DTLS is negotiated in a session established using the Session Initiation Protocol (SIP

This document specifies the Content-ID header field for usage in the Session Initiation Protocol (SIP). This document also updates RFC 5621, which only allows a Content-ID URL to reference a body part that is part of a multipart message-body. This update enables a Content-ID URL to reference a complete message-body and metadata provided by some additional SIP header fields.This document updates RFC 5368 and RFC 6442 by clarifying their usage of the SIP Content-ID header field.

This specification defines a new SIP header field, Feature-Caps. The Feature-Caps header field conveys feature-capability indicators that are used to indicate support of features and capabilities for SIP entities that are not represented by the Uniform Resource Identifier (URI) of the Contact header field. SIP entities that are represented by the URI of the SIP Contact header field can convey media feature tags in the Contact header field to indicate support of features and capabilities. This specification also defines feature-capability indicators and creates a new IANA registry, "Proxy-Feature Feature-Capability Indicator Trees", for registering feature-capability indicators. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6809. Holmberg, et al.