XMPP as defined in XMPP Core  does not support direct interaction between endpoints, since it requires a client to authenticate an XML stream with a "home" server and send of all of its outbound XML stanzas through that server (which potentially can route those stanzas through a peer server for delivery to the intended recipient). However, in some scenarios it is desirable to establish end-to-end XML streams between two endpoints instead of relying on the standard client-server architecture. These scenarios include:
The first scenario is addressed by Link-Local Messaging (XEP-0174) . The second and third scenarios are addressed by Jingle XML Streams (XEP-0247) . Both of those technologies result in the establishment of a direct or mediated connection between two endpoints, such as a direct TCP connection, a bytestream through SOCKS5 (SOCKS5 Bytestreams (XEP-0065) ) or XMPP itself (In-Band Bytestreams (XEP-0047) ), or other future transport methods such as RFC 6544 .
Once two endpoints have opened a direct or mediated connection, they can establish an XML stream over that connection for end-to-end "("e2e") communication. We call this an "e2e stream".
The initiator and recipient essentially follow the process defined in RFC 6120 to establish XML streams between themselves.
First, the initiator opens an XML stream to the recipient over the negotiated transport.
In accordance with RFC 6120, the initial stream header SHOULD include the 'to' and 'from' attributes. In the case of XEP-0174, these SHOULD be the username@machine-name advertised in the PTR record. In the case of Jingle XML Streams, these SHOULD be the bare JIDs (<email@example.com> or <domain.tld>) of the entities as communicated via XMPP.
If the initiator supports stream features and the other stream-related aspects of XMPP 1.0 as specified in RFC 6120, then it SHOULD include the version='1.0' flag as shown in the previous example.
The recipient then responds with a stream header as well:
If both the initiator and recipient included the version='1.0' flag, the recipient SHOULD also send stream features as specified in RFC 6120:
The mere exchange of stream headers results in an unencrypted and unauthenticated channel between the two entities. The entities SHOULD upgrade the channel to an encrypted stream using the XMPP STARTTLS command defined in XMPP Core  using RFC 5246 , optionally followed by SASL negotiation for mutual authentication (see RFC 4422 ).
End-to-end XML streams can be negotiated between two XMPP clients, between an XMPP client and a remote XMPP service (i.e., a service with which a client does not have a direct XML stream, such as a remote Multi-User Chat (XEP-0045)  room), or between two remote XMPP services. Therefore, if standard X.509 certificates are used then a party to an e2e XML stream will present either a client certificate or a server certificate as appropriate. If X.509 certificates are used, they MUST at a minimum be generated and validated in accordance with the certificate guidelines guidelines provided in RFC 6120 ; however, applications of end-to-end XML streams MAY define supplemental guidelines for certificate validation in the context of particular architectures, such as XEP-0174 for link-local streams and XEP-0247 for direct or mediated streams negotiated through XMPP servers.
To ease the transition from the PGP-based object encryption method specified in Current Jabber OpenPGP Usage (XEP-0027) , clients using TLS for e2e streams MAY use the OpenPGP TLS extension defined in RFC 5081  (if available).
Use of other TLS extensions MAY be appropriate as well, including those defined in RFC 5246  and RFC 5054 .
Once the streams are established, either entity then can send XMPP message, presence, and IQ stanzas, with or without 'to' and 'from' addresses.
To end the stream, either party closes the XML stream:
The other party then closes the stream in the other direction as well:
Both parties then SHOULD close the logical or physical connection between them.
End-to-end streams SHOULD be encrypted; see the Stream Encryption section of this document.
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) .
This document requires no interaction with the XMPP Registrar .
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The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.
The primary venue for discussion of XMPP Extension Protocols is the <firstname.lastname@example.org> discussion list.
Discussion on other xmpp.org discussion lists might also be appropriate; see <http://xmpp.org/about/discuss.shtml> for a complete list.
Errata can be sent to <email@example.com>.
The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".
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Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/
Updated missing 'ice-tcp' reference to RFC 6544.
Initial published version.
First draft, split off from XEP-0174.