<title>Jingle SOCKS5 Bytestreams Transport Method</title>
<abstract>This specification defines a Jingle transport method that results in sending data via the SOCKS5 Bytestreams (S5B) protocol defined in XEP-0065. Essentially this transport method reuses XEP-0065 semantics for sending the data and defines native Jingle methods for starting and ending an S5B session.</abstract>
<remark><p>Added proxy-error action; added a block-size attribute in the transport-accept action when negotiating a fallback to IBB, analogous to changes in XEP-0261; editorial review.</p></remark>
<remark><p>Major update to make Jingle S5B inherit more features from ICE and ICE-TCP. Added priorities and candidate identifiers. Renamed streamhost element to candidate element. Updated candidate selection to use priorities, and it is now required for both clients to send a candidate-used or candidate-error notification. Defined type attribute to differentiate between various kinds of candidates. More clearly described how S5B negotiation is completed, including an activated notification from responder to initiator when the candidate used is a proxy. Noted reuse of fast-mode methodology from S5B optimization specification. Because of incompatibilities with the previous version, changed the namespace to urn:xmpp:jingle:transports:s5b:1.</p></remark>
<remark><p>Minor changes to track modifications to XEP-0166; updated security considerations for consistency with other transport methods; added section on service discovery.</p></remark>
<remark><p>Specified that the responder can send <streamhost/> candidates, consistent with the earlier S5B optimization extension; this change required the introduction of streamhost-used and streamhost-error. Also added text to encourage the use of NAT-assisting protocols.</p></remark>
<p>&xep0166; defines a framework for negotiating and managing data sessions over XMPP. In order to provide a flexible framework, the base Jingle specification defines neither data transport methods nor application formats, leaving that up to separate specifications. The current document defines a transport method for establishing and managing data exchanges between XMPP entities using the existing SOCKS5 Bytestreams (S5B) protocol specified in &xep0065;. This "jingle-s5b" method results in a streaming transport method suitable for use in Jingle application types where packet loss cannot be tolerated (e.g., file transfer). Jingle-S5B reuses the protocol flow from <cite>XEP-0065</cite> for the communication with a SOCKS5 streamhost; the communication between two clients to negotiate the possible candidates differs from <cite>XEP-0065</cite> and shares similarities with &xep0176;</p>
<p>This flow is illustrated in the following examples (to simplify the presentation these use a "stub" application instead of a real application type).</p>
<p>It is RECOMMENDED that a client will offer as many <candidate/> elements as possible with itself as the host (i.e., non-proxy candidates). Such candidates might be found using the following methods:</p>
<ul>
<li>Opening the TCP port on all available interfaces the user wants to use (e.g., maybe not an expensive UMTS link), including the IPv4 and IPv6 addresses of that interface (if available).</li>
<li>Using the client's external IP address as discovered through an assisting NAT protocol or other means.</li>
</ul>
<p>If the client knows it is behind a NAT and the router announces UPnP IGD or NAT-PMP support, the client SHOULD map the open port to the external interface of the router and include the public IP address and port information in the <candidate/> offers. To increase the chance of success without using a proxy, this specification allows the responder to also send offers, effectively equivalent to the "fast-mode" for SOCKS5 Bytestreams as previously described at <<linkurl='http://delta.affinix.com/specs/stream.html'>http://delta.affinix.com/specs/stream.html</link>>.</p>
<p>Once the initiator has a set of candidates, it sends a Jingle session-initiate request that contains one or more transport candidates which are a mixture of <cite>XEP-0065</cite> streamhosts and ICE candidates used in <cite>XEP-0176</cite>.</p>
<p>Depending on the application type, a user agent controlled by a human user might need to wait for the user to affirm a desire to proceed with the session before continuing. When the user agent has received such affirmation (or if the user agent can automatically proceed for any reason, e.g. because no human intervention is expected or because a human user has configured the user agent to automatically accept sessions with a given entity), it returns a Jingle session-accept message. This message MUST contain a &TRANSPORT; element qualified by the 'urn:xmpp:jingle:transports:s5b:1' namespace, which SHOULD in turn contain one <candidate/> element for each SOCKS5 Bytestreams candidate generated by or known to the responder, but MAY instead be empty if the responder does not wish to offer any candidates or wishes to send each candidate as the payload of a transport-info message.</p>
<p>If the responder sends candidates in the session-accept, the chances of a successful connection are increased. For example, the initiator might be behind a NAT or might have no access to a proxy, whereas the responder might have a public IP address, might know about a proxy, or might have NAT penetration support like NAT-PMP in a router. (Whereas this "fast-mode" was a special extension previously, it is the default in jingle-s5b.) However, the responder MUST NOT offer as a candidate any host/port combination that has already been offered by the initiator; this helps to prevent failure of negotiation with the proxy.</p>
<p>In the following example, Juliet's client opens one port. The provided <candidates/> are the (private) IPv4 address of the interface, a (public) IPv6 address, and the public IPv4 address created by mapping the private IP address/port using NAT-PMP.</p>
<examplecaption="Responder sends session-accept with candidates"><