• Abstract: Session Initiation Protocol (SIP) allows proxy servers to initiate TCP connections and send asynchronous UDP datagrams to User Agents in order to deliver requests. However, many practical considerations, such as the existence of firewalls and NATs, prevent servers from connecting to User Agents in this way. Even when a proxy server can open a TCP connection to a User Agent, most User Agents lack a certificate suitable to act as a TLS server. This specification defines behaviors for User Agents, registrars and proxy servers that allow requests to be delivered on existing connections established by the User Agent. It also defines keep alive behaviors needed to keep NAT bindings open and specifies the usage of multiple connections for high availability systems.

• Abstract: Service usage might require some form of compensation and this is also true for many communication systems where an entity receiving a call should be able to charge the caller. This is necessary for allowing fair communication between two communicating parties and is a major strategy for reducing the viability of SPAM. This draft proposes an approach for doing this in SIP using the Security Assertion Markup Language (SAML). It relies on a third party to act as a payment provider and is designed for low value transactions. It does not aim to provide the same capability as other authentication, authorization and accounting systems. This draft is in a fairly early state and has many details that are missing. Earlier versions of this document did not use SAML. This version offers a sketch of what the SAML based solution would look like but still lacks many details that would be needed for an actual implementation.

• Abstract: This document describes how to use the SIP REFER method and the dialog package to manipulate conversations, dialogs, and sessions on remote User Agents. Specifically it extents the REFER mechinims to allow the specificate of a response that a UA should send in a dialog. This functionality is most useful for collections of loosely coupled User Agents that wish to present a coordinated user experience. It does not require a Third-Party Call Control controller to be involved in any of the manipulated dialogs.

Abstract: One of the techniques used in SPAM prevention and various solutions for denial of service attacks is to force the SIP client requesting a service to perform a calculation that limits the rate and increases the cost of the request. This draft defines a way to allow a UAS to ask the UAC to compute a computationally expensive hash based function and present the result to the UAS. Although the computation is expensive for the UAC to compute, it is cheap for the UAS to verify. The solution also allows for proxies to compute and check the puzzle on behalf of the UAC or UAS.

• Abstract: This document creates an Internet Assigned Number Authority (IANA) registry for the tel Uniform Resource Identifier (URI) parameters, and their values. It also lists the already existing parameters to be used as initial values for that registry.