Preferences of those transport protocols. Transport protocols for SIP services at domain B, and the relative Of DNS procedures are needed for proxy 1 to discover the available So that there is always an intersection of capabilities. It supports, and relative preferences for those transport protocols.Īll proxies must implement both UDP and TCP, along with TLS over TCP, Proxy 2 has its own set of transport protocols Transport protocols it supports and a preference for using those The proxy sending the request has a particular set of Thus, clients need toīe able to automatically determine which transport protocols areĪvailable. SIP can also use TLS.Ĭurrently, use of TLS is defined for TCP only. Many other protocols, SIP can run over a variety of transport The choice of transport protocol is particularly noteworthy. The SIP server in domain B, in order to forward the call for second is for proxy 2 to identify a backup for proxy 1 in theĮvent it fails after forwarding the request.įor the first aspect, proxy 1 specifically needs to determine the IPĪddress, port, and transport protocol for the server in domain B. Specific problems that SIP uses DNS to help solve, and provides aĭNS is needed to help solve two aspects of the general call flowĭescribed in the Introduction. To do this, proxy 1 makes use of DNS procedures, usingīoth SRV and NAPTR records. Proxy 2 forwards the call to the called party, UA 2.Īs part of this call flow, proxy 1 needs to determine a SIP serverįor domain B. To the proxy for the domain of the called party (domain B), which is Wishes to call Joe in domain B To do so, it communicates In this diagram, a caller in domain A (UA1) Typical SIP configuration, referred to as the SIP "trapezoid", is User agents, and intermediate elements are known as proxy servers. Server protocol used for the initiation and management ofĬommunications sessions between users. The Session Initiation Protocol (SIP) ( RFC 3261 ) is a client. RFC 3263 SIP: Locating SIP Servers June 2002 13 Authors' Addresses. 15 Rosenberg & Schulzrinne Standards Track 12 8 The Transport Determination Application. ![]() 9 4.4 Consideration for Stateless Proxies. This document describes those DNSġ Introduction. ItĪlso uses DNS to allow a server to send a response to a backup client The Session Initiation Protocol (SIP) uses DNS procedures to allow aĬlient to resolve a SIP Uniform Resource Identifier (URI) into the IPĪddress, port, and transport protocol of the next hop to contact. Distribution of this memo is unlimited.Ĭopyright (C) The Internet Society (2002). Official Protocol Standards" (STD 1) for the standardization stateĪnd status of this protocol. Please refer to the current edition of the "Internet Internet community, and requests discussion and suggestions for This document specifies an Internet standards track protocol for the Session Initiation Protocol (SIP): Locating SIP Servers Updated by: 7984, 8553 Network Working Group J. RFC 3263: Session Initiation Protocol (SIP): Locating SIP Servers
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