SIP 中继链接 ，英文为SIP Trunking， 是一种基于会话发起协议(Session Initiation Protocol, SIP) 的IP电话 (VoIP) 和流媒体服务。 网络通讯服务提供商（Internet telephony service provider，ITSP） 通过它向配备基于SIP的IP用户交换机 (IP-PBX)以及统一通信设备的客户提供通信以及统一通信（unified communications）服务。 常见的这类软件应用主要提供语音、视频以及其他流媒体服务（比如桌面共享，网络会议以及共享黑板等）。

SIP trunking is a Voice over Internet Protocol (VoIP) and streaming media service based on the Session Initiation Protocol (SIP) by which Internet telephony service providers (ITSPs) deliver telephone services and unified communications to customers equipped with SIP-based private branch exchange (IP-PBX) and Unified Communications facilities. Most Unified Communications software applications provide voice, video, and other streaming media applications such as desktop sharing, web conferencing, and shared whiteboard.