SIP is a signalling protocol used for establishing, modifying and terminating sessions with one or more participants on the Internet. The emergence of SIP promises simple and efficient handling of multimedia sessions among multiple users. This article gives a survey of SIP in distributed systems. First, we provide an overview of SIP by presenting its characteristics and functionality, and also describe the relationship between SIP and distributed systems. Secondly, we present current issues about SIP, such as QoS, security and NAT/Firewall. Finally, usages of SIP for now are discussed and it includes VoIP and IMS.