SIP is the internet standard for real time voice and video communication. SIP (Session Initiation Protocol) was developed by the IETF and published as RFC 3261.

SIP is an internet protocol for live communications used in setting up and tearing down voice or video calls. It is a signaling protocol used to create, modify, and terminate sessions with one or more participants in an IP network. A session can be a straightforward two-way phone call or it can be a multi-media conference session with many persons participating. SIP has made possible an array of services that seemed unthinkable just a few years ago: internet conferencing, IP telephony, instant messaging, presence, voice and video communication, data collaboration, online gaming, application sharing, and much more.

SIP is doing for real-time communications what HTTP did for the web and SMTP for email. It is the main driver in the acceleration of the IP Telephony revolution. With SIP Telephony, a viable alternative to traditional PBX has emerged. SIP telephone systems deliver features that enhance users’ mobility and productivity, while securing substantial cost-saving advantages. This is making proprietary hardware based PBXs obsolete.

Some of the most common questions about SIP are answered in this SIP FAQ.


Hosted / Virtual / Cloud How does Fax work with VoIP Other Protocols
Arrow What is a Hosted PBX? Arrow What is T38 fax? Arrow What is RTP?
Arrow Hosted PBX Vs On-Premise Arrow What is FoIP – Fax over IP? Arrow What is SDP?
Arrow Hosted PBX Provider – What to look for Arrow FAX Work in VoIP Environments Arrow What is H323?
Arrow A Hosted PBX for your business? Arrow What is Fax to Email? Arrow What is RTCP?


General Info (IP PBX & VoIP technology) All About SIP Features and Benefits of an IP PBX
Arrow What is a PBX Phone System? Arrow Can you List all Known SIP Responses? Arrow What is an Auto-attendant?
Arrow What is Voice over IP? Arrow What are SIP Phones? Arrow Benefits of an IP PBX VoIP Phone System?
Arrow VoIP-Defined Arrow SIP Call Session Between 2 Phones Arrow How an IP PBX / VoIP Phone System Works
Arrow IP PBX, SIP & VoIP FAQ Arrow What SIP-based IP PBX’s are Available? Arrow What is IVR?
Arrow Learn About VoIP Gateways Arrow What is a SIP Server? Arrow What is DID – Direct Inward Dialing?
Arrow VoIP Definitions Arrow Sip Phones / VoIP Phones Types Arrow What is a Voicemail System?
Arrow What are IP Phones / IP Telephones? Arrow What is SIP? Arrow 10 Reasons to Switch to an IP PBX
Arrow What is a STUN Server? Arrow What is SIP Forking? Arrow What are the Benefits of an IP PBX?
Arrow What is ALG? Arrow SIP Methods / Requests and Responses? Arrow What is Unified Communications?
Arrow What is a VoIP Telephone? Arrow What are SIP Trunks? Arrow What is Voicemail to Email?
Arrow What is a Good Source of VoIP Info? Arrow What is a SIP-URI? Arrow What are BLF Function Keys?
Arrow What is IP Telephony? Arrow 3CX’s Unified Communications features


Other Functionalities Legacy Technology (ISDN)
Arrow What is ECHO Cancellation? Arrow What Do FXS and FXO Mean?
Arrow What Does ENUM Mean? Arrow What is a TDM PBX?
Arrow Different Types of CODECS?


These FAQ’s are also available in:

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