Administrator’s Guide for SIP-T2 Series/T19(P) E2/T4 Series/T5 Series/CP860/CP920 IP Phones 
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If you want to find Request for Comments (RFC) documents, type 
http://www.ietf.org/rfc/rfcNNNN.txt
 (NNNN is the RFC number) into the location field of your 
browser. 
This guide mainly takes the SIP-T46G IP phones as example for reference. For more details on 
other IP phones, refer to 
Yealink phone-specific user guide
. 
For other references, look for the hyperlink or web info throughout this administrator guide. 
Understanding VoIP Principle and SIP Components 
This section mainly describes the basic knowledge of VoIP principle and SIP components, which 
will help you have a better understanding of the phone’s deployment scenarios. 
VoIP Principle 
VoIP 
VoIP (Voice over Internet Protocol) is a technology using the Internet Protocol instead of 
traditional Public Switch Telephone Network (PSTN) technology for voice communications. 
It is a family of technologies, methodologies, communication protocols, and transmission 
techniques for the delivery of voice communications and multimedia sessions over IP networks. 
The H.323 and Session Initiation Protocol (SIP) are two popular VoIP protocols that are found in 
widespread implementation. 
H.323 
H.323 is a recommendation from the ITU Telecommunication Standardization Sector (ITU-T) 
that defines the protocols to provide audio-visual communication sessions on any packet 
network. The H.323 standard addresses call signaling and control, multimedia transport and 
control, and bandwidth control for point-to-point and multi-point conferences. 
It is widely implemented by voice and video conference equipment manufacturers, is used 
within various Internet real-time applications such as GnuGK and NetMeeting and is widely 
deployed by service providers and enterprises for both voice and video services over IP 
networks. 
SIP 
SIP (Session Initiation Protocol) is the Internet Engineering Task Force’s (IETF’s) standard for 
multimedia conferencing over IP. It is an ASCII-based, application-layer control protocol 
(defined in RFC 3261) that can be used to establish, maintain, and terminate calls between two 
or more endpoints. Like other VoIP protocols, SIP is designed to address functions of signaling 
and session management within a packet telephony network. Signaling allows call information 
to be carried across network boundaries. Session management provides the ability to control 
attributes of an end-to-end call.