3pcc
Encyclopedia
In the traditional telephony
context, third party call control allows one entity (which we call the controller) to set up and manage a communications relationship or telephone call
between two or more other parties. Third party call control (referred to as 3pcc) is often used for operator services (where an operator creates a call that connects two participants together) and conferencing.
Similarly, many SIP
services are possible through third party call control. These include the traditional ones on the PSTN
, but also new ones such as click-to-dial. Click-to-dial allows a user to click on a web page
to speak to a customer service representative. The web server then creates a call between the user and a customer service representative. The call can be between two phones, a phone and an IP host, or two IP hosts.
Third party call control is possible using only the mechanisms specified within RFC 3261 [1]. Indeed, many different call flows are possible, each of which will work with SIP compliant user agents. However, there are benefits and drawbacks to each of these flows. The usage of third party call control also becomes more complex when aspects of the call utilize SIP extensions or optional features of SIP. In particular, the usage of RFC 3312 [2] (used for coupling of signaling to resource reservation) with third party call control is non-trivial, and is discussed in Section 9 of RFC 3725 [3]. Similarly, the usage of early media (where session data is exchanged before the call is accepted) with third party call control is not trivial; both of them specify the way in which user agents generate and respond to SDP
, and it is not clear how to do both at the same time. This is discussed further in Section 8.
Third Party Call Control is perfectly suited for delivery of 9-1-1 calls in a Next Generation 9-1-1
environment. It allows for re-connection of the media stream to an alternate end point if the original destination end point becomes unavailable without dropping the original emergency call (which has a separate media stream to the 3PCC server). Additionally, it minimizes bandwidth requirements between the 3PCC server and the emergency call
handling end point because all mixed media uses the same RTP stream. Finally, it does not rely on a destination end point for end to end reliability but rather on a more robust centralized data center with several redundantly deployed servers.
Telephony
In telecommunications, telephony encompasses the general use of equipment to provide communication over distances, specifically by connecting telephones to each other....
context, third party call control allows one entity (which we call the controller) to set up and manage a communications relationship or telephone call
Telephone call
A telephone call is a connection over a telephone network between the calling party and the called party.-Information transmission:A telephone call may carry ordinary voice transmission using a telephone, data transmission when the calling party and called party are using modems, or facsimile...
between two or more other parties. Third party call control (referred to as 3pcc) is often used for operator services (where an operator creates a call that connects two participants together) and conferencing.
Similarly, many SIP
Session Initiation Protocol
The Session Initiation Protocol is an IETF-defined signaling protocol widely used for controlling communication sessions such as voice and video calls over Internet Protocol . The protocol can be used for creating, modifying and terminating two-party or multiparty sessions...
services are possible through third party call control. These include the traditional ones on the PSTN
Public switched telephone network
The public switched telephone network is the network of the world's public circuit-switched telephone networks. It consists of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all inter-connected by...
, but also new ones such as click-to-dial. Click-to-dial allows a user to click on a web page
Web page
A web page or webpage is a document or information resource that is suitable for the World Wide Web and can be accessed through a web browser and displayed on a monitor or mobile device. This information is usually in HTML or XHTML format, and may provide navigation to other web pages via hypertext...
to speak to a customer service representative. The web server then creates a call between the user and a customer service representative. The call can be between two phones, a phone and an IP host, or two IP hosts.
Third party call control is possible using only the mechanisms specified within RFC 3261 [1]. Indeed, many different call flows are possible, each of which will work with SIP compliant user agents. However, there are benefits and drawbacks to each of these flows. The usage of third party call control also becomes more complex when aspects of the call utilize SIP extensions or optional features of SIP. In particular, the usage of RFC 3312 [2] (used for coupling of signaling to resource reservation) with third party call control is non-trivial, and is discussed in Section 9 of RFC 3725 [3]. Similarly, the usage of early media (where session data is exchanged before the call is accepted) with third party call control is not trivial; both of them specify the way in which user agents generate and respond to SDP
Session Description Protocol
The Session Description Protocol is a format for describing streaming media initialization parameters. The IETF published the original specification as an IETF Proposed Standard in April 1998, and subsequently published a revised specification as an IETF Proposed Standard as RFC 4566 in July...
, and it is not clear how to do both at the same time. This is discussed further in Section 8.
Third Party Call Control is perfectly suited for delivery of 9-1-1 calls in a Next Generation 9-1-1
Next Generation 9-1-1
Next Generation 9-1-1 refers to an initiative aimed at updating the 9-1-1 service infrastructure in the United States and Canada to improve public emergency communications services in a wireless mobile society...
environment. It allows for re-connection of the media stream to an alternate end point if the original destination end point becomes unavailable without dropping the original emergency call (which has a separate media stream to the 3PCC server). Additionally, it minimizes bandwidth requirements between the 3PCC server and the emergency call
Emergency Call
Emergency Call is a British film released in 1952 by Nettlefold Films. The film was directed by Lewis Gilbert and stars Jack Warner in a familiar role playing a policeman, Anthony Steel, Joy Shelton and Sid James as a dubious boxing promoter....
handling end point because all mixed media uses the same RTP stream. Finally, it does not rely on a destination end point for end to end reliability but rather on a more robust centralized data center with several redundantly deployed servers.
See also
- Calling partyCalling partyThe calling party is a person who initiates a telephone call over the public switched telephone network, usually by dialing a telephone number....
- Called partyCalled partyThe called party is a person who answers a telephone call. The person who initiates a telephone call is the calling party....
- Next Generation 9-1-1Next Generation 9-1-1Next Generation 9-1-1 refers to an initiative aimed at updating the 9-1-1 service infrastructure in the United States and Canada to improve public emergency communications services in a wireless mobile society...
- Click-to-callClick-to-callClick-to-call, also known as click-to-talk, click-to-chat and click-to-text, is a form of Web-based communication in which a person clicks an object to request an immediate connection with another person in real-time either by phone call, Voice-over-Internet-Protocol , or text...
- Third Party Control ProtocolThird Party Control ProtocolThird Party Control Protocol is a client-server protocol with three types of primitives:* Request ,* Notify ,* Responses...
External links
- RFC 3261 — SIP: Session Initiation Protocol
- RFC 3312 — Integration of Resource Management and Session Initiation Protocol (SIP)
- RFC 3725 — Best Current Practices for Third Party Call Control (3pcc) in the Session Initiation Protocol (SIP)
- RFC 4032 — Update to the Session Initiation Protocol (SIP) Preconditions Framework