Conference Call Device

Description

The Conference Call Device (CCD) is a core application server within the IMS architecture, standardized in 3GPP TS 23.153. It functions as the central controller for multimedia conference sessions, handling both signaling and media aspects. The CCD interacts with other IMS core elements, such as the Serving-Call Session Control Function (S-CSCF) and the Home Subscriber Server (HSS), using SIP (Session Initiation Protocol) for session control. It receives SIP INVITE requests for conference creation or participant addition, authenticates and authorizes users based on subscription data, and orchestrates the establishment of media connections between all conference participants.

Architecturally, the CCD comprises several logical components: a Conference Policy Control Function, a Conference Focus, and Media Processing capabilities. The Conference Focus is the central SIP user agent that maintains the dialog state with each participant and manages the conference roster. The Conference Policy Control Function enforces policies regarding who can join, invite others, or manipulate the conference (e.g., muting). For media handling, the CCD may either act as a Media Mixer, combining audio/video streams from all participants into a single composite stream sent to each, or as a Media Relay/Controller, instructing endpoints to send media to a dedicated Media Resource Function Processor (MRFP) for mixing.

Its operation involves several key procedures. For ad-hoc conference creation, a user initiates a basic call and then uses SIP REFER or other mechanisms to instruct the CCD to add other parties. For scheduled conferences, the CCD acts on pre-provisioned data. During the conference, the CCD handles mid-call events like participant join/leave, media renegotiation, and DTMF tone collection for in-conference controls (e.g., 'press 1 to mute'). It also provides charging information to the offline and online charging systems (OCS, OFCS) for billing purposes. The CCD's role is critical in ensuring a seamless, low-latency, and feature-rich conferencing experience, abstracting complexity from end-user devices.

Purpose & Motivation

The CCD was introduced to standardize and enable rich, carrier-grade conferencing services within the emerging IP Multimedia Subsystem (IMS) framework defined in 3GPP Release 5. Prior to IMS, multiparty voice calls were possible in circuit-switched networks (e.g., using GSM's Multi-Party Service), but these were limited in features, tightly coupled to voice, and difficult to integrate with emerging IP-based multimedia services. The motivation was to create a flexible, scalable, and network-centric conferencing platform that could support voice, video, and data sessions, enabling new revenue-generating services for operators.

It solves the problem of fragmented, proprietary conferencing solutions by providing a standardized reference architecture and procedures. This ensures interoperability between equipment from different vendors and across different operator networks, allowing users to have a consistent experience. The CCD model centralizes complex conference control logic in the network, reducing the capability requirements on user equipment. This allows even simple handsets to participate in advanced conferences, as the intelligence resides in the network-based CCD. Furthermore, by being part of the IMS core, it can leverage IMS mechanisms for authentication, security, QoS authorization, and integrated charging, providing a secure and billable service.

The creation of the CCD was driven by the industry's move towards all-IP networks and the desire to offer enhanced communication services beyond basic voice calls. It addressed the limitations of peer-to-peer conferencing models, which were difficult to scale, control, and monetize. By defining the CCD, 3GPP provided a foundation for a wide range of commercial and enterprise conferencing services, from simple three-way calls to large-scale scheduled webinars with media recording and floor control.