The IMS: IP Multimedia Concepts And Services, Second Edition

6.2. PoC features

6.2.1. PoC communication

PoC supports various types of communication models to meet the differing needs of group communication. The main differences between these models relate to group policy and session setup. In other words, how do users create a group and add/delete group members? How do they activate a group session and how is access control arranged? In dial-out group communication, a user invites a group of users to participate in a group session. The invited users receive an indication of the incoming session and they may join in using either an automatic or manual answer. The invited group may be a pre-arranged PoC group or a list of users selected from the calling user's phone book as a temporary arrangement (so-called ad hoc PoC group). In the latter case, in particular, the ability to see other users' availability, or presence statuses, before making the dial-out session brings clear additional value for the user. A dial-out session suits unplanned situations or cases where the participants must be handpicked.

There are some special rules for pre-arranged PoC groups (defined in OMA). First, a PoC session between group members is established when any individual member of the same pre-arranged PoC group invites other members of the group to join in. Second, the communication starts after the first pre-arranged group member accepts the invitation and the controlling PoC server grants media permission to the initiator of the prearranged group. Third, ...