Inter-domain group-communications

A method for distributing multicast data of a multicast service to service participants in a first domain, the method comprising the following steps performed by a Push-to-talk Over Cellular Application Server, PoC AS, of the first domain:

• (a) receiving a service initiation request from a PoC AS of another domain comprising information on the service participants to participate in the multicast service being located in the first domain controlled by the PoC AS of the first domain,
• (b) deciding, based on the information on the service participants, whether to utilize point-to-point links or a point-to-multipoint link for distributing the multicast data within the first domain,
• (c) establishing, depending on the deciding step (b), either a point-to-point link to a respective one of the service participants in the first domain or a point-to-multipoint link to the service participants in the first domain as a transport medium for the multicast data, and
• (d) distributing the multicast data to the service participants in the first domain via the established transport medium,
• the method further comprising acknowledging the service initiation request thereby establishing a point-to-point link to the PoC AS of the another domain, wherein a multicast service identifier is used to identify data of the multicast service on the point-to-point link.

A Push-to-talk Over Cellular Application Server, PoC AS, of a first domain for distributing multicast data of a multicast service to different domains each controlled by a different PoC AS, the PoC AS of the first domain comprising:

• a receiver to receive from a client in the first domain a service initiation request for setting up the multicast service between a plurality of service participants, wherein the service initiation request identifies the plurality of service participants that are to participate in the multicast service,
• a processor to identify, based on the identification of the plurality of service participants, the domains to which the plurality of service participants belong and that are not controlled by the PoC AS of the first domain, and
• a transmitter to distribute the multicast data to the PoC ASs of the identified domains on a per-domain basis,
• wherein the distributing of the multicast data to the PoC ASs of the identified domains comprises distributing a single copy of the respective multicast data via a point-to-point link to a PoC AS of a respective domain for further distribution to the service participants in the respective domain.

A non-transitory computer readable medium storing instructions that, when executed by a processor of a Push-to-talk Over Cellular Application Server, PoC AS, of a first domain of different domains each controlled by a different PoC AS, cause the PoC AS of the first domain to distribute multicast data of a multicast service to different domains, by:

• receiving from a client in the first domain a service initiation request for setting up the multicast service between a plurality of service participants, wherein the service initiation request identifies the plurality of identifying service participants that are to participate in the multicast service,
• identifying, based on the identification of the plurality of service participants, the domains to which the plurality of service participants belong and that are not controlled by the PoC AS of the first domain, and
• distributing the multicast data to the PoC ASs of the identified domains on a per-domain basis,
• wherein the distributing of the multicast data to the PoC ASs of the identified domains comprises distributing a single copy of the respective multicast data via a point-to-point link to a PoC AS of a respective domain for further distribution to the service participants in the respective domain.

A non-transitory computer readable medium storing instructions that, when executed by a Push-to-talk Over Cellular Application Server, PoC AS, of a first domain, cause the PoC AS of the first domain to distribute multicast data of a multicast service to service participants in the first domain, by:

• receiving a service initiation request from a PoC AS of another domain comprising information on the service participants to participate in the multicast service being located in the first domain controlled by the PoC AS,
• deciding based on the information on the service participants, whether to utilize point-to-point links or a point-to-multipoint link for distributing the multicast data within the first domain,
• establishing, depending on the deciding, either a point-to-point link to a respective one of the service participants in the first domain or a point-to-multipoint link to the service participants in the first domain as a transport medium for the multicast data, distributing the multicast data to the service participants in the first domain via the established transport medium, and
• acknowledging the service initiation request thereby establishing a point-to-point link to the PoC AS of the another domain, wherein a multicast service identifier is used to identify data of the multicast service on the point-to-point link.