Libflute: Add SSM source address to Transmitter configuration

[davidjwbbc]

TS 29.581 V18.6.0 added the ability to specify the multicast source address to use in User Plane packets generated by the MBSTF. Therefore we need the FLUTE library to take and use that source address in its FLUTE session output.

• Where a UDP tunnel is configured between the rt-libflute app (e.g. MBSTF) and the FLUTE receiver (e.g. MB-UPF), the configured User Plane source address will be used as the IP source address of encapsulated multicast UDP packets. The source port will continue to duplicate the destination port.
• Where no UDP tunnel is configured between the rt-libflute app (e.g. an app other than MBSTF) and the FLUTE receiver, the source address of the unencapsulated multicast UDP packets will be the source IP address of the local transmission interface to which the socket is bound. If there is no local interface which can bind the given source address, then an exception will be raised to indicate the error. The source port number remains ephemeral.

[rjb1000]

Just checking, @davidjwbbc: Is is valid to have unencapsulated packets between the MBSTF and the MB-UPF? I thought the UDP tunnel was always used at reference point Nmb9.

[davidjwbbc]

Just checking, @davidjwbbc: Is is valid to have unencapsulated packets between the MBSTF and the MB-UPF? I thought the UDP tunnel was always used at reference point Nmb9.

The second bullet should not have mentioned the MBSTF. I've corrected the description wording to be clearer about what should be implemented.

[davidjwbbc]

Implemented changes, currently testing.