MBSTF: Do not send multiple MPDs on reactivation of STREAMING DistSession

[davidjwbbc]

Brief description

When a PULL STREAMING DistSession, using a DASH manifest (MPD file URL) is reactivated (has been active, transitioned to inactive and then activated again), the MPD file is fetched and transmitted multiple times in a short period of time.

Steps to reproduce

1. Run the MBSTF (as described by the tutorial in steps 1, 2 and 3). (Add -e debug to the MBSTF command line to add additional debug logging)
2. Start capturing the FLUTE session using Wireshark (tutorial step 4).
3. Create a PULL DASH streaming DistSession and activate it and deactivate it (tutorial step 7).
4. Activate the DistSession again (reuse the "ACTIVE" patch from tutorial step 7).
5. Wait for the FLUTE session to resume for a few seconds and then stop capturing using Wireshark.

Result

After resuming the DistSession (step 4 above) the MPD is sent multiple times at the start of resumption, as seen in the Wireshark capture. The MPD is also refetched several times, in a short period, from the media origin as noted in the MBSTF log output.

Expected result

The MPD should only be sent once on resumption and there should only be one refetch request until the next MPD update.

[rjb1000]

We think we can live with this bug in the short term. Because the MPD retains the same TOI in the FLUTE session, the output is not incorrect and the MBSTF Client should just ignore the repetition. The reason for fixing is mainly to remove the inefficiency of needlessly sending the object three times instead of just once (or not at all).