Comment # 6 on bug 72112 from Patrick Ohly

SyncEvolution 1.4.99.1 also uses Bluez >= 5.15 Suspend/Resume to really freeze
the transfer.

  By default, the new API freezes a sync by stopping to consume data on the
  local side of the sync.

  In addition, the information that the sync is freezing is now also handed
  down to the transport and all sources. In the case of PBAP caching, the local
  transport notifies the child where the PBAP source then uses Bluez
  5.15 Transfer1.Suspend/Resume to freeze/thaw the actual OBEX transfer.

  If that fails (for example, not implemented because Bluez is too old
  or the transfer is still queueing), then the transfer gets cancelled
  and the entire sync fails. This is desirable for PBAP caching and
  Bluetooth because a failed sync can easily be recovered from (just
  start it again) and the overall goal is to free up Bluetooth bandwidth
  quickly.