+-----+      +---+                +--+
  |MAAR1|      |CMD|                |CN|
  +-----+      +---+                +*-+
     |           |                   *
    MN           |                   *     +---+
  attach.        |               *****    _|CMD|_
detection        |         flow1 *       / +-+-+ \
     |           |               *      /    |    \
 local BCE       |               *     /     |     \
 allocation      |               *    /      |      \
     |--- PBU -->|           +---*-+-'    +--+--+    `+-----+
     |          BCE          |   * |      |     |     |     |
     |        creation       |MAAR1+------+MAAR2+-----+MAAR3|
     |<-- PBA ---|           |   * |      |     |     |     |
 local BCE       |           +---*-+      +-----+     +-----+
 finalized       |               *
     |           |         Pref1 *
     |           |              +*-+
     |           |              |MN|
     |           |              +--+
                                                            
  Operations sequence                  Packet flow