[ RFC 2622 ] 
     ----------------------                   ----------------------
     |            7.7.7.1 |-------|   |-------| 7.7.7.2            |
     |                    |     ========      |                    |
     |   AS1              |      EX1  |-------| 7.7.7.3     AS2    |
     |                    |                   |                    |
     |            9.9.9.1 |------       ------| 9.9.9.2            |
     ----------------------     |       |     ----------------------
                               ===========
                                   |    EX2
     ----------------------        |
     |            9.9.9.3 |---------
     |                    |
     |   AS3              |
     ----------------------
[ RFC 2622 ] 
     ----------------------                   ----------------------
     |            7.7.7.1 |-------|   |-------| 7.7.7.2            |
     |                    |     ========      |                    |
     |   AS1              |      EX1  |-------| 7.7.7.3     AS2    |
     |                    |                   |                    |
     |            9.9.9.1 |------       ------| 9.9.9.2            |
     ----------------------     |       |     ----------------------
                               ===========
                                   |    EX2
     ----------------------        |
     |            9.9.9.3 |---------
     |                    |
     |   AS3              |
     ----------------------