Initiator                                                  Responder
| 1. UDP(I1)                                                       |
+----------------------------------------------------------------->|
|                                                                  |
| 2. UDP(R1(.., NAT_TRAVERSAL_MODE(ICE-HIP-UDP), ..))              |
|<-----------------------------------------------------------------+
|                                                                  |
| 3. UDP(I2(.., NAT_TRAVERSAL_MODE(ICE-HIP-UDP), ENC(LOC_SET), ..))|
+----------------------------------------------------------------->|
|                                                                  |
| 4. UDP(R2(.., ENC(LOC_SET), ..))                                 |
|<-----------------------------------------------------------------+
|                                                                  |