Initiator                  Control Relay Server             Responder
| 1. UDP(I1)                       |                                |
+--------------------------------->| 2. UDP(I1(RELAY_FROM))         |
|                                  +------------------------------->|
|                                  |                                |
|                                  | 3. UDP(R1(RELAY_TO, NAT_TM,    |
|                                  |        TA_P))                  |
| 4. UDP(R1(RELAY_TO, NAT_TM,      |<-------------------------------+
|        TA_P))                    |                                |
|<---------------------------------+                                |
|                                  |                                |
| 5. UDP(I2(ENC(LOC_SET)),         |                                |
|        NAT_TM, TA_P))            |                                |
+--------------------------------->| 6. UDP(I2(ENC(LOC_SET),        |
|                                  |      RELAY_FROM, NAT_TM, TA_P))|
|                                  +------------------------------->|
|                                  |                                |
|                                  | 7. UDP(R2(ENC(LOC_SET),        |
| 8. UDP(R2(ENC(LOC_SET),          |        RELAY_TO))              |
|        RELAY_TO))                |<-------------------------------+
|<---------------------------------+                                |
|                                  |                                |