Mobile Host               Control Relay Server              Peer Host
| 1. UDP(UPDATE(ESP_INFO,          |                                |
|          ENC(LOC_SET), SEQ))     |                                |
+--------------------------------->| 2. UDP(UPDATE(ESP_INFO,        |
|                                  |          ENC(LOC_SET), SEQ,    |
|                                  |          RELAY_FROM))          |
|                                  +------------------------------->|
|                                  |                                |
|                                  | 3. UDP(UPDATE(ESP_INFO, SEQ,   |
|                                  |          ACK, ECHO_REQ_SIGN,   |
|                                  |          RELAY_TO))            |
| 4. UDP(UPDATE(ESP_INFO, SEQ,     |<-------------------------------+
|          ACK, ECHO_REQ_SIGN,     |                                |
|          RELAY_TO))              |                                |
|<---------------------------------+                                |
|                                  |                                |
| 5. UDP(UPDATE(ACK,               |                                |
|          ECHO_RESP_SIGNED))      |                                |
+--------------------------------->| 6. UDP(UPDATE(ACK,             |
|                                  |          ECHO_RESP_SIGNED,     |
|                                  |          RELAY_FROM))          |
|                                  +------------------------------->|
|                                  |                                |
|                   7. connectivity checks over UDP                 |
+<----------------------------------------------------------------->+
|                                  |                                |
|                      8. ESP data over UDP                         |
+<----------------------------------------------------------------->+
|                                  |                                |