TURN                                 TURN          Peer         Peer
client                               server         A            B
  |                                    |            |            |
  |--- Allocate request -------------->|            |            |
  |    Transaction-Id=0xA56250D3F17ABE679422DE85    |            |
  |    SOFTWARE="Example client, version 1.03"      |            |
  |    LIFETIME=3600 (1 hour)          |            |            |
  |    REQUESTED-TRANSPORT=17 (UDP)    |            |            | 
  |    DONT-FRAGMENT                   |            |            |
  |                                    |            |            |
  |<-- Allocate error response --------|            |            |
  |    Transaction-Id=0xA56250D3F17ABE679422DE85    |            |
  |    SOFTWARE="Example server, version 1.17"      |            |
  |    ERROR-CODE=401 (Unauthorized)   |            |            |
  |    REALM="example.com"             |            |            |
  |    NONCE="obMatJos2gAAAadl7W7PeDU4hKE72jda"     |            |
  |    PASSWORD-ALGORITHMS=MD5 and SHA256           |            |
  |                                    |            |            |
  |--- Allocate request -------------->|            |            |
  |    Transaction-Id=0xC271E932AD7446A32C234492    |            |
  |    SOFTWARE="Example client 1.03"  |            |            |
  |    LIFETIME=3600 (1 hour)          |            |            |
  |    REQUESTED-TRANSPORT=17 (UDP)    |            |            |
  |    DONT-FRAGMENT                   |            |            |
  |    USERNAME="George"               |            |            |
  |    REALM="example.com"             |            |            |
  |    NONCE="obMatJos2gAAAadl7W7PeDU4hKE72jda"     |            |
  |    PASSWORD-ALGORITHMS=MD5 and SHA256           |            |
  |    PASSWORD-ALGORITHM=SHA256       |            |            |    
  |    MESSAGE-INTEGRITY=...           |            |            |
  |    MESSAGE-INTEGRITY-SHA256=...    |            |            |
  |                                    |            |            |
  |<-- Allocate success response ------|            |            |
  |    Transaction-Id=0xC271E932AD7446A32C234492    |            |
  |    SOFTWARE="Example server, version 1.17"      |            |
  |    LIFETIME=1200 (20 minutes)      |            |            |
  |    XOR-RELAYED-ADDRESS=192.0.2.15:50000         |            |
  |    XOR-MAPPED-ADDRESS=192.0.2.1:7000            |            |
  |    MESSAGE-INTEGRITY-SHA256=...    |            |            |