Figure 1: SNMPv3 packet format

                     -------------------------
       /|\           | msgVersion            |
        |            |-----------------------|
        |            | msgID                 |
        |            |-----------------------|         USM Security Parameters
        |            | msgMaxSize            |
        |            |-----------------------|    /-------------------------------
        |            | msgFlags              |   / | msgAuthoritativeEngineID    |
     scope of        |-----------------------|  /  |-----------------------------|
   authentication    | msgSecurityModel      | /   | msgAuthoritativeEngineBoots |
        |            |-----------------------|/    |-----------------------------|
        |            |                       |     | msgAuthoritativeEngineTime  |
        |            | msgSecurityParameters |     |-----------------------------|
        |            |                       |     | msgUserName                 |
        |            |-----------------------|\    |-----------------------------|
        |     /|\    |                       | \   | msgAuthenticationParameters |
        |      |     |                       |  \  |-----------------------------|
        |      |     |                       |   \ | msgPrivacyParameters        |
        |  scope of  | scopedPDU             |    \-------------------------------
        | encryption |                       |
        |      |     |                       |
        |      |     |                       |
        |      |     |                       |
       \|/    \|/    |                       |
                     -------------------------