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 |                       |
     |      |     |                       |
     |      |     |                       |
     |      |     |                       |
    \|/    \|/    |                       |
                  -------------------------