RADIUS packets, whether requests or responses, always include a type. These constants are provided to make it easier to specify types when using radius_create_request() and when comparing the result of radius_send_request().
RADIUS_ACCESS_REQUEST 
     (integer)
    
      An Access-Request, used to authenticate a user against a RADIUS server.
      Access request packets must include a
      RADIUS_NAS_IP_ADDRESS
      or a
      RADIUS_NAS_IDENTIFIER
      attribute, must also include a
      RADIUS_USER_PASSWORD,
      RADIUS_CHAP_PASSWORD
      or a
      RADIUS_STATE
      attribute, and should include a
      RADIUS_USER_NAME
      attribute.
     
RADIUS_ACCESS_ACCEPT 
     (integer)
    An Access-Accept response to an Access-Request indicating that the RADIUS server authenticated the user successfully.
RADIUS_ACCESS_REJECT 
     (integer)
    An Access-Reject response to an Access-Request indicating that the RADIUS server could not authenticate the user.
RADIUS_ACCESS_CHALLENGE 
     (integer)
    An Access-Challenge response to an Access-Request indicating that the RADIUS server requires further information in another Access-Request before authenticating the user.
RADIUS_ACCOUNTING_REQUEST 
     (integer)
    An Accounting-Request, used to convey accounting information for a service to the RADIUS server.
RADIUS_ACCOUNTING_RESPONSE 
     (integer)
    An Accounting-Response response to an Accounting-Request.
RADIUS_COA_REQUEST 
     (integer)
    A CoA-Request, sent from the RADIUS server to indicate that the authorisations within the user session have changed. A response must be sent in the form of a CoA-ACK or a CoA-NAK.
This constant is available in PECL radius 1.3.0 and later.
RADIUS_COA_ACK 
     (integer)
    A CoA-ACK, sent to the RADIUS server to indicate that the user authorisations have been updated.
This constant is available in PECL radius 1.3.0 and later.
RADIUS_COA_NAK 
     (integer)
    A CoA-NAK, sent to the RADIUS server to indicate that the user authorisations could not be updated.
This constant is available in PECL radius 1.3.0 and later.
RADIUS_DISCONNECT_REQUEST 
     (integer)
    A Disconnect-Request, sent from the RADIUS server to indicate that the user session must be terminated.
This constant is available in PECL radius 1.3.0 and later.
RADIUS_DISCONNECT_ACK 
     (integer)
    A Disconnect-ACK, sent to the RADIUS server to indicate that the user session has been terminated.
This constant is available in PECL radius 1.3.0 and later.
RADIUS_DISCONNECT_NAK 
     (integer)
    A Disconnect-NAK, sent to the RADIUS server to indicate that the user session could not be terminated.
This constant is available in PECL radius 1.3.0 and later.