Java class to represent the Online enumerated type.
Documentation from the relevant specification:
The Online AVP (AVP code 1009) is of type Enumerated. If the Online AVP is embedded within a Charging-Rule-Definition AVP, it defines whether the online charging interface from the PCEF for the associated PCC rule shall be enabled. The absence of this AVP within the first provisioning of the Charging-Rule-Definition AVP of a new PCC rule indicates that the default charging method for online shall be used. If the Online AVP is embedded within the initial CCR on command level, it indicates the default charging method for online pre-configured at the PCEF is applicable as default charging method for online. The absence of this AVP within the initial CCR indicates that the charging method for online pre-configured at the PCEF is not available. If the Online AVP is embedded within the initial CCA on command level, it indicates the default charging method for online. The absence of this AVP within the initial CCA indicates that the charging method for online pre-configured at the PCEF is applicable as default charging method for online. The default charging method provided by the PCRF shall take precedence over any pre-configured default charging method at the PCEF