This attribute specifies the quality of service for both the forward
and backward direction for this connection.
Class 1 supports a QOS that meets Service Class A performance
requirements (Circuit emulation, constant bit rate video).
Class 2 supports a QOS that meets Service Class B performance
requirements (Variable bit rate audio and video).
Class 3 supports a QOS that meets Service Class C performance
requirements (Connection-Oriented Data Transfer).
Class 4 supports a QOS that meets Service Class D performance
requirements (Connectionless Data Transfer).
Class 0 is the unspecified bit rate QOS class; no objective is
specified for the performance parameters.