This attribute indicates the intermediate rate used in the physical
layer rate adaptation process. This field is valid between the
network and the IWF. For user data rates of 300 bit/s to 4800 bit/s
the intermediate rate is 8 kbit/s. For a user data rate of 9600 bit/s the
intermediate rate is 16 kbit/s. For user data rates of 1200 bit/s to
19200 bit/s the intermediate rate is 32 kbit/s. Data rates above this
have no intermediate rate.