This attribute indicates the Initial Cell Rate (ICR) parameter for this
connection. ICR is the rate at which a source should send initially
and after an idle period.
For nailed-up connections, this attribute is determined by the
provisioned value of the initialCellRate attribute. For signalled
connections, it is indicated in the ABR Setup Parameters
Information Element.
The ICR for a connection is a value between the MCR and the PCR.
Furthermore, ICR has an upper bound determined by the
transientBufferExposure divided by fixedRoundTripTime.