Page "Resilient Packet Ring" Paragraph 2

All traffic on the ring is assigned a Class of Service ( CoS ) and the standard specifies three classes.

Class A ( or High ) traffic is a pure committed information rate ( CIR ) and is designed to support applications requiring low latency and jitter, such as voice and video.

Class B ( or Medium ) traffic is a mix of both a CIR and an excess information rate ( EIR ; which is subject to fairness queuing ).

Class C ( or Low ) is best effort traffic, utilizing whatever bandwidth is available.

This is primarily used to support Internet access traffic.