The most likely
candidates for higher speed RPR are 40 Gbps and 100 Gbps. In addition the standard
defines rings of up to 255 nodes and 2000 km in circumference.
Layer Model
The RPR layer model and its relationship with the OSI reference model are illustrated
in Figure 12.1. The RPR standard specifies the MAC control sublayer, the MAC datapath
sublayer, the reconciliation sublayers, the MAC service interface and the PHY
service interface.
The MAC service interface provides service primitives used by MAC clients to exchange
data with one or more peer clients, or to transfer local control information
between the MAC and MAC client. The MAC control sublayer controls the datapath
sublayer, maintains the MAC state and coordination with the MAC control sublayer
of other MACs, and controls the transfer of data between the MAC and its client. The
MAC datapath sublayer provides data transfer functions for each ringlet.
The PHY service interface is used by the MAC to transmit and receive frames on
the physical media. Distinct reconciliation sublayers specify mapping between specific
PHYs and medium independent interfaces (MIIs). The standard includes the definition
of a reconciliation sublayer for each of the most commonly used PHYs and permits
other reconciliation sublayers.
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