332 Chapter 12
Ring Structure
RPR employs a ring structure using unidirectional, counter-rotating ringlets. Each ringlet
is made up of links with data flow in the same direction. The ringlets are identified as
ringlet0 and ringlet1, as shown in Figure 12.2.
Stations on the ring are identified by an IEEE 802 48-bit MAC address. All links on
the ring operate at the same data rate, but may exhibit different delay properties.
The RPR MAC Specification
The services provided by the MAC sublayer allow the local MAC client to exchange
data with peer client entities in other stations, and to exchange parameters to control
the operation of the local MAC entity. The client may omit some parameters, and leave
their control to the discretion of the MAC sublayer; the MAC sublayer will set these
parameters according to the standard definitions. Optionally the MAC operation can be
fully controlled by the client, but in that case it is the client responsibility to use these
parameters in a way that does not violate the standard behavior of the MAC.
Figure 12.1 RPR service and reference model relationship to the ISO OSI reference model
RPR Layers
Higher Layers
Logical Link Control (LLC) MAC client
MAC control
Fairness
Topology and
protection
OAM
MAC data path
Physical layer
Medium
MAC service
interface
PHY service
interface
OSI reference
model layers
Application
Presentation
Session
Transport
Network
Data-link
Physical
Figure 12.
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