R PR Packet Add Drop and Forward

The RPR operation consists of three basic operations: add, drop, and forward. These operations mimic the add/drop mechanisms that are used in traditional SONET networks, where circuits get added, dropped, and cross-connected inside a ring.

The ad vantage th at RPR has over a traditional Ethernet switched packet ring is that Ethernet 802.3 MAC operation processes packets at each node of the ring irrespective of whether the packet destination is behind that node. In contrast, RPR 802.17 MAC forwards the traffic on the ring without doing any intermediary switching or buffering if the traffi c does not belong to the node. This reduces the amount of work individual nodes have to do.

In the RPR operation shown in Figure 2-15, traffic that does not belong to a particular node is transited (forwarded) on the ring by the 802.17 MAC. In the Ethernet 802.3 MAC operation, the traffic is processed and buffered at each node for the switching function to determine the exit interface.

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