Implementation of a Single RRPP Ring (When the Ring is Complete)
Implementation of a Single RRPP Ring
When all the links and nodes on a single ring are Up, the master node is in Complete state.
In Figure 1, the master node blocks its secondary interface to prevent broadcast loops caused by data packets. The blocked secondary interface can only receive RRPP packets but cannot forward data packets. Hello packets sent by the master node to monitor the ring status can pass through the secondary interface.
Polling Mechanism
The master node uses a polling mechanism to monitor the ring status and perform operations by sending Hello packets.
Hello timer and Fail timer
The polling mechanism uses the Hello timer and Fail timer.
The value of the Hello timer specifies the interval at which the master node sends Hello packets from the primary interface.
The value of the Fail timer specifies the maximum delay in which the primary interface sends a Hello packet and the secondary interface receives the Hello packet.
The value of the Fail timer must be three times or larger the value of the Hello timer.
The master node determines whether to unblock the secondary interface by sending a Hello packet according to the value of the Hello timer and checking whether the secondary interface receives the Hello packet within the delay specified by the Fail timer.
Process of the polling mechanism
The process of the polling mechanism is as follows:
The master node periodically sends a Hello packet from its primary interface based on the value of the Hello timer.
The Hello packet is transmitted along transit nodes on the ring, as shown in Figure 1. The master node typically receives the Hello packet on its secondary interface.
If the secondary interface on the master node receives the Hello packet before the Fail timer times out, the master node considers the ring complete.
If the secondary interface on the master node does not receive the Hello packet after the Fail timer times out, the master node considers the ring faulty.