LRTT is a measure of link delay experienced by classA frames from the head of the
congestion domain to the tail of the congestion domain and back. A station implementing
the Conservative method sends LRTT request frames to each station in the ring
at regular intervals; each station in the ring (regardless of the fairness method being
deployed by such station) returns a LRTT response frame for each LRTT request frame
received. LRTT values are maintained in each station implementing the conservative
method for each station in the ring.
340 Chapter 12
Each station advertises its fairness method using the topology attribute discovery
(ATD) frames defined later on in this document. Stations deploying the aggressive and
conservative methods interoperate on the ringlet. Both methods converge to the fairRate
value when the offered traffic at stations on the ringlet is constant.
Topology Discovery and Protection
Protection and topology discovery protocols are tightly related to each other. Protection
information is used to update the topology data base, and a common frame carries information
relevant to both functions.
Protection provides reliable mechanisms for fewer than 50 millisecond protection for
all protected traffic on a ring.
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