Comtech EF Data CDM-760 - Manual (Page 404)

Appendix K Revision 2
CDM-760 Advanced High-Speed Trunking Modem MN-CDM760
K–4
In Max/Priority mode, every classification rule is assigned a “not to exceed” Maximum Data Rate
and a Priority Level. You may assign up to 32 classification rules using any combination of the
classifiers listed in Table K-2.
If you do not need to limit the total traffic that can be assigned to a particular rule, then you
may set the Maximum Data Rate to a number that is excessively large, e.g. 999999 kbps.
In Max/Priority mode, the highest priority level traffic (i.e., Priority Level 1) will be drained until
empty or until the Maximum Data Rate is met for all Priority Level 1 classification rules before
attempting to drain any lower-priority level (i.e., Priority Level 2) classification rules. If, at any
point, a packet arrives into the modem that has a higher priority than what the modem is
currently draining, the modem will stop draining the lower-priority traffic and will immediately
drain the higher-priority traffic until all higher-priority traffic is drained, or until the Maximum
Data Rate of the QoS classification is met. If two or more rules are assigned to the same priority
and Weighting is not being used, the drain of the classification rules will be in round-robin
fashion (i.e., 1, 2, 3, 1, 2, 3, 1, 2, 3) regardless if each has a different Maximum Data Rate.
This type of drain mechanism ensures that the highest-priority traffic is always attended to. This
type of drain algorithm can “starve” lower-priority traffic, completely blocking that lower-
priority traffic.
You may enable WRED (Weighted Random Early Detection) on a per-classification rule basis.
With WRED enabled, a QoS classification will randomly drop packets after reaching 50% of the
QoS classification buffer depth (2500 packets of the same classification).
When you enable the Filter option for a rule, all packets that meet this classification rule will be
discarded.
K.3.3.2 Min/Max Mode
Min/Max QoS mode is commonly used in ACM circuits in conjunction with Weighting (see Sect.
K.4).
In Min/Max mode, every classification rule is assigned a Minimum Date Rate and a “not to
exceed” Maximum Data Rate. You may assign up to 32 classification rules using any combination
of the classifiers listed in Table K-2.
If you do not require minimum bandwidth for every classification, then you may set this value to
0 kbps.
If you do not need to limit the total traffic that can be assigned to a particular rule, then you
may set the maximum data rate to a number that is excessively large, e.g., 999999 kbps.
In Min/Max mode, traffic for each rule will drain in a round-robin fashion until every Minimum
Data Rate is met. Once all the minimums are met, only then can the Packet Processor begin to
drain any additional data associated with that rule, until either the Maximum Data Rate is met
or the rule has no more data to drain.