Paradise Datacom Quantum, Инструкция по установке и эксплуатации

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Quantum and Evolution Series Installation and Operating Handbook
8-46
Assume at this point (when Class 0 ideally wants 900 000bps) that the Class 1 data stream
is flowing at 350 000bps. Since 350 000bps is less than the CIR of Class 1 then it will get
all the bandwidth it needs. Class 0 will get its guaranteed 500 000 bps, but will be allocated
only an additional 150 000bps (bringing its total to 650 000bps) because this is all of the
spare bandwidth, and is less than the Class 0 BIR value.
In another example, assume Class 2 is being received at 400 000bps and Class 1 at 950
000bps. In this situation the Class 1 data stream will be allocated 800 000bps, its
maximum, while Class 2 will be allocated only 200 000bps. The spare bandwidth is
allocated to Class 1 first because it has a higher priority. When the BIR of Class 1 is
reached, the remaining spare bandwidth will be allocated to Class 2.
8.12.9.4.2 Diffserv DSCP Class
It is possible to classify data streams based on the Differentiated Services Code Point
(DSCP) value in the IP packet header. The DSCP class bits are the top three bits of the DS
field in an IP header (the other three bits of the field indicate drop precedence, which can
be mimicked using the Priority setting for the stream in the modem). Each packet passed to
the modem must have this field set to the appropriate value in order for the modem to
recognize the different data streams. The modem maps the eight possible DSCP classes
directly to eight equivalent internal modem classes (each of which can be allocated its own
CIR, BIR, etc.). DSCP Class 0 maps to internal modem QoS Class 0, etc., down to DSCP
Class 7 which maps to QoS Class 7. Class 7 has the highest priority.
An example traffic shaping scheme based on DSCP classification is shown below.