PT-7728 User’s Manual Featured Functions
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The PT-7728 will check a packet received at the ingress port for IEEE 802.1D traffic classification,
and then prioritize it based upon the IEEE 802.1p value (service levels) in that tag. It is this 802.1p
value that determines which traffic queue the packet is mapped to.
Traffic Queues
The PT-7728 hardware has multiple traffic queues that allow packet prioritization to occur. Higher
priority traffic can pass through the PT-7728 without being delayed by lower priority traffic. As
each packet arrives in the PT-7728, it passes through any ingress processing (which includes
classification, marking/re-marking), and is then sorted into the appropriate queue. The switch then
forwards packets from each queue.
The PT-7728 supports two different queuing mechanisms:
y Weight Fair: This method services all the traffic queues, giving priority to the higher priority
queues. Under most circumstances, this method gives high priority precedence over
low-priority, but in the event that high-priority traffic except the link capacity, lower priority
traffic is not blocked.
y Strict: This method services high traffic queues first; low priority queues are delayed until no
more high priority data nePT to be sent. This method always gives precedence to high priority
over low-priority.
Configuring Traffic Prioritization
Quality of Service (QoS) provides a traffic prioritization capability to ensure that important data is
delivered consistently and predictably. The PT-7728 can inspect IEEE 802.1p/1Q layer 2 CoS tags,
and even layer 3 TOS information, to provide a consistent classification of the entire network. The
PT-7728’ QoS capability improves your industrial network’s performance and determinism for
mission critical applications.
QoS Classification
The PT-7728 supports inspection of layer 3 TOS and/or layer 2 CoS tag information to determine
how to classify traffic packets.
Queuing Mechanism
Setting Description Factory Default
Weight Fair PT-7728 has 4 priority queues. In the weight fair
scheme, an 8, 4, 2, 1 weighting is applied to the four
priorities. This approach prevents the lower priority
frames from being starved of opportunity for
transmission with only a slight delay to the higher
priority frames.
Weight Fair
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