Cambium Networks PTP 820S, Техническое описание, Страница: 101 / 208

Chapter 4: Feature Description Ethernet Features
Figure 58 PTP 820S Queue Manager
In the figure above, traffic is passing from left to right. The traffic passing from the ingress path is
routed to the correct egress destination interfaces via the egress service points. As part of the
assignment of the service points to the interfaces, users define the group of eight queues through
which traffic is to be transmitted out of the service point. This is part of the service point egress
configuration.
After the traffic is tunneled from the ingress service points to the egress service points, it is
aggregated into one of the eight queues associated with the specific service point. The exact
queue is determined by the CoS calculated by the ingress path. For example, if the calculated CoS
is 6, the traffic is sent to queue 6, and so on.
Before assigning traffic to the appropriate queue, the system makes a determination whether to
forward or drop the traffic using a WRED algorithm with a predefined green and yellow curve for
the desired queue. This operation is integrated with the queue occupancy level.
The 2K queues share a single memory of 2 Gbits. PTP 820S enables users to define a specific size
for each queue which is different from the default size. Moreover, users can create an over-
subscription scenario among the queues for when the buffer size of the aggregate queues is lower
than the total memory allocated to all the queues. In doing this, the user must understand both the
benefits and the potential hazards, namely, that if a lack of buffer space occurs, the queue manager
will drop incoming frames without applying the usual priority rules among frames.
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