Cambium Networks PTP 820S, Техническое описание, Страница: 100 / 208

Chapter 4: Feature Description Ethernet Features
Rate Metering (Policing) at the Service Point + CoS Level
Users can define a single rate meter for each CoS on a specific service point, up to a total number
of 1024 rate meters per network element at the service point and CoS per service point levels.
The following statistics are available for each service point + CoS rate meter:
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Green Frames (64 bits)
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Green Bytes (64 bits)
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Yellow Frames (64 bits)
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Yellow Bytes (64 bits)
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Red Frames (64 bits)
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Red Bytes (64 bits)
QoS on the Egress Path
Queue Manager
The queue manager (QM) is responsible for managing the output transmission queues. PTP 820S
supports up to 2K service-level transmission queues, with configurable buffer size. Users can
specify the buffer size of each queue independently. The total amount of memory dedicated to the
queue buffers is 2 Gigabits.
The following considerations must be taken into account in determining the proper buffer size:
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Latency considerations – If low latency is required (users would rather drop frames in the
queue than increase latency) small buffer sizes are preferable.
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Throughput immunity to fast bursts – When traffic is characterized by fast bursts, it is
recommended to increase the buffer sizes to prevent packet loss. Of course, this comes at the
cost of a possible increase in latency.
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Users can configure burst size as a tradeoff between latency and immunity to bursts, according
the application requirements.
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The 2K queues are ordered in groups of eight queues. These eight queues correspond to CoS
values, from 0 to 7; in other words, eight priority queues.
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The following figure depicts the queue manager. Physically, the queue manager is located
between the ingress path and the egress path.
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