KSZ9563RNXC-TR datasheet(39/226 Pages) MICROCHIP

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DS00002419D-page 39

KSZ9563R

4.4.12

PORT MIRRORING

the device supports “port mirroring” comprehensively as:

• “Receive Only” Mirror-on-a-Port

• “Transmit Only” Mirror-on-a-Port

• “Receive and Transmit” Mirror-on-a-Port

4.4.12.1

“Receive Only” Mirror-on-a-Port

All the packets received on the port are mirrored on the sniffer port. For example, 1 is programmed to be “receive sniff”

and the host port is programmed to be the “sniffer”. A packet received on port 1 is destined to port 2 after the internal

lookup. The packet is forwarded to both port 2 and the host port. The device can optionally even forward “bad” received

packets to the “sniffer port”.

4.4.12.2

“Transmit Only” Mirror-on-a-Port

All the packets transmitted on the port are mirrored on the sniffer port. For example, port 1 is programmed to be “transmit

sniff” and the host port is programmed to be the “sniffer port”. A packet received on port 2 is destined to port 1 after the

internal lookup. The device forwards the packet to both port 1 and the host port.

4.4.12.3

“Receive and Transmit” Mirror-on-a-Port

All the packets received on port A and transmitted on port B are mirrored on the sniffer port. For example, port 1 is pro-

grammed to be “receive sniff”, port 2 is programmed to be “transmit sniff”, and the host port is programmed to be the

“sniffer port”. A packet received on port 1 is destined to port 2 after the internal lookup. The device forwards the packet

to both port 2 and the host port.

Multiple ports can be selected as “receive sniff” or “transmit sniff”. In addition, any port can be selected as the “sniffer

port”.

4.4.13

SCHEDULE AND RATE LIMITING

Each device port has two egress packet scheduling options, which can be applied when the port is configured for two

or four queues. Additionally, each port has ingress and egress rate limiter features.

4.4.13.1

Strict Priority Scheduling

When an egress port is configured as two or four queues, and strict priority scheduling is selected, each queue will take

absolute priority over all lower priority queues. If a packet is available to transmit from queue 3 (the highest priority

queue), then it will take priority for transmission over any packet that will also be available in any of the other queues.

A packet in queue 2 will be transmitted only if no packet is available in queue 3. Weighted round robin is an alternative

to strict priority scheduling.

4.4.13.2

Weighted Round Robin (WRR) Scheduling

WRR scheduling is an alternative to strict priority scheduling for egress queues. It is referred to as fair queuing because

it gives proportionally higher priority to the highest priority queue, but not absolute priority.

4.4.13.3

Rate Limiting

The device supports independent ingress and egress hardware rate limiting on each port. Normally these two features

are considered mutually exclusive, and users are discouraged from using both on the same port.

For 10BASE-T, a rate setting above 10Mbps means the rate is not limited. Likewise, for 100BASE-TX, a rate setting

above 100Mbps means the rate is not limited. On the receive side, the data receive rate for each priority at each port

can be limited by setting up ingress rate control registers. On the transmit side, the data transmit rate for each priority

queue at each port can be limited by setting up egress rate control registers. The size of each frame has options to

include minimum inter-frame gap (IFG) or preamble byte, in addition to the data field (from packet DA to FCS).

For ingress rate limiting, the device provides options to selectively choose frames from all types, multicast, broadcast,

and flooded unicast frames. The data rate from those selected type of frames is counted. Packets are dropped at the

ingress port when the data rate exceeds the specified rate limit.

For egress rate limiting, the leaky bucket algorithm is applied to each output priority queue for shaping output traffic.

Inter-frame gap is stretched on a per frame base to generate smooth, non-burst egress traffic. The throughput of each

output priority queue is limited by the egress rate specified.

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