Port Priority; Port Rate Limiting (Ingress); Egress Margin - Trango Systems TrangoLINK GigaPlus User Manual

In WRR QoS Mode, both COS and DSCP bits are used. The DSCP field in the IP packet
will contain a number from 0-63 in the Type of Service (TOS) field, which can be mapped
to a priority level, which is subsequently mapped to a queue.
WRR mode allows weights to be applied to each queue to allow the QoS engine to
spend at least some portion of time emptying the queues. This mode is useful for
allowing at least some of the lower priority traffic to get through the link and ensuring
that MOST high priority traffic will go through. Both COS and DSCP fields are monitored
on the incoming traffic for assignment of packets to the queues.
The traffic can be classified into 8 priorities (0-7 based on the VLAN tag COS/DSCP bits).
This is done external to the GigaPlus unit using a switch or application to set the priority
tag field or by the application. Once the tagged traffic with COS/DSCP priority bits set
arrives in the GigaPlus Ethernet port, the internal switch will perform prioritization on
the traffic by mapping it to one of 8 queues.

Port Priority

The port priority feature allows for untagged traffic arriving into each Ethernet port to
have priority level assigned to it. If the arriving traffic is already tagged then that tag
priority level will be honored over the port priority. The port priority setting will
determine which port traffic is forwarded in the event of more traffic coming into all the
ports than the capacity of the system can handle.
Port priority can augment port rate limiting, especially in when ACM is active and the
link has downshifted to a lower modulation. The port command is used to set the port
priority for each port.

Port Rate Limiting (Ingress)

The port rate limiting feature is used to restrict the ingress traffic rate on a specific
Ethernet port. This is useful for Service Level Agreements (SLAs) when both ports of the
GigaPlus are being used to supply two customers and the channel capacity is limited to
less than the sum of the capacity of the two Ethernet ports.
For example, if both ports are set to 1000BaseT, and the RF channel capacity is 375
Mbps, setting GE1 to rate limit of 125 Mbps and GE2 to a rate limit of 250 Mbps will
always guarantee that both users have the bandwidth of the channel reserved for them.

Egress Margin

Egress margin is used to fine tune the behavior QoS when using VLAN tagged traffic
marked with COS priority (802.1p), or when using port priority to assign priorty to
untagged traffic on multiple ports.
Traffic coming into the Ethernet ports is bursty by nature and may exceed the radio link
capacity if the radio speed is less than the Ethernet line speed (10/100/1000 Mbps). To
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Trango Systems, Inc. GigaPlus User Manual Rev 3.1