Moxa EDS-82810G [51/113] Configuring traffic prioritization

EDS-828 Series Featured Functions

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Traffic Prioritization

The EDS-828 classifies traffic based on layer 2 of the OSI 7 layer model, and the switch prioritizes received

traffic according to the priority information defined in the received packet. Incoming traffic is classified based

upon the IEEE 802.1D frame and is assigned to the appropriate priority queue based on the IEEE 802.1p service

level value defined in that packet. Service level markings (values) are defined in the IEEE 802.1Q 4-byte tag,

and consequently traffic will only contain 802.1p priority markings if the network is configured with VLANs and

VLAN tagging. The traffic flow through the switch is as follows:

A packet received by the EDS-828 may or may not have an 802.1p tag associated with it. If it does not, then

it is given a default 802.1p tag (which is usually 0). Alternatively, the packet may be marked with a new 802.1p

value, which will result in all knowledge of the old 802.1p tag being lost.

Because the 802.1p priority levels are fixed to the traffic queues, the packet will be placed in the appropriate

priority queue, ready for transmission through the appropriate egress port. When the packet reaches the head

of its queue and is about to be transmitted, the device determines whether or not the egress port is tagged for

that VLAN. If it is, then the new 802.1p tag is used in the extended 802.1D header.

The EDS-828 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 EDS-828 hardware has multiple traffic queues that allow packet prioritization to occur. Higher priority

traffic can pass through the EDS-828 without being delayed by lower priority traffic. As each packet arrives in

the EDS-828, 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 EDS-828 supports two different queuing mechanisms:

• 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 exceeds the link capacity, lower priority traffic is not blocked.

• Strict: This method services high traffic queues first; low priority queues are delayed until no more high

priority data needs 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 EDS-828 Series 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 EDS-828 Series’ QoS

capability improves your industrial network’s performance and determinism for mission critical applications.

QoS Classification