User`s manual

Moxa E Series Managed Ethernet Switch Featured Functions
3-41
Traffic Prioritization
Moxa switches classify 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 Moxa switch 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 Moxa switch will check a packet received at the ingress port for IEEE 802.1D traffic classification, and
then prioritize it based on 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 hardware of Moxa switches has multiple traffic queues that allow packet prioritization to occur. Higher
priority traffic can pass through the Moxa switch without being delayed by lower priority traffic. As each packet
arrives in the Moxa switch, 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.
Moxa switches support two different queuing mechanisms:
• Weight Fair: This method services all the traffic queues, giving priority to the higher priority queues.
Under most circumstances, the Weight Fair method gives high priority precedence over low priority, but in
the event that high priority traffic does not reach 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. The Strict 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 Moxa switch 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 Moxa switch’s QoS capability
improves your industrial network’s performance and determinism for mission critical applications.
CoS Classification
There are two CoS classification settings depending on the specific model of the switch
Type Model
Type1 EDS-510E
Type2 EDS-G508E, EDS-G512E-4GSFP, EDS-G516E-4GSFP