User manual

Startup and Functions
6874_en_09 PHOENIX CONTACT 3-33
The port prioritizing method is suitable for termination devices that do not support tagging
and thus cannot generate priorities.
"High" port prioritization sets the internal priority of the packets received at this port to
priority level 7. In the switch, these packets will be processed with priority information 7
within the tag (preferred handling and forwarding method only within the MMS, however,
when forwarding to the receiver, the packets are in the original state). The "Low" port
prioritization means that the priority of packets received at this port is not influenced by the
switch. This implies that existing tags must be taken into consideration or that other priority
rules must be observed.
Setting the Port Priority
Figure 3-20 Setting the port priority
– On the "Port Configuration" web page, both available priority levels can be selected
under "Priority Level".
3.3.4.3 Strict Priority
The switch supports two priority queues for adjusting the packet processing sequence
(traffic classes according to IEEE 802.1D). Data telegrams that are received are assigned
to these classes according to their priority, which is specified in the VLAN/prioritization tag:
– Data packets with values between "0" and "3" in the priority field are low priority
(default).
– Data packets with values between "4" and "7" in the priority field are high priority and
transmitted via the switch.
MMS uses "Strict Priority" for transmitting data telegrams. First, all high-priority data
packets are assigned, once these are transmitted, low-priority telegrams are assigned.
This function prevents delays in high-priority data transmission, due to large volumes of
low-priority data traffic. Low-priority traffic is rejected when the memory or data channel is
overloaded.