FL SWITCH LM ...
2-10
PHOENIX CONTACT 7278_en_04
2.2.4.1 VLAN/prioritization tag
The LMS processes incoming data packets with regard to prioritization information
contained in the Ethernet packet (VLAN/prioritization tag).
The tag enables the specification of a priority level from 0 to 7, which the LMS assigns to
one of its two internal queues. By default upon delivery, the packets with priorities from 0 to
3 are treated as low-priority packets whereas packets with priorities from 4 to 7 are high-
priority Ethernet packets.
Processing rules
The switch controller in the LMS forwards received packets to one of the receive queues
according to the following decisions:
– BPDU packets are always assigned to the high-priority queue.
– Packets with unknown unicast addresses are always assigned to the low-priority
queue.
– Packets are assigned to the high-priority queue if the priority from the
VLAN/prioritization tag is mapped to the "high" level (default priority 4 to 7).
– The internal port priority "high" results in priority level 7 handling, i.e., the basic settings
for data packet assignment to the high-priority queue are made.
– All residual data is assigned to the low-priority queue.
2.2.4.2 Strict priority
The switch supports two priority queues for adjusting the packet processing sequence
(traffic classes according to IEEE 802.1D). The switches therefore support the QoS
functions required by PROFINET RT and meet conformance class A. 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 transmitted via the
switch with high priority.
The LMS 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.
To Next Page
Loading...
