Prioritization - Phoenix Contact FL SWITCH SMN 6TX/2POF-PN User Manual

8089_en_03
3.3.4

Prioritization

The switch supports four priority queues for adjusting the internal packet processing se-
quence (traffic classes according to IEEE 802.1D). Data telegrams that are received are as-
signed to these classes according to the priority of the data packet, which is specified in the
VLAN/prioritization tag:
– Data packets with the value "0" or "1" in the priority field are transmitted with the lowest
priority (default).
– Data packets with the value "2" or "3" in the priority field are transmitted with the second
lowest priority.
– Data packets with values between "4" and "5" in the priority field are transmitted with the
second highest priority by the switch.
– Data packets with values between "6" and "7" in the priority field are transmitted with the
highest priority by the switch.
Processing rules
The switch controller in the FL SWITCH SMN forwards received packets to one of the re-
ceive queues according to the following decisions:
– BPDU packets are always assigned to the high-priority queue.
– Packets with VLAN/prioritization tag are forwarded according to the queues listed
above.
– All remaining data is assigned to the low-priority queue.
3.3.4.1 Class of Service (CoS)
Class of Service refers to a mechanism used to take into consideration the value of the pri-
ority field (values 1 to 7) in VLAN data packets with a tag. The switch assigns the data
streams in various processing queues, depending on what priority information is contained
in the CoS tag. The switch supports four internal processing queues.
3.3.4.2 Quality of Service (QoS)
Quality of Service affects the forwarding and handling of data streams and results in individ-
ual data streams being given differential treatment (usually preferential). QoS can be used,
e.g., to guarantee a transmission bandwidth for individual data streams. The switch uses
QoS in connection with prioritization (see CoS). The broadcast limiter can also be referred
to as a QoS function.
3.3.4.3 Flow control
Flow control can provide advantages during transmission in large network topologies in
which peak loads are to be expected. The switch supports flow control.
Startup and functions
23
PHOENIX CONTACT