Phoenix Contact FL SWITCH 2005, Руководство пользователя, Страница: 26 / 98

FL SWITCH 2000
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PHOENIX CONTACT 107065_en_01
4.2.2 Prioritization
The switch supports eight priority queues (traffic classes according to IEEE 802.1Q) for ad-
justing the internal packet processing sequence. Data telegrams that are received are as-
signed to these classes according to their priority, which is specified in the VLAN/prioritiza-
tion tag, where the value “0” in the tag indicates the lowest priority and the value “7” indicates
the highest priority.
Processing rules
The switch controller in the device forwards received packets to the available receive
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.
4.2.2.1 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 the priority information contained in
the CoS tag. The switch supports four internal processing queues.
4.2.2.2 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.