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Startup and functions
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4.2.5 Prioritization
In order to prioritize data packets, the switch evaluates the Ethernet frame of incoming pack-
ets in addition to the VLAN tag. If the switch detects that it is handling incoming packets from
a PROFINET telegram, it forwards this packet independently of any current, more highly pri-
oritized data traffic, as necessary. This enables a reliable, fast connection from PROFINET
devices to the higher-level controller.
4.2.5.1 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.
4.2.5.2 Quality of Service (QoS)
Quality of Service affects the forwarding and handling of data streams and results in individ-
ual data streams being treated differently (usually preferential). One possible use of QoS is
to guarantee a transmission bandwidth for individual data streams. The switch uses QoS in
connection with prioritization (see CoS).