User Documentation

User Manual Managed Switches
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Traffic prioritization uses the four traffic queues that are present in your Weidmüller managed Switch
to ensure that high priority traffic is forwarded on a different queue from lower priority traffic. This is
what provides Quality of Service (QoS) to your network.
Weidmüller managed Switch traffic prioritization depends on two industry-standard methods:
 IEEE 802.1D  A layer 2 marking scheme.
 Differentiated Services (DiffServ)  A layer 3 marking scheme.
IEEE 802.1D Traffic Marking
The IEEE Std 802.1D, 1998 Edition marking scheme, which is an enhancement to IEEE Std 802.1D,
enables Quality of Service on the LAN. Traffic service levels are defined in the IEEE 802.1Q 4-byte
tag, which is used to carry VLAN identification as well as IEEE 802.1p priority information. The 4-byte
tag immediately follows the destination MAC address and Source MAC address.
The IEEE Std 802.1D, 1998 Edition priority marking scheme assigns an IEEE 802.1p priority level
between 0 and 7 to each frame. The priority marking scheme determines the level of service that this
type of traffic should receive. Refer to the table below for an example of how different traffic types can
be mapped to the eight IEEE 802.1p priority levels.
IEEE 802.1p
Priority Level
IEEE 802.1D Traffic Type
0
Best Effort (default)
1
Background
2
Standard (spare)
3
Excellent Effort (business critical)
4
Controlled Load (streaming multimedia)
5
Video (interactive media); less than 100 milliseconds of latency and jitter
6
Voice (interactive voice); less than 10 milliseconds of latency and jitter
7
Network Control Reserved traffic
Even though the IEEE 802.1D standard is the most widely used prioritization scheme in the LAN
environment, it still has some restrictions:
 It requires an additional 4-byte tag in the frame, which is normally optional for Ethernet
networks. Without this tag, the scheme cannot work.
 The tag is part of the IEEE 802.1Q header, so to implement QoS at layer 2, the entire
network must implement IEEE 802.1Q VLAN tagging.
 It is only supported on a LAN and not across routed WAN links, since the IEEE 802.1Q tags
are removed when the packets pass through a router.
Differentiated Services (DiffServ) Traffic Marking