EDS-518A Series User’s Manual
Featured Functions
3-29
Using Traffic Prioritization
EDS-518A’s traffic prioritization capability provides Quality of Service (QoS) to your network by
making data delivery more reliable. You can prioritize traffic on your network to ensure that high
priority data is transmitted with minimum delay. Traffic can be controlled by a set of rules to
obtain the required Quality of Service for your network. The rules define different types of traffic
and specify how each type should be treated as it passes through the switch. MOXA EDS-518A
can inspect both IEEE 802.1p/1Q layer 2 CoS tags, and even layer 3 TOS information to provide
consistent classification of the entire network. EDS-518A’s QoS capability improves the
performance and determinism of industrial networks for mission critical applications.
The Traffic Prioritization Concept
What is Traffic Prioritization?
Traffic prioritization allows you to prioritize data so that time-sensitive and system-critical data
can be transferred smoothly and with minimal delay over a network. The benefits of using traffic
prioritization are:
y
Improve network performance by controlling a wide variety of traffic and managing
congestion.
y
Assign priorities to different categories of traffic. For example, set higher priorities for
time-critical or business-critical applications.
y
Provide predictable throughput for multimedia applications, such as video conferencing or
voice over IP, and minimize traffic delay and jitter.
y
Improve network performance as the amount of traffic grows. This will save cost by reducing
the need to keep adding bandwidth to the network.
How Traffic Prioritization Works
Traffic prioritization uses the four traffic queues that are present in your EDS-518A 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.
EDS-518A traffic prioritization depends on two industry-standard methods:
y
IEEE 802.1D
—a layer 2 marking scheme.
y
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. This determines the level of service that that 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.
