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Configuring Switching
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SonicOS 5.7: Advanced Switching Feature Guide and Screencast Tutorial
Configuring Layer 2 Quality of Service
Quality of service (QoS) refers to a method of resource control that provides different priority to different
types of applications, data, or users. QoS can also be used to guarantee a certain bit rate, delay, jitter, or error
rate to a type of network traffic. When network capacity is not large enough to accommodate all traffic at
full speed, QoS performance guarantees are essential in the delivery of delay senistive applications such as
Voice over IP (VoIP), online gaming, and Internet TV.
Layer 2, or Ethernet, QoS, provided by SonicOS 5.7 on the SonicWALL NSA 2400MX, is appropriate for
real-time streaming multimedia applications such as those mentioned above. At Layer 2, VLANs may also
be used to separate traffic of different QoS levels (VLAN tagging is defined in IEEE 802.1Q).
SonicOS Layer 2 QoS supports Class of Service (CoS) as specified in IEEE 802.1p. CoS uses a 3 bit field
within the Ethernet frame header. It provides 8 levels of priority for use with QoS algorithms to handle
different types of traffic.
SonicOS also supports Differentiated Services Code Point (DSCP). Also known as Differentiated Services
or DiffServ, DSCP uses a 6-bit field in the header of IP packets (Layer 3) for packet classification, and
provides a simple method of providing QoS guaranteed service to voice or video while using best-effort for
traffic that is not delay sensitive. Best -effort service is the default for most Internet traffic and does not
provide any guarantees.
The SonicWALL NSA 2400MX appliance can be configured to trust Class of Service (CoS) (IEEE 802.1p)
and/or trust Differentiated Services Code Point (DSCP) per port and treat the frames appropriately.
The Switching > Layer 2 QoS page allows the administrator to configure QoS settings per interface.
Figure 16 shows the Switching > Layer 2 Qos page.
Figure 16 Switching > Layer 2 QoS Page