NETGEAR AV Line M4250 GSM4210PX 8-Port Gigabit PoE+ Compliant Managed AV Switch with SFP (220W) - Manual (Page 454)

Quality of Service concepts
In a switch, each physical port consists of one or more queues for transmitting packets
on the attached network. Multiple queues per port are often provided to give preference
to certain packets over others based on user-defined criteria. When a packet is queued
for transmission in a port, the rate at which it is serviced depends on how the queue is
configured and possibly the amount of traffic present in the other queues of the port.
If a delay is necessary, packets are held in the queue until the scheduler authorizes the
queue for transmission. As queues become full, packets can no longer be held for
transmission and are dropped by the switch.
Quality of Service (QoS) is a means of providing consistent, predictable data delivery
by distinguishing packets with strict timing requirements from those that are more
tolerant of delay. Packets with strict timing requirements are given special treatment in
a QoS-capable network. With this in mind, all elements of the network must be QoS
capable. The presence of at least one node that is not QoS capable creates a deficiency
in the network path, and the performance of the entire packet flow is compromised.
Class of Service
The Class of Service (CoS) queueing feature lets you directly configure certain aspects
of switch queueing. This provides the desired QoS behavior for different types of network
traffic when the complexities of DiffServ are not required. The priority of a packet arriving
at an interface can be used to steer the packet to the appropriate outbound CoS queue
through a mapping table. CoS queue characteristics that affect queue mapping, such
as minimum guaranteed bandwidth or transmission rate shaping, are user-configurable
at the queue (or port) level.
Eight queues per port are supported.
CoS configuration concepts
You can set the Class of Service trust mode for an interface. Each port on the switch can
be configured to trust one of the packet fields (802.1p or IP DSCP), or to not trust any
packet’s priority designation (untrusted mode). If the port is set to a trusted mode, it
uses a mapping table appropriate for the trusted field being used. This mapping table
indicates the CoS queue to which the packet must be forwarded on the appropriate
egress port. Of course, the trusted field must exist in the packet for the mapping table
to be of any use. If this is not the case, default actions are performed. These actions
involve directing the packet to a specific CoS level configured for the ingress port as a
whole, based on the existing port default priority as mapped to a traffic class by the
current 802.1p mapping table.
Main User Manual 454 Configure Quality of Service
AV Line of Fully Managed Switches M4250 Series Main User Manual