Specifications

DGS-3048 Layer 2 Switch CLI Reference Manual
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QOS COMMANDS
The DGS-3048 switch supports 802.1p priority queuing. The Switch has 8 priority classes of service. These
priority classes of service are numbered from 7 (Class 7) — the highest priority class of service — to 0 (Class 0)
— the lowest priority class of service. The eight priority queues specified in IEEE 802.1p (p0 to p7) are mapped to
the Switch’s priority classes of service as follows:
• Priority 0 is assigned to the Switch’s Q0 class.
• Priority 1 is assigned to the Switch’s Q1 class.
• Priority 2 is assigned to the Switch’s Q2 class.
• Priority 3 is assigned to the Switch’s Q3 class.
• Priority 4 is assigned to the Switch’s Q4 class.
• Priority 5 is assigned to the Switch’s Q5 class.
• Priority 6 is assigned to the Switch’s Q6 class.
• Priority 7 is assigned to the Switch’s Q7 class.
Priority scheduling is implemented using two types of methods, strict priority and round-robin priority. If no
changes are made to the QoS priority scheduling settings the method used is strict priority.
For strict priority-based scheduling, packets residing in the higher priority classes of service are transmitted first.
Only when these classes of service are empty, are packets of lower classes of service allowed to be transmitted.
Higher priority packets always receive preference regardless of the amount of lower priority packets in the buffer
and regardless of the time elapsed since any lower priority packets have been transmitted. By default, the Switch is
configured to empty the buffer using strict priority.
NOTICE: The default QoS scheduling arrangement is a strict priority
schedule. To customize scheduling to set up round-robin queue clearing,
the MAX. Latency and MAX. Packets values need to be changed using
the config scheduling command. See config scheduling below.
To use implement round-robin (weighted) priority, the Switch’s eight priority classes of service can be configured
to reduce the buffer in a round-robin fashion - beginning with the highest priority class of service, and proceeding
to the lowest priority class of service before returning to the highest priority classes of service.
The weighted-priority based scheduling alleviates the main disadvantage of strict priority-based scheduling − in
that lower priority class of service get starved of bandwidth − by providing a minimum bandwidth to all classes of
service for transmission. This is accomplished by configuring the maximum number of packets allowed to be
transmitted from a given priority class of service and the maximum amount of time a given priority class of service
will have to wait before being allowed to transmit its accumulated packets. This establishes a Class of Service
(CoS) for each of the Switch’s eight hardware priority classes of service.
The possible range for maximum packets is: 0 to 15 packets.
The QoS commands in the Command Line Interface (CLI) are listed (along with the appropriate parameters) in the
following table.
Command Parameters
config scheduling <class_id 0-7> max_packet <value 0-15>
show scheduling
config 802.1p user_priority <priority 0-7> <class_id 0-7>
show 802.1p user_priority
config 802.1p default_priority [<portlist> | all] <priority 0-7>