Service Manual

• Trac in priority groups is assigned to strict-queue or weighted round-robin (WRR) scheduling in an ETS conguration and is
managed using the ETS bandwidth-assignment algorithm. Dell Networking OS de-queues all frames of strict-priority trac
before servicing any other queues. A queue with strict-priority trac can starve other queues in the same port.
• ETS-assigned bandwidth allocation and strict-priority scheduling apply only to data queues, not to control queues.
• Dell Networking OS supports hierarchical scheduling on an interface. The control trac on Dell Networking OS is redirected to
control queues as higher priority trac with strict priority scheduling. After the control queues drain out, the remaining data
trac is scheduled to queues according to the bandwidth and scheduler conguration in the DCB map. The available bandwidth
calculated by the ETS algorithm is equal to the link bandwidth after scheduling non-ETS higher-priority trac.
• The conguration of bandwidth allocation and strict-queue scheduling is not supported at the same time for a priority group.
• Bandwidth assignment: By default, equal bandwidth is assigned to each dot1p priority in a priority group. To congure the
bandwidth assigned to the port queues associated with dot1p priorities in a priority group, use the bandwidth percentage
parameter. The sum of the bandwidth allocated to all priority groups in a DCB map must be 100% of the bandwidth on the link.
You must allocate at least 1% of the total bandwidth to each priority group.
• Scheduling of priority trac: dot1p priority trac on the switch is scheduled to the current queue mapping. dot1p priorities
within the same queue must have the same trac properties and scheduling method.
• ETS conguration error: If an error occurs in an ETS conguration, the conguration is ignored and the scheduler and
bandwidth allocation settings are reset to the ETS default value: 100% of available bandwidth is allocated to priority group 0 and
the bandwidth is equally assigned to each dot1p priority.
If an error occurs when a port receives a peer’s ETS conguration, the port’s conguration resets to the ETS conguration in the
previously congured DCB map. If no DCB map was previously applied, the port resets to the default ETS parameters.
ETS Prerequisites and Restrictions
On an S6000 switch, ETS is enabled by default on Ethernet ports with equal bandwidth assigned to each 802.1p priority. You can
change the default ETS conguration only by using a DCB map.
The following prerequisites and restrictions apply when you congure ETS bandwidth allocation or strict-priority queuing in a DCB
map:
• When allocating bandwidth or conguring strict-priority queuing for dot1p priorities in a priority group on a DCBx CIN interface,
take into account the CIN bandwidth allocation (see Conguring Bandwidth Allocation for DCBx CIN) and dot1p-queue mapping.
• Although ETS bandwidth allocation or strict-priority queuing does not support weighted random early detection (WRED), explicit
congestion notication (ECN), rate shaping, and rate limiting because these parameters are not negotiated by DCBx with peer
devices, you can apply a QoS output policy with WRED and/or rate shaping on a DCBx CIN-enabled interface. In this case, the
WRED or rate shaping conguration in the QoS output policy must take into account the bandwidth allocation or queue
scheduler congured in the DCB map.
Priority-Group Conguration Notes
When you congure priority groups in a DCB map:
• A priority group consists of 802.1p priority values that are grouped together for similar bandwidth allocation and scheduling, and
that share the same latency and loss requirements. All 802.1p priorities mapped to the same queue must be in the same priority
group.
• In a DCB map, each 802.1p priority must map to a priority group.
• The maximum number of priority groups supported in a DCB map on an interface is equal to the number of data queues (4) on
the port. Each priority group can support more than one data queue.
• You can enable PFC on a maximum of two priority queues on an interface.
• If you congure more than one priority group as strict priority, the higher numbered priority queue is given preference when
scheduling data trac.
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Data Center Bridging (DCB)