Concept Guide

The internal Priority assigned for the packet by Ingress FP is used by the memory management unit (MMU) to assign the packet to right
queue by indexing the internal-priority to queue map table (TABLE 1) in hardware.
PRIO2COS setting for honoring the PFC protocol packets from the Peer switches is as per above Packet-Dot1p->queue table (Table 2).
The packets that come in with packet-dot1p 2 alone will be assigned to PG6 on ingress.
The packets that come in with packet-dot1p 2 alone will use Q1 (as per dot1p to Queue classication – Table 2) on the egress port.
• When Peer sends a PFC message for Priority 2, based on above PRIO2COS table (TABLE 2), Queue 1 is halted.
• Queue 1 starts buering the packets with Dot1p 2. This causes PG6 buer counter to increase on the ingress, since P-dot1p 2 is
mapped to PG6.
• As the PG6 watermark threshold is reached, PFC will be generated for dot1p 2.
Generation of PFC for a Priority for Untagged Packets
In order to generate PFC for a particular priority for untagged packets, and conguring PFC for that priority, you should nd the queue
number associated with priority from TABLE 1 and Associate a DCB map to forward the matched DSCP packet to that queue. PFC frames
gets generated with PFC priority associated with the queue when the queue gets congested.
Congure Enhanced Transmission Selection
ETS provides a way to optimize bandwidth allocation to outbound 802.1p classes of converged Ethernet trac.
Dierent trac types have dierent service needs. Using ETS, you can create groups within an 802.1p priority class to congure dierent
treatment for trac with dierent bandwidth, latency, and best-eort needs.
For example, storage trac is sensitive to frame loss; interprocess communication (IPC) trac is latency-sensitive. ETS allows dierent
trac types to coexist without interruption in the same converged link by:
• Allocating a guaranteed share of bandwidth to each priority group.
• Allowing each group to exceed its minimum guaranteed bandwidth if another group is not fully using its allotted bandwidth.
ETS Prerequisites and Restrictions
The following prerequisites and restrictions apply when you congure ETS bandwidth allocation or queue scheduling.
• Conguring ETS bandwidth allocation or a queue scheduler for dot1p priorities in a priority group is applicable if the DCBx version used
on a port is CIN (refer to Conguring DCBx).
• When allocating bandwidth or conguring a queue scheduler for dot1p priorities in a priority group on a DCBx CIN interface, take into
account the CIN bandwidth allocation (refer to Conguring Bandwidth Allocation for DCBx CIN) and dot1p-queue mapping.
NOTE
: The IEEE 802.1Qaz, CEE, and CIN versions of ETS are supported.
Creating an ETS Priority Group
An ETS priority group species the range of 802.1p priority trac to which a QoS output policy with ETS settings is applied on an egress
interface.
1 Congure a DCB Map.
CONFIGURATION mode
dcb-map dcb-map-name
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Data Center Bridging (DCB)