Service Manual

DCBx requires the link layer discovery protocol (LLDP) to provide the path to exchange DCB parameters
with peer devices. Exchanged parameters are sent in organizationally specific TLVs in LLDP data units.
The following LLDP TLVs are supported for DCB parameter exchange:
PFC parameters PFC Configuration TLV and Application Priority Configuration TLV.
ETS parameters ETS Configuration TLV and ETS Recommendation TLV.
Data Center Bridging in a Traffic Flow
The following figure shows how DCB handles a traffic flow on an interface.
Figure 32. DCB PFC and ETS Traffic Handling
Priority-Based Flow Control
In a data center network, priority-based flow control (PFC) manages large bursts of one traffic type in
multiprotocol links so that it does not affect other traffic types and no frames are lost due to congestion.
When PFC detects congestion on a queue for a specified priority, it sends a pause frame for the 802.1p
priority traffic to the transmitting device. In this way, PFC ensures that PFC-enabled priority traffic is not
dropped by the switch.
PFC enhances the existing 802.3x pause and 802.1p priority capabilities to enable flow control based on
802.1p priorities (classes of service). Instead of stopping all traffic on a link (as performed by the
traditional Ethernet pause mechanism), PFC pauses traffic on a link according to the 802.1p priority set on
a traffic type. You can create lossless flows for storage and server traffic while allowing for loss in case of
LAN traffic congestion on the same physical interface.
The following illustration shows how PFC handles traffic congestion by pausing the transmission of
incoming traffic with dot1p priority 4.
Data Center Bridging (DCB)
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