Priority-Based Flow Control - Dell S4048–ON Configuration Manual

S-series 10gbe switches

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Table of Contents

InterProcess

InterProcess Communication (IPC) traffic within high-performance computing clusters to share information.

Communication

Server traffic is extremely sensitive to latency requirements.

(IPC) traffic

To ensure lossless delivery and latency-sensitive scheduling of storage and service traffic and I/O convergence of LAN, storage, and

server traffic over a unified fabric, IEEE data center bridging adds the following extensions to a classical Ethernet network:

802.1Qbb — Priority-based Flow Control (PFC)

802.1Qaz — Enhanced Transmission Selection (ETS)

802.1Qau — Congestion Notification

Data Center Bridging Exchange (DCBx) protocol

NOTE: Dell Networking OS supports only the PFC, ETS, and DCBx features in data center bridging.

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

Figure 32. Illustration of Traffic Congestion

The system supports loading two DCB_Config files:

FCoE converged traffic with priority 3.

iSCSI storage traffic with priority 4.

In the Dell Networking OS, PFC is implemented as follows:

PFC supports buffering to receive data that continues to arrive on an interface while the remote system reacts to the PFC

Data Center Bridging (DCB)