Reference Guide

InterProcess
Communication
(IPC) traffic
InterProcess Communication (IPC) traffic within high-performance computing clusters to share
information. Server traffic is extremely sensitive to latency requirements.
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: In FTOS version 8.3.12.0, only the PFC, ETS, and DCBx features are supported 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 priority 3.
Figure 31. Priority-Based Flow Control
The system supports loading two DCB_Config files:
• FCoE_DCB_Config
• iSCSI_DCB_Config
In the FTOS operating system, 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 operation.
• PFC uses DCB MIB IEEE 802.1azd2.5 and PFC MIB IEEE 802.1bb-d2.2.
236