Administrator Guide

• Priority-based flow control (PFC)
• Enhanced transmission selection (ETS)
DCB refers to a set of IEEE Ethernet enhancements that provide data centers with a single, robust, converged
network to support multiple traffic types, including local area network (LAN), server, and storage traffic.
Through network consolidation, DCB results in reduced operational cost, simplified management, and easy
scalability by avoiding the need to deploy separate application-specific networks.
For example, instead of deploying an Ethernet network for LAN traffic, additional storage area networks
(SANs) to ensure lossless fibre-channel traffic, and a separate InfiniBand network for high-performance inter-
processor computing within server clusters, only one DCB-enabled network is required in a data center. The
Dell Networking switches that support a unified fabric and consolidate multiple network infrastructures use a
single input/output (I/O) device called a converged network adapter (CNA).
A CNA is a computer input/output device that combines the functionality of a host bus adapter (HBA) with a
network interface controller (NIC). Multiple adapters on different devices for several traffic types are no longer
required.
Data center bridging satisfies the needs of the following types of data center traffic in a unified fabric:
• LAN traffic consists of a large number of flows that are generally insensitive to latency requirements,
while certain applications, such as streaming video, are more sensitive to latency. Ethernet functions as a
best-effort network that may drop packets in case of network congestion. IP networks rely on transport
protocols (for example, TCP) for reliable data transmission with the associated cost of greater
processing overhead and performance impact.
• Storage traffic based on Fibre Channel media uses the SCSI protocol for data transfer. This traffic
typically consists of large data packets with a payload of 2K bytes that cannot recover from frame loss.
To successfully transport storage traffic, data center Ethernet must provide no-drop service with lossless
links.
• Servers use 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 Dell Networking OS version 9.4.0.x, 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 large amounts of queued LAN traffic do
Data Center Bridging (DCB) 276