DCB refers to a set of IEEE Ethernet enhancements that provide data centers with a single, robust, converged network to support multipletraffic types, including local area network (LAN), server, and storage traffic. Through network consolidation, DCB results in reducedoperational 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, include additional storage area networks (SANs) to ensure losslessFibre Channel traffic, and a separate InfiniBand network for high-performance inter-processor computing within server clusters, only oneDCB-enabled network is required in a data center. The Dell Networking switches that support a unified fabric and consolidate multiplenetwork 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:Traffic DescriptionLAN traffic LAN traffic consists of many flows that are insensitive to latency requirements, while certain applications, such asstreaming video, are more sensitive to latency. Ethernet functions as a best-effort network that may drop packetsin the case of network congestion. IP networks rely on transport protocols (for example, TCP) for reliable datatransmission with the associated cost of greater processing overhead and performance impact LAN traffic consistsof a large number of flows that are generally insensitive to latency requirements, while certain applications, such asstreaming video, are more sensitive to latency. Ethernet functions as a best-effort network that may drop packetsin case of network congestion. IP networks rely on transport protocols (for example, TCP) for reliable datatransmission with the associated cost of greater processing overhead and performance impact.Storage traffic Storage traffic based on Fibre Channel media uses the Small Computer System Interface (SCSI) protocol for datatransfer. This traffic typically consists of large data packets with a payload of 2K bytes that cannot recover fromframe loss. To successfully transport storage traffic, data center Ethernet must provide no-drop service withlossless links.InterProcessCommunication(IPC) trafficInterProcess Communication (IPC) traffic within high-performance computing clusters to share information. Servertraffic 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 servertraffic 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) protocolNOTE: Dell Networking OS supports only the PFC, ETS, and DCBx features in data center bridging.Priority-Based Flow ControlIn a data center network, priority-based flow control (PFC) manages large bursts of one traffic type in multiprotocol links so that it does notaffect 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 transmittingdevice. 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 ofservice). Instead of stopping all traffic on a link (as performed by the traditional Ethernet pause mechanism), PFC pauses traffic on a linkaccording to the 802.1p priority set on a traffic type. You can create lossless flows for storage and server traffic while allowing for loss incase 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) 253
