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Lossless Ethernet - Whats that !!

Fibre Channel protocols assume that the underlying fabric is lossless even during network congestion, to ensure that storage traffic is delivered reliably and in a timely manner. The Fibre Channel transport protocol uses link level credit based flow control that guarantees no loss of frames under normal conditions. Ethernet by contrast is a best-effort network, and may drop packets when the network is busy, resulting in retransmissions, storage protocol time-outs, and even lost data. While FCoE SANs can be built with current Ethernet fabrics, providing the mission critical reliability and data integrity required by enterprise data centers requires enhancements to Ethernet to create fully lossless fabrics.

New standards are under development that will create a new, more capable family of Ethernet protocols. These standards, referred to collectively as Converged Enhanced Ethernet (CEE) are being developed in IEEE 802.1, 802.3, and IETF standards bodies. However, the critical technologies required to enable FCoE are available now, based on a subset of the standards that have been agreed to by the standards participants. Thus FCoE can be deployed now, with lossless characteristics.

Convergence Enhanced Ethernet (CEE) capable products will enable lossless Ethernet fabrics by using IEEE 802.1p Class Based Flow Control (CBFC), to pause traffic base on the priority levels. 802.1p allows virtual lanes to be created within an Ethernet link with each virtual lanes assigned a priority level. During periods of heavy congestion lower priority traffic can be paused, while allowing high priority and latency sensitive tasks such as data storage to continue. IEEE 802.1Q (Virtual LAN) can be use to partition the physical Ethernet fabric to create high levels of security by isolating traffic types and to enhance Quality of Service by configuring guaranteed bandwidth and latencies per VLAN. Using VLANs and 802.1p flow control several lanes of high performance lossless

FCoE can be established on a single 10 Gigabit Ethernet fabric. Ethernet will be further enhanced by the proposed IEEE 802.1au Congestion Notification (CN), which will provide end to end flow control capabilities by allowing congestion points to notify a rate limiter when congestion is occurring, so that the traffic can be throttled back.

IBM Networking Portfolio video:

Source:  Fabric Convergence with Lossless Ethernet and FCoE,  Technology Brief