Product specifications

Deploying a Converged Storage Network Using a Cisco FCoE Switch

Appendix D: Data Center Bridging Technology

The following descriptions of Enhanced Ethernet were taken from Ethernet: The Converged Network

Ethernet Alliance Demonstration, which was presented at the Super Computing 2009 (SC09) conference

and published by the Ethernet Alliance in November 2009.

Data Center Bridging (DCB)

For Ethernet to carry LAN, SAN, and IPC traffic together and achieve network convergence, some

necessary enhancements are required. These enhancement protocols are summarized as data center

bridging (DCB) protocols, also referred to as Enhanced Ethernet (EE), which are defined by the IEEE

802.1 data center bridging task group. A converged Ethernet network is built based on the following

DCB protocols:

 DCBX and ETS

 Priority Flow Control

 Fibre Channel over Ethernet (FCoE)

 iSCSI

DCBX and ETS

Existing Ethernet standards cannot control and manage the allocation of network bandwidth to

different network traffic sources and types (traffic differentiation). Neither can existing standards allow

prioritizing of bandwidth usage across these sources and traffic types. Data center managers must

over-provision network bandwidth for peak loads, accept customer complaints during these periods, or

manage traffic on the source side by limiting the amount of nonpriority traffic entering the network.

Overcoming these limitations is a key to enabling Ethernet as the foundation for true converged data

center networks supporting LAN, storage, and interprocessor communications.

Enhanced Transmission Selection (ETS) protocol addresses the bandwidth allocation issues among

various traffic classes to maximize bandwidth usage. The IEEE 802.1Qaz standard specifies the

protocol to support allocation of bandwidth among priority groups. ETS allows each node to control

bandwidth per priority group. When the actual load in a priority group does not use its allocated

bandwidth, ETS allows other priority groups to use the available bandwidth. The bandwidth-allocation

priorities allow the sharing of bandwidth between traffic loads, while satisfying the strict priority

mechanisms already defined in IEEE 802.1Q that require minimum latency.

Bandwidth allocation is achieved as part of a negotiation process with link peers—this is called DCB

Capability eXchange protocol (DCBX). It provides a mechanism for Ethernet devices (bridges, end

stations) to detect the DCB capability of a peer device. It also allows configuration and distribution of

ETS parameters from one node to another.