Dell Broadcom NetXtreme Family of Adapters Betriebsanweisung PDF herunterladen (Seite 228)

NetXtreme II User Guide

September 2013

Broadcom Corporation

Page 228 DCB Capabilities Document INGSRVT78-CDUM100-R

DCB CAPABILITIES

ENHANCED TRANSMISSION SELECTION (ETS)

Enhanced Transmission Selection (ETS) provides a common management framework for assignment of bandwidth to traffic

classes. Each traffic class or priority can be grouped in a Priority Group (PG), and it can be considered as a virtual link or

virtual interface queue. The transmission scheduler in the peer is responsible for maintaining the allocated bandwidth for

each PG. For example, a user can configure FCoE traffic to be in PG 0 and iSCSI traffic in PG 1. The user can then allocate

each group a certain bandwidth. For example, 60% to FCoE and 40% to iSCSI. The transmission scheduler in the peer will

ensure that in the event of congestion, the FCoE traffic will be able to use at least 60% of the link bandwidth and iSCSI to

use 40%. See additional references at http://www.ieee802.org/1/pages/802.1az.html.

PRIORITY FLOW CONTROL (PFC)

Priority Flow Control (PFC) provides a link-level flow control mechanism that can be controlled independently for each traffic

type. The goal of this mechanism is to ensure zero loss due to congestion in DCB networks. Traditional IEEE 802.3 Ethernet

does not guarantee that a packet transmitted on the network will reach its intended destination. Upper-level protocols are

responsible to maintain the reliability by way of acknowledgement and retransmission. In a network with multiple traffic

classes, it becomes very difficult to maintain the reliability of traffic in the absence of feedback. This is traditionally tackled

with the help of link-level Flow Control.

When PFC is used in a network with multiple traffic types, each traffic type can be encoded with a different priority value and

a pause frame can refer to this priority value while instructing the transmitter to stop and restart the traffic. The value range

for the priority field is from 0 to 7, allowing eight distinct types of traffic that can be individually stopped and started. See

additional references at http://www.ieee802.org/1/pages/802.1bb.html.

DATA CENTER BRIDGING EXCHANGE (DCBX)

Data Center Bridging eXchange (DCBX) is a discovery and capability exchange protocol that is used for conveying

capabilities and configuration of ETS and PFC between link partners to ensure consistent configuration across the network

fabric. In order for two devices to exchange information, one device must be willing to adopt network configuration from the

other device. For example, if a C-NIC is configured to willingly adopt ETS and PFC configuration information from a

connected switch, and the switch acknowledges the C-NIC’s willingness, then the switch will send the C-NIC the

recommended ETS and PFC parameter settings. The DCBX protocol uses the Link Level Discovery Protocol (LLDP) to

exchange PFC and ETS configurations between link partners.

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Dell Broadcom NetXtreme Family of Adapters Betriebsanweisung Seite 228