As final conclusions, there are some important remarks to be expressed. The changes in the Ethernet protocol will introduce the concept of Quality of Service to the technology. This modifications also brings some features of upper layers to the second layer protocol. All the modifications aims to join the characteristics needed in DCB with efficiency and simplicity at implementation. These main modifications are implemented through the Ethernet switches, that where constantly improved with the growth of networking and the Internet.
The data centers are increasingly appearing around the globe and are really important to the computing architecture of nowadays. The effort of proposing a series of modifications to a well based technology such as Ethernet were is a good approach to DCB. The series of enhancements is not limited by the three described in the text, and the IEEE DCB task group is still working on other modifications to improve the adaptation of Ethernet to Data Center Networking.
The Ethernet is a best-effort technology that provides a unreliable layer 2 connection and has a high frame loss rate at congestion situations. This pattern should be modified to offer control among the switches transmission and different quality of service to the various types of data traffic presents in the Data Center Networks.
the Ethernet Flow Control proposed by IEEE 802.3x uses PAUSE messages to preventing frame transmission of a switch in a determined link. This PAUSE messages paralyze the entire traffic transmission of a switch, altough in the data center context, it is desirable that a switch could have paused transmissions only in specific types of traffic. With this issue, the priority concept must be introduce in the original process of flow control.
In ETS, the queues are used to provided scheduling algorithms to frame transmission. The variety of queues used make the forwarding process dynamic, and the queues abstraction represents types of traffic that passes trough a switch. With queues, the bandwidth allocation to each type of traffic can be optimized to its necessities and characteristics.
The VLAN tags will provide a implementation of the Classes of Service defined at the Priority-Based Flow Control. As all Ethernet frames must be related to a VLAN, the Classes of Service will be represented as VLAN tag numbers. With this approach, it is possible to specify the classes that should be based trough the pause messages using the VLAN tag number.
The feedback messages carry a congestion measure to inform a source(Reaction Point) that a reduction must be done in the transmission rate. When a RP receives such message, its decreases the transmission rate calculating the new value as a function of the feedback value. This decreasing rate is limited by a half reduction, i.e, the new transmission rate will be, at maximum, a half of its initial value.