Enhancements for Scheduled Traffic | What is IEEE802.1Qbv?

Before we get into the specifics of 802.1Qbv, let's look at the problems with existing methods of traffic output control.
Even with existing Ethernet, it is possible to add priority information to Ethernet FRAMES and implement communication priority control in accordance with the priority bit value of each Ethernet FRAMES at a layer 2 SWITCHES hub. (See Figures 1 and 2 for examples of SWITCHES hub configurations and priority bits on Ethernet FRAMES.)
However, this only realizes priority control of FRAMES transmission order, and in communications between devices across SWITCHES hub, as shown in Figure 3, there are cases where transmission cannot be performed when it should be, and it is not possible to predict whether an Ethernet FRAMES will reach the destination device within a certain time.

①There are 8 Output Queues.
②Based on the value of the Priority Bit in the VLAN TAG of the Ethernet FRAMES, it determines which queue to store the output Ethernet FRAMES in.

The value of the Priority Code Point (PCP) bit field determines which of the eight queues the message will be stored in.

On the other hand, the basic concept of 802.1Qbv is to add a protection window to the existing queue mechanism.
The timing at which gates are opened and closed is controlled by a gate control list.
The gate control list sets the queues that can be sent and the period during which they can be sent for each protection window.
It is possible to predict that Ethernet FRAMES in each queue will arrive at the destination device within a certain amount of time.

An example of transmission based on the gate control list is shown in Figure 5.
According to the schedule in the gate control list, only the scheduled queues are allowed to send during each protection window period.

The transmission from the output port will be as shown in Figure 6.

In this column, we explained 802.1Qbv (Enhancements for Scheduled Traffic).
In the next column, we will explain 802.1Qbu (Frame Preemption).