56.6.5.5 Enhanced Transmission Selection (ETS)

The ETS algorithm is defined in IEEE 802.1Qaz: Enhanced Transmission Selection for Bandwidth Sharing between Traffic and allows traffic on specific queues to be bandwidth-limited. Any of the active queues can be selected as ETS. If ETS is required, then at least two of the active queues should be selected as ETS. It must not be used in conjunction with DWRR.

An ETS-enabled queue has lower priority than a CBS-enabled queue or a fixed priority queue with a higher index.

For each ETS-enabled queue, the bandwidth requirement must be configured for each queue as a percentage of total bandwidth (an 8-bit register is used and the sum of values programmed should not exceed decimal 100). This will be the maximum bandwidth to be granted to that queue. The actual scheduling algorithm operates in a round-robin style from lowest indexed queues up to the highest indexed queue in sequence. The bandwidth allocation percentage is stored in programmable registers starting at offset 0x590 – these are the same registers used for DWRR.

If CBS is also used in conjunction with ETS, the sum of the ETS queue percentages should equal the remaining bandwidth after the CBS allocation has been deducted.

Transmit cut-thru must not be enabled if the transmit scheduler is used.