Best algorithm for EV selection in UE ECMP packet spraying

Determine the most effective per-packet Entropy Value (EV) selection algorithm for Ultra Ethernet's ECMP-based packet spraying load balancing, including scenarios where some flows require in-order delivery and therefore occupy fixed paths.

Background

Ultra Ethernet uses Equal-Cost Multi-Pathing (ECMP) to load balance traffic by hashing packet headers, with the Entropy Value (EV) field allowing endpoints to influence path selection. By varying EVs per packet, UE enables packet spraying to avoid persistent hash collisions and traffic polarization.

Selecting EVs effectively is non-trivial, especially when some flows must remain in-order and thus pin certain paths, while others can be sprayed. The specification mentions several optional load-balancing approaches but deliberately leaves the choice open to enable vendor differentiation and further research.