See the current issue of IEEE Spectrum for a nice description of Bob Briscoe’s Re-ECN, A Fairer, Faster Internet Protocol:
Refeedback introduces a second type of packet markingâ€”think of these as credits and the original [ECN] congestion markings as debits. The sender must add sufficient credits to packets entering the network to cover the debit marks that are introduced as packets squeeze through congested Internet pipes. If any subsequent network node detects insufficient credits relative to debits, it can discard packets from the offending stream.
To keep out of such trouble, every time the receiver gets a congestion (debit) mark, it returns feedback to the sender. Then the sender marks the next packet with a credit. This reinserted feedback, or refeedback, can then be used at the entrance to the Internet to limit congestionâ€”you do have to reveal everything that may be used as evidence against you.
Refeedback sticks to the Internet principle that the computers on the edge of the network detect and manage congestion. But it enables the middle of the network to punish them for providing misinformation.
The limits and checks on congestion at the borders of the Internet are trivial for a network operator to add. Otherwise, the refeedback scheme does not require that any new code be added to the networkâ€™s equipment; all it needs is that standard congestion notification be turned on. But packets need somewhere to carry the second mark in the â€œIPâ€ part of the TCP/IP formula. Fortuitously, this mark can be made, because there is one last unused bit in the header of every IP packet.
This is a plan that will allow interactive uses of the Internet to co-exist happily with bulk data transfer. It’s quite brilliant and I recommend it as an alternative to a lot of nonsense that’s been floated around this space.