On Sat, 10 Oct 2015, David Lang wrote:
On Fri, 9 Oct 2015, Joe Touch wrote:
On 10/9/2015 10:58 PM, David Lang wrote:
RFC3449 doesn't completely address the current situation, but it
provides a very good place to start, and it seems to me that the
solitions it explores to address the conerns that it (and you) raise are
actually being addressed pretty completely. There are still some areas
to talk about (ECN interaction for example) and we wshould be talking
about those issues rather than arguing that the proposal violates holy
writ.
I'm OK with the recommendations for the endpoints to modify their ACK
behavior, but still am concerned that stripping out ACKs in the middle
of the network is problematic for a number of reasons, only some of
which are addressed in RFC3449 (which also recommends against deploying
them in the general Internet, so if that's your justification then it's
very clearly in direct opposition).
Remember that this can only take place when there is enough of a bottleneck
that enough of a queue has built up that multiple ack packets are sitting in
the queue waiting to be transmitted. Such a queue is only going to build up
if the link is a bottleneck [1]. As I undertsand the current Industry Best
Practice, unless you have ISPs deliberatly not upgrading (ala the Netflix
fights), the core systems almost never queue and so such algorithms would
never kick in.
So even if I could wave a magic wand and deploy this on every router, it
would only have an effect in a few places. Endpoint links where the available
bandwidth drastically changes are not the exclusive list of palces that this
would effect, but I think it's pretty close.
Also, since it costs CPU to go through the queue looking for ACK packets to try
and combine, it is a feature unlikly to be enbled on high speed devices. It
would probably only be enabled when the savings in the reduced number of ACKs
that would be transmitted is significant enough to be worth the effort. Endpoint
devices for home users where there is probably also a highly asymmetric link are
a very clear win. Core routers are almost never going to be a win.
David Lang
David Lang
[1] the exception to this is when you have a hop where the transport
quanomizes the data the way Wifi and Cell networks do, So if you have a
half-duplex link like normal Wifi or a time-slot MAC like a Cell network in
the middle of the path, this sort of thing could trigger there, but I'm not
convinced that it would be a bad thing there. Full duplex Wifi links that can
transmit continuously don't need this
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