[Cerowrt-devel] Ideas on how to simplify and popularize bufferbloat control for consideration.
moeller0 at gmx.de
Sat Jul 26 07:18:34 EDT 2014
On Jul 25, 2014, at 22:57 , David Lang <david at lang.hm> wrote:
> On Fri, 25 Jul 2014, Wes Felter wrote:
>> The Netgear stock firmware measures bandwidth on every boot or link up (not sure which) and I would suggest doing the same for CeroWRT.
>> Do you need to measure Internet bandwidth or last mile bandwidth? For link bandwidth it seems like you can solve a lot of problems by measuring to the first hop router. Does the packer pair technique work on TDMA link layers like DOCSIS?
> The trouble is that to measure bandwidth, you have to be able to send and receive a lot of traffic.
Well that is what you typically do, but you can get away with less measurement traffic: in an ideal quiescent network sending two packets back to back should give you the bandwidth (packet size / incoming time difference of both packets), or send two packets of different size (needs synchronized clocks, then difference of packet sizes / difference of transfer times).
> unless the router you are connecting to is running some sort of service to support that,
But this still requires some service on the other side. You could try to use ICMP packets, but these will only allow to measure RTT not one-way delays (if you do this on ADSL you will find the RTT dominated by the typically much slower uplink path). If network equipment would be guaranteed to use NTP for decent clock synchronization and would respond to timestamp ICMP messages with timestamp reply measuring bandwidth might be “cheap” enough to keep running in the background, though.
Since this looks too simple there must be a simple reason why this would fail. (It would be nice if ping packets with timestamps would have required the echo server top also store its incoming timestamp in the echo, but I digress)
I note that gargoyle uses a sparse stream of ping packets to a close host and uses increases in RTT as proxy for congestion and signal to throttle down stream link…
> you can't just test that link, you have to connect to something beyond that.
So it would be sweet if we could use services that are running on the machines anyway, like ping. That way the “load” of all the leaf nodes of the internet continuously measuring their bandwidth could be handled in a distributed fashion avoiding melt-downs by synchronized measurement streams…
> David Lang
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