[Cerowrt-devel] routers you can throw off the back of a truck
moeller0 at gmx.de
Fri Jan 22 02:05:01 EST 2016
> On Jan 19, 2016, at 00:06 , Jonathan Morton <chromatix99 at gmail.com> wrote:
>> On 18 Jan, 2016, at 18:14, Michael Richardson <mcr at sandelman.ca> wrote:
>> Jonathan Morton <chromatix99 at gmail.com> wrote:
>>> I haven’t yet found a robust way to automatically sense link capacity from
>>> the upstream side. You’ll therefore need to set a conservative static
>>> value for the uplink capacity.
>> As the maintainer of a PPPoE concentrator, and operator of some networks,
>> I've been considering whether one can estimate the bandwidth using round
>> trip PPP IPCP keep alives. Clearly, if both ends participate in time
>> stamping then it is much better, but I've been wondering if we can do some
>> incremental deployment on one side or the other.
>> Sadly, I mostly just think about this while cycling; I haven't written any
>> code yet.
> In most PPPoE deployments I know about, there is also a modem from which the actual, precise link rates can usually be queried. Where that’s not the case, IPCP (or is it LPCP?) probes would be a reasonable workaround, but it must still be understood that the signal it provides is only valid under saturating traffic, which complicates implementation.
Erm, if one send probes of differing sizes, one can calculate the total effective bandwidth even without saturating the link (which unfortunately is an inseparable compound of ingress and egress, but will be heavily dominated by the lower, so typically the egress. And it should be relatively simple to flood the link while sending probes, in other words Valent’s router should be able to create the saturatng load on demand ;)
> - Jonathan Morton
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