Re: [ippm] [spring] Monitoring metric to detect and locate congestion

Hi Ruediger,

I have read your draft and presentation with interest as I am a
big supporter and in some lab trials  of end to end network path probing.

Few comments, observations, questions:

You are essentially measuring and comparing delay across N paths traversing
known network topology (I love "network tomography" name !)

* First question - this will likely run on RE/RP and in some platforms path
between LC and RE/RP is completely deterministic and can take 10s or 100s
of ms locally in the router. So right here the proposal to compare anything
may not really work - unless the spec mandates that actually timestamping
is done in hardware on the receiving LC. Then CPU can process it when it
has cycles.

* Second question is that congestion usually has a very transient character
... You would need to be super lucky to find any congestion in normal
network using test probes of any sort. If you have interfaces always
congested then just the queue depth time delta may not be visible in end to
end measurements.

* Third - why not simply look at the queue counters at each node ? Queue
depth, queue history, min, avg, max on a per interface basis offer tons of
information readily available. Why would anyone need to inject loops of
probe packets in known network to detect this ? And in black box unknown
networks this is not going to work as you would not know the network
topology in the first place. Likewise link down/up is already reflected in
your syslog via BFD and IGP alarms. I really do not think you need end to
end protocol to tell you that.

+

s/nodes L100 and L200 one one/nodes L100 and L200 on one/

:)

Many thx,
R.

On Wed, Feb 26, 2020 at 8:55 AM <Ruediger.Geib@telekom.de> wrote:

> Dear IPPM (and SPRING) participants,
>
>
>
> I’m solliciting interest in a new network monitoring metric which allows
> to detect and locate congested interfaces. Important properties are
>
>    - Same scalability as ICMP ping in the sense one measurement relation
>    required per monitored connection
>    - Adds detection and location of congested interfaces as compared to
>    ICMP ping (otherwise measured metrics are compatible with ICMP ping)
>    - Requires Segment Routing (which means, measurement on forwarding
>    layer, no other interaction with passed routers – in opposite to ICMP ping)
>    - Active measurement (may be deployed using a single sender&receiver
>    or separate sender and receiver, Segment Routing allows for both options)
>
>
>
> I’d be happy to present the draft in Vancouver.. If there’s community
> interest. Please read and comment.
>
>
>
> You’ll find slides at
>
>
>
>
> https://datatracker.ietf.org/meeting/105/materials/slides-105-ippm-14-draft-geib-ippm-connectivity-monitoring-00
>
>
>
> Draft url:
>
>
>
> https://datatracker.ietf.org/doc/draft-geib-ippm-connectivity-monitoring/
>
>
>
> Regards,
>
>
>
> Ruediger
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>