Hi Tony,
please see inline (##PP2):
On 17/07/2026 18:30, Tony Li wrote:
Hi Peter,
##PP
I see thinks differently, but let's not argue about that, does not lead us
anywhere.
In the spirit of intellectual integrity, you owe a reference, as does EBR.
##PP2
I have no problem with that.
##PP
The problem described in that paper is a result of the entire traffic shifting
between links A and B. That is not what DC does. DCM always keeps the traffic
on the link A and moves part of it on B. It also monitors B's utilization and
stops adding more before B becomes congested. DCM is also done for local links
only, which is different to what is described in that paper, where all routers
react. So we are far from conditions described in that paper.
I disagree. You are shifting traffic away from a congested link. Even if it
is not all traffic, it must be some significant chunk of traffic to have any
effect. As soon as you do that, the link can (and should) transition back to
uncongested state. You want to get things back to uncongested because you want
the headroom for future (fractal) congestion events.
##PP2
There are some thresholds with hysteresis involved to avoid shifting
traffic back and forth.
##PP
We do not react to spikes. And we do incremental offload. All to avoid what
you described.
Then you are not solving the problem.
##PP2
we are, but maybe a different one that you intended to solve with TTE.
DCM is not trying to solve the microburst problem.
2. TTE does not support multiple congested links in the network at the same
time. Using multiple LFA/TI-LFA paths simultaneously on different nodes can
easily lead to loops.
One can avoid this via SSPF.
##PP
if your protection is via local LFA, which does not use any extra labels, SSPF
is not going to help you, because your backup traffic is using the native SID.
SSPF will prevent possible looping.
##PP2
RCF 8402 allows SSPF SODs to be protected:
"Note that Fast Reroute (FRR) [RFC5714
<https://datatracker.ietf.org/doc/html/rfc5714>] mechanisms are
still compliant with the Strict Shortest Path First algorithm. In
other words, a packet received with a Strict-SPF SID may be
rerouted through an FRR mechanism"
In such case I'm not sure how does it solves the problem of backup
paths being used in multiple places in the area.
thanks,
Peter
Tony
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