<div dir="ltr">As Mark says YMMV as different providers will have markedly different conventions, however one additional challenge that will be widespread is that most carriers are not placing their L2/3 hardware in the cable landing stations, preferring instead to extend from the CLS to more centralized POP locations via Layer 1. So what you will see between a city pair like Tokyo-Seattle, which very obviously will require some wet capacity, will actually be some combination of wet and terrestrial. Between the terrestrial extensions and L2/3 overhead it would be difficult to determine exactly what the underlying cable(s) are even if you had a good idea of what the CLS to CLS latency was.<div><br></div><div>At a previous $dayjob, for example, we had both 100% terrestrial and partially wet links in use to connect our core POPs in Seattle and Vancouver directly. While at the Layer 1 level, the wet link had about a 20% longer optical distance, the distance was short enough that a trace would generally return 3 or 4 ms between core nodes pretty much irrespective of the situation (and the trunks terminated into the same routers in the core anyway, which is a whole other story), so it would have been impossible to tell which path was used even though I knew exactly what the backbone architecture looked like.</div><div><br></div><div>Again, YMMV as different providers will have different standards and different city pairs will be easier to determine than others, but there is no "use this one weird trick" rule here.</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, Sep 29, 2021 at 8:50 AM Mark Tinka <mark@tinka.africa> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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<div>On 9/29/21 04:23, PAUL R BARFORD wrote:<br>
</div>
<blockquote type="cite">
<div style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)"> <span style="margin:0px;font-size:12pt;background-color:rgb(255,255,255)"><span style="margin:0px;font-family:Calibri,Helvetica,sans-serif">Hello,</span></span>
<div style="margin:0px;font-size:12pt;background-color:rgb(255,255,255)"><br>
</div>
<div style="margin:0px;font-size:12pt;background-color:rgb(255,255,255)"><span style="margin:0px;font-family:Calibri,Helvetica,sans-serif">I am a researcher at the University
of Wisconsin. My colleagues at Northwestern University and
I are studying submarine cable infrastructure.</span></div>
<div style="margin:0px;font-size:12pt;background-color:rgb(255,255,255)"><br>
</div>
<div style="margin:0px;font-size:12pt;background-color:rgb(255,255,255)"><span style="margin:0px;font-family:Calibri,Helvetica,sans-serif;color:rgb(34,34,34);background-color:rgb(255,255,255);display:inline">Our interest is in identifying submarine links
in traceroute measurements. Specifically, for a given
end-to-end traceroute measurement, we would like to be able
to identify when two hops are separated by a submarine
cable. Our initial focus has been on inter-hop latency,
which can expose long links. The challenge is that
terrestrial long-haul links may have the same or longer link
latencies as short submarine links. So, we're interested in
whether there may be other features (e.g., persistent
congestion, naming conventions in router interfaces, peering
details, etc.) or techniques that would indicate submarine
links. </span></div>
<div style="margin:0px;font-size:12pt;background-color:rgb(255,255,255)"><span style="margin:0px;font-family:Calibri,Helvetica,sans-serif;color:rgb(34,34,34);background-color:rgb(255,255,255);display:inline"><br>
</span></div>
<div style="margin:0px;font-size:12pt;background-color:rgb(255,255,255)"><span style="margin:0px;font-family:Calibri,Helvetica,sans-serif;color:rgb(34,34,34);background-color:rgb(255,255,255);display:inline">Any thoughts or insights you might have would be
greatly appreciated - off-list responses are welcome.</span><br>
</div>
</div>
</blockquote>
<br>
Back in the day, when submarine cables were not as rife, it was not
uncommon to see things like "FLAG" or "APCN-2" or "SMW-3" in
traceroutes. I haven't seen such in a very long time, but likely
some operators may still do this.<br>
<br>
For traceroutes that cross oceans visibly, e.g., lhr-jfk, mrs-mba,
hnd-lax, mru - cdg, e.t.c., you could glean from there. But many
operators do not follow any "common norm" to annotate things like
this, so YMMV.<br>
<br>
You also find some countries that will use a submarine festoon
either as a primary or backup route for a terrestrial link. In such
cases, the distances may be the same, or even shorter across the
festoon, e.g., consider a festoon cable between Cape Town - Durban,
vs. a land-based run for the same two points.<br>
<br>
Considering how wide-spread submarine links are for both short and
long spans, I think folk are simply treating them as any other link,
from an operational perspective. You may be able to come up with a
semi-automatic mechanism to measure this, but I fear without
deliberate and consistent human intervention, the data could get
stale very quickly.<br>
<br>
Mark.<br>
</div>
</blockquote></div><br clear="all"><div><br></div>-- <br><div dir="ltr" class="gmail_signature"><div dir="ltr"><div>- Dave Cohen<br><a href="mailto:craetdave@gmail.com" target="_blank">craetdave@gmail.com</a><br>@dCoSays</div><div><a href="http://www.venicesunlight.com" target="_blank">www.venicesunlight.com</a></div></div></div>