[j-nsp] curious optic issue

[Alexandre Snarskii]

On Mon, Jan 28, 2013 at 09:50:06AM +0200, Saku Ytti wrote:
> I've seen at least twice now issues on XFP where temperature starts to draw
> weird saw-tooth, like this http://ytti.fi/ddm2.png

About the same issue here: http://snar.spb.ru/xe.png. 

Differences between our and your cases: 
- we observed this behaviour on SFP+ (MPC-3D-16XGE, MX960 and MX480,
JunOS 11.4 and 10.4), not on XFP/MX80.
- other ports were not affected by this "temperature shift" in our case.
Similarities: 
- SFP+ removal/re-insertion is the easiest way to "fix" SFP+, MPC reboot 
helps too.
- No JTAC case, third-party DWDM SFP+. 

Some months ago we observed even more interesting situation: seven SFP+ 
in DWDM trunk (10xSFP+) started "freezing" in about the same time. 
All "freezing" SFPs were from the same vendor, and one of "non-freezing" 
SFPs was from the same vendor, whith the only difference - this SFP was 
removed and re-inserted into trunk in summer, while other SFPs in trunk 
worked since end of the March.... 
So, now I'm waiting for May when this SFP should freeze too and prove 
my hypothesis: there is some monotonically increasing counter (not sure 
if it is on SFP or in JunOS code) that messes up with temperature 
readings.

[....]
> At least now I can go to DC, plug with my JNPR-crash-tool and crash
> competitors routers with no traces in syslogs.

If my hypothesis is true, you have to wait for about eight months
before crash happens :) 

-- 
In theory, there is no difference between theory and practice. 
But, in practice, there is.