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Re: [HSSG] fault signalling

On Tue, 18 Sep 2007, Geoff Thompson wrote:

> Mikael-
> You need to be careful about the level of complexity that you are asking for. 
> Each item can e a significant expense. After all, there is only one important 
> question that has to be answered for a single hop system. That would be "Do I 
> need to put a repairman at the other end of the link?"
> The more important question in that context (when you lose a link) usually 
> becomes (a) do I need to send a repairman to the far end equipment or do I 
> need to send a cable crew to find a break and (b) can I tell the difference 
> between the two without going through the step of sending a technician to the 
> far equipment?
> In my view, it is perfectly reasonable to use test equipment on the fiber to 
> make determination (b). After all, the link is down so there is no reason not 
> to move the fiber to a piece of test equipment. If it is a WDM fiber, then 
> you will hopefully know if the loss is all of the wavelengths or some subset.

Let's try to give this another dimension. A common scenario for us is the 

We have equipment in two different data centers, at each side of a city. 
Turnup of a patch involves at least three parties to do patching (each end 
hosting provider, might involve our engineer at each end to do patching, 
and then the dark fiber provider). The person responsible for the turnup 
is in another country, trying to coordinate all this. Going between the 
sites might involve a 2 hour drive in city traffic, typically we only have 
a single engineer doing each end.

Now, if one end has too much attenuation due to dirty patch, this is 
extremely helpful to know without doing that two hour drive. Yes, this can 
be solved by doing one end first and so on, and it's typically done so, 
but in some cases we'll discover that one party hasn't done their part 
etc, and the remote end is done first.

So basically, there is real cost (man hours) that can be reduced in both 
initial and maintenance phase by having proper management. We're today 
paying the OC192 vs 10GE premium to accomplish this for DWDM, because 
there it's extra helpful, but without DOM we might do the same even for 
dark fiber (DOM does help quite a lot, at least when both ends are 

Are there any calculations on cost for what I'm proposing, so it can be 
put into perspective? I don't see us using 100GE without DOM anyway, so 
the information I would like to have via OAM is actually available to the 
unit in my scenario, what I'm asking is for a communication channel where 
it can tell the other end what's going on.

Mikael Abrahamsson    email: