RE: dark fiber and sfp distance limitations

[John van Oppen]

The best OTDR data I have ever gotten prior to signing an agreement for strands 
is the readings from another pair on the same route.That being said most 
dark fiber agreements have some sort of minimum performance specifications in 
them.

John van Oppen
Spectrum Networks LLC
Direct: 206.973.8302
Main: 206.973.8300
Website: http://spectrumnetworks.us


-Original Message-
From: William Herrin [mailto:herrin-na...@dirtside.com] 
Sent: Friday, January 01, 2010 5:11 PM
To: ML
Cc: nanog@nanog.org
Subject: Re: dark fiber and sfp distance limitations

On Fri, Jan 1, 2010 at 7:24 PM, ML  wrote:
> Pardon my ignorance in this area but is too much to ask for OTDR data before
> signing contracts?  In addition to data on the make of the fiber if you
> wanted to do xWDM in the future.

Yes, it's too much to ask. They won't splice your path until you sign
the contracts and you can't get useful OTDR and loss readings until
the fiber is spliced.

You can probably put an escape clause in the contract that lets you
exit with little or no cost if the readings aren't good enough after
the fact. If you're not time-constrained, you can probably request a
pre-check for a modest fee after main splicing but before trenching to
your endpoints.

Regards,
Bill Herrin

-- 
William D. Herrin  her...@dirtside.com  b...@herrin.us
3005 Crane Dr. .. Web: <http://bill.herrin.us/>
Falls Church, VA 22042-3004

RE: dark fiber and sfp distance limitations

[Frank Bulk - iName.com]

and to add, OTDR at several wavelengths, just in case you want to do
xWDM in the future.

Frank

-Original Message-
From: ML [mailto:m...@kenweb.org] 
Sent: Friday, January 01, 2010 6:24 PM
To: Mike
Cc: nanog@nanog.org
Subject: Re: dark fiber and sfp distance limitations

On 1/1/2010 5:52 PM, Mike wrote:
> I am looking at the possibility of leasing a ~70 mile run of fiber. I
> don't have access to any mid point section for regeneration purposes,
> and so I am wondering what the chances that a 120km rated SFP would be
> able to light the path and provide stable connectivity. There are a lot
> of unknowns including # of splices, condition of the cable, or the
> actual dispersion index or other properties (until we actually get
> closer to leasing it). Its spare telco fibers in the same cable binder
> they are using interoffice transport, but there are regen huts along the
> way so it works for them but may not for us, and 'finding out' is
> potentially expensive. How would someone experienced go about
> determining the feasibillity of this concept and what options might
> there be? Replies online or off would be appreciated.
>
> Thanks.
>
>

Pardon my ignorance in this area but is too much to ask for OTDR data 
before signing contracts?  In addition to data on the make of the fiber 
if you wanted to do xWDM in the future.

NDAs shall be signed of course

Re: dark fiber and sfp distance limitations

[Kevin Hodle]

On Mon, Jan 4, 2010 at 4:01 AM, Martin, Paul  wrote:
>
> If you only want 1gig, then if the SP provides it, won't it be cheaper
> to simply get a 1gig circuit from them that hands off to you on a GigE
> port rather than pay for all the various higher spec equipment that
> you'd otherwise require?
>
> Paul.

Yes, a carrier provided lit service (wavelength, EoMPLS) would
obviously be less expensive than leasing dark for a single 1GE channel
(especially for longer spans), but I'm assuming OP has already
considered this and is going with a dark fiber option for one of the
following reasons:

A) Expected rapid growth in transfer volume, wherein a dark fiber
solution provides the OP with the flexibility to rapidly upgrade to
either a multi-channel xWDM 1GE, single channel 10GE, or xWDM 10GE
solution immediately, as opposed to a lit solution where he would be
restricted by the provisioning time line of the carrier (dark quickly
becomes a more attractive solution than lit services as bandwidth
needs increase)

B) Specific business requirements (ie security concerns) that preclude
the usage of 3rd party's network/transmission gear from carrying
traffic deemed 'sensitive', 'confidential', etc. You fill in the
blanks. The idea is laughable to many operators, but sometimes a
board's ideal model of data security is not exactly in line with
business and technical realities (Usually this means money in your
pocket).

-- 
Cheers,
Kevin

 :: :: Kevin Hodle | http://www.linkedin.com/in/kevinhodle
 PGP Key ID  | fingerprint
 0x803F24BE  | 1094 FB06 837F 2FAB C86B E4BE 4680 3679 803F 24BE

"Elegance is not a dispensable luxury but a factor that decides
between success and failure. "
-Edsgar Dijkstra

RE: dark fiber and sfp distance limitations

[Martin, Paul]

If you only want 1gig, then if the SP provides it, won't it be cheaper
to simply get a 1gig circuit from them that hands off to you on a GigE
port rather than pay for all the various higher spec equipment that
you'd otherwise require?

Paul.



-Original Message-
From: Kevin Hodle [mailto:kevin.ho...@gmail.com] 
Sent: 02 January 2010 23:36
To: Mike
Cc: nanog@nanog.org
Subject: Re: dark fiber and sfp distance limitations

On Fri, Jan 1, 2010 at 4:52 PM, Mike 
wrote:
> I am looking at the possibility of leasing a ~70 mile run of fiber. I
don't
> have access to any mid point section for regeneration purposes, and so
I am
> wondering what the chances that a 120km rated SFP would be able to
light the
> path and provide stable connectivity. There are a lot of unknowns
including
> # of splices, condition of the cable, or the actual dispersion index
or
> other properties (until we actually get closer to leasing it). Its
spare
> telco fibers in the same cable binder they are using interoffice
transport,
> but there are regen huts along the way so it works for them but may
not for
> us, and 'finding out' is potentially expensive. How would someone
> experienced go about determining the feasibillity of this concept and
what
> options might there be? Replies online or off would be appreciated.

I second the recommendation that you request OTDR traces from whomever
you are leasing the glass from, and further request traces for each
strand in *both* directions (a end to z end, z end to a end) at
multiple wavelengths, say 1530nm-1640nm at a maximum of 200GHz
wavelength spacing  to properly identify potential problem locations
in the future when you want to build out a  10GE metro DWDM solution
(You really do want to know about that old mechanical splice 20km into
your run, etc). An OTDR will provide you with granular loss/gain event
details for your entire span, while a power meter/light source will
only tell you your overall span loss.  While your fiber provider may
not pony up OTDR results until after you've executed the contract,
they should be able to give you a rough estimate of the total loss (in
dB for a 1550nm signal) for the span you are looking at leasing, and
you can build provisions into your contract that enforce an absolute
maximum loss on the span, in which case the provider will be forced to
take necessary actions to replace old poorly executed splices with
fusion splices, isolate and correct bends, etc. As most have pointed
out - EDFA should not be required for a 1GE single channel solution,
and probably would not be required for a simple 1GE CWDM setup either.
Once you graduate to an active 10GE DWDM solution EDFA's will be more
of a necessity (possibly with dispersion compensation, depending on
your vendor this may be an entirely separate shelf module or may be
build into the amp card). The addition of EDFA's in a multi-channel
solution also adds complexity (if you want to build a scalable/cost
effective solution). Most EDFA's have a maximum and minimum
per-channel input power, and ideally you would want to have each
channel near the same power level before hitting the EDFA. Depending
on your gear, topological complexity, etc this may require the use of
an optical spectrum analyzer to verify individual channel power levels
so the correct amount of attenuation can be added to each channel
before it hits the EDFA, however for a single point to point span this
will probably not be a concern.


-- 
Cheers,
Kevin

 Kevin Hodle | http://www.linkedin.com/in/kevinhodle

 PGP Key ID  | fingerprint
 0x803F24BE  | 1094 FB06 837F 2FAB C86B E4BE 4680 3679 803F 24BE

"Elegance is not a dispensable luxury but a factor that decides
between success and failure. "
-Edsgar Dijkstra




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Re: dark fiber and sfp distance limitations

[Kevin Hodle]

On Fri, Jan 1, 2010 at 4:52 PM, Mike  wrote:
> I am looking at the possibility of leasing a ~70 mile run of fiber. I don't
> have access to any mid point section for regeneration purposes, and so I am
> wondering what the chances that a 120km rated SFP would be able to light the
> path and provide stable connectivity. There are a lot of unknowns including
> # of splices, condition of the cable, or the actual dispersion index or
> other properties (until we actually get closer to leasing it). Its spare
> telco fibers in the same cable binder they are using interoffice transport,
> but there are regen huts along the way so it works for them but may not for
> us, and 'finding out' is potentially expensive. How would someone
> experienced go about determining the feasibillity of this concept and what
> options might there be? Replies online or off would be appreciated.

I second the recommendation that you request OTDR traces from whomever
you are leasing the glass from, and further request traces for each
strand in *both* directions (a end to z end, z end to a end) at
multiple wavelengths, say 1530nm-1640nm at a maximum of 200GHz
wavelength spacing  to properly identify potential problem locations
in the future when you want to build out a  10GE metro DWDM solution
(You really do want to know about that old mechanical splice 20km into
your run, etc). An OTDR will provide you with granular loss/gain event
details for your entire span, while a power meter/light source will
only tell you your overall span loss.  While your fiber provider may
not pony up OTDR results until after you've executed the contract,
they should be able to give you a rough estimate of the total loss (in
dB for a 1550nm signal) for the span you are looking at leasing, and
you can build provisions into your contract that enforce an absolute
maximum loss on the span, in which case the provider will be forced to
take necessary actions to replace old poorly executed splices with
fusion splices, isolate and correct bends, etc. As most have pointed
out - EDFA should not be required for a 1GE single channel solution,
and probably would not be required for a simple 1GE CWDM setup either.
Once you graduate to an active 10GE DWDM solution EDFA's will be more
of a necessity (possibly with dispersion compensation, depending on
your vendor this may be an entirely separate shelf module or may be
build into the amp card). The addition of EDFA's in a multi-channel
solution also adds complexity (if you want to build a scalable/cost
effective solution). Most EDFA's have a maximum and minimum
per-channel input power, and ideally you would want to have each
channel near the same power level before hitting the EDFA. Depending
on your gear, topological complexity, etc this may require the use of
an optical spectrum analyzer to verify individual channel power levels
so the correct amount of attenuation can be added to each channel
before it hits the EDFA, however for a single point to point span this
will probably not be a concern.


-- 
Cheers,
Kevin

 Kevin Hodle | http://www.linkedin.com/in/kevinhodle

 PGP Key ID  | fingerprint
 0x803F24BE  | 1094 FB06 837F 2FAB C86B E4BE 4680 3679 803F 24BE

"Elegance is not a dispensable luxury but a factor that decides
between success and failure. "
-Edsgar Dijkstra

Re: dark fiber and sfp distance limitations

[Mikael Abrahamsson]

On Sat, 2 Jan 2010, Justin M. Streiner wrote:

Some OTDRs (or, more correctly, fiber test sets that include OTDR 
capabilities) are multi-function devices that will show you the overall 
length (assuming the span is not broken somewhere in the middle), of the 
span, plus attenuation and reflections (spikes) at your desired wavelength in 
one complete package.


Well, that I can understand, what I can't understand is why someone would 
*ONLY* do OTDR. Attenuation testing end-to-end (as opposed to classic OTDR 
that do the testing from single end) is needed for accurate measurements, 
and if it shows something strange, then it's warranted to break out the 
OTDR. If your equipment can do both in one go, fine.


I'm a big believer in running my own tests when possible, and not just 
relying on $provider's word.  It also allows me to verify what their 
engineering reports tell me about the condition of a span.


I guess it's all a matter of how much effort you want to put into 
provisioning. Personally I'm happy enough if the DOM readings (indicating 
attenuation) on the optics seem reasonable considering the distance of the 
fiber. If they seem strange, then yes, by all means, break out the testing 
kit.


--
Mikael Abrahamssonemail: swm...@swm.pp.se

Re: dark fiber and sfp distance limitations

[Nick Hilliard]

On 02/01/2010 18:37, Justin M. Streiner wrote:
> I'm a big believer in running my own tests when possible, and not just
> relying on $provider's word.  It also allows me to verify what their
> engineering reports tell me about the condition of a span.

+1

There's nothing like having hard data to shove in front of the noses of
connectivity providers (whether colo / cross-connect or metro dark fibre
providers) when unexplained problems suddenly start happening for no
apparent reason.  "This is what it was like before and this is what it's
like now, and this ledge here shows that the problem is on a segment that
you manage. Please explain".

Nick

Re: dark fiber and sfp distance limitations

[Justin M. Streiner]

On Sat, 2 Jan 2010, Mikael Abrahamsson wrote:


On Fri, 1 Jan 2010, Justin M. Streiner wrote:


 The first thing you need to do is test the fiber with an OTDR.  If you
 don't have one, you can probably contract a local cabling company to test
 it for you.


Why would you want an OTDR report on the fiber, when an attenuation report is 
probably more accurate? OTDR is good for locating WHERE a problem is, but if 
you're seeing .2 dB/km attenuation end-to-end, there is little reason to 
break out the OTDR.


Some OTDRs (or, more correctly, fiber test sets that include OTDR 
capabilities) are multi-function devices that will show you the overall 
length (assuming the span is not broken somewhere in the middle), 
of the span, plus attenuation and reflections (spikes) at your desired 
wavelength in one complete package.


I'm a big believer in running my own tests when possible, and not just 
relying on $provider's word.  It also allows me to verify what their 
engineering reports tell me about the condition of a span.


jms

Re: dark fiber and sfp distance limitations

[Michael K. Smith]

On 1/2/10 2:58 AM, "Mikael Abrahamsson"  wrote:

> On Fri, 1 Jan 2010, Justin M. Streiner wrote:
> 
>> The first thing you need to do is test the fiber with an OTDR.  If you
>> don't have one, you can probably contract a local cabling company to
>> test it for you.
> 
> Why would you want an OTDR report on the fiber, when an attenuation report
> is probably more accurate? OTDR is good for locating WHERE a problem is,
> but if you're seeing .2 dB/km attenuation end-to-end, there is little
> reason to break out the OTDR.

If I was of the opinion that the telco in the original message would act
upon output data to clean up fibers/jumpers/splices, then the OTDR is the
way to go because you can show them exactly where the issues are in the
entire length of fiber.

If the telco isn't going to make any modifications then an optical power
meter would probably be sufficient.  Either you can hit the distance in your
loss budget or not.

Mike

RE: dark fiber and sfp distance limitations

[Carlos Alcantar]

In my experience in leasing dark fiber strands over long distance the
providers usually give the option for regen colo space.  And in some
cases they wanted to know full specs of the equipment you are going to
be using so there is no questions if it will work or not.


Carlos Alcantar
Race Telecommunications, Inc.
101 Haskins Way
South San Francisco, CA 94080
P: 650.649.3550 x143
F: 650.649.3551
E: car...@race.com



-Original Message-
From: Mike [mailto:mike-na...@tiedyenetworks.com] 
Sent: Friday, January 01, 2010 2:53 PM
To: nanog@nanog.org
Subject: dark fiber and sfp distance limitations

I am looking at the possibility of leasing a ~70 mile run of fiber. I 
don't have access to any mid point section for regeneration purposes, 
and so I am wondering what the chances that a 120km rated SFP would be 
able to light the path and provide stable connectivity. There are a lot 
of unknowns including # of splices, condition of the cable, or the 
actual dispersion index or other properties (until we actually get 
closer to leasing it). Its spare telco fibers in the same cable binder 
they are using interoffice transport, but there are regen huts along the

way so it works for them but may not for us, and 'finding out' is 
potentially expensive. How would someone experienced go about 
determining the feasibillity of this concept and what options might 
there be? Replies online or off would be appreciated.

Thanks.

Re: dark fiber and sfp distance limitations

[Rene Avi]

On 02.01.2010 13:22, Richard A Steenbergen wrote:

On Sat, Jan 02, 2010 at 12:35:15PM +0100, Rene Avi wrote:

With regards to suggested EDFA amplification tricks and similar: If
the requirement is not > 15...@1g or 8...@10g/DWDM then I personally
strongly disencourage the use of optical amps. 200km / 41dB 1G SFPs
are available with costs way below dual EDFAs plus spare, and the
chance for the untrained to get eye damages in the process of
implementation is far less. So put some laser googles at around 400
USD/each to the purchase list. If one decides to do so then add a
post-amplifier on each *end* of the fiber link to increase the signal
before hitting the receiver, and do not pump in star-wars class laser
power at the beginning ;) .


Depends where you buy your EDFAs, I suspect you could probably get them
for less than the cost of a single channel of super long reach optics if
you tried hard enough. 


Respectfully disagree here - been there (googled^H^Hmarket research, 
talked to both manufactures and resellers for the last year), bought 
sample and went through lab tests. Still was unable to find 
trustful/working EDFAs near the cost of a pair of 40dB SFPs. 200km SFPs 
are even cheaper than 'original' Cisco CWDM-SFPs (standard 80km). We 
have them on stock for resale (no commercials intended here), so this 
price indication is near real-time ;)



If you needed to add DWDM later on, and/or
dispersion compensation for 10G links the EDFAs will be needed anyways,
so sometimes it just makes sense to solve the problem once with an amp
rather than trying to solve it on a per-channel basis.


It depends on the requirement - of course.

When Mike is heading for 10G DWDM demand levels he will probably have to 
amplify and cromatic-disperse-compensate with 120km G.652 (depending on 
the transceiver type) in any case. There are plenty of commercial 
solutions available for such spans, or he can try a building-block 
approach.


My point is to skip EDFAs in a single 1G 120km fiber setup for 
commercial aspects, let alone technical reasons (complexity, safety), if 
there is no requirement for more bandwidth. IMHO even with multiple 1G 
CWDM-style setups, but your mileage may of course vary.



You're also vastly exagerating the power of what are effectively metro
reach amps, you're really in no danger of making an eye hazard unless
you start slapping on ultra long-haul 1500+km transport gear with class
3B lasers 


In Mikes scenario this might be as a +10dB pre-amp would do the trick 
with low power, but a post-amp (+17dB gain with levels around 
-20..-30dBm to get some additional power budget) is what I would use if 
EDFAs are a stringent requirement.


Most new long-haul transport systems have an automatic power-off feature 
 for optical protection (e.g.the splice teams after a fiber 
cut/disconnect) now because of this.


> (i.e. you're in far more danger from someone with a green
laser pointer ordered from the Internet :P). 


Agreed, but failed to save the whales - 
http://www.youtube.com/watch?v=Tuxf2xJ08Cc



Remember that 1550nm is
infrared and very effectively filtered by the human eye, so even a
+17dBm output EDFA (the max output for most metro systems) is still
going to be class 1M and effectively safe as long as you don't stare at
it in a microscope.


Or stare in the beam at 500mW/27dBm without noticing because it is 
infrared, and there is no eyelid closure reflex. I tend not to take 
chances for my colleagues and me but as common knowledge says it is 
everyones own decision to look into the laser with the remaining good eye.


Cheers,
--
Rene Avi

next layer Telekommunikationsdienstleistungs- und Beratungs GmbH
Mariahilfer Guertel 37/7 | A-1150 Wien |  FB 257486g |  HG  Wien
tel: +43 664 31764 00 | fax: +43 517649  | web: www.nextlayer.at
my layers: Fiber/Metro | D/CWDM | Cisco | Juniper | I/BGP | MPLS

Re: dark fiber and sfp distance limitations

[Richard A Steenbergen]

On Sat, Jan 02, 2010 at 12:35:15PM +0100, Rene Avi wrote:
> With regards to suggested EDFA amplification tricks and similar: If
> the requirement is not > 15...@1g or 8...@10g/DWDM then I personally
> strongly disencourage the use of optical amps. 200km / 41dB 1G SFPs
> are available with costs way below dual EDFAs plus spare, and the
> chance for the untrained to get eye damages in the process of
> implementation is far less. So put some laser googles at around 400
> USD/each to the purchase list. If one decides to do so then add a
> post-amplifier on each *end* of the fiber link to increase the signal
> before hitting the receiver, and do not pump in star-wars class laser
> power at the beginning ;) .

Depends where you buy your EDFAs, I suspect you could probably get them
for less than the cost of a single channel of super long reach optics if
you tried hard enough. If you needed to add DWDM later on, and/or
dispersion compensation for 10G links the EDFAs will be needed anyways,
so sometimes it just makes sense to solve the problem once with an amp
rather than trying to solve it on a per-channel basis.

You're also vastly exagerating the power of what are effectively metro
reach amps, you're really in no danger of making an eye hazard unless
you start slapping on ultra long-haul 1500+km transport gear with class
3B lasers (i.e. you're in far more danger from someone with a green
laser pointer ordered from the Internet :P). Remember that 1550nm is
infrared and very effectively filtered by the human eye, so even a
+17dBm output EDFA (the max output for most metro systems) is still
going to be class 1M and effectively safe as long as you don't stare at
it in a microscope.

-- 
Richard A Steenbergenhttp://www.e-gerbil.net/ras
GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC)

Re: dark fiber and sfp distance limitations

[Rene Avi]

On 02.01.2010 02:10, William Herrin wrote:

On Fri, Jan 1, 2010 at 7:24 PM, ML  wrote:

Pardon my ignorance in this area but is too much to ask for OTDR data before
signing contracts?  In addition to data on the make of the fiber if you
wanted to do xWDM in the future.


Yes, it's too much to ask. They won't splice your path until you sign
the contracts and you can't get useful OTDR and loss readings until
the fiber is spliced.


In my experience the fiber splice/patch-teams have quite accurate 
estimations on the overall attenuation of unprovisioned paths. They know 
the distance (0.25dB/km for G.652 @ 1550nm), the number of connectors 
(0.35dB per plug average here) and splices (0.1dB/spice). YMMV though. 
We add +20% safety, include an escape clause wherever possible and cross 
our fingers.


With regards to suggested EDFA amplification tricks and similar: If the 
requirement is not > 15...@1g or 8...@10g/DWDM then I personally 
strongly disencourage the use of optical amps. 200km / 41dB 1G SFPs are 
available with costs way below dual EDFAs plus spare, and the chance for 
the untrained to get eye damages in the process of implementation is far 
less. So put some laser googles at around 400 USD/each to the purchase 
list. If one decides to do so then add a post-amplifier on each *end* of 
the fiber link to increase the signal before hitting the receiver, and 
do not pump in star-wars class laser power at the beginning ;) .


Cheers,
--
Rene Avi

next layer Telekommunikationsdienstleistungs- und Beratungs GmbH
Mariahilfer Guertel 37/7 | A-1150 Wien |  FB 257486g |  HG  Wien
tel: +43 664 31764 00 | fax: +43 517649  | web: www.nextlayer.at
my layers: Fiber/Metro | D/CWDM | Cisco | Juniper | I/BGP | MPLS

Re: dark fiber and sfp distance limitations

[Mikael Abrahamsson]

On Fri, 1 Jan 2010, Justin M. Streiner wrote:

The first thing you need to do is test the fiber with an OTDR.  If you 
don't have one, you can probably contract a local cabling company to 
test it for you.


Why would you want an OTDR report on the fiber, when an attenuation report 
is probably more accurate? OTDR is good for locating WHERE a problem is, 
but if you're seeing .2 dB/km attenuation end-to-end, there is little 
reason to break out the OTDR.


Also, for 1G there is little reason to worry about dispersion mentioned in 
the thread, receive power is basically the only thing to worry about.


--
Mikael Abrahamssonemail: swm...@swm.pp.se

Re: dark fiber and sfp distance limitations

[Nick Hilliard]

On 02/01/2010 00:24, ML wrote:
> Pardon my ignorance in this area but is too much to ask for OTDR data
> before signing contracts?  In addition to data on the make of the fiber
> if you wanted to do xWDM in the future.

fibre grade / quality, absolutely.  otdr is difficult, because fibre
providers usually splice up a specific path for a specific order.  This
means that they cannot always provide the otdr without first going to some
trouble and expense.  So you may find yourself having to specify acceptable
attenuation limits in advance, then putting in an order and then getting
the otdr + accurate attenuation results after the order has been accepted.
Obviously, you assume some risk in terms of hoping that the optics that you
buy for the circuit will actually do the job.

Nick

Re: dark fiber and sfp distance limitations

[William Herrin]

On Fri, Jan 1, 2010 at 7:24 PM, ML  wrote:
> Pardon my ignorance in this area but is too much to ask for OTDR data before
> signing contracts?  In addition to data on the make of the fiber if you
> wanted to do xWDM in the future.

Yes, it's too much to ask. They won't splice your path until you sign
the contracts and you can't get useful OTDR and loss readings until
the fiber is spliced.

You can probably put an escape clause in the contract that lets you
exit with little or no cost if the readings aren't good enough after
the fact. If you're not time-constrained, you can probably request a
pre-check for a modest fee after main splicing but before trenching to
your endpoints.

Regards,
Bill Herrin

-- 
William D. Herrin  her...@dirtside.com  b...@herrin.us
3005 Crane Dr. .. Web: 
Falls Church, VA 22042-3004

Re: dark fiber and sfp distance limitations

[ML]

On 1/1/2010 5:52 PM, Mike wrote:

I am looking at the possibility of leasing a ~70 mile run of fiber. I
don't have access to any mid point section for regeneration purposes,
and so I am wondering what the chances that a 120km rated SFP would be
able to light the path and provide stable connectivity. There are a lot
of unknowns including # of splices, condition of the cable, or the
actual dispersion index or other properties (until we actually get
closer to leasing it). Its spare telco fibers in the same cable binder
they are using interoffice transport, but there are regen huts along the
way so it works for them but may not for us, and 'finding out' is
potentially expensive. How would someone experienced go about
determining the feasibillity of this concept and what options might
there be? Replies online or off would be appreciated.

Thanks.




Pardon my ignorance in this area but is too much to ask for OTDR data 
before signing contracts?  In addition to data on the make of the fiber 
if you wanted to do xWDM in the future.


NDAs shall be signed of course

Re: dark fiber and sfp distance limitations

[Alexander Harrowell]

On Friday 01 January 2010 23:19:30 Richard A Steenbergen wrote:
> On Fri, Jan 01, 2010 at 02:52:33PM -0800, Mike wrote:
> > I am looking at the possibility of leasing a ~70 mile run of fiber. I
> > don't have access to any mid point section for regeneration purposes,
> > and so I am wondering what the chances that a 120km rated SFP would be
> > able to light the path and provide stable connectivity. There are a lot
> > of unknowns including # of splices, condition of the cable, or the
> > actual dispersion index or other properties (until we actually get
> > closer to leasing it). Its spare telco fibers in the same cable binder
> > they are using interoffice transport, but there are regen huts along the
> > way so it works for them but may not for us, and 'finding out' is
> > potentially expensive. How would someone experienced go about
> > determining the feasibillity of this concept and what options might
> > there be? Replies online or off would be appreciated.
>
> That shouldn't be too difficult, especially at only 1G (though pesonally
> I can't imagine why you would bother leasing dark fiber for that :P).
> There are several ways you could do it, including 120km+ rated SFPs
> (iirc there have been 200km SFPs out for a while too), an external
> optical amplifier (ideally you'd want to amp in the middle, but with a
> single channel you should be fine w/pre-amp), and a digital FEC wrapper
> to extend the receive sensitivity. Remember that the distance spec on
> optics is mostly a rough guideline, so depending on the fiber conditions
> and number of splices/panels along the way you could potentially expect
> to get the entire distance out of a "standard" 100km optic.

There was an excellent thread on this list last year about using "unusual" 
high power lasers for long range optical networking.

http://www.merit.edu/mail.archives/nanog/2008-10/msg00226.html


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Re: dark fiber and sfp distance limitations

[Richard A Steenbergen]

On Fri, Jan 01, 2010 at 02:52:33PM -0800, Mike wrote:
> I am looking at the possibility of leasing a ~70 mile run of fiber. I 
> don't have access to any mid point section for regeneration purposes, 
> and so I am wondering what the chances that a 120km rated SFP would be 
> able to light the path and provide stable connectivity. There are a lot 
> of unknowns including # of splices, condition of the cable, or the 
> actual dispersion index or other properties (until we actually get 
> closer to leasing it). Its spare telco fibers in the same cable binder 
> they are using interoffice transport, but there are regen huts along the 
> way so it works for them but may not for us, and 'finding out' is 
> potentially expensive. How would someone experienced go about 
> determining the feasibillity of this concept and what options might 
> there be? Replies online or off would be appreciated.

That shouldn't be too difficult, especially at only 1G (though pesonally
I can't imagine why you would bother leasing dark fiber for that :P). 
There are several ways you could do it, including 120km+ rated SFPs
(iirc there have been 200km SFPs out for a while too), an external
optical amplifier (ideally you'd want to amp in the middle, but with a
single channel you should be fine w/pre-amp), and a digital FEC wrapper
to extend the receive sensitivity. Remember that the distance spec on
optics is mostly a rough guideline, so depending on the fiber conditions
and number of splices/panels along the way you could potentially expect
to get the entire distance out of a "standard" 100km optic.

-- 
Richard A Steenbergenhttp://www.e-gerbil.net/ras
GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC)

Re: dark fiber and sfp distance limitations

[Justin M. Streiner]

On Fri, 1 Jan 2010, Mike wrote:

I am looking at the possibility of leasing a ~70 mile run of fiber. I don't 
have access to any mid point section for regeneration purposes, and so I am 
wondering what the chances that a 120km rated SFP would be able to light the 
path and provide stable connectivity. There are a lot of unknowns including # 
of splices, condition of the cable, or the actual dispersion index or other 
properties (until we actually get closer to leasing it). Its spare telco 
fibers in the same cable binder they are using interoffice transport, but 
there are regen huts along the way so it works for them but may not for us, 
and 'finding out' is potentially expensive. How would someone experienced go 
about determining the feasibillity of this concept and what options might 
there be? Replies online or off would be appreciated.


The first thing you need to do is test the fiber with an OTDR.  If you 
don't have one, you can probably contract a local cabling company to test 
it for you.


How do you plan to drive transport over the fiber?  GE?  10G?  >10G? 
CWDM?  DWDM?


To drive a signal that far without a regen somewhere in the middle, your 
best bet might be something in the xWDM space, and then you can provision 
labmdas for GE, 10G, etc...  There are boxes out there (Ciena, Infinera, 
Cisco ONS, etc) that can do this.


How do you plan to handle responses to fiber cuts, signal degradation, 
someone at $telco unplugging the wrong jumper, etc?


jms