Install single mode or multi mode?

[tim.clark1]

I am replacing existing infrastructure components.  There currently is no fiber in place.  There will be a WS-C3750X-12S-E switch in the data center and WS-C29060S-48LPS-L switches at the IDF's.  There are 5 IDF's.  Since we are starting from scratch on the fiber, should we go with single mode to be ready for future speeds in excess of 10G?  Distance is not an issue.  The closest IDF is approx. 65 feet away, and the furthest away is approx. 600 feet.  Is there a minimum distance with single mode we should be concerned with?  I keep seeing some info about attenuators needed for some applications, etc.

[Leo Laohoo]

Single-mode optics are DOUBLE the price of multi-mode optics.  

If the distance between the two IDF is only 65 feet, then putting multi-mode fibre (OM3 or OM4) between the two makes sense.  For future proofing, you want OM4.  

Another thing, if you are, for example, cabled the two IDF with OM4, make sure the patch cable is also OM4.  Fibre optics transmission is not something you want to skimp on.  :)

[Marvin Rhoads]

I agree with Leo's answer. I'd definitely go with OM4 multimode. Besides the added cost (with little or no benefit in your environment), single mode connection points are more susceptible to dirt, dust etc. on the fiber tips and patch panels.

Are you set on the Cat 3750X? I ask because there's now a 3850 all-SFP offering as well. (WS-C3850-12S or -24S).The 3850 is a very nice kit. IP Base or better offers embedded Wireshark among other cool features.

Re your question on single mode attenuation needed over short distances, that's generally only the case if you should need to for some reason end up using -ER (or -ZR) transceivers. Those extended reach and further SFPs have a maximum optical launch power well above the receiver's design specification so it is quite possible you will over-drive and burn out a receiver if you use them in very short runs.

[tim.clark1]

Thanks for your input.  I am not very concerned about the cost of the SFP's at this point since we are only talking about 8 of them.  The equipment that we get in our building we tend to keep (are stuck with - e.g. no fiber at all right now) for at least 10 years.  That is why I am considering single mode fiber - for the future when we want to achieve uplink speeds over 10G and above the limits of multi mode fiber.

The SFP's we would use are the GLC-LH-SMD= so it sounds like attenuators would not be needed no matter what the distance is.

The 3850 switch sounds interesting.  I will look into it and the price difference.

Thanks again.

[Leo Laohoo]

10 years ago, I've heard people say that single-mode will be more efficient in handling 10Gbps/40Gbps but I've always ask them to show proof and they never get back to me.  

Right now, you can push 100 Gbps using multi-mode fibre as well as single-mode fibre.  Currently plans are underway to start developing 25Gbps/50Gbps for SAN ... still using both single-mode and multi-mode.  

The reason why I'm saying this is because you need to be very careful in deciding to use single-mode when you've got a very, very short distance.   I have personally seen the effects when you use MM optics on a SM fibre (and vice versa) and one case of using SM in a very, very short run.

[Marvin Rhoads]

Leo - I had the same arguments made to me 15 years ago when planning a major fiber to the desktop deployment (15,000 users) - but then I'm older. :D

Seriously though: Tim - look at Cisco's recent Bidi technology - 40 Gbps over 150m of 2-strand OM4:

[viyuan700]

"10 years ago, I've heard people say that single-mode will be more efficient in handling 10Gbps/40Gbps "

Hi Leo,

At 10G even an OM4 MMF can have distance of 300-500m whereas on SM it can go upto 2-50Km. If you want to go 2Km can you use MMF even an OM4? Unless we develop OM 5,6,7.... also how many customers have that big offices wich spans in Km.

Take the case here distance is from 65-600 feet away means 20-185 m. For 40G/100G talking about distance of 150m so will this be future proof?

Interesting question can be will the customer would need 40G/100G in next 10 years...

[Leo Laohoo]

Interesting question can be will the customer would need 40G/100G in next 10 years...

10 years????  Depends on the industry.  If you currently using 10 Gbps in your uplink to anywhere from access-to-distro and/or distro-to-core, you'll see the need and want to go to 100 Gbps between now and up to three years.  Some big organization are already implementing 100 Gbps now.  Some organization will not need 10 Gbps /40 Gbps/100 Gbps.  But some do.  Again, it's a case-to-case basis.  

At 10G even an OM4 MMF can have distance of 300-500m whereas on SM it can go upto 2-50Km. If you want to go 2Km can you use MMF even an OM4?

If you have a new build, then yes.  If you've got existing infrastructure, unless you're organization is awash with cash, you don't want to go around upgrading, for example OM3 to OM4, unless you have to.  But that's the point.  Let's say you have dark fibre all over the place (like we do).  Let say the oldest fibre you've got is OM2.  How do you keep proper documentation and standards?  You can't.  Not easily.  I don't care what the new OM4 can do (distance wise).  The problem is no one can remember what type of cable (or where the documentation is located).  In our case, we have to go down to basic common sense.  If it's long range (like beyond 100 metres), stick SM.