Pros/Cons in migrating from OM3 to OM4 (All Meraki setup)

[RWelch]

Currently all SPF+ or SPF modules connect OM3 fiber between MX and MS or MS-to-MS devices.  

Are there any pros/cons if upgrading all OM3 to OM4 fiber (LAN wise or WAN wise)?

Dual WAN uplinks are CAT8 wiring to the business grade fiber boxes.

[PhilipDAth]

When I advise customers about installing new fibre plants, I always recommend OM4 if they can afford it.  Fibre plants can have a lifetime of 25 years.  This will give them the most options over the next 25 years.

If they can't afford OM4, then go with OM3.

Whatever the main fibre plant is - matching patch leads should be used.

[PhilipDAth]

If you check the SFP compatibility guide and search for lines with only OM4 listed, you'll see even with today's technology, it extends the length of the allowable fibre runs.

https://documentation.meraki.com/General_Administration/Cross-Platform_Content/Small-Form_Factor_Plu...

[cmr]

OM4 is definitely the way to go, but don't worry about having to do it all at once, OM3 and OM4 work together without issues.  I started changing over a few years ago and still operate many mixed runs and they have all been reliable.  i.e. OM4 patch, OM3 structured or the other way round.

[cmr]

In the UK OM4 is now pretty much the same cost as OM3, so an easy decision!

[Mloraditch]

When we have clients run new fiber we always say go with single mode. At least from what I see here in the US there is negligible difference in cost for the physical infrastructure.

The official optics are certainly more expensive but if you use third party optics and just a keep a couple of official on hand for process of elimination during support cases it's affordable and then you don't really have to worry about future speed upgrades (at least as the tech currently works)

[PhilipDAth]

If you are using short-range optics (such as for in-building fibre plants) for 10Gbe (like LRM) that you do take a range hit by using single mode.

OM4 multi-mode Example:

OS2 single-mode example:

[GIdenJoe]

Question of course is what do you hope to gain when laying OM4 fibers in place of current OM3.

If it is to have more pairs, or to have different cable runs for redundancy, then sure new fibers should at least be OM4 if using multimode.

But investing tons into replacing fibers if they are perfectly fine and you are running 10 Gbps over no more than 300 meters you will not have any advantage.

Also be aware that higher speeds like 25 Gbps have much different distances depending on the type of technology used in the transceivers.

[RWelch]

OM4 offers up to 40% higher bandwidth, enhanced stability and reliability.  In this upgrade, distance isn't quite a factor as there will be 9 multimode OM4 fiber patch cables replacing the existing OM3 patch cables all under 5 meters in length.  All SFP+ or SFP modules remain the same.  Just looking to maximize throughput and low latency.  OM4 will remain in place for future hardware upgrades.  Will it make any or enough difference going from OM3 to OM4?  We shall see.  OM4 price to upgrade was quite reasonable.  

Thanks for everyone's feedback.

[GIdenJoe]

You are looking at it wrong then.
I don't know how they get the figure of 40% higher bandwidth... because this depends heavily on the type of transceiver you are using and the set speed you have.  The rating of the cable is only a measure of physical properties like minimum bend radius, and loss of dB per amount of distance.  As long as you don't lose x over a certain distance you can safely use these speeds.

You always have to look at fiber this way.
- You want to run a certain speed over a certain distance.  Then looking at the datasheets you will know what kind of transceivers are compatible and what fiber options you have.

For example you will have to run 150 meters fiber and you want 25 Gbps speeds over that: when you look at tmgmatrix.cisco.com you will see what is possible.  For example the SFP-25G-SR-S can support 25G over 70 meters of OM3 or 100 meters over OM4.  So yes there is a difference but in distance.  But if you look a bit further you have the SFP-10/25G-CSR-S which can support 25G over 300 meters OM3 or 400 meters OM4 because the module supports RS-FEC.


So taking the time and effort of just changing your patch cables will not return you any gains in latency or bandwidth.  It will merely gain you a different color of fiber patch cables.

Extra latency comes from the switching process and potential buffering on devices and the main latency on the fiber is merely a function of the speed of light.

[RWelch]

@GIdenJoe thanks for the feedback.  As I mentioned, OM4 remain in place for future hardware upgrades.  Always appreciate the dialogue and expert feedback within the Meraki Community.

[GIdenJoe]

No problem 😉
It makes sense to install the newer type in newer installations which we all do or to replace a broken older cable with a newer one.
I just question replacing a whole bunch if it isn't necessary especially if it are not even fiber runs but local patchpanels.