Fiber optics cabling/connector/module options

I have several rudimentary questions about fiber optics cabling & connectors. I understand the basics of MMF and SMF, and the distance factors of each for different BW ratings.  I'll ask a series of questions, and hopefully gain a better "big picture" understanding of things I still get hung up on (when having to choose optics and connector options for Cisco gear):

- Do the connector types have to match on each end of a fiber cable? For example, if a module on one end of a MMF link is using LC connectors, does the other module also have to use LC?

- Similar to the above - if I have a fiber cable w/ existing SC connectors on both ends, can I safely add SC->LC patch cables to both ends (or just to one end) to plug into LC modules?

- If I have an LC->LC length of MMF, can I safely add an LC->LC patch cable to extend its distance (for example, to reach a relocated data center beyond the original termination point)?

- What exactly is the purpose of having a fiber patch panel in-between the endpoints (or at both ends - in both locations fronting the actual equipment)?  Does this buy me flexibility in what types of connectors/modules I use at each end?

- example: a customer has a Cisco 2900XL switch with a fiber module (see attached - these look like LC connectors - plus, it reads 100Base-FX above ports 23 & 24), and it hooks into the displayed patch panel.  On the OTHER end, the customer has a 2960G switch w/ SFP ports.  If I had to choose an optics module for this unit (specifically, a WS-C2960G-24TC-L), what would be a compatible module?

I'll award points for clear answers to all of the above, OR TO A SOLID REFERENCE GUIDE that covers all of this. If I could award more than 500, I would - this is a lot of questions, I know.

Thanks in advance.


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cardsfan73Asked:
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packetguyCommented:
Here is a great overall reference: http://www.thefoa.org/
I'm also providing specific answers to your questions:

- Do the connector types have to match on each end of a fiber cable? For example, if a module on one end of a MMF link is using LC connectors, does the other module also have to use LC?
A. No, they don't have to match. The connectors exist for different purposes. Traditionally round ST connectors were used on infrastructure patch panels, because they let you switch one side of a pair to a single backup fiber in case a strand went bad. But on equipment, square SC (and later the tiny LC) were used to achieve high port density in limited rack space. However, the data rates of the devices at each end DO have to match. So 100BaseFX must go to 100BaseFX, and 1000BaseFX to 1000BaseFX.

- Similar to the above - if I have a fiber cable w/ existing SC connectors on both ends, can I safely add SC->LC patch cables to both ends (or just to one end) to plug into LC modules?
A. Yes, that's very common. You can go from any connector to any connector via adapter patch cables: SC/LC, ST/SC, or ST/LC.


- If I have an LC->LC length of MMF, can I safely add an LC->LC patch cable to extend its distance (for example, to reach a relocated data center beyond the original termination point)?
A. It depends on the distance. Every fiber run has a "loss budget", which is the maximum dB loss the signal can sustain and still be usable. Fiber itself has a loss per foot, and connectors and splices of various kinds also add attenuation, or loss. You can calculate the loss during network design, following procedures such as those outlined here: http://www.thefoa.org/tech/lossbudg.htm.  Or on installed fiber you can connect a calibrated laser source on one end and measure the loss at the far end using a fiber light meter.

- What exactly is the purpose of having a fiber patch panel in-between the endpoints (or at both ends - in both locations fronting the actual equipment)?  Does this buy me flexibility in what types of connectors/modules I use at each end?
A. This practice is part of the Structured Cabling concept, which applies to copper as well. Patch panels give you a test point for validating the fiber or copper run, but let you use replaceable patch cables for the frequently manhandled connections between panel and equipment. It's a lot easier to replace a patch cable than to reterminate a fiber or copper drop. This also gives you more flexibility in cable management, via cable raceways and patch panel trays -- especially with fiber, which is more fragile than copper. Structural fiber also comes in multi-fiber cables of 12, 48, or 128 strands, and the patch panel provides a place to break out those strands to stable connectors, which buffer the delicate bulk fiber from the manual interconnect environment. Fiber patch cables, which have sturdy outer sheaths and strain relief boots, take the abuse of plug and unplug between panel and device.

- example: a customer has a Cisco 2900XL switch with a fiber module (see attached - these look like LC connectors - plus, it reads 100Base-FX above ports 23 & 24), and it hooks into the displayed patch panel.  On the OTHER end, the customer has a 2960G switch w/ SFP ports.  If I had to choose an optics module for this unit (specifically, a WS-C2960G-24TC-L), what would be a compatible module?
A. The 2900XL uses SC connectors, which is very common for 100BaseT fiber. The 2960G has GigE fiber ports -- 1000BaseFX -- using LC connectors. The optical signal will have no problem going from SC over the structured fiber to an LC connector at the far end, but the devices don't have compatible interfaces, and won't be able to communicate. Fiber doesn't do "auto negotiation" like copper does. A GBIC or SFP module is always 1000BaseFX, and the modules are also either single or multimode, and can be short- or long-haul.

Be careful around singlemode fiber -- the energy in these lasers can damage your vision, and the damage often doesn't become apparent for days. Most devices have a red "warning" LED inside the transmit side of a connector to let you know when it's energized, but not all do. And that warning doesn't travel down the fiber -- the other end can be hot but invisible. If you work around SM fiber, invest in a set of protective goggles (about $100).
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luc_roySystem AdminCommented:
you are on the money "packetguy:"

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cardsfan73Author Commented:
Really an awesome response, packetguy - thank you. I'm awarding full points, but could I bounce one more follow-up question off of you?

Regarding the aforementioned C2960 switch, it looks like there is an SFP 100Base-FX module (GLC-GE-100FX=) available (which uses LC connectors). Based on your other responses, can I assume this module would work in the 2960 for the other end of this connection, as long as I put an LC->SC patch cable in there?

Thanks again for the detail you provided above - exactly what I was looking for, and I'll check out the links you referenced.
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cardsfan73Author Commented:
Excellent
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packetguyCommented:
Yes, you can use that module. It's designed for transitioning networks from 100 Gbps to 1000 Gbps. This part is widely available on ebay for under $200. But for not much more you could buy a refurbished Cisco 2950G-24 switch and a couple of GBIC modules and run the fibre link at full GigE speeds. It all depends on how much bandwidth you need between the sites. Whenever buying used Cisco gear on ebay, I always go with a company that offers a one-year warranty, because the time spent dealing with duds is just too expensive.
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cardsfan73Author Commented:
Excellent - thank you again, very much.
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