Friday 13 December, 2019 | RSS Feed

Common Fiber Network Issues

by www.fiber-mart.com

Something that I take a lot of pride in, is the technical support and service that my department provides our customers on a daily basis, free of charge. I always feel a huge sense of satisfaction when the technical department can provide a solution to our customer’s questions. 
Why is my fiber Ethernet link not working?
One common problem many of our customers have come to me with is “Why is my fiber Ethernet link not responding, I even get a link light but I am not getting any transmission of data?”, This old problem raised its ugly head as recently as last week. This reoccurring fiber related issue usually results from speed mismatches between the Ethernet equipment. As we know, Ethernet commonly transmits data at 10 Mbps, 100 Mbps, 1000 Mbps (1 Gig), 10 Gig and now 40 Gig. Both copper and fiber switches exist to support these speeds. As an example, a copper switch that runs at 1000 Mbps will list the port speeds as 10/100/1000. This is because copper can negotiate network speeds, meaning if a 100 Mbps device is plugged into the 10/100/1000 port, the switch can slow down the port to the 100 Mbps speed. This statement is not true when it comes to fiber. A fiber port cannot negotiate its speeds, so in this same situation the fiber equipment MUST be 1000 Mbps on each end. Typically, I see where a 1000 Mbps fiber switch port is plugged into a media converter that is rated for 100 Mbps, or vice versa, this will cause a link failure because of the speed mismatch. The reason fiber Ethernet ports do not negotiate speeds is solely due to light sources. For example, 10 Mbps fiber runs using an 850nm LED light source, 100 Mbps uses a 1300nm LED and 1000 Mbps utilizes a 850nm VCSEL (Vertical Cavity Surface Emitting Laser), so it really comes down to economics. Fiber Ethernet ports that could auto negotiate speeds would have to be built with a minimum of three light sources, theoretically tripling the price of the port. The easiest answer is to just make sure that the fiber port speed and the media converter are an exact match, as in my example from last week, the customer purchased a 1000 Mbps media converter and the problem was solved.
Why does my fusion splicer work better some days than it does on others?
Without a doubt, the single most reoccurring question the technical department receives is related to fusion splicing, or should I say the inconsistent results when splicing a fiber. The conversation always starts with the statement. “Why does my (insert manufacturer here) fusion splicer work very well some days and other days it seems to produce failing results”? One thing I stress when splicing is at a minimum, to perform an Arc Check every time you start the splicer. An arc check is calibrating the splicer against the current environmental conditions. Temperature, relative humidity and barometric pressure all contribute to the performance of a fusion splicer. When turning on a splicer, it will be performing splices according to the last time an arc check was performed. If the environment has changed, bad splices can occur. Bubbles, cracks, high attenuation and broken splices are usually a result of incorrect splice settings and can usually be corrected by running the arc check program.
A few things you need to know when performing an arc check;
• Number one: Always use Singlemode fiber when performing an arc check, even if you are splicing multimode that day, Singlemode must be used.
• Number two: If an arc check results in a NG (No Good), a second arc check must be performed, in fact several may need to be performed, (I am talking to you Denver), you must see an OK before proceeding.
• Number three: If and when you receive a NG message it is important to press the “Optimize” button, this will make the incremental changes to the splice settings.
MPO/MTP Systems – Polarity Matters
The most difficult questions we receive here have to do with the use and implementation of MPO/MTP multi-fiber cables and cassettes. Here at FIS we are constantly training our sales and support staff on the correct methods and polarities associated with these connectors. MPO/MTP connectors usually contain 8, 12, or 24 fibers in a single connection; because of the volume of fibers used, routing the fibers to the correct location can be confusing. MPO/MTP are used for space saving and also for multiple lane transmissions to achieve 40 and 100 Gig (8 fibers used for 40 gig and 20 used for 100 gig). About a month ago, I had a customer that could not get his fibers to the correct destinations using these connectors, and the solution was not easy to come to.
A little back story first; when using MPO/MTP connectors there are typically three polarity options (A, B, and C) A and B are the most commonly used and make up over 90% of our sales. Polarity B is the easiest to implement but cannot be used for Singlemode, let me explain. Polarity B cables install the connectors in a key up to key up configuration, this will flip the fibers so that transmit and receive fibers exit flipped on the other side of the cable, and this is a good thing. Typically, these cables are inserted into rack mountable cassettes that break the fiber out into individual LC connectors.
When using method B for both cables and cassettes, straight through patch cords, that we keep in stock, are used for each transmit/receive pair of LC connectors. This is an ideal situation.
When using method A cassettes and cables, this is a key up to key down solution, the problem is that it the cable does not flip the transmit and receive fibers, meaning the installer has to use standard straight through patch cords with the type A method cassettes on one side but on the opposite side MUST use flipped patch cords. This can be confusing and create installation errors. The reason Singlemode must use the A method is that the ferrules are angled and must mate opposite to each other, whereas multimode are flat ferrules and we do not have to work with an angle.
Now back to my customer’s issues a month ago, they were using method B cables and cassettes so the patch cord issue did not come in to play here. After long conversations we determined that they had installed method A mating sleeves (key up to key down) in the cassettes and not method B (key up to key up) like it should have been. By installing the wrong mating sleeves it flipped the fibers in a way that routed the fibers to the wrong ports.
When choosing a method for MPO/MTP connectors it is important to remember that the cables and the cassettes must be the same polarity/method (A or B) as well as all internal components. It can be frustrating when troubleshooting MPO/MTP issues, but ultimately it takes time to walk through the problem and experience to understand it and give your customer a solution.
It has been said that time is the price we pay for experience and I truly believe it. The FIS technical support staff has truly paid for their expertise and I implore you to take advantage of our 100+ years of combined experience to help you resolve your fiber related questions.  

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