Terminology

There are a lot of terms and acronyms used when talking about Fiber optics, Broadband and E-rate. This page explains the terminology in clear and straight forward language. If you have come across a term not defined here, please let me know.

Fiber – A fiber optic cable is a very thin strand of cable made from glass. For example, imagine a thin piece of string made of glass. The glass cable is covered with an extremely thin plastic covering. When you purchase a fiber optic cable you don’t just buy one strand, you buy multiple strands of glass, for example, 12, 24, 48, 72, 96, 144, 288 or higher. Each fiber optic strand transmits data by pulsing light. There is a piece of electronics at one end of the strand that pulses light. The light passes through the cable and is received by electronics at the other end of the strand.

By pulsing light on and off data in the form of 1’s and 0’s is transmitted from one end of the strand to the other. This is the means by which data is transmitted from one location to another. When you access the internet you are transferring data to and from the internet. With a fiber optic strand you are able to transmit data incredibly fast, this means the pulsing of the light occurs at a high rate. This ability to transmit data fast means you don’t need to wait as long to download web pages, or when you have a video conversation with somebody, you will receive better quality video.

Funding Year – in E-rate the term “funding year” is used a lot. What does this mean ? Funding year 2015 means the year from July 1st 2015 to June 30th 2016. Funding year 2016 means from July 1st 2016 to June 30th 2017. Schools now should be preparing for funding year 2017, especially if they are interested in either building their own network or purchasing dark fiber. For funding year 2017, USAC will start supporting eligible services with funds from July 1st 2017. However, prior to July 1st 2017 the school needs to have issued a competitive bid for the services it needs and then selected a service provider. The school needs to inform USAC of the service provider selection and the funds the school is requesting all prior to the USAC deadline, which is typically mid March. The competitive bid process is started when the school issues a form 470 with an RFP. Once the school chooses a vendor, the school submits a form 471 that states the service provider / vendor chosen and the funds requested. This form 471 has to be competed and submitted typically by Mid March. Applicants can submit their form 470 from July 1st for the following funding year. Most applicants will submit a form 470 from October – early February. By October, the E-rate eligible services list is usually available and the updated form 470 for the funding year is also usually available.

Dark Fiber – Dark fiber is a fiber optic strand that does not yet have the electronics on either end to send pulses of light, i.e. to send data. It’s a term used to mean that fiber has not yet been lit – lit means that you have put electronics on either end of the fiber to send pulses of light down the fiber. Dark fiber is a term typically used when you buy or sell fiber. For example, lets say you have constructed a three mile fiber network from your school district head office building to your middle school. And when I say ‘constructed’ I mean you have engaged contractors to dig up the side walk, or side of the road and bury fiber optic cable in the ground. You will now have (assuming you used 144 strand cable), a fiber optic cable of 144 strands from the school district building to the middle school. You may use two of the strands to transmit data from the district building to the middle school. This leaves 142 unused strands. These unused strands, that don’t have any pulsing of light going down them, would be known by the term “Dark Fiber”, i.e. the fiber is dark, and has not been lit. You could sell this fiber. Somebody may say to you “I am interested in buying 4 strands of dark fiber” in which case you would respond with “Certainly, I have dark fiber available for you to buy”.

Lit Fiber – Lit fiber is fiber optic cable that has been “lit” by placing electronics at either end of the fiber. The electronics pulse light down the cable, thus meaning that data is transmitted from one end of the cable to the other. You would not typically purchase “lit fiber” but rather, purchase lit services. If a service provider ‘lights’ fiber optic cable, they may sell to you access to the Internet at 10Mb/s. If you purchase access to the Internet at 10Mb/s for $50/month, you have purchased a ‘lit service’. If you were to buy dark fiber from a service provider you may say “I have purchased dark fiber from my local provider and I will now light the fiber to provide a connection from my school district building to my middle school. ” These examples are where this term would come into play. Remember, you would typically not buy ‘lit fiber’ from your service provider, but rather a lit service. I’ve tried to explain here how the term is used in the industry, but if you have any questions on this let me know.

Strands – People may use interchangeably the terms ‘strand’ and ‘cable’. Typically though, a fiber optic cable is made up of multiple strands of fiber. As explained in the definition of ‘Fiber’ when you buy a fiber optic cable, you will buy a bundle of fiber optic strands, with each strand having the ability to transmit data. If you wanted to buy fiber from your elementary school to your middle school, you may ask your service provider if they will sell you 2 strands of dark fiber. You are specifying you want 2 distinct strands of fiber that will be dedicated to the connection between the elementary school and the middle school. When you are buying dark fiber, you will need to specify how many strands you want to buy. Most likely, your purchase of dark fiber for connectivity will require the purchase of 2 or 4 strands. If you were to construct a network from your elementary school to your middle school, you may specify to your contractor that you want to install 144 strand fiber optic cable. When I say construct, I mean you engage contractors to bury the cable from the elementary school to the middle school. When you are constructing your own fiber optic network I recommend you install as many strands as you can, to allow for future growth of your network. If you were to compare the cost of constructing a 12 strand network from the elementary school to the middle school versus a 144 strand network the incremental cost to install the additional strands (strand 13 to strand 144) is minimal when compared to the total cost of network construction. For example, the labor required to dig up the road, the machinery required etc.. is all the same, whether you are deploying a 12 strand network or a 144 strand network. It’s much better to lay down plenty of strands the first time you construct, versus coming back later and increasing the strand count of the network.

IRU – IRU means Indefeasible Right of Use. It is a term used when you purchase dark fiber. It basically means you have a strong form of ownership of the dark fiber you have purchased. It is a stronger form of ownership than a lease. However, it is critical that you have a IRU contract that spells out, within the body of the contract, the form of ownership you have. IRU is a somewhat ambiguous term, and thus, the contract should spell out exactly the form of ownership you require.