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Different topologies, features and more

Multimode fiber optic vs singlemode fiber optic

First of all we are going to explain to you is that there are two types of optical fiber, we are talking about the so-called fibers multimode and the single mode.

The multimode fibers They are fibers that allow the simultaneous transmission of several beams of light (modes), each beam is reflected at a different angle within the core of the cable. Unlike single-mode optical fibers, multimode optical fibers, in order to allow this, need to have a larger core diameter than the former. Within multimode optical fibers there are two other types that we are just going to mention: they are those with a stepped index, and those with a gradual index. The latter achieve a slightly higher range. Multimode fibers are cheaper to manufacture (compared to single-mode fiber optics) and their range is relatively small (about 10 km) compared to single-mode.

Conversely, singlemode fibers They only allow one mode of transmission. This is achieved by reducing the diameter of the core. It is reduced so much that there are hardly any bounces, the light beam propagates parallel to the axis. Its distance can be up to 400 km, but the cost of its manufacture is expensive. As it is already known, one of the advantages that optical fiber has with respect to the copper pair, is that it is barely attenuated. In a copper pair we can speak that in a kilometer distance, 25 dB can be attenuated (it is an approximate average, since each pair is attenuated differently), but the attenuation level of the optical fiber is much lower, in one kilometer is attenuated 0.30 dB.

FTTx modalities that exist

After these explanations and clarifications we go with the different modalities of FTTx. It is evident that for all of you the best known and most listened to is FTTH (Fiber-to-the-home), and it is the only one that can be sold to the subscriber as optical fiber, since, in the rest of the types of FTTx, fiber optical does not reach the user’s home to the PTRO (optical PTR).

FTTH

It is also known as Fiber-to-the-homeIn this type of fiber optic, it goes directly to the home, where we will have an optical PTR to connect the fiber cable directly to the operator’s ONT or to our router if it includes the ONT in the same device. This fiber optic modality is the only one that reaches the subscriber’s home, and is the most used in Spain due to its performance, both in terms of speed and latency.

FTTB

Also known as Fiber-to-the-buildingIn this fiber mode, the connection to the building is reached with fiber optics, the fiber ends directly at the RITI or RITU at a CTO. Once the fiber optic has reached the intermediate distribution point, the end subscribers in the building or in the house are accessed using VDSL2 technology, copper pair or directly over twisted pair (Cat 6 network cable). Thanks to this modality, we will have fiber to the building itself, to later carry the connection using different lower-cost technologies.

FTTC

It is also known as Fiber-to-the-cabinetIn this fiber mode, you reach a telecommunications cabin or closet near your home, normally it should be less than 300 meters away.

FTTN

It is also known as Fiber-to-the-node, this fiber modality is similar to FTTN, but in this case, the telecommunications cabin or closet is further from the home, more than 300 meters away, therefore, we will have worse performance in general terms.

Other FTTx modalities

After having seen the main FTTx modalities that currently exist, there are other minority denominations that are not usually used, or at least, are used very little, but it is important to know them to know what we are talking about.

FTTO

Also known as Fiber-to-the-officeIt is exactly the same as FTTH, but instead of being domestic ‘homes’, they are ‘offices’. This means that the optical fiber reaches the interior of the subscriber’s office itself. Logically, this FTTO could have specific configurations for companies such as embedded videoconferencing platform, VoIP, without TV and with guaranteed Internet connection speeds, but this will depend on each Internet operator.

FTTP

It is known as Fiber-to-the-premisesIt is usually a general term to designate FTTH and FTTB architectures, it is also designated to fiber optic networks that include both homes and small businesses.

What modality can we find in Spain?

Currently the most widely used modality of FTTx is FTTH, fiber optic to the home. Depending on where your house is located, FTTH could reach you through a CTO hanging from one of the facades of your house, or directly through a RITU in the community of owners if the urbanization or the block of flats is of recent construction.

If it comes to you directly through a hanging CTO, the technicians will pull the outdoor fiber cable through the facade until it reaches your house, and once inside, they will place the PTRO (optical PRT) where you will connect the yellow fiber cable, and it will go directly to the operator’s ONT.

If the fiber reaches the RITU, there the operator or operators will have their different CTOs, and the technician will simply have to connect the fiber cable that comes from your home to the RITU, to the CTO of your operator. Installation is clearly much simpler in this type of FTTH connections, because all the fiber optic cable is already pulled through the different conduits, it is only necessary to connect the cable that comes from your home to the CTO, and from the PTRO of your home to the operator’s ONT to have an Internet connection.

We must not forget that FTTH technology and also the rest of FTTx, make use of passive optical networks (PON), generally they make use of GPON technology that is the one used by Internet operators, although they are already modernizing the entire fiber network optics incorporating XG-PON technology to provide us with even more symmetrical speed. The fiber optic cabling does not need to be replaced, but it is necessary to change the OLTs and ONTs to make them compatible with the new standard that is about to arrive to offer speeds higher than 1Gbps symmetrical in our homes.

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