To meet the demand for increased bandwidth, fiber optics was chosen, a transmission medium that also offers greater security and higher quality. Fiber optics has been widely recognized among all transmission media as the most suitable for providing high-bandwidth services. Fiber to the Home (FTTH) is the latest technological advancement that allows for high-speed services using only fiber optic cables and optical elements to connect operator central offices to users. FTTH has surpassed 20 million subscribers worldwide and continues to grow.
History:
In 1975, the first commercial fiber optic communications system was installed in Bournemouth, United Kingdom. Six months later, another system was installed in Japan, and the following year, GTE and AT&T installed two systems in California and Chicago, USA, respectively.
In the 1980s, CATV operators began replacing metallic cables with fiber optic cables to create Hybrid Fiber/Coaxial (HFC) networks and Fiber To The Curb (FTTC) systems, as the technology did not allow for cost-competitive fiber optic connections to subscribers.
NTT in Japan made a significant investment in research to overcome the technological challenges that would facilitate this expansion. As a result, in 1990, NTT announced a plan to implement this technology, which would be completed by 2025, to make all of Japan available, considering it the most suitable for the future. To this end, NTT invited the world's leading manufacturers, such as AT&T, Fujitsu, Hitachi, and Fujikura, to begin developing the necessary systems for FTTH networks. In 1994, NTT announced that by the year 2000, the installation costs for FTTH systems would be the same as those for metallic cables.
In 2001, NTT began offering FTTH service, drastically reducing installation costs. As a result, the number of users began to increase rapidly, prompting other operators to follow suit. Currently, more than 40 countries worldwide have deployed FTTH networks.
FTTx
is the generic term for any broadband network architecture in telecommunications that uses fiber optic cables to replace all or part of the metallic cables used in the final connection to the subscriber. The acronym FTT stands for Fiber To The, and the letter replacing the "x" indicates the point to which the optical fiber extends. Beyond this point, and up to the user's premises, the cables will be metallic.
The different FTTx architectures are as follows:
FTTN - Fiber To The Node;
FTTC - Fiber To The Curb.
FTTB - Fiber To The Building.
FTTH - Fiber To The Home; no metallic cables are used.
FTTP/FTTU - Fiber To The Premise (USA) / Fiber To The User, indicate that the fiber runs directly from the operator's facilities to the premises of companies or users who need high speeds and require dedicated fiber.
Optical Distribution Networks (ODN):
An FTTH network can be divided into three main parts: the equipment room or central office, the optical distribution network (ODN), and the connection/equipment at the user's premises.
The equipment room, headend, or central office, as it may be called, has the necessary equipment to transmit and receive information to/from subscribers and content providers. Therefore, it must have voice, video, and data receiving equipment, which is then redistributed among users using an Optical Network Terminal (OLT).
The ODN provides the optical transmission medium from the OLT to the user, and vice versa.
The ODN is a critical part of FTTH networks, since user headends and equipment can be easily upgraded over periods of 20, 30, or more years and will still use the same ODN; therefore, the installation must be reliable to withstand the test of time.
There are two main types of optical networks:
- Active Optical Network (AON), which uses active elements that require power and allows for long distances between the equipment room and subscribers.
- Passive Optical Network (PON), in which all network elements are passive, so no power is needed at any intermediate point in the network. These are the most widely used, especially in large networks, and although the maximum distance is 10 to 60 km, this is considered sufficient. Passive networks generally do not require any upgrades in the event of a technological change.
PON Network Technology
PON networks are primarily distinguished by the active technology connected at their ends, which gives them different qualities and capabilities. The current PON networks are as follows:
- BPON: This derives from the older APON standard ITU-T G.983, which is based on Asynchronous Transfer Mode (ATM), allowing download speeds of 155, 622, and 1244 Mbps and upload speeds of 155 or 622 Mbps, in asymmetric or symmetric modes. The maximum distance from the central office to subscribers is 20 km, and the maximum number of subscribers per fiber is 32.
- EPON/GEPON: These are based on Ethernet and Gigabit Ethernet traffic, respectively, as defined in the IEEE 802.3ah standard. Their download and upload speeds are symmetric at 1244 Mbps, and the maximum distance to subscribers is 10 km, although an extension to 20 km is being studied. Up to 32 subscribers can share each optical fiber leaving the central office. It is widely adopted worldwide, but especially in Asia and the Pacific, with over 13 million users.
- GPON: This is an evolution of the BPON standard according to the ITU-T G.984 standard and offers high download and upload speeds, reaching up to 2488 Mbps in both symmetric and asymmetric modes; it can utilize ATM, Ethernet, and TDM traffic. The maximum number of users per fiber is 64, although the possibility of increasing this to 128 is being studied. The maximum distance to subscribers can reach 60 km. All these characteristics represent improvements over other technologies, which is why it has been chosen by most operators who have begun deployment after its development, as is the case with Telefónica in Spain.
Network Topologies:
Networks designed to connect to subscribers have been developed taking into account user expectations and potential needs, resulting in the following topologies:
- Point-to-Point (P2P): This consists of a direct connection from the central office to the subscriber. A group of point-to-point links from the same source connection results in a star topology. This topology is used for offices or users who require dedicated traffic.
- Point-to-Multipoint (P2MP): Each fiber leaving the headend serves multiple users through passive or active elements. This topology is also called a tree topology.
- Ring: Fibers leave the central office and return at the end of their path, allowing service to be provided to users through branches with splitters or active elements. This topology offers the possibility of connection redundancy.
It is possible to build networks that combine different topologies to diversify the offering, improve reliability, or allow greater flexibility for future expansions or modifications.
The most commonly used topologies in FTTH systems are P2P and P2MP.
Instrumentation for FTTH Networks:
The instrumentation required to install and maintain FTTH networks varies depending on the specific network tasks. These tasks can be divided into:
- Installation of equipment at the central office.
- Installation of the optical distribution network (ODN).
- Subscriber installation and activation.
- Maintenance of central office equipment.
- Maintenance of the optical distribution network.
- Subscriber maintenance.
Installation and Maintenance of Central Office Equipment
: The following instrumentation is required:
- GPON selective optical power meter, with at least the following measurement characteristics: wavelengths 1310, 1490, and 1550 nm, maximum power level ≥ +6 dBm. This instrument allows verification of the optical output power of the OLT (Figure 2).
- Video analyzers: CATV, VHD, IPTV, MPEG, and MPEG2.
- Audio analyzers: VoIP, PSTN.
- Cable analyzers.
- Data and protocol analyzers: Ethernet, ATM, xDSL (ADSL2+, VDSL…). (Figures 3 and 4).
The analyzers will allow verification of compliance with the applicable standards.
The installation of the optical distribution network requires construction equipment and instrumentation for verification and testing.
Construction equipment:
- Fiber optic fusion splicer. (Figure 5).
- Connector cleaning and inspection tools.
Measurement instrumentation:
- OTDR with wavelengths of 1310 and 1550 nm, a dynamic range
of ≤ 32 dB, and a launch fiber (Dummy Fiber) of ≤ 300 meters to locate any potential faults in the installation. (Figure 6).
- Light source with wavelengths of 1310, 1490, and 1550 nm, an output level of ≤ -10 dBm, and an optical power meter with a minimum sensitivity of -40 dBm to measure network losses or any optical element. (Figure 7).
Instrumentation for new subscriber connections
- Fusion splicer or mechanical splicers or field connector assembly kit. (Figures 8, 9, and 10).
- GPON selective optical power meter for wavelengths of 1310, 1490, and 1550 nm and a minimum sensitivity of -40 dBm, allowing verification that the optical signal reaching the subscriber and the signal emitted by the ONT are at the appropriate level.
- OTDR with a wavelength of 1625 or 1650 nm, equipped with a bandpass filter and a 300-meter dummy fiber to locate any potential faults in the installation when the fiber is illuminated. (Figure 11).
- ONT or simulator, to verify communication with the OLT.
- Connector cleaning and inspection tools.
- 650 nm visible light source, for locating fibers and faults at short distances; not essential, but advisable due to its usefulness and low cost.
Instrumentation for optical distribution network maintenance
- OTDR with a wavelength of 1625 or 1650 nm, equipped with a bandpass filter and a 300-meter dummy fiber to locate any potential faults in the installation when the fiber is illuminated.
Instrumentation for subscriber maintenance
- GPON selective optical power meter for wavelengths of 1310, 1490, and 1550 nm with a minimum sensitivity of -40 dBm, which will allow verification that the optical signal reaching the subscriber and the signal emitted by the ONT are at the correct level.
- OTDR with a wavelength of 1625 or 1650 nm, equipped with a bandpass filter and a 300-meter dummy fiber to locate any potential faults in the installation when the fiber is illuminated.
- Activity detectors, which allow verification of whether communication between the OLT and ONT has been established at the optical level.
- Connector cleaning and inspection tools.
Instrumentation requires specialized technical personnel with a high level of training in performing mechanical fusions or splices and using the instrumentation. However, maintenance personnel require more expertise than installation personnel, as they must be able to interpret measurement results to locate faults. It is important to define test protocols for the most common faults to reduce resolution time. Telecom Unitronics specializes in training experts in new technologies through specific courses tailored to the technical needs of each professional.
Telecom Unitronics is a pioneer in introducing the latest instrumentation solutions for new key, radio frequency, and fiber optic networks. Our quality philosophy has led us to seek out the most advanced solutions by identifying the best manufacturers of measurement and test instrumentation.
Author: Pedro Notario, Technical Director of TELECOM UNITRONICS.
More information or a quote.
