Today, optical cable has become widespread in the creation of telecommunication networks. Its characteristic features include indicators such as:
- high data transfer speed;
- lack of sensitivity to various interferences;
- compared to copper cables, low weight and overall dimensions;
- long service life;
- possibility of increasing the distance between transmitting devices up to 800 km.
Perhaps the only disadvantages that can be identified when creating a network from fiber optics are the high cost of materials and equipment, the labor-intensive process of cable installation associated with the need for welding when laying main lines.
Optical cable design
- 1 - central power element
- 2 - optical fibers
- 3 - plastic tube modules
- 4 - film
- 5 - thin inner shell made of polyethylene
- 6 - Kevlar threads or armor
- 7 - outer thick polyethylene shell
Fiber Bandwidth
Over the past few decades, fiber optic cable capacity has increased significantly. At the same time, developments to improve one of the advanced data transmission technologies do not stop even for a minute. In essence, the speed of signal transmission largely depends on the distance between the equipment, the type of fiber media and the number of connecting joints in the trunks.
For example, a multimode optical cable used to build an internal network (between data servers) over a distance of approximately 200 meters can provide speeds of up to 10 Gbit/s.
For laying external communications, where the distance between transmitters can reach several tens of kilometers, single-mode optical fiber is used. The structure of such a cable allows for flow rates of more than 10 Gbit/s. True, this is far from the limit of the capabilities of optics. With increasing consumer demand, there will be a need to increase the power of equipment, and even replacing equipment that allows for data transfer speeds of 160 Gbit/s is not able to fully utilize the potential of the carrier.
Types of fiber optic cable
According to its structure, fiber optic cable is divided into two categories:
- multimode;
- single-mode.
Multimode optical cable has proven itself as a conductor that transmits signals over short distances. First of all, this is due to the structure of the fiber itself, in the name of which the word “many” does not mean what is considered a good indicator. The recommended distance, when laying a multimode cable, from the transmitting device to the user should be no more than one kilometer. At this distance, the conductor shows excellent ability to transmit light flux with virtually no loss and is capable of providing speeds of up to 10 Gbit/s. Thus, it can be used when building a network in a small area or as an optical cable for indoor installation.
Single-mode optical cable is primarily intended for transmitting data over long distances, which can be tens or even hundreds of kilometers. Due to its structure, this type of fiber has better qualities and is capable of maintaining a constant high speed of information flow with virtually no attenuation in the optical cable. Thus, the throughput of a single-mode optical carrier is limited directly by the transmitting devices and, with powerful equipment installed, can reach several Tbit/s.
Necessary equipment for transmitting information via fiber optic cable
Today, fiber optic networks have become widespread among companies providing their subscribers with access to the Internet. In this case, to carry out data transmission, not counting intermediate couplings and other related equipment, the following equipment is used:
from the provider side: - special DLC equipment, also known as a multiplexer. It allows data transmission via fiber optic cable over long distances at constantly maintained high speeds.
on the subscriber side: - ONT router, which is the terminal client equipment and allows access to the Internet via a fiber optic network. Allows access at speeds up to 2.5 Gbit/s.
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26 terabits/s over fiber with one laser
A group of German engineers led by Professor Wolfgang Freude from the University of Karlsruhe applied the OFDM (Orthogonal Frequency Division Multiplexing) technique, which is widely used in wireless communications (802.11 and LTE), digital television (DVB-T) and ADSL, to fiber optics. .
It is more difficult to use OFDM in optical fiber, because here you need to divide the light flux into subcarriers. Previously, the only way to do this was to use a separate laser for each subcarrier. Comparison of different types of multiplexing
A separate laser and a separate receiver are used to broadcast at each frequency, so hundreds of lasers can simultaneously transmit a signal in one fiber optic channel. According to Professor Freude, the total capacity of the channel is limited only by the number of lasers. “An experiment has already been carried out and a speed of 100 terabits/s has been demonstrated,” he said in an interview with the BBC. But for this we had to use about 500 lasers, which in itself is very expensive.
Freude and his colleagues have developed a technology for transmitting more than 300 subcarriers of different colors over an optical fiber with a single laser that operates in short pulses. An interesting phenomenon called optical frequency combing comes into play here. Each small pulse is “smeared” across frequencies and time, so that the signal receiver, with the help of good timing, can theoretically process each frequency separately.
After several years of work, German researchers finally managed to find the correct timing, select suitable materials and implement in practice the processing of each subcarrier using a fast Fourier transform (FFT). The Fourier transform is an operation that associates a function of a real variable with another function of a real variable. This new function describes the coefficients when decomposing the original function into elementary components - harmonic vibrations with different frequencies.
FFT is ideal for decomposing light into subcarriers. It turned out that a total of about 350 colors (frequencies) can be extracted from a typical pulse, and each of them is used as a separate subcarrier, as in the traditional OFDM technique. Last year, Freude and his colleagues conducted an experiment and showed in practice a speed of 10.8 terabits/s, and now they have further improved the accuracy of frequency recognition.
According to Freude, the timing and FFT technology he developed could well be implemented on a chip and find commercial application.
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Optical fiber
1. What do the terms “termination” of a cable system and “splicing” of a fiber optic cable mean? Termination is the procedure for connecting a cable, wire or fiber to switching equipment. Splicing is the mechanical splicing of fiber ends to each other using a clamp coupling (splice). 2. Explain the concepts of “basic parameters” of the cable system and
"fiber optic cable attenuation"? Attenuation is the process of weakening the light flux in an optical fiber. Factors causing attenuation can be different: - attenuation caused by light absorption. Defined as the conversion of a light pulse into heat associated with resonance in the fiber material. There are internal absorptions (associated with the fiber material) and external absorptions (the presence of microimpurities). Optical fibers currently produced have very low amounts of microimpurities, so external absorption can be neglected. - attenuation of light in an optical fiber caused by radiation scattering. Scattering is one of the main factors in the attenuation of light in a fiber. This type of attenuation is primarily associated with the presence of impurities in the optical fiber, as well as defects in the optical fiber core. The presence of such inclusions leads to the fact that the light flux, propagating along the optical fiber, deviates from the correct trajectory, as a result of which the refraction angle is exceeded and part of the light flux exits through the cladding. Also, the presence of foreign impurities leads to partial reflection of the light flux in the opposite direction, the so-called backscattering effect; - light attenuation associated with optical fiber bends, there are two types of bends: 1. Microbending, this type of bending is caused by microscopic changes in the geometric parameters of the fiber core as a result of manufacturing. 2. Macrobending, a type caused by a large bend of an optical fiber that exceeds the minimum radius, causing partial light escape from the fiber core. The bending radius at which the light pulse propagates without any distortion is 10 centimeters (for single-mode fibers). Increasing the minimum bend radius increases the dispersion effect. Factors necessary to determine the total attenuation coefficient are: optical signal input and output losses, absorption and scattering losses, bending losses, and mechanical connector losses. The attenuation coefficient is defined as the ratio of the power introduced into the optical fiber to the power received from the optical signal fiber. Measured in decibels (dB). 3. Describe the design and characteristics of single-mode fiber optic cable. Fiber optic cable consists of thin light-conducting glass or plastic cores in a glass reflective sheath, enclosed in a protective braid. Singlemode fiber - (singlemode) SM, 9-10/125 microns, that is, 9-10 micrometers is the diameter of the core, 125 microns is the diameter of the cladding. A light beam with wavelengths of 1300 and 1550 nm and an attenuation of 1 dB/km is transmitted. 4. Describe the design and characteristics of multimode fiber optic cable. multimode fiber - (multimode) MM, 62.5/125 and 50/125 microns: core diameter is 62.5 or 50 micrometers. A light beam with wavelengths of 850 and 1300 nm and attenuation of 1.5-5 dB/km is transmitted.
5. What fiber standards should be used?
system administrator when organizing a fiber optic
cable system? Currently, the following correspondences to the IEC 60793 recommendation and the ITU-T recommendation are defined with the addition of a wavelength of a certain type of optical fiber:
Type B1.1 comply with ITU-T G652 (a, b) with a wavelength of 1.31 µm and ITU-T G654a with a wavelength of 1.55 µm;
Type B1.2 b conforms to ITU-T G654(b) with wavelength 1.55 µm;
Type B1.2 c conforms to ITU-T G654(c) with wavelength 1.55 µm;
Type B1.3 conforms to ITU-T G652 (c, d) with wavelength 1.31 µm;
Type B2 complies with ITU-T G.653 (a, b) and ITU-T G.655 (a, b) with a wavelength of 1.55 µm;
Type B4 c complies with ITU-T G.655 (c) with a wavelength of 1.55 µm;
Type B4 d conforms to ITU-T G.655(d) with wavelength 1.55 µm;
Type B4 e complies with ITU-T G.655(e) with a wavelength of 1.55 µm;
Type B5 complies with ITU-T G.656 with a wavelength of 1.55 µm;
Type B6 a conforms to ITU-T G.657 A1/2 wavelength 1.31 µm;
Type B6 b corresponds to ITU-T G.657 B2/3 with a wavelength of 1.31 µm.
6. What standards of cable system administration should
use system administrator? The creation of cable systems is based on many
standards. Here are the basic standards necessary for
high-speed data transmission and mandatory compliance
system administrator services.
EIA/TIA 568 - standard for creating telecommunications services
and industrial buildings, cable planning
building systems, methodology for constructing a telecommunications system
service and industrial buildings.
EIA/TIA 569 is a standard describing the requirements for premises,
in which structured cabling is installed
communication system and equipment.
EIA/TIA 606 - telecommunications administration standard
infrastructure in office and production
EIA/TIA 607 is a standard that sets requirements for
telecommunications grounding system infrastructure
and equalization of potentials in service and production
It is possible to use standards other than EIA/TIA
for the construction of ISO structured cabling systems.
ISO 11801 - standard for structured cabling systems
general purpose in buildings and campuses. He is functional
similar to the EIA/TIA 568 standard. 7. What functions do cable management systems perform?
systems? Give an example of implementation. Troubleshooting a network is a fairly complex process.
and the procedure for registering changes in connection state
manually is just as difficult and unreliable. Therefore most often
and networks use cable administration systems
systems that allow you to monitor the performance of the system
and its individual components and troubleshoot problems in a minimum
short time. 8. List the subsystems of a building cabling system and their functions.
Workplace subsystem. The workplace subsystem is designed to connect end users (computers, terminals, printers, telephones, etc.) to the information outlet. Includes patch cables, adapters, as well as devices that allow you to connect terminal equipment to the network through an information socket. The work of the SCS ultimately ensures the operation of the workplace subsystem.
Horizontal subsystem. The horizontal subsystem covers the space between the Information outlet at the workplace and the horizontal cross-connection in the telecommunications cabinet. It consists of horizontal cables, information sockets and a part of the horizontal cross-connect that serves the horizontal cable. It is recommended that each floor of the building be served by its own Horizontal subsystem. All horizontal cables, regardless of the type of transmission medium, should not exceed 90 m in the area from the information outlet at the workplace to the horizontal cross-connect. At least two horizontal cables must be laid for each workplace.
Backbone subsystem. The backbone subsystem connects the main cross-connect in the hardware room with intermediate cross-connects and horizontal cross-connects. The backbone subsystem must include a cable installed vertically between floor cross-connections in a multi-story building, as well as a cable installed horizontally between cross-connections in an extended building.
Equipment subsystem. The equipment subsystem consists of electronic communication equipment for collective (general) use, located in a hardware room or in a telecommunications cabinet, and the transmission medium necessary for connection to the distribution equipment serving the horizontal or backbone subsystems.
The highway of the building complex. When a cabling system spans more than one building, the components that provide communication between buildings constitute the campus backbone. This subsystem includes the medium over which the main signals are transmitted, the corresponding switching equipment designed to terminate this type of medium, and electrical protection devices to suppress dangerous voltages when the medium is exposed to lightning and/or high-voltage electricity, the peaks of which can penetrate the cable inside the building.
Administrative subsystem. The administrative subsystem brings together the subsystems listed above. Consists of patch cables that physically connect various subsystems, and markings to identify cables, patch panels, etc.
9. List the characteristics of the campus cabling system according to
standard TIA/EIA 568. In accordance with the standard for constructing cable systems TIA/EIA 568, SCS has the following characteristics: the topology of any subsystems is star; types of devices and rooms connecting cable subsystems: horizontal closet and cross (HC), intermediate closet and cross (1C), main closet and cross (MC) and equipment room (ER) - room for active network equipment; the number of intermediate closets between the main and horizontal closet is no more than 1 closet; between any two horizontal closets - no more than 3 closets; the maximum length of the backbone segment for twisted pair is 90 m; does not depend on the cable type; the maximum length of the backbone segment for optical fiber depends on the type of cable (see figure)
10. Give examples of implementing cable system markings in accordance with the administration standard. GOST R53246-2008 Color code marking depending on the class of optical fiber
11. What is a functional network diagram? When and how
does the system administrator do?
12. List the technical metrics of fiber optic cabling
systems. How to correct them after deviations from
nominal values? Frame Delay Ratio. Latency is a critical parameter,
of great importance for applications running
in real time. This option has already been discussed
as a technical metric for 100 Base Ethernet.
The forum documents provide a theoretical calculation of this
parameter for Metro Ethernet. In practice it is quite problematic
complexity of modern systems).
Frame Loss Ratio (FLR). Frame loss
This is the proportion of frames that are not delivered to the recipient, from
total number of frames transmitted during the reporting period (hour,
day, month).
The impact of packet loss on user traffic, as well as
delays vary and depend on the type of data being transmitted.
Accordingly, losses can have different effects on quality
QoS services depending on applications, services
or high-level telecommunication protocols,
used for information exchange. For example, losses
not exceeding 1%, acceptable for applications such as Voice
over IP (VoIP), but increasing them to 3% makes it impossible
provision of this service.
On the other hand, modern applications respond flexibly
to an increase in losses, compensating for it with a decrease in speed
transmission or the use of adaptive compression mechanisms
Mathematical descriptions of FLR are also presented in the documents
FDV (Frame Delay Variations) is one
of the critical parameters for applications running in
real time.
FDV is defined as the difference in latency of several selected
packets sent from one device to another. This metric only applies to successfully delivered
packets for a certain time interval. Her math races
Four are given in the forum documents.
Bandwidth was dripping. Channel bandwidth
is the theoretical maximum of possible transmitted
information and very often this concept when measuring
replaced by the concept of channel capacity,
which reflects the real possibility of the environment, i.e. the volume
data transmitted by a network or part of it per unit of time.
Bandwidth is not a user characteristic,
since it characterizes the execution speed
internal network operations - transfer of data packets between
network nodes through various communication devices.
Channel bandwidth usage percentage per unit
time is called channel utilization. Disposal of the duct
also often used as a metric. Bandwidth
measured in either bits per second or packets
per second. Throughput can be instantaneous,
average and maximum.
Average throughput is calculated by dividing
the total volume of transmitted data at the time of transmission,
and a sufficiently long period of time is selected
Hour, day or week.
Instantaneous throughput is different from average
throughput in that it is selected for averaging
a very small period of time, for example 10 ms or 1 s.
Maximum throughput is the greatest
instantaneous throughput recorded during
observation period.__
13. What business metrics does the system administrator use when
operation of the cable system? There are three main business metrics for IS performance.
Expected system recovery time MTTR (Mean
Time to Restore). This metric is set by business units
company system administrator services. There are types of business
which can exist without IP only a few
minutes, and then the cost of downtime per minute will become critical
Other types of businesses may need to wait for the system to be restored
several days without financial losses. This is critical
metric for planning a recovery procedure. Price
on the use of preventive measures for recovery
systems grows exponentially depending on
MTTR values. System uptime is a metric characterizing
system operating time. This metric is similar to the metric
MTBF, discussed in Chapter 8, but takes into account not only
technical problems, as well as network maintenance problems. She
used to measure network reliability and stability and
displays the time the network has been running without interruption or need
reboots for administration or maintenance purposes.
System reliability is sometimes measured as a percentage (usually
not less than 99%). Too high a value may mean insufficient
system administrator qualifications, since
Some processes require routine stopping and rebooting.
Mean Time Between Failures MTBF
Failures), or time between failures, is a performance metric
equipment specified by the manufacturer. Since modern
computer equipment works quite reliably
(very often the manufacturer gives a lifetime warranty),
then some manufacturers do not provide this metric in their technical
documentation. The system administrator should
in this case, take it from published analytical data
for this type of equipment.
System rise time Uptime is the resulting
a metric that tells how much time a user
does not use the IS due to problems diagnosing errors and
system recovery, i.e. this is the total time for
search for errors, their diagnosis, recovery time and
launching the IC in industrial mode. This metric is given
business units to system administrator services in
SLA. It is determined based on financial capabilities
enterprise and, accordingly, its equipment with means
diagnostics and recovery. For admin services
systems, this metric is reporting and determines their ability
maintain the IS in working order. Service Availability has a direct impact
impact on the actual quality of the service consumed
user. There are three most important criteria,
determining service availability: service introduction time
(Service Activation Time), connection availability (Connection
Availability), service recovery time after a failure (Mean
Time to Restore Service - MTTR).
Service implementation time is the time that passes from
the moment the user orders a new service (or modifies the parameters of an existing service) until the moment when
the service will be activated and available to the user. Time
installation can take from a few minutes to several
months. For example, to modify an existing
service (at the user's request) in order to increase
its performance may require gasket
fiber optic cable to the user's location,
which will take a long time.
The connection availability determines how long the user's
the connection complies with the contract parameters.
Typically, the value of this parameter is indicated in the service description
in percentage (sometimes in minutes). Connection Availability
calculated as the percentage of time during which
the user connection was in full working order
state (the user received and transmitted
data), from the total duration of the reporting period.
The service provider (for example, a telecom operator) usually excludes
from downtime, the period of performing routine maintenance
work, since the user is aware of the upcoming prevention
notified in advance.
The service recovery time after a failure is defined as
expected time required to restore normal
functioning of the service after a failure. This metric is already
discussed in Chapter 8. Additionally, we note some of its
peculiarities. Most networks provide some
redundancy level with automatic recovery
services in case of failures or malfunctions. For
In such situations, the telecom operator sets MTTR equal to
a few seconds or even milliseconds. If
intervention of technical personnel is required, this is the time
is usually taken equal to several minutes, less often -
14. What system administrator services should be
involved in the fiber optic restoration process
cable system?
15. What kind of work to restore fiber optic cable
system and in what case the system administrator will give
outsourcing company?
16. Give an example of applying the basic error detection model
system administrator during “slow” operation of the fiber optic
cable system.
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Fiber optic cable - from selection to use
Fiber optic cable is not only a product that can be purchased on the website of the Finfort-Intertrading company, it is, first of all, an integral component for building a reliable, trouble-free Internet network.
Optical fiber transmits data at very high speeds. With each new modernization, not only the quality, but also the volume of transmitted information increases. The bandwidth of a fiber optic cable is already measured in Tbit/s. But this is not the limit - there is an opportunity for a multiple increase in throughput.
How to choose a fiber optic cable?
There are many specifications for fiber optics that cover different aspects such as dimensions, bandwidth, strength, bend radius, connector selection, and even the color of the protective jacket that protects the cable from damage.
Among the main parameters that you need to know, it is worth highlighting the length of the optical fiber, diameter, bandwidth of the fiber optic cable, transparency window, signal attenuation.
If you order a cable on the Finfort-Intertrading website, always take it with a reserve - in case you need to rearrange the equipment within the premises, additional meters or a whole reel will never hurt!
To connect the fiber optic cable to the equipment, you need optical connectors. The most popular are SC and ST connectors. All types of cable connectors are available on the product page of the Finfort-Intertrading website - choose the ones that suit you!
Selecting and purchasing a fiber optic cable on the Finfort-Intertrading website is not difficult. What you may not know are some nuances that few people pay attention to.
Never look directly into the fiber section. The optical energy transmitted through the cable is not visible to the eye, but it can permanently damage the retina.
Be careful when splicing fibers. Fiber optic chips are tiny, almost invisible, sharp pieces of glass that can damage the skin of your hands or get into your eyes. Use tape to collect the broken pieces.
Make sure that the number of fibers in the cable of one network (outside and inside the building) matches as much as possible.
As you install fiber, test and document data such as the attenuation of each fiber. Write down a description of the optical power during transmission and reception, indicate optical loss, location of the patch panel, and type of connector for each connection.
Of course, this is not all information about fiber optic cables. Detailed technical specifications are described on the website of the Finfort-Intertrading company in the product section. Come in, choose, order!
Fiber optic or simply optical cable is one of the most popular conductors. It is used everywhere both to create new cable systems and to update old ones. This is because fiber optic cable has many advantages over copper cable. These are the ones we will look at in this article.
- Bandwidth
The higher the bandwidth, the more information can be transmitted. Fiber optic cable provides high throughput: up to 10 Gbit/s and higher. These are better performance than copper cable. It is also worth considering that the transmission speed will be different for different types of cable. For example, single-mode fiber optic cable provides more bandwidth than multimode fiber.
- Distances and speed
When using fiber optic cable, information is transmitted at higher speeds and over longer distances with virtually no signal loss. This capability is achieved due to the fact that the signal is transmitted through optics in the form of light rays. Fiber optics does not have the 100 meter distance limitation that can be seen with unshielded copper cable without an amplifier. The distance over which a signal can be transmitted will also depend on the type of cable used, the wavelength and the network itself. Distances range from 550 meters for a multimode cable type to 40 kilometers for a single mode cable type.
- Safety
With fiber optic cable, all your information is safe. The signal transmitted through optics is not radiated and is very difficult to intercept. If the cable was damaged, it is easy to track, since it will allow light to pass through, which will ultimately lead to a stop in the entire transmission. This way, if there is an attempt to physically hack your fiber optic system, you will definitely know about it.
It is worth noting that fiber optic networks allow you to place all electronics and equipment in one centralized location.
- Reliability and durability
Optical fiber provides the most reliable data transmission. An optical cable is immune to many factors that can easily affect the performance of a copper cable. The center of the core is made of glass, which insulates from electric current. The optics are completely resistant to radio and electromagnetic radiation, mutual interference, impedance problems and many other factors. Fiber optic cable can be laid near industrial equipment without any concern. Additionally, fiber optic cable is not as sensitive to temperature as copper cable and can easily be placed in water.
- Appearance
Fiber optic cable is lighter, thinner and more durable compared to copper. Achieving higher transmission speeds using copper cable will require using a better type of cable, which is usually heavier, has a larger diameter, and takes up more space. The small size of the optical cable makes it more convenient. It is also worth noting that testing fiber optic cable is much easier than copper cable.
- Conversion
The wide distribution and low cost of media converters significantly simplify data transfer from copper cable to fiber optic. Converters provide an uninterrupted connection with the ability to use existing equipment.
- Cable welding
Although welding fiber optic cable today is more labor intensive than crimping copper cable, using special welding tools makes the process much easier.
- Price
The cost of fiber optic cable, components and equipment is gradually decreasing. At the moment, fiber optic cable is more expensive than copper cable only within a short period of time. But with long-term use, fiber optic cable will be cheaper than copper cable. Fiber is easier to maintain and requires less network equipment. In addition, there are more and more fiber optic solutions available these days, from active optical HDMI cables to professional digital signage solutions like ZeeVee's ZyPer4K, which was recently unveiled at NEC's Solutions Showcase 2015, allowing for easy extensions. and switch uncompressed 4K video, audio and control signals using standard 10Gb technology Ethernet over fiber optic cable.
For simple, low-cost fiber optic systems, distances between repeaters of up to 5 km are possible. Repeater distances of up to 300 km are now readily available for high quality commercial systems. Systems (without repeaters) have been developed for distances of up to 400 km. In laboratory conditions
Distances close to 1000 km have been achieved, but they are not yet available on the market. One European company has announced that it is currently developing a fiber optic cable that can be laid along the earth's equator and, without any repeaters, it will be possible to transmit a signal from one end to the other! How is this possible? With a slightly radioactive shell, incoming low-energy photons excite electrons in the shell, which in turn emit higher-energy photons. This creates some form of auto-amplification. The following chapters will explain the terms used to the reader.
In the 4 Mbps twisted pair cable market, repeater distances of up to 2.4 km are available. For coaxial cables at speeds less than 1 Mbit/s, distances of up to 25 km between repeaters are possible.
].2.5. Size and Weight Fiber Optic
Compared to all other transmission cables, fiber optic cables are very small in diameter and extremely lightweight. A four-core fiber optic cable weighs approximately 240 kg/km, while a *36-core fiber optic cable weighs only approximately 3 kg more. Because they are smaller in size than traditional cables of the same capacity, they are typically easier to install in existing environments, and installation time and cost are generally lower because they are lightweight and easier to work with.
Traditional cable can weigh from 800 kg/km for 36 twisted pair cable to 5 t/km for high quality large diameter coaxial cable.
1.2.6. Use in flammable gas environments Fiber optics
Multi-mode fibers that work with LED light sources are suitable for use in flammable areas. Until recently, it was believed that all types of fibers were suitable for use in flammable areas; however, research has shown that certain fiber systems with high-powered light sources (lasers) can raise the temperature of the metal surface they shine on to the point of ignition of flammable gases, and can also cause sparks under certain conditions.
Unless traditional cable-based communication systems are very strictly designed and adhere to certain internal safety standards, they are not suitable for use in flammable areas. Conventional cables, even those carrying low currents, can create sparks or arcs between themselves unless current limiting means are used in the transmission circuits.
Electromagnetic waves involve a combination of electric and magnetic fields. Let's consider an electric charge. It creates an electric field around itself. If a charge moves, it creates a magnetic field. It was theoretically shown and...
Here, the transmitter and receiver establish an initial synchronization, then continuously transmit data, maintaining it throughout the transmission session. This is achieved through special data encoding schemes, such as Manchester encoding (Manchester...
Here, the transmitter and receiver operate independently and exchange a synchronizing bit pattern at the beginning of each message chip (frame). There is no fixed dependency between one message frame and the next. This is similar to...
The journal Nature Photonics published a description of a new technology for transmitting data over optical fiber at speeds of up to 26 Tbit/s instead of the current maximum of 1.6 Tbit/s.
A group of German engineers led by Professor Wolfgang Freude from the University of Karlsruhe applied the OFDM (Orthogonal Frequency Division Multiplexing) technique, which is widely used in wireless communications (802.11 and LTE), digital television (DVB-T) and ADSL, to fiber optics. .
It is more difficult to use OFDM in optical fiber, because here you need to divide the light flux into subcarriers. Previously, the only way to do this was to use a separate laser for each subcarrier.
Comparison of different types of multiplexing
A separate laser and a separate receiver are used to broadcast at each frequency, so hundreds of lasers can simultaneously transmit a signal in one fiber optic channel. According to Professor Freude, the total capacity of the channel is limited only by the number of lasers. “An experiment has already been carried out and a speed of 100 terabits/s has been demonstrated,” he said in an interview with the BBC. But for this we had to use about 500 lasers, which in itself is very expensive.
Freude and his colleagues have developed a technology for transmitting more than 300 subcarriers of different colors over an optical fiber with a single laser that operates in short pulses. An interesting phenomenon called optical frequency combing comes into play here. Each small pulse is “smeared” across frequencies and time, so that the signal receiver, with the help of good timing, can theoretically process each frequency separately.
After several years of work, German researchers finally managed to find the correct timing, select suitable materials and implement in practice the processing of each subcarrier using a fast Fourier transform (FFT). The Fourier transform is an operation that associates a function of a real variable with another function of a real variable. This new function describes the coefficients when decomposing the original function into elementary components - harmonic vibrations with different frequencies.
FFT is ideal for decomposing light into subcarriers. It turned out that a total of about 350 colors (frequencies) can be extracted from a typical pulse, and each of them is used as a separate subcarrier, as in the traditional OFDM technique. Last year, Freude and his colleagues conducted an experiment and showed in practice a speed of 10.8 terabits/s, and now they have further improved the accuracy of frequency recognition.
According to Freude, the timing and FFT technology he developed could well be implemented on a chip and find commercial application.
Most fiber technicians are aware of the difference between multimode fiber and singlemode fiber. But not everyone is informed about the characteristics of optical fibers and the protocols for transmitting information over them. The article provides descriptions of specific characteristics of optical fibers and Ethernet transmission protocols, which sometimes cause conflicting interpretations.
Characteristics of optical fibers
There is probably not a cable specialist working with optical fiber who does not know the difference between multimode fibers and single-mode fibers. We are not going to repeat common truths in this article. Let us dwell on the specific characteristics of optical fibers, which sometimes give rise to contradictory interpretations.
Optical fibers allow data transmission signals to propagate along them, provided that the light signal is introduced into the fiber at an angle that provides total internal reflection at the interface between two media of two types of glass having different refractive indices. In the center of the core there is especially pure glass with a refractive index of 1.5. The core diameter ranges from 8 to 62.5 microns. The glass surrounding the core, called the optical cladding, is slightly less impurity-free and has a refractive index of 1.45. The total diameter of the core and shell ranges from 125 to 440 μm. Polymer coatings are applied over the optical shell to strengthen the fiber, protective threads, and outer shell.
When optical radiation is introduced into a fiber, a light beam incident on its end at an angle greater than the critical one will propagate along the interface between two media in the fiber. Each time radiation hits the core-cladding interface, it is reflected back into the fiber. The angle of input of optical radiation into the fiber is determined by the maximum permissible input angle, called numerical aperture or aperture fibers. If you rotate this angle along the axis of the core, a cone is formed. Any beam of optical radiation incident on the end of the fiber within this cone will be transmitted further along the fiber.
Being inside the core, optical radiation is repeatedly reflected from the interface between two transparent media having different refractive indices. If the physical dimensions of the optical fiber core are significant, individual rays of light will be introduced into the fiber and subsequently undergo reflection at different angles. Since the optical energy rays were introduced into the fiber at different angles, the distances they travel will also be different. As a result, they reach the receiving portion of the fiber at different times. The pulsed optical signal transmitted through the fiber will be expanded compared to the one that was sent, therefore, the quality of the signal transmitted through the fiber will deteriorate. This phenomenon is called mode dispersion(DMD).
Another effect, which also causes deterioration of the transmitted signal, is called chromatic dispersion. Chromatic dispersion is caused by the fact that light rays of different wavelengths propagate along the optical fiber at different speeds. When transmitting a series of light pulses through an optical fiber, mode and chromatic dispersion can eventually cause the series to merge into one long pulse, causing signal bit interference and loss of transmitted data.
Another typical characteristic of optical fiber is attenuation. The glass used to make the optical fiber (OF) core is very clean, but still not perfect. As a result, light may be absorbed by the glass material in the optical fiber. Other optical signal losses in a fiber can include scattering and loss, as well as attenuation from poor optical connections. Fiber splice losses can be caused by misalignment of fiber cores or fiber end faces that have not been properly polished and cleaned.
Network protocols for optical transmission Ethernet
Let us list the main Ethernet transmission protocols over multimode and single-mode optical fibers.
10BASE-FL- 10 Mbit/s Ethernet transmission over multimode fiber.
100BASE-SX- 100 Mbit/s Ethernet transmission over multimode fiber optic at a wavelength of 850-nm. The maximum transmission distance is up to 300 m. Longer transmission distances are possible when using single-mode OFF. Backwards compatible with 10BASE-FL.
100BASE-FX- 100 Mbit/s Ethernet transmission (Fast Ethernet) over multimode fiber optic at a wavelength of 1300 nm. The maximum transmission distance is up to 400 m for half-duplex connections (with collision detection) or up to 2 km for full-duplex connections. Long distances are possible using single-mode OF. Not backward compatible with 10BASE-FL protocol.
100BASE-BX- 100 Mbit/s Ethernet transmission over single-mode OB. Unlike the 100BASE-FX protocol, which uses two optical fibers, 100BASE-BX operates over a single fiber with WDM (Wavelength-Division Multiplexing) technology, which allows you to separate the signal wavelengths at reception and transmission. For transmission and reception, two possible wavelengths are used: 1310 and 1550 nm or 1310 and 1490 nm. Transmission distance up to 10, 20, or 40 km.
1000BASE-SX- 1 Gbit/s Ethernet transmission (Gigabit Ethernet) over multimode fiber optic at a wavelength of 850-nm and over a maximum distance of up to 550 m, depending on the fiber optic class used.
1000BASE-LX- 1 Gbit/s Ethernet transmission (GigabitEthernet) over multimode OB at a wavelength of 1300-nm to a maximum distance of up to 550 m. The protocol is optimized for transmission over long distances (up to 10 km) over single-mode OB.
1000BASE-LH- - 1 Gbit/s Ethernet transmission over single-mode fiber over a maximum distance of up to 100 km.
10GBASE-SR- 10 Gbit/s Ethernet transmission (10 GigabitEthernet) over multimode fiber optic at a wavelength over 850-nm. The transmission distance can be 26 m or 82 m, depending on the type of optical fiber used with a 50- or 62.5 µm core. Supports transmission over a distance of 300 m over multimode optical fiber of class OM3 and higher, with a broadband coefficient of at least 2000 MHz/km.
10GBASE-LX4- 10 Gbit/s Ethernet transmission over multimode fiber optic at a wavelength of 1300 nm. Uses WDM technology to transmit over distances of up to 300 m over multimode fibers. Supports transmission over single-mode fiber over distances of up to 10 km.
To conclude the article, we provide some data on the types of multimode optical fibers used and transmission standards. The data is summarized in Table 1 (excerpts from the Standards).
International Standard: ISO/IEC 11801 “GenericCabling for Customer Premises”
International Standard: IEC 60793-2-10 “Product Specifications - Sectional Specification for Category A1 Multimode Fibers”
ANSI/TIA/EIA-492-AAAx “Detail Specification for Class 1a Graded-Index Multimode Optical Fibers”
(1) Class OM1 multimode fiber optic with 62.5-μm or 50-μm core.
(2) class OM2 multimode optical fiber with a 50-μm or 62.5-μm core.
(3) Class OM4 was ratified by IEEE in June 2010 and is the 802.ba Standard for 40G/100G Ethernet. Operates over distances of up to 1000 m over 1 Gbit/s Ethernet, 550 m over 10 Gbit/s Ethernet and 150 m over 40 Gbit/s and 100 Gbit/s Ethernet network protocols.
(4) International Standard ISO/IEC 11801 defines the maximum value of RF attenuation. IEC and TIA standards describe the (minimum) or average attenuation of a “bare” OB.