When used for communications, a satellite acts as a repeater. Its height above the Earth means that signals can be transmitted over distances that are very much greater than the line of sight. An earth station transmits the signal up to the satellite. This is called the up-link and is transmitted on one frequency. The satellite receives the signal and re-transmits it on what is termed the down link which is on another frequency.
The circuitry in the satellite that acts as the receiver, frequency changer, and transmitter is called a transponder. This basically consists of a low noise amplifier, a frequency changer consisting a mixer and local oscillator, and then a high power amplifier. The filter on the input is used to make sure that any out of band signals such as the transponder output are reduced to acceptable levels so that the amplifier is not overloaded. Similarly the output from the amplifiers is filtered to make sure that spurious signals are reduced to acceptable levels.
The signal is received and amplified to a suitable level. It is then applied to the mixer to change the frequency in the same way that occurs in a super-heterodyne radio receiver. As a result the communications satellite receives in one band of frequencies and transmits in another.
In view of the fact that the receiver and transmitter are operating at the same time and in close proximity, care has to be taken in the design of the satellite that the transmitter does not interfere with the receiver. This might result from spurious signals arising from the transmitter, or the receiver may become de-sensitized by the strong signal being received from the transmitter. The filters already mentioned are used to reduce these effects.
- Geosynchronous (GEO) satellite orbit (22,300 miles) rotates at the same speed as the earth’s rotation. Three satellites can cover most of the globe.
- Medium earth orbit (MEO) satellites are closer to users on Earth but 10-18 are required for continuous coverage.
- Low earth orbit (LEO); satellites are closest to users (300-500 miles) but 40-70 satellites are required for full coverage.
According to the Satellite Industry Association (SIA) report, as of June, 2011.
the following statistics were observed;
Operational Satellites by Orbit
- Of the 986 satellites on orbit, 37% are commercial communications satellites
- There are 480 LEO Satellites (49%), 405 GEO Satellites (41%), 65 MEO (7%) and 35 ELI or 4% (Elliptical Orbit)
Operational Satellites by Function
- Commercial Communications 365 Satellites (37%),
- Civil Communications 108 Satellites (11%),
- Military Communications 84 Satellites (9%),
- Meteorological 44 Satellites (4%),
- Military Surveillance and other 89 Satellites (8%),
- Navigation 75 Satellites (8%),
- Remote Spacing 92 Satellites (9%),
- Space Science 59 Satellites (6%),
- other 50 (7%)
The key Satellite Network Elements include;
- Space Segment – Satellite, in geostationary orbit, middle earth orbit, or low earth orbit.
- Ground Segment
- Telemetry, Tracking, and Control (TT&C): used to “fly” the satellite.
- Gateway/Hub: used to manage communication payload
- User Terminals: devices used to connect to satellite network; can be receive-only or transmit; mobile or fixed; a dish, a laptop, or a handheld, depending on application, site, etc.
Satellites function as a cell or Microwave tower in the sky, transmitting data from one point on the earth to another.
Attributes of Satellite Systems
- Large Geographic Coverage interconnecting widely distributed networks, providing broadcasting services over a country, region, or entire hemisphere “last mile” connectivity for telecom services, broadband and video services
- Instant infrastructure, whether for network redundancy or emergency connectivity.
- Mobility, whether for voice, data or broadband or mobile video.
Satellites in Telecommunications
- Commercial satellites are an essential component of the global communications infrastructure
- Satellites carry the world’s media content around the globe
- Satellites deliver television, radio and broadband services directly to consumers
- Satellites offer mobile and portable voice, data and video globally
- Satellite networks link businesses among widely-dispersed locations
- Satellites provide connectivity and network restoration for remote and rural telecommunications operators
- Satellites are critical to disaster recovery and emergency preparedness
- Satellites provide critical communications and network restoration services following natural disasters
- The satellite industry is a subset of both the telecommunications and space industries
- Satellite industry revenues represent 61% of space industry revenues and 4% of telecommunications industry revenues
The ability and means to communicate with or otherwise interact with a system, to use system resources to handle information, to gain knowledge of the information the system contains, or to control system components and resources.
An actual assault perpetrated by an intentional threat source that attempts to alter the a system, its resources, its data, or its operations.
A list of entities that are blocked or denied privileges or access.
A computer connected to the Internet that has been secretly compromised with malicious logic to perform activities under the remote command and control of a remote administrator.
A model for enabling on-demand network access to a shared pool of configurable computing capabilities or resources (e.g., networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction.
The systems and assets, whether physical or virtual, so vital to society that the incapacity or destruction of such may have a debilitating impact on the security, economy, public health or safety, environment, or any combination of these matters.
The use of mathematical techniques to provide security services, such as confidentiality, data integrity, entity authentication, and data origin authentication.
The interdependent network of information technology infrastructures that includes the Internet, telecommunications networks, computer systems, and embedded processors and controllers.
The unauthorized movement or disclosure of sensitive information to a party, usually outside the organization, that is not authorized to have or see the information.
The processes and specialized techniques for gathering, retaining, and analyzing system-related data (digital evidence) for investigative purposes.
Enterprise Risk Management
A comprehensive approach to risk management that engages people, processes, and systems across an organization to improve the quality of decision making for managing risks that may hinder an organization’s ability to achieve its objectives.
The measures that protect and defend information and information systems by ensuring their availability, integrity, and confidentiality.
The process and methods for analyzing information from networks and information systems to determine if a security breach or security violation has occurred.
The numerical value used to control cryptographic operations, such as decryption, encryption, signature generation, or signature verification.
Software that compromises the operation of a system by performing an unauthorized function or process.
An actual assault perpetrated by an intentional threat source that attempts to learn or make use of information from a system but does not attempt to alter the system, its resources, its data, or its operations.
An evaluation methodology whereby assessors search for vulnerabilities and attempt to circumvent the security features of a network and/or information system.
A digital form of social engineering to deceive individuals into providing sensitive information.
A set of software tools with administrator-level access privileges installed on an information system and designed to hide the presence of the tools, maintain the access privileges, and conceal the activities conducted by the tools.
The level of confidence that software is free from vulnerabilities, either intentionally designed into the software or accidentally inserted at any time during its lifecycle, and that the software functions in the intended manner.
A computer program that can replicate itself, infect a computer without permission or knowledge of the user, and then spread or propagate to another computer.
A list of entities that are considered trustworthy and are granted access or privileges.
Cyber Security also known as Information Security involves protecting computers, networks, programs, and Data from unintended or unauthorized access, change or destruction;
Government agencies, the Military, Corporations, Financial Institutions, Hospitals process a great deal of confidential information on computers; and then transmit data across networks to other computers;
Cyber attacks (i.e. Network outages, hacking, computer viruses) affect in various ways ranging from inconvenient to life threatening; and as the number of mobile users, digital applications and Data Networks increase; so do the opportunities for exploitation by attackers.
With the growing volume and sophistication of cyber attacks, ongoing attention is required to protect sensitive business and personal information; as well as safeguard National security.
Optical fibers are circular dielectric wave-guides that can transport optical energy and information. they have a central core surrounded by a concentric cladding material. A protective coating is used to reduce cross talk between adjacent fibers and loss-increasing micro-bending that occurs when fibers are pressed against rough surfaces. To provide further protection, fibers are commonly incorporated into cables.
A fiber Optic cable consists therefore of the following components: Core, Cladding, Coating, Strength member, and Cable Jacket. As shown below.
This is the very center of the cable and is the medium of propagation of the light wave/optical signal. It is made up of silica glass/plastic with high index of refraction;typical core diameter ranges from 8 microns for single mode fiber up to 1000 microns for Plastic Optical Fiber (POF).
- Hollow Core Optic fiber
In almost every fiber-optic network, light travels through plastic or glass fibers — in hollow core optic fiber (which is the latest invention), light travels through an air gap, allowing for networks that are faster, have more bandwidth, and traverse greater distances.
In a vacuum, the speed of light is 2.99792458 x 108 m/s; approximately 3.00×108 m/s, approximately 186,282 miles/s. In air for visible light which has an index of refraction 1.003, it is about 299,700 kilometers (186,200 miles) /s while the same light travelling through glass of index of refraction 1.5, will travel at a speed of 200,000 kilometers (120,000 miles) /s. This tells us that the light is fastest in a vacuum, faster through air and fast glass.
Therefore, the hollow-core optical fiber allows light to travel along its length at around 99.7% the speed of light in a vacuum, or a 30% improvement over conventional (silica glass) optic fibers. The light will travel through hollow tubes.
These hollow-core fibers have lower signal loss (allowing for longer distances between repeaters), and the increased speed of light through an air gap(about 30% faster than plastic/glass) reduces latency.
The cladding is made of a silica glass/plastic material just like the core but of a lower refractive index. The difference in index of refraction forms a mirror at the boundary of the core and the cladding; and because of it’s lower refractive index compared to that of the core, it reflects the light back into the center of the core.
This is the phenomenon of total internal reflection which occurs when a light wave is moving from a denser medium (high index of refraction, e.g water) to a less dense medium (lower index of refraction, e.g air); and the angle of incidence is greater than the critical angle.
The cladding together with the core form a single solid strand of fiber, either glass or plastic. Total internal reflection in the fiber, as a result of the properties of the core and cladding, thereby guiding the light wave down the fiber makes it a wave guide.
A buffer is something that reduces shock or forms a barrier between adversaries.
The buffer coating is a protective layer surrounding the cladding. Typically it made up of a thermoplastic material for Tight Buffer Fiber Cables and a Gel material for Loose Tube Fiber cables.
Loose tube cables are designed for harsh environment conditions in the outdoors. They protect the Fiber core, cladding, and Coating by enclosing everything within fairly rigid protective sleeves or tubes. Many loose tube cables contain a water resistant Gel surrounding the fibers. The gel helps protect the fibers from moisture, making the cables ideal for high humidity environments, where water or condensation may otherwise be problematic. The gel filled tubes can expand or contract with temperature changes, as well. Despite the benefits, gel filled loose tube cables are not the right choice if the Cable needs to be submerged in water, or routed around multiple bends. Excess Strain may cause the fibers to emerge from the gel.
On the other hand, Tight buffered cables are optimal for indoor applications. Being more robust than loose-tube cables, they are best suited for moderate length LAN or WAN connections, long indoor runs, direct burial, and for underwater use. Rather than using the gel Layer loose tube has, tight buffered cables have a two-layer coating. The first is plastic, and the other, waterproof acrylate. The Acrylate keeps moisture away from the cable. The Core is never exposed when bend or compressed underwater. Tight buffered cables may be easier to install, because there is no gel to clean up and it does not require a fan out kit for Splicing or termination.
This further protects the fiber from over stretching during installation; also from expansion and contraction due to temperature changes.
In single and double fiber cables, the strength members are wrapped around the coating; while in multi strand cables, the strength member is in the center of the bundle
This is the last item on the construction. It provides the final protection from the environment in which the cable is installed. Of concern is the intended placement of the cable. Different jacket suite different environments/ solutions such as indoor, outdoor, aerial or buried installations.
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