• VSAT Overview -

  Advances in digital processing and the introduction of higher powered communication satellites with more efficient antennas enabled the development of low-cost small earth stations, known as VSAT (with 1.8m or smaller antennas) which have led to the establishment of numerous satellite networks. It describes a small terminal that can be used for two-way communications via satellite. VSAT networks offer value-added satellite-based services capable of supporting the Internet, data, video, LAN, voice/fax communications, and can provide powerful, dependable private and public network communications solutions. They are becoming increasingly popular, as VSATs are a single, flexible communications platform that can be installed quickly and cost effectively to provide telecoms solutions for consumers, governments and corporations.

• Satellite Advantages -

  Geostationary Orbit: Most communication satellites in use today are geostationary. They orbit the earth directly over the equator, approximately 22 000 miles (35 400 km) up. At this altitude, one complete trip around the earth (relative to the sun) takes 24 hours. Thus, the satellite remains over the same spot on the surface of the earth (geo) at all times, and stays fixed in the sky (stationary) from any point on the surface from which it can be "seen." A single geostationary satellite can "see" approximately 40 percent of the earth's surface. Three such satellites, spaced at equal intervals (120 angular degrees apart), can provide coverage of the entire civilized world. Capacity: A single transponder on one of these satellites (the part of the satellite that transmits signals back to Earth) is capable of handling approximately 100 million bits of information per second. This means that if the transponder is accessed for only 90 seconds per day, close to a billion bytes of data would be transferred - the equivalent of 865 000 double-spaced pages. With this immense capacity, today's communication satellites are an ideal medium for transmitting and receiving almost any kind of content, from simple data to the most complex and bandwidth-intensive video, audio and data content. Coverage: Satellite is the only broadband wide-area network technology that is available everywhere - in even the most remote urban and rural areas, anywhere in the world. By contrast terrestrial broadband technologies are strikingly limited in their coverage area. These broadband technologies, such as DSL, ISDN and cable networks reach only a limited percentage of homes and businesses. Scalability: Satellite networks are much less costly to deploy, maintain and operate than terrestrial network technologies. Terrestrial networks require heavy infrastructure for broadband data networks (such as DSL, ISDN and cable). High overhead costs for these infrastructures are passed on to the customer. In remote areas where such infrastructure does not exist, the expense of building such networks is often prohibitive. Deployment: Satellite networks can be rolled out to hundreds or thousands of locations in a fraction of the time required for a comparable terrestrial network. Multicast Capability: To send a file to 1,000 recipients over a terrestrial network requires sending 1,000 separate and identical messages, each of which consumes valuable bandwidth and server resources. They are also likely to arrive at different locations at different times. Satellite IP multicasting, on the other hand, can simultaneously deliver content to a virtually unlimited number of end-user locations - at speeds up to 40 Mbps.

• TDMA vs SCPC -

  TDMA - Time Division Multiple Access Time Division Multiple Access is a communications technology that allows realizing shared star-type two-way satellite IP networks. The remote satellite stations are connected by satellite (satellite- to-satellite links) with the central hub Earth station that manages incoming and outgoing traffic influx. Linkstar DVB-RCS technology (Digital Video Broadcasting – Return Channel Satellite) allows to create satellite networks for Internet access over satellite, web-based applications, e-mail, distance education, digital media streaming, and all general applications, which do not require availability of constant bandwidth. IDirect unique technology of its kind permits to determine the best access method to transmission equipment, which uses TDM protocol (Time Division Multiple) for outbound service and Direct TDMA protocol for inbound channels. It is an ideal choice for establishing geographical networks aimed to support management applications, videoconference, Voice over IP, web applications and real time applications generally. SCPC - Single Channel Per Carrier Single Channel Per Carrier (SCPC) permits to realize two-way point-to-point satellite networks for transmission of video, voice and data. The dedicated, not shared satellite bandwidth is allocated exclusively to two satellite stations that establish the network with bandwidth capacity from 64 Kbps up to 2 Mbps or even more from point A to point B. The needs of the customer, the type of transmitted signal and the size of the channel will determine the type of satellite modem that will be most appropriate from cost/benefit point of view for each specific technological solution.

• C-Band -

  C-Band is a portion of electromagnetic spectrum in the microwave range of frequencies ranging from 4 to 6 GHz. C-band is primarily used for satellite communications, normally downlink 3.7–4.2 GHz, uplink 5.9–6.4 GHz, usually 24 36-MHz transponders on board a satellite. Most C band satellites use linear polarization, while a handful (particularly older Intelsat satellites) use circular polarization. The applications include full-time satellite TV networks or raw satellite feeds, although subscription programming also exists. There are over thirty C-band satellites in Geosynchronous orbit serving North America, which provide more than 1,000 video channels and countless audio services. In the past, direct C-Band reception was the only satellite television option available to consumers. Since the introduction of high-powered direct broadcast satellite systems, which normally use small 18-inch (45 cm) stationary dishes (in contrast to the large dishes and motors required by C-Band systems) in the mid 1990's , the number of homes using C-Band satellite systems in the United States for general reception has vastly declined while small-dish systems enjoyed unprecedented success. Despite this, C-Band satellites continue to be a key important distribution method for cable networks in the United States (to cable head-ends and mini-dish DBS services) and other network/broadcast users. For example, most satellite-distributed syndicated and network television shows are pre-aired for affiliate and Canadian pick-up by C-Band. Radio stations picking up satellite-fed programming also constitute an important American user of C-Band, with a major American radio "neighborhood" located on the AMC 8 satellite at the 139° west orbital position. Typical antenna sizes on C-band capable systems for home reception in North America range from 7.5 to 12 feet (2 to 3.5 m). In other regions of the world, such as Europe and parts of Asia, considerably smaller dishes can be used due to high-powered satellites in this band and more distance between satellites in the orbital arc (as opposed to the two-degree spacing common over North America). C-Band usage is less common in Europe, where the Ku band has traditionally dominated. In many parts of the world, C-Band is often used to cover a very broad area, for example all of Africa or China. Indeed, many C-Band satellites have "global" beams with gigantic coverage areas. For example, the global beam of a satellite positioned at the 78.5° E orbital slot (over the Indian Ocean) has a coverage range extending over most of Europe, Asia, Africa, and Australia. C-Band in the V-SAT industry is out of date and not recommended any longer, as the signal gets disturbed by Microwave emitting transmitters like Mobile Phone Uplinks or Wireless LAN because their frequencies are too close to C-Band frequencies. C-Band is considered to be more resistant towards rain fade. But if Ku-Band or Ka-Band systems are designed well, rain fade disruptions do not occur. C-Band V-SAT equipment is more expensive on the BUC and OMT side. Besides major equipment suppliers have stopped the production of transmission equipment for the known negative effects of this Band. C-Band is only recommended for areas in which Ku Band satellite coverage is not available and for areas in which interferences by other Microwave sources are excluded.

• Ku- Band -

  Ku Band is a portion of the electromagnetic spectrum in the microwave range of frequencies ranging from 12 to 18 GHz. Ku band is primarily used for satellite communications, particularly for satellite backhauls from remote locations back to a television network's studio for editing and broadcasting. Ku band is split into multiple segments that vary by geographical region by the International Telecommunication Union (ITU). Several highly used segments in the Americas (ITU Region 2) are: The 11.7 to 12.2 GHz band is allocated to the FSS (fixed satellite service, uplink 14.0 to 14.5 GHz). There are more than 22 FSS Ku-band satellites orbiting over North America, each carrying 12 to 24 transponders, 20 to 120 watts per transponder, and requiring a 0.8-m to 1.5-m antenna for clear reception. The 12.2 to 12.7 GHz segment is allocated to the BSS (broadcasting satellite service). BSS/DBS direct broadcast satellites normally carry 16 to 32 transponders of 27 MHz bandwidth running at 100 to 240 watts of power, allowing the use of receiver antennas as small as 18 inches (450 mm). Several highly used segments in Europe and Africa (ITU Region 1) are: The 11.45 to 11.7 and 12.5 to 12.75 GHz bands are allocated to the FSS (fixed satellite service, uplink 14.0 to 14.5 GHz). The 11.7 to 12.5 GHz segment is allocated to the BSS (broadcasting satellite service). Other ITU allocations have been made within the Ku band to the Fixed Service (microwave towers), Radio Astronomy Service, Space Research Service, Mobile Service, Mobile Satellite Service, Radiolocation Service (radar), and Radio navigation. However, not all of these services are actually operating in this band and others are only minor users. NBC was the first television network to uplink a majority of its affiliate feeds via Ku-band in 1983. Ku Band has become the standard in V-SAT Broadband Internet applications. It is, if well designed, not affected by interferences or rainfalls. Within the last years the price for the equipment has dropped to a level which allows satellite broadband operators to offer products and services at affordable prices.

• C-Band Myth -

  Many of our customers, especially those located in Africa, ask us about the difference between C- and KU band. Satellite communication systems are subject to international agreements and regulations. The International Telecommunication Union (ITU) regulates frequency use and defines "bands" The following bands are commonly used: - C-band was the first band to be used for satellite communication systems. However, when the band became overloaded (due to the same frequency being used by terrestrial microwave links) satellites were built for the next available frequency band, the Ku-band. Today C-Band also gets disturbed by mobile phones. - Ku-band is typically used for broadcasting and 2-way Internet connections. C-band: The C-band frequency range has one significant problem. It is the frequency region assigned to terrestrial microwave radio communication systems. There are a myriad of these microwave systems located all over the world and they carry a large volume of commercial communications. Consequently, the VSAT locations needed to be restricted in order to prevent interference with the terrestrial microwave communication systems. As mobile phones get used more and more in countries all over Africa as well, the use of C-Band in future will certainly rather decrease than increase. Ku-band: The Ku-band frequency range is allocated to be exclusively used by satellite communication systems, thereby eliminating the problem of interference with microwave systems. Due to higher power levels at new satellites Ku-band allows for significantly smaller earth station antennas and RF units to be installed at the VSAT location. The myth: At the inception of satellite communications in Africa, C-band was the only option. It has been the long held belief that Ku-band could not be deployed in Africa due to the torrential rains associated with the continent. However, with the technology progress in the satellite industry, more powerful satellites now exist and equipment (4 Watt Transceivers) has been developed which strengthens the link quality even in fierce conditions, thereby eliminating the impact of heavy showers. Its all a matter of correct design and proper equipment. C-Band Downlink: 3.7 – 4.2 GHz Uplink: 5.9 – 6.4 GHz Advantages: Less disturbance from heavy rain fade Disadvantages: Needs a larger satellite dish (diameters of minimum 2-3m) Powerful (=expensive) RF unit Much more expensive bandwidth Much more expensive hardware Interference from microwave links Ku Band Downlink: 11.7 – 12.2 GHz Uplink: 14.0 – 14.5 GHz Advantages: Cheaper and more powerful bandwidth No interference from microwave links and other technologies Operates with a smaller satellite dish (diameters from 0.5m) -> cheaper and more easy installation Needs less power -> cheaper RF unit Disadvantages: Sensitive to heavy rain fade (significant attenuation of the signal) / can be managed by appropriate dish size or transmitter power. 4 Watt for Africa In regions with heavy rainfalls, especially in the equatorial region, we recommend a 4 Watt Transceiver. Even if not necessarily required, this product is strongly recommended in order to avoid breakdowns during heavy weather conditions.

• What is a Teleport -

  Satellite teleports are permanent satellite uplink facilities located throughout the world. Teleports were built for maintaining high quality communications with orbiting satellites. A teleport consists of a number of facilities for data transmission and reception via a satellite connection. The main tasks of the teleport are Sending internet data to the satellite Reception of signals from the satellite for control of signal presence at the satellite and its quality Providing permanent capacity for work of the satellite channel Some teleport facilities offer global coverage through the Intelsat, Eutelsat, PanAmSat, Arabsat, Nilesat, Thaicom, Telstar and Amos satellites. C, Ku and Ka band teleport services are often provided. Antennas up to 12 meters across are dedicated to occasional services to ensure high availability and maximum flexibility when a story breaks.

• What is Contention Ratio -

  Unfortunately there are many definitions on the market about what contention ratio (or overbooking ratio) really means. This has caused a lot of confusion on the customer side, so let us give here some explanations on the topic: All communication networks share the total bandwidth available since not everyone subscribed to use the network actually uses it at the same time. This allows the costs to be reduced by sharing the bandwidth resource among many users. Especially as the bandwidth in satellite networks is quite cost intensive providers often run high contention ratios of 1:100 or more. As a comparison, many terrestrial DSL networks are designed for contention ratios of 1:8 to 1:12. Thus the bandwidth is 'resold' many times and contention is a measurement of this sharing factor. Always ask for the definition of contention! Unfortunately there is no standard method which defines how contention is measured and this enables some broadband suppliers to 'squeeze' the truth in order to make their offers look attractive. There are two factors which are often applied to get a 'contention' figure. The first is called 'utilization'. This simply is a percentage of users sharing the same bandwidth space who can be expected to actually sit and work at their computer terminal. Typical figures range on assumptions from 25% for home based user networks to 50% for business based user networks. The second factor is less precise and is based on a statistical calculation of how many users can be expected to actually be sending/receiving data over the Internet at any instantaneous point of time. Statistical contention is probabilistic in nature and therefore is difficult to use for comparisons of different offered services. Different figures are produced using different variances and distribution models. The bottom line is that contention figures by themselves do not give you a guide on performance unless you know what the utilization is and what statistical model was used. Price of service is a better guide of actual contention since by increasing contention (thus reselling bandwidth more times) a lower price can be offered. As for most things in life, if you pay less, you get less!

• Quality of Service -

  We work very hard to offer you the best possible Internet service for your money. Whereas most competitors publish "burst rates" which then can only be reached during night times, we give you more detailed information on the quality of service to be expected. Internet speeds are always published as burst rates and always state the maximum value of possible data transfer over the link. Burst rates always assume optimal network environments, which do rarely occur. Quality of Service in 2-way satellite industry is not only defined by the maximum data rate a customer can expect. Its always related to the following factors: maximum burst rate (speed) continuity of speed overall availability of service and the most important factor is: transferred DATA VOLUME As satellite capacity is quite expensive, operators try to put as many customers on one stream as possible. This "sharing" or "overbooking" strongly influences the provider's overall Quality of Service. Whereas some providers assume that only one of four systems is online at the same time (they call this SAR), we define contention as the number of users on the same stream in a worst case scenario. That means we assume that 100% of all customers are always online. Not only 25%. Contention and Quality of Service As satellite providers quite often run high contention ratios in order to offer attractive prices, customers need to understand that contention strongly influences the Quality of Service. Its quite important to understand how contention is calculated or defined. As we assume that worst case, at a contention of e.g. 1:50 maximum, 50 customers share the same link, we can define that in a worst case scenario a customer will get 1/50th minimum speed of the maximum burst rate. That means, for a contention of 1:50 the guaranteed minimum rate for 1024 kilobits is 20.8 kilobits.

• Packet Delay -

  Because of the distance between the earth and the satellites (roughly 22,000 miles/36.000 km) data takes about 600 milliseconds (both ways) to do the round trip into the Internet and back to the user. In total the user may experience minimum packet roundtrip times (before experiencing a reaction after action) of 600ms or 0.6 seconds. In reality and due to the fact that the satellite or internet sites are under load, round trip times may increase up to 1200 or 1300 ms. This delay, or latency as it is often called, requires satellite Internet carriers to use special software acceleration techniques to deliver a high-speed satellite Internet connection. The delay cannot be influenced as it is physically determined by the distance between the satellite and the earth. In case of the protocols HTTP and FTP a very big cache in the satellite and in the satellite terminal provides acceleration through an intelligent prefetch. As a result, with standard protocols the user might experience only very small delays in stationary contents and acceptable delays in dynamic contents.

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