Satellite Internet and VSAT Information Centrum
Last updated: 15th December 2005, Available in English, French, German, Italian, Spanish, Portugese
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This site is an online collection of articles, technical speicifcations, advices, useful tools, reviews and links related to the 2-way Satellite Internet access systems which are gaining higher popularity nowadays. While we have tried to collect the most important information available, related to VSAT services offered in Europe, Middle East, Africa and Asia, the site may contain material for Satellite Internet access offers in Americas as well.
What is Satellite Internet?
Satellite Internet is a term used to describe the method of accessing the global Internet network via the satellite spacecraft. Usually, most of the customers choose satellite due to unavailability of the local terrestrial DSL or ISDN infrastructure or the local telecoms creating monopolies which result in too expensive costs broadband Internet access services. Additionally, there is a category of Satellite Internet subscribers which use their systems to access the network in remote areas or moving vehicles, such as SNG, naval vessels and disaster recovery teams. There are two main types of Satellite Internet service: two-way and one-way, which is usually complemented by a one-way multicast service, also known as offline data delivery in order to download large data volumes like movies and music files efficiently.
Two-way VSAT Service
Two-way Satellite Internet access service is a completely autonomous set up which does not require any IP connectivity from the subscriber - it can provide Satellite Internet access anywhere in the satellite coverage map. This means that almost in any point of our planet there is a chance to get a high-quality, affordable broadband Internet access. The two-way Satellite Internet access subscriber is required to purchase and install the Earth Station equipment which is generally referred as VSAT - Very Small Aperture Terminal - equipment . The VSAT Earth Station, in it's turn, establishes two-way radio circuit with the satellite spacecraft and is used both for downloading and uploading data from and to Internet.
VSAT Description
Very Small Aperture Terminal refers to an equipment package, installed at customer's premises in order to establish a 2-way radio link circuit with the satellite. The term originates from the fact that usually VSAT describes equipment packages with less than 3 meter diameter antenna. The total amount of VSAT systems installed around the globe is varying and, upon the studies held in 2003, is near 700,000. VSAT systems are used in a wide range of applications, from providing Direct-to-Home Satellite Internet access to residential users, Internet Cafe businesses, Hot Spots and Wireless Service Providers and used in industrial, educational and commercial niches as well, such as gas stations, naval vessels, point of sales, remote hospitals and similar.
VSAT Platforms and Technologies
There is a large number of VSAT platforms evolved in order to provide connectivity services worldwide. The most popular VSAT platforms used in order to provide Satellite Internet access services and Enterprise network connectivity in general are:
- ViaSat LinkStar and SurfBeam - MF-TDMA (DVB-RCS) and DOCSIS standards
- Hughes DirecWay - Legacy TDMA standard
- iDirect NetModem and Infiniti Series Routers - Deterministic TDMA standards
- Gilat SkyEdge, SkyBlaster - MF-TDMA (DVB-RCS) standard
- Shiron InterSky - MF-TDMA (DVB-RCS) standard
Different VSAT platforms use different technologies and know-hows in order to access the satellite radio space segment and share it among multiple subscribers. The most efficient technology wins the most performing VSAT platform and satisfied users. Many of sharing techniques are based on TDMA which stands for Time Division Multiple Access technology and usually are variants of TDMA. The concept of sharing the satellite space segment among multiple subscribers is based on allocating a group of users the same transmit and/or receive frequency segments and dividing it into many timeslots. Every user either is allocated it's own dedicated timeslot or they use the frequency as specified by the platform and the sharing technology. Most primitive technologies allow users to transmit randomly, decreasing the overall performance of the network down to almost 15-20% while innovative and "smart" concepts, such as iDirect Corporation propriteary Deterministic TDMA, dedicate timeslots to every subscriber, raising the performance bar at near 98%.
Selecting the right VSAT technology is one of the most important factors to consider when comparing Satellite Internet access offers from multiple providers. For example, when it comes to provide broadband Internet access simultaneously with Voice over IP (VoIP) or Videoconferencing applications, it makes sense to make sure to choose the platform which can provide both shared and dedicated bandwidth quotas.
FDMA (Frequency Division Multiple Access) technology deserves separate paragraph as this is a method almost an opposite to TDMA. FDMA is the oldest of the technology in order to provide collective access to the satellite space segment. FDMA principles are basing on statically dividing the frequency spectrum into multiple slots, per each subscriber. FDMA is mostly used in Full Duplex SCPC (Single Channel Per Carrier) VSAT systems or systems using an SCPC uplink in order to provide completely dedicated bandwidth circuit. SCPC VSAT systems are usually in demand by VoIP service providers because VoIP, as well as other real-time streaming applications, require dedicated bandwidth quota to work.
One-way DVB Service
This is the most affordable Satellite Internet access service available on the market. With one-way scenario, the subscriber uses it's narrowband terrestrial or wireless Internet connection (dial-up, ISDN or leased line, GPRS, EDGE, CDMA, etc) as an outbound transmit circuit. The Satellite ISP acts as the downlink provider, enabling the subscriber to download data via satellite. This concept is very popular as many users require broadband links for data download purposes only and usually do not require a broadband uplink channel. Additionally, the benefits are that one-way Satellite Internet equipment costs are pretty low as this scenario works on a standard satellite TV antennas and universal LNB available almost in every satellite shop locally. Usually, Satellite ISP use DVB (Digital Video Broadcasting) standard as the transport for IP packets and the customer is required to install a sub-$100 priced DVB router or internal PCI card such as Technisat Skystar 2.
Additionally, it is worth to mention that many of Satellite Internet subscribers, for example in Russian Federation and Ukraine, choose one-way service due to complicated licensing procedures implied by the government in order to import VSAT equipment and utilize two-way services. One-way Satellite Internet access requires absolutely no licenses or government permissions in most of the countries, although it's always better to consult the local Ministry of Telecommunications or appropriate inistitution before subscribing to the service.
One-way Multicast Service
Multicast service, also referred as offline data delivery, is a popular method to push extremely large amounts of data such as multimedia files - movies and music simultaneously to many subscribers at once. This concept brings additional benefit both to users and providers: subscribers receive the ability to request and download entertainment content at a very low cost and the provider enjoys additional revenues and decreased satellite space segment usage. Additionally, One-way Multicast services are often used to deliver large data chunks to remotely located branches of a single enterprise, similarly to the concept described above.
Satellite Related Links
Brief History of Satellites
The first satellite ever mentioned in human mankind is dated fall 1945, an article written by RAF electronics officer, Arthur C. Clarke (shown on the left). His article, called Wireless World, described the spacecraft - satellites - high above the Earth surface, used to distribute television signals. Unfortunately the article did not bring any immediate effect as only after ten years, in 1955, the idea was evaluated and carefully studied by John R. Pierce of AT&T Bell Laboratories. John R. Pierce suggested a medium orbit repeater acting like a mirror for the signals emitted by the Earth stations. Back in 1955, when the TAT-1 trans-atlantic cable could only handle 36 simultaneous telephony calls, the idea of placing a repeater providing the ability to manage 1,000 simultaneous calls have born the commercial communications satellite.
USSR was the first country to launch the satellite, called Sputnik-1 in 1957. At the same time, NASA and US Department of Defense was busy with experiments on passive (ECHO) and active repeaters which are able to amplify the signal to provide a better quality of communications. The results were an active communications satellite called RELAY, built by NASA, AT&T's TELSTAR (this name is still used nowadays by Loral Skynet), and Hughes Syncom. By 1964, all three projects were operational. The era of satellite communications had begun from the point when Communications Satellite Corporation (COMSAT), a US government formed organization, chose the geosynchronous orbit satellite built by Hughes - that was Early Bird, which was launched on April 6, 1965.
By the end of 1965, Early Bird was transmitting more than 150 telephone circuits and 80 hours of television signals. Early Bird satellite provided 10 times the trans-atlantic cable capacity at only 1/10th of the original price. Situation has changed in 1980's to opposite when terrestrial technologies emerged with fibre optic circuits fighting back the niche of global carriers of the world's traffic. Still, satellites are being launched 10-20 every year with accent to TV
broadcasting, Satellite Internet access provision in remote areas and reliable communication carriers. Many countries with their national ISP networks depend on satellites for Internet and telephony service provision, especially in developing regions such as Africa, Asia and Middle East.
TCP/IP over Satellite and TCP Accelerators
TCP/IP protocol suite is the set of communication protocols and standards Internet was built on. TCP/IP consists of TCP - Transmission Control Procol and IP - Internet Protocol which form a protocol stack. The Internet protocol suite derived itself from the DARPA desearch made in early 70's. By developing common standards to interconnect various networks together, it became possible to form the unique and solid Internet as we know it today. TCP/IP has saved much of it's characteristics which were originally developed in 70-80's and oriented mostly to terrestrial based networks, when Satellite Internet access and VSAT systems are yet to be utilized commercially. Despite significant optimizations and enhancements proposed over the many years, TCP/IP operation has not changed significantly since RFC 793, published in 1981.
Applying standard TCP/IP to Satellite Internet access circuits leads to the underutilization of the link and degraded performance. Despite satellite circuits having advanced FEC (Forward Error Correction) algorithms, there is still a big issue of round trip latency due to that geostationary satellites are 30,000 km above the earth surface: it takes approximatley half a second for the signal to travel from the user to the satellite and back to the teleport. Additionally, there is a packet loss possible, as with any wireless circuit, including WiFi. These issues cause TCP/IP to automatically reduce it's window size as a precaution and the slow start algorithm to work incorrectly.
There is a number of solutions available in order to overcome TCP/IP performance degradation. Usually, these solutions are named TCP accelerators and Performance Enhancing Proxies such as BusinessCom PEP, Hughes PEP, Mentat Skygateway, Comtech TurboVR, Tellique and others. TCP accelerators are available both with one-way and two-way Satellite Internet services. TCP accelerators use different techniques to substitute TCP/IP with a protocol set which is more optimized for Satellite Internet access and wireless circuits in general. Most of solutions use UDP as the primitive IP packets transport while speed and window size negotiations are done inside the TCP accelerator protocol set, being a know how of it's developers.
Most of the TCP accelerators also bundle a number of well known techniques in order to improve the performance of the Satellite Internet circuit as seen by the common user. These techniques usually include DNS caching, HTTP pre-fetching and one the fly traffic compression.
TCP/IP and Internet Protocols Related Links
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