Glossary of Satellite Terms   (back to Satellite Products listing)



1.2 Meter Satellite Dish – Satellite dishes are measured in Square Meters. They may be elliptical or round. Satellite dishes reflect the satellite signal to the feed horn where the signal is captured and decoded by the LNB. Other common sizes for satellite dishes are .74 Meter, .98 Meter, 1.8 Meter and 2.4 Meter.

ACCOUNTING AUTHORITY RESPONSIBILITIES (ITU) – When acting on behalf of a maritime mobile station for which it has accepted responsibility, an accounting authority shall be responsible for obtaining payment of the collection charges for maritime mobile communications from the maritime mobile station. Guaranteeing payment of the collection charges to the service providers for traffic originated by the maritime mobile station. Ensure that these payments are made in accordance with the ITU Regulations and Recommendation D.90. Maintaining up-to-date and accurate records of the maritime mobile stations for which it has responsibility. Any change in status, ship owner if known, and termination/commencement of contract must be notified immediately to interested/regularly used service providers and to the Administration that licensed the maritime mobile station. Where changes have occurred, a new and updated list of maritime mobile stations should be issued by the accounting authority at least every 90 days to interested/regularly used service providers and to the Administration who licensed the maritime mobile station, with changes to the previously issued information clearly indicated. Alternatively, a “no change” notification may be issued. The updated information should consist of: satellite identity number/ships call sign; ship/mobile name; commencement date.

AZIMUTH – The rotational Axis of a mobile satellite system.  Most mobile systems have a greater than 360 degree rotation so that scanning for a signal is not impeded by a physical limit on the mobile dish.

BANDWIDTH – The amount of data that can be transmitted in a fixed amount of time. Most commonly expressed in bits-per-second (bps with a small b) but occasionally in Bytes-per-second (Bps with an upper case B).  Kbps is Kilobits per second, or 1000 bits per second. Mbps is a million bits per second. The old dial-up modems commonly used 56Kbps.

BGAN and BGAN-X – Broadband Global Area Network provided by Inmarsat’s 4th generation (I4) satellites to provide up to 492 Kbps bandwidth on a single device (bonding for much higher speeds using more than one device easily). Land based terminals tend to be given the term BGAN but satellite terminals that use the very same network operating by air (Swift Broadband), land or sea (Fleet Broadband) are termed BGAN-X.

BGAN Class – refer to the maximum capable speeds of a BGAN terminal. These ratings are applied by Inmarsat who certify all BGAN terminals. Inmarsat states that all terminals must be able to deliver no less than 70% of the published Inmarsat bit rate for the class that it is rated for. The difference in speeds between a Class 1 and Class 2 BGAN terminal is quite small (94% as fast) for a standard Internet connection (charged by the Megabyte). The main difference between these BGAN class types is a Class 1 has much faster streaming services that are charged-by-the-minute. Streaming services are unshared data connections and are often used by news broadcasters to stream live video from remote locations.

Download Upload Streaming Services – Unshared Connect
BGAN Terminal Class Definition Standard Connect Standard Connect Charged by the minute connection Example Equipment Types
BGAN Class 3 348 Kbps  240 Kbps 32 Kbps, 64 Kbps Explorer 300/iSatHub
BGAN Class 2  464 Kbps 448 Kbps 32 Kbps, 64 Kbps, 128 Kbps Explorer 510/540/325
BGAN Class 1  492 Kbps 492 Kbps 32 Kbps, 64 Kbps, 128 Kbps, 256 Kbps, 450Kbps* Explorer 700/710/727
* 450 Kbps streaming is only available on the Explorer 700/710 and the in-motion Explorer 727 when parked.

BROADBAND – is simply “High-Speed” Internet access that is much faster than the old “Dial-up” Internet access.

BUC– The “Block Up Converter” is simply the transmitter for a satellite dish. BUC’s are rated by wattage, the higher the wattage, the better the upload performance, especially during bad weather.

C-Band – The C band is primarily used for voice and data communications as well as backhauling. Because of its weaker power it requires a larger antenna, usually above 1.8m (6ft). However, due to the lower frequency range, it performs better under adverse weather conditions on the ground. It operates in the frequency range for VSAT satellite communication from 3.7 to 4.2 GHz for downlink and 5.925 to 6.425 GHz for uplink communication. C-Band systems are lightheartedly referred to as a “BUD” or Big Ugly Dish.

CERTUS (Iridium) – Mobile terminal hardware designed to work on the Iridium Next satellite network (example Sailor 4300)

CIRCommitted Information Rate.

CIR is the guaranteed speed you can rely on with your satellite connection. Your speeds will not drop below this amount. CIR is normally associated with an unshared channel where there are no other subscribers using that channel. This means that full speed is available at all times. Since a 1:1 CIR channel is not shared, it is typically much more expensive as the satellite provider cannot sell to other users so expect to pay a premium for CIR. Some companies use the term CIR loosely in describing their shared plans, however, these plans are not 100% guaranteed to committed speeds. Please compare with MIR

Contention Ratio

Contention Ratio refers to the number of subscribers that are sharing the connection at the same time. Many “consumer” organizations like Hughesnet have contention ratios that approach 400 to 1, which makes the speeds crawl.  Most Standard plans are between 10:1 to 20:1 contention ratios.

dBW – Decibel Watts is a measurement of energy beamed from a satellite to a point on the earth. The higher the dBW, the stronger the signal strength, and the small satellite dish that is required.

DHCP – Dynamic Host Configuration Protocol, pronounced as four letters. A protocol for assigning dynamic IP addresses to devices on a network.  With dynamic addressing, a device may have a different IP address each time it connects to the network. DHCP also supports a mix of static and dynamic IP addresses.  Windows ICS uses the address range of through when it assigns addresses. It also works fine when computers on the ICS network are assigned addresses in that range statically, but it is a good idea to use high numbers to avoid conflicts.

DNS – Domain Name System (or Service or Server), pronounced as three letters. An Internet service that translates domain names into IP addresses. Because domain names are alphabetic, they’re easier to remember. The Internet however, is really based on IP addresses. Every time you use a domain name, therefore, a DNS service must translate the name into the corresponding IP address. For example, the domain name translates to The DNS system is, in fact, its own network. If one DNS server doesn’t know how to translate a particular domain name, it asks another one, and so on, until the correct IP address is returned.

DOWNLOAD – Information that comes to your computer from the Internet.  The typical Download speeds of an iDirect connection is between 2500 Kbps and 4500 Kbps (Kilobits per second)
Dynamic IP Refers to the addresses assigned by the router your computer is connected to each time you log into the network. The IP address is how all information flows to and from your computer. Like a street address, it is this address that is required for communication. The reason it is Dynamic (And not static) is it changes each time that you log on to a network (or the Internet). Alternatively, a static IP address never changes for your computer.

EIRP – Effective Isotropically Radiated Power, is the measure of the strength of the signal leaving a satellite antenna in a particular direction, equal to the product of the power supplied ot the satellite transmit antenna and its gain in that direction.

ELEVATION – The vertical axis (up & down) motion of pointing the satellite dish.

FAP/FUP – Fair Access/Usage Policy, pronounced as a word that rhymes with gap. Satellite connections, while always on, are not unlimited. Bandwidth is a finite resource, so the method used to provide high download bandwidth for all while preventing any one user from hogging that bandwidth is FAP.

FLAT PANEL ANTENNA – Using either a “multitude of tiny antennas” to generate electronically steerable beams or by use of “meta-materials” or a combination of both to generate the same result this technology has achieved remarkable throughputs. At this stage the technology is still in development and in the maritime environment where there is rapid movement in 3 axes the performance still does not match more traditional antennas such as stabilised, parabolic dishes unfortunately

FOOTPRINT – The satellite signal strength as it falls on the Earth. It can also be called a coverage map.

GEO – a geostationary Earth orbit or geosynchronous equatorial orbit is a circular orbit 35,786 kilometres above the Earth’s equator and following the direction of the Earth’s rotation. An object in such an orbit has an orbital period equal to the Earth’s rotational period (one sidereal day) and thus appears motionless, at a fixed position in the sky, to ground observers. Communications satellites and weather satellites are often placed in geostationary orbits, so that the satellite antennas (located on land or fixed platforms on Earth) that communicate with them do not have to rotate to track them, but can be pointed permanently at the position in the sky where the satellites are located. Cf. LEO; MEO & HEO

Gain – In electromagnetics, an antenna’s power gain or simply “gain” is a key performance number which combines the antenna’s directivity and electrical efficiency. In a transmitting antenna, the gain describes how well the antenna converts input power into radio waves headed in a specified direction. In a receiving antenna, the gain describes how well the antenna converts radio waves arriving from a specified direction into electrical power.

GOODPUT – In computer networks, goodput is the application-level throughput (i.e. the number of useful information bits delivered by the network to a certain destination per unit of time). The amount of data considered excludes protocol overhead bits as well as retransmitted data packets. This is related to the amount of time from the first bit of the first packet sent (or delivered) until the last bit of the last packet is delivered.

For example, if a file is transferred, the goodput that the user experiences corresponds to the file size in bits divided by the file transfer time. The goodput is always lower than the throughput (the gross bit rate that is transferred physically), which generally is lower than network access connection speed (the channel capacity or bandwidth).

HEO – High Earth orbit is a geocentric orbit with an altitude entirely above that of a geosynchronous orbit (35,786 kilometres ). The orbital periods of such orbits are greater than twenty-four hours, therefore satellites in such orbits have an apparent retrograde motion – that is, even if they are in a prograde orbit (90° > inclination >= 0°), their orbital velocity is lower than Earth’s rotational speed, causing their ground track to move westward on Earth’s surface.

HTS – High-throughput satellite is a classification for communications satellites that provide at least twice, though usually by a factor of 20 or more, the total throughput of a classic FSS satellite for the same amount of allocated orbital spectrum thus significantly reducing cost-per-bit. ViaSat-1 and EchoStar XVII (also known as Jupiter-1 do provide more than 100 Gbit/s of capacity, which is more than 100 times the capacity offered by a conventional FSS satellite. When it was launched in October 2011 ViaSat-1 had more capacity (140 Gbit/s) than all other commercial communications satellites over North America combined

I2 – Inmarsat 2nd generation satellites were launched in 1990-2 and, despite a planned design lifespan of 10 years, the final I-2 satellite continued in active service until December 2014, more than two decades later.

I3 – Inmarsat 3rd generation satellites are expected to remain in operation, providing communication and safety services in the L-band, until around 2018. Equipment working with the I3 satellites is often referred to as E&E (existing and evolved ) equipment and examples are Mini-M; GAN and Fleet range (not Fleet Broadband or Fleet One; see I4)

I4 – Inmarsat 4th generation satellites are expected to support L-band services without the need for replacement until the early-2020s. Inmarsat-4 F1 Asia-Pacific 143.5° east launched 11 March 2005 BGAN family, SPS and lease services; Inmarsat-4 F2 Europe, Middle-East, Africa 64.4° east launched 8 November 2005 BGAN family, SPS and lease services; Inmarsat-4 F3 Americas 98° west launched 18 August 2008 BGAN family and lease services 13 years; Inmarsat-4A F4 Europe, Middle-East, Africa 24.8° east launched 25 July 2013 BGAN family, SPS and lease services 15 years. Examples of equipment that works with I4 satellites are Fleet Broadband; Isatphone; BGAN; Isathub and Swift Broadband.

I5 – Inmarsat 5th generation satellites GX ka band network

ICCID – Integrated Circuit Card Identifier Each SIM is internationally identified by its ICCID and is the identifier of the actual SIM card itself – i.e. an identifier for the SIM chip. ICCIDs are stored in the SIM cards and are also engraved or printed on the SIM card body.  The number can be up to 22 digits long.

IDU – Indoor Unit.  It use to refer to equipment the satellite dish connects to inside of a building, such as a satellite modem.

IMSI – The International Mobile Subscriber Identity or IMSI/ˈɪmz/ is a 15 digit number that uniquely identifies every user/SIM of a cellular/satellite network. It is stored as a 64-bit field and is sent by the mobile device to the network.

IP ADDRESS – Internet Protocol, pronounced as two separate letters. IP specifies the format of packets, and the addressing scheme used on the Internet. The Internet combines IP with a higher-level protocol called Transmission Control Protocol (TCP), which establishes the connection between a destination and a source.

IP by itself is something like the postal system. It allows you to address a package and drop it in the system, but there’s no direct link between you and the recipient. TCP/IP (pronounced as 5 letters), on the other hand, establishes a connection between two hosts so that they can send messages back and forth for a period of time. IP addresses are in the form of a 32-bit numeric address written as four numbers separated by periods. Each number can be zero to 255. For example, could be an IP address.

Within a LAN, you can assign IP addresses at random as long as each one is unique; addresses which are public to the Internet must be within assigned ranges in order to avoid duplication. The authorities that assign public Internet addresses have designated certain ranges as never to be used on the Internet; by convention, those are normally used as private addresses on a LAN. The ranges for private addresses are all addresses starting with 10 (e.g., addresses between and, and addresses between and

IRIDIUM NEXT – network consisting of 66 active satellites to replace the existing constellation with another nine in-orbit and six on-ground spares. These satellites are in LEO orbit (vs Geostationary) providing true global coverage including the polar regions with low latency data transmission . The constellation is planned to provide L-band data speeds, initially of up to 352 kbit/s; then 704Kbps and eventually 1.4Mbps on Certus equipment

Iridium LBS -Iridium Extreme  ( 9575 ) LBS (Location Based Services) is a data service that allows you to cost-effectively send and receive short burst data transactions efficiently over the Iridium network. GPS Tracking on the Iridium Extreme 9575 goes over a channel on the Iridium network called LBS. LBS is different from the channel that sends voice, data, and SMS. The Iridium Extreme 9575 satellite phone has an integrated GPS. This allows you to send GPS tracking pings over the Iridium network, giving you coverage everywhere on the planet.

There are a few ways to use the Iridium Extreme 9575 as a Personal GPS Tracking Device. The most popular option is for the user to set the Iridium Extreme 9575 to utilize the SMS functionality of your service plan. Your airtime invoice will show an outbound SMS message for each time tracking information was sent.

For example, if you want to turn on tracking for a single day hike you have planned, you might select a 30-minute time interval and transmit over an 8-hour period. This means you would send about 16 SMS messages. On most Iridium service plans this would cost well under $10, which is not much for the feeling of safety and letting your family and friends know exactly where you are exploring. However, If you intend to use tracking services heavily on a year-round basis, it is more economical to use the Iridium Extreme 9575 LBS feature instead of SMS messaging to transmit your position reports. LBS is billed according to the total bytes of data transmitted.

Iridium RUDICS – The Iridium Router-Based Unrestricted Digital Internetworking Connectivity Solutions (RUDICS) is an enhanced data service that allows customers who have requirements for large data transfers the ability to transfer data via reliable, affordable, multi-protocol Mobile Originated (MO) and Mobile Terminated (MT) circuit switched data connectivity across the Iridium satellite network.

RUDICS is an Iridium data service that allows customers to send and receive data traffic over the Iridium network using an optimized circuit switched data channel. It utilizes circuit switching technology via a dial-up modem and ISDN for low-bandwidth data transfer for ISUs, enabling a host application to originate and terminate numerous connections simultaneously. This solution utilizes Network Access Servers to provide modem ports, supporting both Mobile-Originated (MO) and Mobile-Terminated (MT) Circuit Switch Data calls.

RUDICS is designed to be incorporated into an integrated data solution, taking advantage of the global nature of the Iridium communications system and combining that with a digital connection between the Iridium Gateway and a Partner’s host application. Integrated data solutions are applications such as remote asset monitoring, control, and data file transfer. Often these applications are designed to support hundreds or thousands of remote units.

Kbps – Kilobits Per Second.  Thousands of bits that are transferred in one second. KBps represents (Upper case B) represents thousands of bytes (a byte is made up of 8 bits) in one second.


The Ka band is primarily used for two-way consumer broadband and military networks. Ka band dishes can be much smaller and typically range from 60cm-1.2m (2′ to 4′) in diameter. Transmission power is much greater compared to the C, X or Ku band beams. Due to the higher frequencies of this band, it can be more vulnerable to signal quality problems caused by rain fade.


(pronounced “kay-yoo”) The antenna sizes, ranging from 0.7m to 2.4m, are much smaller than for C band: higher frequency means higher gain can be achieved with smaller antenna sizes than C-band. Networks in this band can be more susceptible to rain fade, especially in tropical areas. Ku communication is the microwave range of the electromagnetic frequency from 11.7 to 12.7 GHz (downlink frequencies) and 14 to 14.5 GHz (uplink frequencies). An interesting note is that older and gray market radar detector/jammers operate on the Ku-Band frequency and have caused interference to disable VSAT satellite systems.

LATENCY (also known as ping time) – Internet traffic travels at the speed of light. That means that a New York to California fiber optic connection will take 0.03 seconds (30 milliseconds) round trip. In reality, the overhead processes of a dozen or more routers and switches adds a bit of time, so an average connection would be about 50 to 90 milliseconds.

With satellite connections the distances are so vast that even light speed isn’t fast enough. Why? Because all stationary satellites are located 22,300 miles above the equator, so the round trip is 90,000 miles or more. The speed of light is 186,000 MPH, so the time it takes for a round trip is just under 500 milliseconds (1/2 second). (If you were standing directly under a satellite on the equator, the speed-of-light round trip would be 476 milliseconds).

Some of the better providers have just over 500 milliseconds latency period. This half a second latency is outstanding for VOIP voice communication over satellite, as the pause between speakers is not nearly noticed. Many other satellite providers, (such as Hughesnet) have a latency of over 1 second.

Latency is not good for real-time gaming because the time it takes for the game to notice you’ve pulled the trigger is half a second or longer.

LEO Low Earth Orbit is an orbit around Earth with an altitude between the Earth’s surface and 2,000 kilometers (Earth’s diameter 12,742Km  ), with an orbital period of between about 84 and 127 minutes. Cf. MEO; HEO and Geostationary Orbits


Being a relatively low frequency, L-band is easier to process, requiring less sophisticated and less expensive RF equipment, and due to a wider beam width, the pointing accuracy of the antenna does not have to be as accurate as the higher bands. Only a small portion (1.3-1.7GHz) of L-Band is allocated to satellite communications on Inmarsat.  Inmarsat uses L-band for their Fleet Broadband, Inmarsat-F and C.

L-Band is also used for low earth orbit satellites, military satellites, and terrestrial wireless connections like GSM mobile phones. It is also used as an intermediate frequency for satellite TV where the Ku or Ka band signals are down-converted to L-Band at the antenna LNB, to make it easier to transport from the antenna to the below deck, or indoor equipment.  L-band is rain fade immune i.e. signal is not degraded during heavy rain. Since there is not much bandwidth available in L-band, it is a costly commodity.

LNB – Line Noise Block, which is simply the receiver on a satellite dish.

MEO – Medium Earth orbit sometimes called intermediate circular orbit (ICO), is the region of space around the Earth above low Earth orbit (altitude of 2,000 km ) and below geostationary orbit (altitude of 35,786 km ) Cf. LEO; HEO and Geostationary Orbits

MESH SATELLITE NETWORK – The orbiting satellite acts as a “router in space” and can direct traffic to other VSAT dishes on the ground. This topology cuts satellite latency (ping times) in half because data doesn’t need to make two round trips to the orbiting satellite as with the more common Star topology satellite network. Mesh networks can also be a combination of Star and Mesh where some traffic may be routed through an Earth based NOC.

MIR – Maximum Information Rate

Typically expressed in kilobits per second (also known as BIR – Burst Information Rate, or PIR – Peak Information Rate) is the theoretical maximum to which your bandwidth can increase as bandwidth becomes available. This is the size of the complete data pipe that you are sharing with others, and the rate normally advertised by providers. In practice, it is rare that you will ever actually achieve this rate, even when you are the only subscriber to the service. There are overheads and bottlenecks both on the vessel and on shore. Typically one would achieve bandwidths of between 50% and 90% of the advertised rate. If this does not meet your requirements, you will need to subscribe to a higher level of service, or increase your CIR, both of which will cost more money. N.B. be sure to determine the theoretical maximum bandwidth limit of your equipment based on the link budget so that you are not paying for a large MIR which physics dictates you could never actually receive! (Please compare with CIR)

MSISDN – (pronounced as /’em es ai es di en/ or MISS-den commonly interpreted as Mobile Station International Subscriber Directory Number) is a phone number uniquely identifying a subscription in a Telecommunications Mobile mobile network. It is the mapping of the telephone number to the SIM in a mobile/cellular/satellite phone. 

NANO-SATELLITES – Usually from 1-10Kg weight with multiple units working together in formation (A.K.A. “swarm”) they retain the same or similar capabilities as a conventional one (size of a double decker bus), while costing much less and can be built quicker. As they can be replaced at less cost and expire quicker they can also keep pace better with the changes in technology

ODU – Out Door Unit.  Refers to the radio BUC and LNB on the satellite dish.

PING TIME – the term round-trip delay time or round-trip time (RTT) is the time required to send a signal in both directions over a particular communication link. This is the soonest that it is possible to receive an acknowledgement of a message.

QoS – Quality of Service is a term used to show the requirements of some applications and users are more critical than others, which means that some traffic needs preferential treatment. By using QoS mechanisms, network administrators can use existing resources efficiently and ensure the required level of service without reactively expanding or over-provisioning their networks. Traditionally, the concept of quality in networks meant that all network traffic was treated equally. The result was that all network traffic received the network’s best effort, with no guarantees for reliability, delay, variation in delay, or other performance characteristics. With best-effort delivery service, however, a single bandwidth-intensive application can result in poor or unacceptable performance for all applications.

RAIN FADE – refers primarily to the absorption of a microwave radio frequency (RF) signal by atmospheric rain, snow, or ice, and losses which are especially prevalent at frequencies above 11 GHz. It also refers to the degradation of a signal caused by the electromagnetic interference of the leading edge of a storm front. Rain fade can be caused by precipitation at the uplink or downlink location. However, it does not need to be raining at a location for it to be affected by rain fade, as the signal may pass through precipitation many miles away, especially if the satellite dish has a low look angle. From 5 to 20 percent of rain fade or satellite signal attenuation may also be caused by rain, snow, or ice on the uplink or downlink antenna reflector, radome or feed horn. Rain fade is not limited to satellite uplinks or downlinks, it also can affect terrestrial point to point microwave links (those on the earth’s surface).

ROUTER – A device that forwards data packets along networks. Typically, a router will have a single WAN connection (like the Internet) and one or more LAN connections (such as the computers in an office). As computers on the LAN make requests from Internet servers, the router forwards those requests to the Internet, and then routes the response to the computer that made the request.

Routers can be distinct devices that do nothing but routing, or they can be combined in a single box with other devices including Modems, Hubs or Switches, and wireless Access Points.

SCPC – Single channel per carrier refers to using a single signal at a given frequency and bandwidth. Most often, this is used on broadcast satellites to indicate that radio stations are not multiplexed as subcarriers onto a single video carrier, but instead independently share a transponder. It may also be used on other communications satellites, or occasionally on non-satellite transmissions.

In an SCPC system, satellite bandwidth is dedicated to a single source. This makes sense if it is being used for something like satellite radio, which broadcasts continuously. Another very common application is voice, where a small amount of fixed bandwidth is required. However, it does not make sense for burst transmissions like satellite internet access or telemetry, since a customer would have to pay for the satellite bandwidth even when they were not using it.

Where multiple access is concerned, SCPC is essentially FDMA. Some applications use SCPC instead of TDMA, because they require guaranteed, unrestricted bandwidth. As satellite TDMA technology improves however, the applications for SCPC are becoming more limited.

SKEW – The rotation of a dish around its center point. Seen as a clockwise or counter-clockwise rotation when facing the front of the dish.

Skew is needed to align the antenna with the polarization of the satellite signal when the dish is not located on the same longitude as the satellite. When a dish is west of the satellite, the skew is a negative number, and from the front of the dish the left edge will be higher than the right. When the dish is east of the satellite it will have a positive skew, with the left edge lower than the right edge.

SLA – Service Level Agreement – In terms of satellite service provision an SLA refers to the effective “up time” for a service over a month or year expressed as a percentage with 100% representing a service that is never off (a situation that would be extremely unusual in the sphere of satellite communications (typical SLAs would be around the 95% and upwards)

STAR TOPOLOGY NETWORKS – use an Earth based NOC (Network Operations Center) to route all traffic to and from the orbiting satellite to the smaller VSAT dish clients which requires. Star Network differ from Mesh Networks, because Mesh networks avoid an Earth Based NOC, and route traffic from the orbiting satellite. The obvious advantage is Mesh Networks latency (ping time) is half as much as a star networks because Mesh doesn’t need to take two round trips to the satellite in order for bit of information to be requested and received from a client Star Network VSAT site. Mesh networks are also inherently more secure because data is transmitted from VSAT dish to VSAT dish.

STATIC IP – Refers to an IP that is permanently assigned, and does change each time that you log on to a network (or the Internet). It is possible for a static IP to be a private one, meaning that a computer with that IP is invisible to other computers on the Internet. That sort of static IP occurs when a computer owner chooses to set the network properties directly for a computer that would otherwise have a Dynamic IP assigned by DHCP.

In the satellite world, most references to static IPs mean public IPs, visible from the Internet. Such IPs are desired for a number of applications such as VPNs or to run a server such as a web cam.

When a satellite modem has a static IP, that IP can only be assigned to a single computer (an exception is the DW4020 modem, which can be ordered with up to 5 static IPs). Other computers on the network will normally be assigned private dynamic IPs by a router with DHCP server. That router/server can be an ICS compute on a DW4000 system, or a broadband router on a DW4020 or DW6000 system.

A computer with a public static IP should always have good Firewall software running to avoid malicious intruders. Computers that are behind a router and have private IPs, dynamic or static, are nearly immune from such intrusion.

TDMA – Time-division multiple access is a channel access method for shared-medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots.[1] The users transmit in rapid succession, one after the other, each using its own time slot. This allows multiple stations to share the same transmission medium (e.g. radio frequency channel) while using only a part of its channel capacity. TDMA is used in the digital 2G cellular systems such as Global System for Mobile Communications (GSM), IS-136, Personal Digital Cellular (PDC) and iDEN, and in the Digital Enhanced Cordless Telecommunications (DECT) standard for portable phones. It is also used extensively in satellite systems, combat-net radio systems, and passive optical network (PON) networks for upstream traffic from premises to the operator. For usage of Dynamic TDMA packet mode communication, see below.

TDMA is a type of time-division multiplexing (TDM), with the special point that instead of having one transmitter connected to one receiver, there are multiple transmitters. In the case of the uplink from a mobile phone to a base station this becomes particularly difficult because the mobile phone can move around and vary the timing advance required to make its transmission match the gap in transmission from its peers.

THROUGHPUT –  is the rate of successful message delivery over a communication channel. The data these messages belong to may be delivered over a physical or logical link, or it can pass through a certain network node. Throughput is usually measured in bits per second (bit/s or bps), and sometimes in data packets per second (p/s or pps) or data packets per time slot. People are often concerned about measuring the maximum data throughput in bits per second of a communications link or network access. A typical method of performing a measurement is to transfer a ‘large’ file from one system to another system and measure the time required to complete the transfer or copy of the file. The throughput is then calculated by dividing the file size by the time to get the throughput in megabits, kilobits, or bits per second. Unfortunately, the results of such an exercise will often result in the goodput which is less than the maximum theoretical data throughput, leading to people believing that their communications link is not operating correctly. In fact, there are many overheads accounted for in throughput in addition to transmission overheads, including latency, TCP Receive Window size and system limitations, which means the calculated goodput does not reflect the maximum achievable throughput

UPLOAD SPEED – Transmitting information from your computer to a location on the Internet.  The typical upload speeds of an iDirect system are 500 to 900 Kbps (Kilobits per second).

VPN – Virtual Private Network, pronounced as 3 letters. Computers connected by dedicated wires form a “private network”. A Virtual Private Network uses the Internet or Public channels and create an encrypted secure date tunnel from point to point.

VSAT – “Very Small Aperture Terminal”. VSAT is two-way (transmit and receive) satellite dish that is normally under 3 square meters in size. VSAT dishes only communicate with geosynchronous orbiting satellites, and they are on client-side of the satellite network (where the Network Operations Center or NOC is on the other side). Frequency bands used by VSAT dishes are C-Band, Ku-Band, Ka-Band and X-Band. A VSAT system is comprised of the reflector (dish or antenna) the Transmitter (BUC) the receiver (LNB), The waveguide, and the indoor unit (IDU) that is the equipment the dish is connected to.

X-Band – The X band is used mainly for military communications and Wideband Global SATCOM (WGS) systems. With relatively few satellites in orbit in this band, there is a wider separation between adjacent satellites, making it ideal for Comms-on-the Move (COTM) applications. This band is less susceptible to rain fade than the Ku Band due to the lower frequency range, resulting in a higher performance level under adverse weather conditions. The X-Band uses 7.9 to 8.4 GHz for the uplink and 7.25 to 7.75 GHz for the downlink. The X-Band is heavily used by military organizations.