A quick guide to terms frequently used in satellite communications



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


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.


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. A dial-up modem normally uses 56Kbps. A typical iDirect connection is 3Mbps download, or about 60 times faster.


Is simply high-speed internet access that’s much faster than dial-up internet access. Normally, broadband is anything faster than 300 Kbps.


The ‘Block Up Converter’ is the transmitter for a satellite dish. BUCs are rated by wattage: the higher the wattage, the better the upload performance, especially during bad weather.


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 4.2GHz for downlink and 5.925 to 6.425GHz for uplink communication. C-band systems are light-heartedly referred to as a ‘BUD’ – or big ugly dish.


Standing for committed 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’s typically much more expensive. Some companies use the term CIR loosely in describing their shared plans. However, these plans are not 100% guaranteed to committed speeds.


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. Ground Control posts its contention ratios so you can predict your connection speed at any time. Most of our standard iDirect plans are between 10:1 and 20:1.


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 smaller the satellite dish that’s required.


Dynamic host configuration protocol is 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’s a good idea to use high numbers to avoid conflicts.


Domain name system (or service or server), is 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 www.datastormusers.com 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.


Information that comes to your computer from the internet. The typical download speeds of an iDirect connection is between 2500Kbps and 4500Kbps (kilobits per second).


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’s an address required for communication. The reason it’s dynamic (and not static) is because it changes each time you log on to a network (or the internet). Alternatively, a static IP address never changes for your computer.


Effective isotropic 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 to the satellite transmit antenna and its gain in that direction.


The vertical axis (up and down) motion of pointing the satellite dish.


Fair access policy, pronounced as a word. 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.


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


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 lets you address a package and drop it in the system, but there’s no direct link between you and the recipient. TCP/IP, 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


Indoor unit. It refers to equipment the satellite dish connects to inside of a building, such as a satellite modem.


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-120cm (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 Ku-band is used typically for consumer direct-to-home access, distance learning applications, retail and enterprise connectivity. The antenna sizes, ranging from 0.7m to 2.4m, are much smaller than C-band because the higher frequency means that higher gain can be achieved with smaller antenna sizes than C-band. Networks in this band are more susceptible to rain fade, especially in tropical areas. Ku communication is the microwave range of the electromagnetic frequency from 11.7 to 12.7GHz (downlink frequencies) and 14 to 14.5GHz (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.


Operating in the frequency range from 1,530 to 2.7 Ghz, the L-band has a longer wavelength, and is therefore not affected by rain fade (which can impact the Ku- and Ka- frequency bands). Indeed the main selling point of the L-band is its resilience and stability. L-band antennas are small and lightweight, so they’re particularly useful for portable and mobile use, such as military, marine, and transport applications. Inmarsat’s FleetBroadband, and the Iridium Certus service, both leverage L-band frequencies; the Cobham Sailor range uses FleetBroadband, and the RockREMOTE and MCD-Missionlink products use Iridium Certus.


(Also known as ping time.) Internet traffic travels at the speed of light – a New York to California fiber optic connection will take 0.03 seconds (30 milliseconds) as a 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 186,000MPH, so the time it takes for a round trip is just under 500 milliseconds (half a second). Ground Control’s iDirect services have very low overhead processes, so you can expect a latency period of just over 500 milliseconds. This half-second latency is outstanding for VOIP voice communication over satellite, as the pause between speakers is barely noticed. Many other satellite providers, such as Hughesnet, have a latency of over one 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.


Line noise block, which is simply the receiver on a satellite dish.


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.


MQTT stands for Message Queuing Telemetry Transport; it is a messaging protocol (i.e. a means of passing messages between components) for the Internet of Things (IoT). It has been designed to be extremely lightweight, making it ideal for connecting remote devices with a small code footprint, and minimal network bandwidth.


Outdoor unit. Refers to the radio BUC and LNB on the satellite dish.


This 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.


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.


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.


Satellite latency refers to how long it takes a single piece of information to make a round trip back and forth over a satellite connection (aka ping time). Data over satellite travels at the speed of light – 186,000 miles per second. The orbiting satellite is 22,300 miles above earth, and must travel that distance four times (computer to satellite, satellite to internet, internet to satellite, satellite to computer). This adds up to a latency of about half a second. This isn’t long, but some applications like real-time gaming don’t like this time delay.

The theoretically fastest possible ping time over a geostationary satellite would be 476 milliseconds, or just under half a second. Ground Control iDirect services have a latency time between 500 to 650 milliseconds, which is half that of consumer-grade service providers. Low latency reduces the length of the pause between talking parties over a satellite VoIP phone connection, among numerous other benefits.


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.


These use an Earth-based NOC (network operations center) to route all traffic to and from the orbiting satellite to the smaller VSAT dish clients. Star networks 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 network’s because mesh doesn’t need to take two round trips to the satellite in order for 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.


Refers to an IP that is permanently assigned, and does change each time that you log on to a network (or the internet). It’s 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.


Uploading is transmitting information from your computer to a location on the internet. Typical upload speeds of an iDirect system are 500 to 900Kbps (kilobits per second).


Virtual private network, pronounced as three letters. Computers connected by dedicated wires form a ‘private network’. A VPN uses the internet or public channels and create an encrypted secure date tunnel from point to point.


Standing for very small aperture terminal, VSAT is two-way (transmit and receive) satellite dish that’s normally under three square meters in size. VSAT dishes only communicate with geosynchronous orbiting satellites, and they’re on the 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). More about how satellite internet works.


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’s 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 8.4GHz for the uplink and 7.25 to 7.75GHz for the downlink. The X-band is heavily used by military organizations.

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