FAQ

What is a VSAT?

A VSAT, for Very Small Aperture Terminal, is a 2-way satellite ground station with a dish antenna that is smaller than 3 meters, as compared to around 10 meters for other types of satellite dishes.

Which are the different VSAT Network Topologies?

Most VSAT networks are usually configured in one of these topologies:

A star topology uses a central uplink site, such as a network operations center (NOC), to transport data back and forth to each VSAT terminal via satellite.

A mesh topology is where each VSAT terminal relays data via satellite to another terminal by acting as a hub, minimizing the need for a centralized uplink site.

A combination of both star and mesh topologies: some VSAT networks are configured by having several centralized uplink sites (and VSAT terminals stemming from it) connected in a multi-star topology with each star (and each terminal in each star) connected to each other in a mesh topology. Others that are configured in only a single star topology sometimes will have each terminal connected to each other as well, resulting in each terminal acting as a central hub. These configurations are utilized to minimize the overall cost of the network, and to alleviate the amount of data that has to be relayed through a central uplink site (or sites) of a star or multi-star network.

What’s the difference between SCPC and MCPC?

Single channel per carrier (SCPC) 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.

With multiple channels per carrier (MCPC), several sub-carriers are combined into a single bit-stream before being modulated onto a carrier transmitted from a single location to one or more remote sites. This uses time-division multiplexing (TDM).

What is DAMA technology?

Demand Assigned Multiple Access (DAMA) refers to contention access schemes that allow multiple communications users to share a discrete portion of the bandwidth.

What is TDMA technology?

Time division multiple access (TDMA) is a technology for shared medium networks. It allows several users to share the same frequency by dividing it into different timeslots. The users transmit in rapid succession, one after the other, each using their own timeslot. This allows multiple users to share the same transmission medium while using only the part of its bandwidth they require. TDMA is used in the Global System for Mobile Communications (GSM), Personal Digital Cellular (PDC) and iDEN digital cellular standards, among others. It is also extensively used in satellite systems, local area networks, physical security systems, and combat-net radio systems.

What is a Tier 1 Network?

Tier 1 Network is an IP network (typically but not necessarily an Internet Service Provider) which connects to the entire Internet solely via Settlement Free Interconnection, commonly known as peering. Another name for a Tier 1 network is "transit-free", because they do not receive a full transit table from any other network.

Although there is no formal definition of the "Internet Tier hierarchy", the generally accepted definition among networking professionals is:

• Tier 1 - A network that peers with every other network to reach the Internet.

• Tier 2 - A network that peers with some networks, but still purchases IP transit to reach at least some portion of the Internet.

• Tier 3 - A network that solely purchases transit from other networks to reach the Internet.

What is a Backhaul?

In telecommunications, backhauling is concerned with transporting traffic between distributed sites (typically access points) and more centralized points of presence.

The choice of backhaul technology must take account of such parameters as capacity, cost, reach, and the need for such resources as frequency spectrum, optical fiber or rights of way.

Backhaul capacity can also be leased from another network operator, in which case the choice of technology is generally made by this other network operator.

What does Bandwidth mean?

Bandwidth is a measure of frequency range and is typically measured in hertz. Bandwidth is a central concept in many fields, including information theory, radio communications, signal processing, and spectroscopy. Bandwidth also refers to data rates when communicating over certain media or devices.

Why satellite technology is the most efficient technology for broadcasting?

Broadcasting is the distribution of audio and/or video signals (programs) to a number of recipients ("listeners" or "viewers") that belong to a large group. This group may be the public in general, or a relatively large audience within the public. When broadcasting is done via the Internet, the term webcasting is often used.

For the transmission of multimedia content, satellite technology is much more efficient than that of fiber. It has more availability of broadband and can simultaneously and quickly deliver information worldwide to an unlimited number of end users, directly from the satellite and without the typical distortion in video and audio quality as it occurs with cable TV.

What is a Co-Location center?

A colocation center ("colo") or carrier hotel is a type of data center where [a] multiple telecommunications or network service providers locate their connections adjacent at the physical layer to each other's networks (points of presence) and [b] users of these services locate network, server and storage gear and interconnect to network service provider(s) with a minimum of cost and complexity.

Increasingly organizations are recognizing the benefits of colocating their mission-critical equipment within a data center. Colocation is becoming popular because of the time and cost savings a company can realize as result of using shared data center infrastructure. Significant benefits of scale (large power and mechanical systems) result in large colocation facilities, typically 50,000 to 100,000 square feet. With IT and communications facilities in safe, secure hands, telecommunications, internet, ASP and content providers, as well as enterprises, enjoy less latency and the freedom to focus on their core business.
Additionally, customers reduce their traffic backhaul costs and free up their internal networks for other uses. Moreover, by outsourcing network traffic to a colocation service provider with greater bandwidth capacity, web site access speeds should improve considerably.

What is a Data Center?

A data center is a facility used to house mission critical computer systems and associated components. It generally includes environmental controls (air conditioning, fire suppression, etc.), redundant/backup power supplies, redundant internet connections and high security.

What is an Earth Station?

An earth station is the ground based (terrestrial) end of a communications link to an object in space. The space end of the link is occasionally referred to as a space station.
Most earth stations are used to communicate with communications satellites, and so are called satellite earth stations.

What does Uplink/Downlink mean?

The term “uplink” means the portion of a communications link used for the transmission of signals from an Earth terminal to a satellite or to an airborne platform. An uplink is the converse of a downlink. An uplink or downlink is distinguished from reverse link or forward link.

Why the Bit Error Rate is a key concept of the Service Level Agreement?

In telecommunication, an error ratio is the ratio of the number of bits, elements, characters, or blocks incorrectly received to the total number of bits, elements, characters, or blocks sent during a specified time interval. The error ratio is usually expressed in scientific notation; for example, 2.5 erroneous bits out of 100,000 bits transmitted would be 2.5 out of 105 or 2.5 × 10-5.
The most commonly encountered ratio is the bit error ratio (BER). For a given communication system, the bit error ratio will be affected by both the data transmission rate and the signal power margin. The BER is an indication of how often a packet or other data unit has to be retransmitted because of an error.

What does Forward Error Correction (FEC) mean?

Forward error correction (FEC) is a system of error control for data transmission, whereby the sender adds redundant data to its messages, which allows the receiver to detect and correct errors (within some bound) without the need to ask the sender for additional data. The advantage of forward error correction is that retransmission of data can often be avoided, at the cost of higher bandwidth requirements on average, and is therefore applied in situations where retransmissions are relatively costly or impossible.

What is Multicast?

Multicast is the delivery of information to a group of destinations simultaneously using the most efficient strategy to deliver the messages over each link of the network only once, creating copies only when the links to the destinations split.
The word "Multicast" is typically used to refer to IP Multicast, the implementation of the multicast concept on the IP routing level, where routers create optimal spanning tree distribution paths for datagrams sent to a multicast destination address in real time. But there are also other implementations of the multicast distribution strategy listed below.

What is a BGAN?

A BGAN, or Broadband Global Area Network, is a satellite-based uplink that provides near-broadband speeds. BGAN hopes to enable a new type of global communications through data and telephony in remote locations around the world. The service is not land-based, so BGAN can provide mobile communications to those working in or traveling to locations where the local telecoms networks are unreliable or non-existent. BGAN is aiming to provide services up to the same speeds as 3G mobile phones.

What is Polarization?

Polarization, also called wave polarization, is an expression of the orientation of the lines of electric flux in an electromagnetic field (EM field). Polarization can be constant, that is, existing in a particular orientation at all times, or it can rotate with each wave cycle.

Polarization is important in wireless communications systems. The physical orientation of a wireless antenna corresponds to the polarization of the radio waves received or transmitted by that antenna. Thus, a vertical antenna receives and emits vertically polarized waves, and a horizontal antenna receives or emits horizontally polarized waves.

Some wireless antennas transmit and receive EM waves whose polarization rotates 360 degrees with each complete wave cycle. This type of polarization, called elliptical or circular polarization, can be either clockwise or counterclockwise. The best communications results are obtained when the transmitting and receiving antennas have the same sense of polarization (both clockwise or both counterclockwise).

Linear Polarization: plane electromagnetic wave is said to be linearly polarized. The transverse electric field wave is accompanied by a magnetic field wave.

Circular Polarization: circularly polarized light consists of two perpendicular electromagnetic plane waves of equal amplitude and 90° difference in phase.

Elliptical Polarization: elliptically polarized light consists of two perpendicular waves of unequal amplitude which differ in phase by 90°.

Which are the frequency bands commonly used for satellite communications?

What is the Latency and what does it depend on?

The Latency is the transmission delay. Network Latency depends on:

• Distance between the Satellite and the Earth Stations
• Bit Error Rate of System Design
• Equipment Configuration
• Satellite Contribution
• Network Loading

What is VoIP?

Voice over Internet Protocol, also called VoIP, IP Telephony, Internet telephony, Broadband telephony, Broadband Phone and Voice over Broadband is the routing of voice conversations over the Internet or through any other IP-based network.

What is Wimax?

WiMAX is defined as Worldwide Interoperability for Microwave Access by the WiMAX Forum. The Forum describes WiMAX as "a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL".

The bandwidth and reach of WiMAX make it suitable for the following potential applications:

• Connecting Wi-Fi hotspots with each other and to other parts of the Internet
• Providing a wireless alternative to cable and DSL for last mile (last km) broadband access
• Providing high-speed mobile data and telecommunications services
• Providing a diverse source of Internet connectivity as part of a business continuity plan. That is, if a business has a fixed and a wireless internet connection, especially from unrelated providers, they are unlikely to be affected by the same service outage
• Providing Nomadic connectivity

Source: Wikipedia