What is maritime VSAT?


VSAT technology is used for two way satellite communications for Internet, data and telephony, typically in rural areas and harsh environments – in this case, maritime environments.

Normally VSAT solutions in the maritime market are delivered as packaged solutions including satellite space segment, equipment and phone and internet services.

VSAT services historically have operated at Ku-band and C-band for the commercial market, using satellites located at the GEO orbital location. Due to the location of the satellites in combination with the movement of vessels, stabilised antennas with tracking are required. A stabilised maritime VSAT antenna typically has a circular antenna (often concealed within a dome) that is 2.4 metres or smaller in diameter. The majority of maritime VSAT antennas range from 60cm to 1.5 metres for Ku-band and 2.4 metres for C-band (though larger C-band antennas are available).

Data rates typically range from 64Kbps up to 8Mbps, but lower and much higher data rates are available. A remote maritime VSAT system typically consists of two parts:


An antenna and transceiver that is placed outdoors (typically inside a radome)

– in maritime this can be referred to as the ‘Above Deck Unit – ADU’



An indoor unit that interacts with the outdoor unit and controls the antenna

– in maritime this can be referred to as the ‘Below Deck Unit – BDU’

Traditional maritime communication systems require vessels to share bandwidth with others, which results in an adequate basic service onboard and can fulfil basic communication needs. However shared bandwidth is inefficient at handling the typically large amounts of data more typically transmitted today; especially, i.e., by operators in the offshore, exploration, cruise or ferry segments. VSAT can offer the solution to this problem.

VSAT services can enable a guaranteed level of bandwidth for the transmission of data or voice at broadband level speeds. These exclusively reserved channels are determined by the following elements, which are important to understand in determining what VSAT solution is best for your needs:

Contention Ratios

Normally, VSAT services are supplied with either dedicated or shared bandwidth. In a shared environment, the free bandwidth is typically shared between the users. The number of users that compete for the available bandwidth is defined within a Contention Ratio. Within a ‘Contended Service’, a contention ratio is given to users as an indication of the number of subscribers who share the fixed amount of bandwidth within a network.

The higher the contention ratio, the greater the number of users that may be trying to use the bandwidth available at any one time and, therefore, the lower the bandwidth speeds. For example, within a contention ratio of 50:1, the maximum number of other users you could be sharing the bandwidth pool with at any one time is 49.

Committed Information Rate

Within a shared bandwidth pool, a Committed Information Rate is a way of guaranteeing bandwidth to the individual end users, ensuring you will get a minimum bandwidth at all times. Usually expressed in kilobits per second (kbit/s or Kbps), the Committed Information Rate (CIR) can refer to the average or minimum amount of bandwidth guaranteed to the user under the contract, usually known as a ‘Service Level Agreement’ (SLA). The Burst Information Rate (BIR), or Maximum Information Rate (MIR) is the theoretical maximum to which bandwidth can increase as it becomes available.

With CIR and Contention Ratios, different suppliers use different definitions, which can make it difficult to make a true comparison between the services available to you. When researching services, ensure that the terminology used is clear, so you are comparing apples with apples.


VSAT Frequency Band