Internet via satellite is a satellite-based Internet access. Geostationary satellites are often used for this purpose, but satellite constellations in low or medium Earth orbits (LEO or MEO) are also used. Basically, a distinction must be made between two types of satellite connection.
In 2-way satellite connection the outward and return channels (downstream and upstream) are established via a satellite (since 2013). Depending on the provider, transmission rate upto 150 Mbit/s or more are available downstream, and in individual cases to be negotiated separately, different transmission rates are available.
1-way satellite link first used more than 25 years ago, in which only the downstream was routed via a satellite, but the upstream ran via terrestrial connections. The data transmission rate of the return channel depended on the technology used. In most cases, modem connections were used via POTS or ISDN connections, which provided up to 128 kbit/s upstream rate. For mobile applications, GPRS, UMTS or GSM connections could also be used for the return channel.
In the case of connections with a terrestrial return channel, some providers used it in parallel with the satellite link for data transmission in the downstream direction. If this return channel is fully utilized, the other packets flow over the satellite transmission route, which is more expensive for the provider. Conversely, this means that if the terrestrial line is not fully utilized – e.g. due to a slow Internet server – all data arrives terrestrially. In the case of providers who did not use this technology, the actual download was carried out exclusively via satellite.
Pros of Internet Access via Satellite
The advantage of satellite connections lies in the combination of the relatively large bandwidth and their wide availability, which is largely location-independent.
The advantage of the pure satellite connection is that it is available completely independently of terrestrial data or telephone lines and does not require a fixed location. It is therefore also available for ships and aircraft. The user only needs to be in or within the transmission area of a suitable satellite.
Another advantage is that the existing Internet connection can also be used to make calls using IP telephony. This eliminates the need for a conventional telephone connection.
Some low-orbit satellite constellations also offer lower signal propagation times than wired data transmission, as electromagnetic waves travel faster in the air and in space.
Cons of Internet Access via Satellite
Due to the great distances and despite the speed of light of about 300,000 km/s, geostationary satellites from the earth station to the satellite and back results in signal transit times of at least 239 ms. In the case of two-way communication via satellite, this distance must be covered twice in order to get requests out and for a response to return. Together with other delay factors, this results in latencies between 500 and 700 ms, which is comparatively much worse than, for example, the usual latencies of 150-200 ms for modem dialing. DSL latencies are of the order of magnitude less than 20 ms. Internet services that use the satellite for round-trip travel are therefore not suitable for video calling and gaming or other applications where high latency is associated with severe limitations.
The Transmission Control Protocol (TCP) is not designed for these high latency times. The Round Trip Time (RTT) resulting from these runtimes means that a TCP connection does not significantly increase the data transfer rate after the so-called slow start, and thus only a few 10 kbit/s could be transmitted under unfavorable conditions, even with a high theoretical data transfer rate. This problem can be circumvented by using Performance Enhancement Proxy.
In most cases, it is not possible to meet the requirements for the most effective use of the theoretically available data transfer rates and the greatest possible application transparency at the same time
. The most effective data transfer rate usage for the one-way service is provided by the client/server variant. It routes the connection upstream and downstream of the satellite connection through a proxy server (client and remote proxy). In order to remain application-transparent, a tunnel variant (VPN/PPTP) is usually offered for the one-way service.
Similar to the use of the Internet via mobile communications, most providers of satellite Internet access also have a fair use policy, which can lead to the throttling of the actual available data rate.