The QOS Problem

Our 2-way satellite services can handle a quite large number of computers. Nevertheless you will experience limitations when connecting more than one computer directly to a satellite modem, as most modems do not have a quality of service management system integrated.

The ViaSat Linkstar modem, as well as the Gilat and the Hughes DIRECWAY modem do not have a quality of service management module implemented. At least not something which would significantly work or improve the situation.

iDirect has implemented some type of QOS in the new iDirect iNFINITI series, which is better than nothing.

Without a QOS mechanism in place, one computer which causes a large upload of data can basically "block" the complete upstream, causing other computers in the network to "freeze". This is called the "freezing effect".

Inefficient Return Channel Use

In TDMA satellite networks, the return channel is handled by a multiple number of satellite channels, in which datagrams are encapsulated. Unfortunately, due to the technology of V-SAT, the datagram size is quite large.

As a result, small packets are "eating up" the number of free channels, causing a quite high inefficiency on the return channel.

By "re-packing" data in a device behind the satellite modem, it is possible to reduce this inefficiency up to 30 to 40 % and improve the overall performance.

Capacity Load Reduction

A data link via geostationary satellites is the most expensive way, but also most efficient way to transport data over an extremely large distance from point A to point B. As a result, each technology to increase the efficiency and reduce the data volume of the transported data is welcome.

By data compression and by sophisticated caching mechanisms, it is possible to reduce the total data volume consumption of a remote terminal up to 25 %.

This results in a 15 to 25 % reduction in satellite capacity and a price reduction achievable by intelligent usage of technology.

Routing and Security Features

Most satellite modems act as "plain gateway" and not as "router". They transport data from point A to point B.

Basic functionalities like NAT, firewall, or routing do not apply.

As a result, customers must additionally implement a router or additional devices capable of managing these basic features.

Slow DNS Resolutions

DNS requests on a satellite link are awfully slow. As each request has to travel twice over the link before a DNS resolution is available, it takes sometimes 2 to 3 seconds before a web page is loaded.

In addition DNS requests generate IP traffic overhead, reducing the overall performance of the satellite link.

Therefore a local caching of DNS results is strongly recommended.

VOIP does not work or works badly

As a result of the low guaranteed return channel bandwidth, most VOIP systems do not work properly. Especially without a device in place which can prioritise traffic.

The effect without prioritising is quite simple. Either the person who receives the call does not understand anything, or the call is simply disconnected the moment a PC on the same network of the VOIP adapter starts accessing the upstream.

That means VOIP without a traffic management device in place does not work and is a waste of money.

The alternative - dedicated bandwidth - is expensive and gives the same problems once the dedicated bandwidth is occupied.

No Bandwith Monitoring

Data volume cannot be consumed endlessly. In order to troubleshoot a system in respect to overconsumption, it is necessary to find out how much data volume is delivered and at what performance.

Most satellite modems do not offer a solution here, keeping the customer "in the dark" about his monthly usage.

Adoption to the correct service grade gets difficult, or even impossible.