Dr Dawie de Wet, Group CEO of Q-KON.

Low Earth Orbit(LEO) satellites are now a reality in Africa, with the satellite landscape set to change forever as more and more LEO satellites are launched. Much of the current early adopter talk focuses on the fact that as LEO satellites are closer to earth, they offer shorter data latency periods – known as “lag” - and that this is a defining specification in use-case scenarios.

Satellite Distances from Earth.

Before we can determine the veracity of this belief, we need to be clear about what exactly latency is, and how it impacts end user and enterprise satellite internet experiences. Is latency (or lag) an issue with other connectivity technologies, and does it stand in the way of large-scale deployment of GEO satellite services?

So, what is latency?

Latency is the time delay that occurs in transmitting information from one point to another. For practical reasons, latency is measured for the round trip, i.e., the time the data takes to travel from source to destination and back again.

Latency is a feature of all data networks, whether fibre, microwave, wireless or satellite. In fibre networks, data travels at about 200 000km/sec. The table below provides examples of network distances from Cape Town to different destinations and typical associated latency values.

Latency in satellite networks

For satellite networks, the data connection path is from the source or user on the ground, to the satellite in orbit and then back to the destination network on earth.

Different satellite constellations are located at different orbital distances from the earth, and are grouped in Low-Earth Orbit (LEO), Medium-Earth Orbit (MEO) and Geostationary Earth Orbit (GEO) constellations.

Since latency is determined by the distance between the satellite and earth and the speed at which the signal travels, distance to the satellite is a key factor in defining latency time. For LEO satellites – those closest to the Earth’s surface, in orbits at heights of between 500 and 1500km above the earth’s surface - the latency will be between 8msec and 25msec. And for GEOs – those furthest from the Earth’s surface, in orbit at some 35,786km above the earth - the latency is 550msec, or just over half a second.

To quantify this 550msec time we can consider that most people speak at a rate of 4 syllables per second, or roughly 2 syllables in 550msec – so this degree of latency is the equivalent of saying “hello”.

So, does latency matter?

If latency is never more than 550msec (or “hello”), and given that today, all forms of satellite are used for voice, video, enterprise and other data applications, all of which can operate perfectly with a latency of 550msec latency, we need to ask why the perception endures that latency is a significant issue.

The full answer to this question would be that “latency not compensated for” does matter. That is to say, latency will adversely affect real-time services such as voice and video calls unless satellite links “fix” the issue. Current satellite technologies do indeed include advanced acceleration and quality-of-service features that perfectly compensate for latency over GEO satellites.

Smarter satellite networks mean no latency issues

The Twoobii Smart Satellite Service is an example of a solution that includes highly advanced quality-of-service features that effectively support voice, video, and other real-time fast data applications. Smart satellite networks compensate for latency in such a way that users don’t experience any problems. In this way, Smart Satellite Networks have proven to be a ‘myth-buster’ when it comes to the notion that latency is somehow an issue for satellite communication networks.

Different networks, different challenges

For Smart Satellite Services to adequately compensate for the adverse effects of latency on data transmission, the satellite link must be able to implement data packet optimisation, priority rules and other data management policies. All of these are of course very feasible when the satellite link has the necessary technology mandate to optimise data traffic in this way.

However, SD-WAN network (software-defined wide area network) architectures are notably different. SD-WAN solutions deployed over fibre and LTE broadband networks have two main disadvantages:

1. These networks maintain a high volume of “keep-alive” traffic; and
2. These networks transmit data in tunnels that nullify satellite optimisation technologies, and impede the benefits of satellite link optimisation.

In this case, SD-WAN networks are compromised over GEO networks and have limited feasibility due to higher keep-alive data costs and poor data speed throughputs, because of the bypassing of the optimisation features.

Designing with latency

Considering the implications of latency and the benefits of Smart Satellite Service features, we have developed the following design option matrix:

Conclusion

Yes … latency over satellite links does matter. However, low latency is not the only consideration. All aspects of end-to-end network architecture and design should be considered in order to implement the optimum solution. For low-data applications, GEO Smart Satellite Networks offer very attractive total-cost-of-ownership models whereas higher data volume links and networks using SD-WAN technology are better serviced with LEO networks.

Dr Dawie deWet (Pr. Eng. M.Sc. Eng.) – Q-KON and their southern African supported satellite broadband service, Twoobii.