Fibre optic cable and landing stations: Your questions answered

The internet superhighway runs as an interconnected web across the world, joining countries and continents via terrestrial and subsea cables. These data wires bring high-speed internet access to the four corners of the globe, providing access to world-class bandwidth.

There are currently around 1.5-million kilometres of subsea cables under the world’s oceans. When they reach the shore, they connect to landing stations. These stations are essentially access points that connect the submarine cables to terrestrial cable networks. But what exactly are these cables and landing stations, and how do they stretch the length and breadth of the planet?

What are fibre optic cables?

Fibre optic cables are composed of thin strands of glass fibres. Insulated inside a plastic casing, they allow long-distance data transfers to happen at the speed of light. The difference between fibre optics and other types of telecommunication cables is that they provide much higher bandwidth speeds across very long distances.

Fibre optic subsea cables criss-cross the globe and there are around 500 cables that are active or under construction. An example of a relatively short cable is one that runs under the Black Sea, connecting Azerbaijan to Turkmenistan. With a length of about 300 kilometres, this is tiny when compared to the 6600 kilometre Marea cable that runs from Virginia Beach in the U.S. to Bilbao in the north of Spain.

What is the SEACOM cable?

SEACOM’s Submarine Network stretches around the African continent, supporting economic growth in the region. The SEACOM cable connects South Africa, Mozambique, Kenya, Tanzania, Djibouti, Egypt, France and India.

The cable went live in July 2009 and was upgraded in 2018 to have a capacity of 1.5 Tbps. The cable connects to nine landing stations along the way, including Mtunzini (South Africa), Mombassa (Kenya) Dar Es Salaam (Tanzania), Maputo (Mozambique), Marseille (France) and even Mumbai (India).

What are landing stations?

Landing stations are locations where the submarine cables meet the land. They are an essential part of the fibre network infrastructure. They distribute the data carried on the networks, joining the submarine cables to terrestrial cables. Another key function of landing stations is to provide power to the underwater cables.

For example, there is a landing station in Mtunzini in KwaZulu-Natal, where the SEACOM cable reaches the South African shores. This cable connects the subsea cable directly to a data centre in Midrand, Johannesburg, which brings superfast internet connectivity to the interior of South Africa.

How do fibre optic cables transmit data?

Fibre optic cables are able to transmit huge amounts of data along very thin wires. This is made possible thanks to a technology called Dense Wavelength Division Multiplexing. Put in layman's terms, this means that more than one wavelength of light is used to send information.

By stacking several wavelengths, extremely high data speeds are made possible. On average, fibre cables can send around 100 gigabytes of data per second, but newer cables are capable of transmitting speeds of around 500 gigs per second.

Why do fibre optic cables sometimes stop working?

Fibre optic cables are relatively tiny. Most are around the thickness of a garden hose. Within each cable are numerous minute glass strands, as thin as a human hair. These are the paths along which the light pulses travel. Despite their small size, they are very robust but damages and outages can occur.

A common cause of outages is natural disasters, such as earthquakes and hurricanes. In 2012, Hurricane Sandy disrupted services on a number of transatlantic cables. The 2011 Fukushima Earthquake in Japan similarly caused outages on the subsea fibre network. For this reason, engineers carefully consider where they lay cables to avoid hotspots of seismic activity.

Another cause of cable outages is human activity. The trawler nets of big fishing vessels often unwillingly get tangled up with subsea cables. Cables close to the shoreline are more at risk of damage, so these are usually metal-plated and laid in special trenches dug into the seabed.

How are fibre optic cables made?

Subsea cables typically include a protective jelly around fibre optic cables and are also contained within multiple layers of plastic and copper wires. Under the water, “repeaters” are connected at certain points. They serve to amplify the signal and are needed to boost signal strength over long distances. The copper wires contained within the cable casing carry around 10 000 volts of electricity to power these repeaters.

How is an undersea fibre cable laid?

Fibre optic cables are wrapped around huge cylindrical drums and loaded onto specialised ships. These large coils are slowly released out the back of the ship at slow speeds. If the crew runs into bad weather, the cables are cut and attached to a buoy. The ship can then seek refuge until the weather has passed, picking up where they left off when conditions improve.

It takes about a year for engineering teams to plan the best route. Areas that are prone to mudslides, volcanic activity, or those that are frequented by fishing trawlers are best avoided. Should damage occur for any reason, that section is cut and either end is attached to a buoy. The two ends are then connected with a stretch of replacement cable and sunk down to the seafloor.

Who owns fibre optic cables?

In the past, it was countries or national telecom providers who funded cables. Nowadays, it is more common for cables to be owned by a consortium or group of owners, including governments, tech firms and other businesses. This helps to share the costs and bring fibre access to more places around the world.

There has been a global shift towards tech companies, such as Google, funding subsea fibre optic networks. In an attempt to fast-track infrastructure development, these companies have been investing in the lion’s share of underwater cable infrastructure.

Looking ahead, will we still use fibre optics in the future?

At present, there is no other alternative to the high-performance connectivity that fibre optic cables provide. More and more subsea cables are being laid all the time, connecting to countries via landing stations. And this trend is only set to grow.

SEACOM is a leading provider of world-class connectivity to South Africa and the rest of the African continent. Our international fibre grid runs through our own submarine cables, as well as connecting to those operated by other network providers. We believe that the internet is a commodity, without which businesses cannot ensure their longevity. For more information or to get a quote for our internet connectivity solutions, email us at marketing@seacom.com or leave us a message.

SEACOM owns Africa’s most extensive network of information and communications technology (ICT) infrastructure, including subsea cables and secure internet connections. We offer a diverse range of flexible, scalable and high-quality solutions for businesses that meet world-class standards for connectivity.

SEACOM is privately owned and operated, making it agile and adaptable to the needs of the customer. This makes us the preferred ICT and internet connectivity partner for African businesses and peripheral service providers. We can guarantee high-speed, low-latency and secure internet connections to corporates and small enterprises.

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