You’ve always been told to hope for the best and prepare for the worst.
Telecommunications professionals have been told the same thing. Perhaps that’s why you’ve heard of “protected” and “unprotected” circuits.
These terms relate to the resilience and redundancy of communication paths.
What is a protected circuit?
Simply put, it’s a circuit with a backup plan.
Path protection is an end-to-end protection scheme that protects against failures on a service provider’s network. While there are different strategies for doing this across various types of networks, the spirit of the idea remains the same: have a redundancy in place in case a cable fails.
The short version: Two points on a protected circuit will remain in communication if one path fails.
How do protected circuits relate to submarine cables?
Submarine cables are critical infrastructure. Any disruption can have significant economic and social consequences.
To mitigate the risk of service outages due to cable breaks—caused by ship anchors, fishing trawlers, natural disasters, or even intentional damage—network operators often implement redundancy through protected circuits.
In the context of submarine cables, a protected circuit typically involves having multiple physical cable paths between two landing points. If one cable is damaged, traffic can be automatically rerouted to the alternative, protected path.
What is an unprotected circuit?
Naturally, an unprotected circuit is one that relies on a single communication path. If this path fails, there's no automatic alternative route for the data to travel. This leads to a service outage until the primary path is repaired.
In submarine cable terms, we see this happen in locations with no real redundancy when cable breaks happen.
One of the best examples in recent history comes from Tonga, after an undersea cable was damaged following the massive eruption of the Hunga Tonga-Hunga Ha'apai volcano. Limited satellite connectivity was available, but the country was largely cut off from the world until the cable was repaired.
