The 2020 National Internet Segment Reliability Research

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The National Internet Segment Reliability Research explains how the outage of a single Autonomous System might affect the connectivity of the impacted region with the rest of the world. Most of the time, the most critical AS in the region is the dominant ISP on the market, but not always.
As the number of alternate routes between AS’s increases (and do not forget that the Internet stands for “interconnected network” — and each network is an AS), so does the fault-tolerance and stability of the Internet across the globe. Although some paths are from the beginning more important than others, establishing as many alternate routes as possible is the only viable way to ensure an adequately robust network.
The global connectivity of any given AS, regardless of whether it is an international giant or regional player, depends on the quantity and quality of its path to Tier-1 ISPs.
Usually, Tier-1 implies an international company offering global IP transit service over connections with other Tier-1 providers. Nevertheless, there is no guarantee that such connectivity will be maintained all the time. For many ISPs at all “tiers”, losing connection to just one Tier-1 peer would likely render them unreachable from some parts of the world.

The Methodology of Internet Reliability Measurement

Examining a case when an AS experiences network degradation, we want to answer the following question: “How many AS’s in the same region would lose connectivity with Tier-1 operators and their global availability along with it?”
Throughout the years we model such a situation because at the dawn of BGP and interdomain routing design its creators assumed that every non-transit AS would have at least two upstream providers to guarantee fault tolerance in case one of them goes down.
However, the current reality is different; with less than half of all ISPs in the world having only one connection to an upstream transit provider. A range of unconventional relationships among transit ISPs further reduces availability.
Have transit ISPs ever failed? The answer is yes, and it happens with increasing frequency. The more appropriate question is — under what conditions would a particular ISP experience service degradation so severe we would call it an outage? If such problems seem unlikely, it may be worth considering Murphy’s Law: “Anything that can go wrong, will”.
To model such a scenario, we have applied the same model for the fourth year in a row. Although again, we did not merely repeat previous calculations — the research is expanding over the years.


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