The Internet is made up of access links that route traffic to high-bandwidth routers and accompany the traffic from its source to its destination using the best available path.
In order to ensure that Internet traffic can be routed anywhere in the world, these individual high-speed fibre optic networks must be interconnected. This interconnection is therefore called backbone or Internet backbone interconnection. Each network is owned by Internet operators, usually private, Tier 1 operators whose networks are interconnected.
These Tier 1 Internet operators create a single global network by bundling their long-distance networks, allowing each of them to access the entire Internet routing table. This allows them to efficiently route traffic to its destination through a succession of local, tier 2 and tier 3 providers. These backbone operators all use the same shared network protocol: TCP (Transmission Control Protocol)/IP (Internet Protocol).
The networks of these Tier 1 operators are connected at the IXP (Internet Exchange Point) level. These exchange nodes, being equipped with high-speed switches and routers, allow traffic to be routed between peers (participants connected to the exchange node using the BGP protocol to make traffic). These interconnection points are often owned by third parties, sometimes on a non-profit basis, thus facilitating the unification of the backbone.
Tier 1 operators participating in the IXP contribute to their financing, but do not charge each other for carrying the traffic of other Tier 1 operators. This type of relationship is known as "peering" or "peering without agreement". Peering avoids possible financial disputes that could impact Internet performance.
There are smaller Tier 2 (Tier 2) and Tier 3 (Tier 3) operators. Tier 3 operators allow businesses and consumers to access the Internet. As these Tier 3 operators do not have their own access to the Internet backbone, they contract with Tier 2 or regional ISPs that have their own networks to carry traffic to a limited geographical area.
As access does not concern all devices connected to the Internet, the second-tier providers in turn contract with the first-tier providers to have access to the global backbone.
In summary, traffic originating from a computer on one side of the globe can connect to a connected computer on the other side of the globe by sending the traffic to a Tier 3 operator. This operator routes the traffic to a Tier 2 operator who redirects it to a Tier 1 backbone operator. The latter then redirects it to the appropriate Tier 2 operator. The operator itself sends this traffic to a Tier 3 operator who delivers the traffic to the destination computer.
Source : Le Monde Informatique
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