1. From best-effort routing to traffic engineering

The Internet Protocol (IP) is used in most networks. It provides a Layer 3 service within the OSI model, routing data from a source host to a destination host. IP is a simple protocol that offers no guarantee of service ("Best Effort" network). Data is routed to the best of each network node's ability.

In an IP network, each network node (called a router) is responsible for routing the data it receives. Thus, data routing is carried out in a distributed mode: each router participates in the construction of the data path thanks to its routing table (figure 1 ).