Two pillars of QoS routing are discussed: the QoS algorithm and the network function to provide each node a consistent view of the topology. Generally, QoS algorithms are believed to be exceedingly complex due to previous announcements that they belong to the class of NP-complete problems. However, a very efficient QoS algorithm, TAMCRA, has ben designed which is slightly more complex that the well-known Dijkstra algorithm and far from hard NP-complete. The topology distribution mechanisms responsible to offer each node in the system a consistent view are complicated due to the coupling of some QoS link metrics with the state of the network resources. The difficulty lies in the different time scales that impact the process: the slowly flooding of topology information and the more rapid variations of the traffic flowing through the links.
Piet Van Mieghem,
H. De Neve,
"Aspects of quality-of-service routing", Proc. SPIE 3529, Internet Routing and Quality of Service, (16 December 1998); doi: 10.1117/12.333731; https://doi.org/10.1117/12.333731