Where to Implement Policies in a Network Topology? Or, QoS Architectures
Key to scaling is to maintain levels of hierarchy: core, distribution, and access
Link speeds should be faster toward the core of the network
Access routers generally do not have to handle high packet switching rates and thus can do complex traffic identification, classification, policing and marking
The overhead of implementing QoS policies in the core would affect a large amount of traffic
Access routers can mark the IP precedence field in the packet header
Core routers simply map precedence to queuing or drop actions
This is similar to the IETF DiffServ architecture (as opposed to the “less scalable” per-flow IETF IntServ architecture)