Section 10.2: QoS Types
10.2.1: Best Efforts Delivery
In a best efforts network, routers and switches make their best effort to deliver packets as quickly as possible. There is no consideration to the traffic type or priority service. Packets are anticipated to be delivered. When QoS operates in a network there is at least a guarantee that data will be delivered and adheres to traffic types and priority services.
10.2.2: Integrated Services Model
A mechanism for dealing with end-to-end QoS is the Integrated Services (IntServ) Model. This involves establishing an end-to-end connection over an internetwork of RSVP-enabled routers. An IP footed signaling protocol known as Resource Reservation Setup Protocol (RSVP) is utilized. RSVP routers request and reserves bandwidth over an internetwork. RSVP returns this to the internetwork once the connection is terminated. QoS is applied on a per flow basis.
10.2.3: Differentiated Services Model
Another mechanism is the Differentiated Services (DiffServ) model. With DiffServ there is no need for advanced reservations. Every network router and switch can independently manage packets. The devices are configured with QoS policies and forwarding decisions are executed appropriately. QoS is applied on a per hop basis and Qos decisions are also based on data held in each packet header. The rest of the chapter focuses on DiffServ because Cisco uses this mechanism with Ethernet.