The integrated services (intserv) model [RFC1633] is based on the use of resource reservation and admission control to achieve QoS, in a guaranteed and predictive manner. The resource reservation protocol (RSVP) [RFC2210] is used to signal the QoS for the flow from the source to the destination. Routers in the network maintain a per-flow state to achieve the reserved resource properly. Admission control authenticates packets before receiving special router treatment.
A flow identifies the packets to apply QoS processing. A flow is defined as a ‘distinguishable stream of related datagrams that results from a single user activity and requires the same QoS’ [RFC1633].
Integrated services is implemented by having the source node start a RSVP reservation through the path to the destination node. Along the path, each router processes this reservation. When reaching the destination, an acknowledgment is sent back on the reverse path to the source node to confirm the reservation. This reservation specifies the flow to be processed for some specified QoS level, such as high priority. When the packets of this specified flow are sent from the source node, they are processed by each router in the same path with the specified QoS level.
The resource reservation protocol (RSVP) [RFC2205] is used to reserve the resource along the path from the source to the destination of a flow that requires specific QoS.
Figure 14.2 shows an example where N1 is the receiver of the flow ...