After the traffic is classified, differentiated service also requires a per-hop behavior to define how to handle the traffic.
The operating system uses bits in the IP header to identify an IP packet's level of service. Routers and switches allocate their resources based on the per-hop behavior information in the IP header's type of service octet field. The type of service octet field was redefined in the Request for Comments (RFC) 1349 and OS/400® V5R1 operating system. A per-hop behavior is the forwarding behavior that a packet receives at a network node. It is represented by a value known as a codepoint. Packets can be marked either at the operating system or at other parts of the network, such as a router. For a packet to retain the service requested, every network node must be aware of Differentiated Service. That is, the equipment must be able to enforce per-hop behaviors. To enforce per-hop behavior treatment, the network node must be able to use queue scheduling and outbound priority management. See Traffic conditioners for more information about what it means to be aware of Differentiated Service.
If your packet passes through a router or switch that is not aware of Differentiated Service, it will lose its level of service at that router. The packet is still handled, but it might experience an unexpected delay. On your system, you can use the predefined per-hop behavior codepoints or you can define your own codepoints. You might not create your own codepoints for use outside your private network. If you do not know which codepoints to assign, see Using codepoints to assign per-hop behaviors .
Unlike integrated service, differentiated service traffic does not require a reservation or per-flow treatment. All traffic placed in the same class is treated equally.
Differentiated service is also used to throttle traffic leaving a system. This means that your system really uses differentiated service to limit performance. Limiting a less-critical application allows a mission-critical application to exit your private network first. When you create a class of service for this policy, you are asked to set various limits on your system. The performance limits include token bucket sizes, peak rate limits, and average rate limits. The help topics within the quality of service (QoS) function of iSeries™ Navigator give you more specific information about these limits.