After traffic is classified, differentiated service also requires a per-hop behavior to define how to handle the traffic.
The server 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 server or at other parts of the network, such as a router. For a packet to retain the service requested, every network node must be differentiated service (DiffServ)-aware. 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 the Traffic conditioners topic for more information about what it means to be DiffServ-aware.
If your packet passes through a router or switch that is not DiffServ-aware, it will lose its level of service at that router. The packet is still handled, but it might experience unexpected delay. On your iSeries™ server, you can use the pre-defined per-hop behavior codepoints or you can define your own codepoint. It is not recommended that you create your own codepoints for use outside your private network. If you do not know which codepoints to assign, review Use codepoints to assign per-hop behaviors topic.
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 can also be used to throttle traffic leaving a server. This means that your iSeries server 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 server. The performance limits include token bucket size, peak rate limit, and average rate limit. The help topics within the quality of service (QoS) function of iSeries Navigator gives you more specific information about these limits.