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Three major aspects of the QoS architecture are:
QoS provides basic support for Differentiated Services, an architecture for specifying and controlling network traffic by class so that certain types of traffic receive priority over others. The differentiated services architecture PHB's (per-hop behaviors).
When marked packets arrive to the VSX machine, they are classified and prioritized according to their DSCP (differential services code-point) values. To enhance performance, QoS does not mark packets with DSCP and does not change their Type of Service (ToS) values. QoS instead relies on peripheral devices (namely routers) to mark packets with the appropriate ToS value.
While Differentiated Services support in routers is usually performed on outbound traffic, QoS for VSX prioritizes traffic on the inbound side because, in VSX deployments, QoS is primarily governed by system resources, namely the CPU, and not by network bandwidth.
To prevent the VSX machine from becoming a bottleneck in the network, prioritization is enforced when packets arrive at the VSX machine, and before CPU processing is assigned.
Inbound prioritization allows an earlier control on the loss and delay rate.
To minimize the impact of QoS functionality on performance, QoS is not done for each interface, but for all the system. One class of services applies to all traffic entering the VSX Gateway or cluster, regardless of the specified interface from which the traffic originates.
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Note - On multi-CPU machines, enforcement is not done system-wide, but for each CPU. Global enforcement is done separately on traffic processed by each CPU. |
