Supermicro SSE-F3548S/SSE-F3548SR Configuration User’s Guide
9 QoS
Typically, networks operate on a best-effort delivery basis providing all traffic equal priorityand an equal
chance of being delivered in a timely manner. However, during congestion, all traffic has anequal chance
of being dropped.The QoS featureallows one to select specific network traffic and prioritize it according
toits relative importancetoprovide preferential treatment. Implementing QoS makes network
performance morepredictable and bandwidth utilization more effective.
The QoS implementation in Supermicro switches is based on the Differentiated Services
(DiffServ)architecture. DiffServarchitecture specifies that each packetis classified upon entry into the
network.The classification is carried in the IP packet header using six bits from the deprecated IP type of
service(ToS) field to carry the classification (class) information. Classification can also be carried in
theLayer 2 frame.
• Classification bits in Layer 2 frames:
Layer 2 frame headers contain a class of service (CoS) value as a 3-bit field in the VLAN Header. Layer 2
CoS values range from 0 for low priority to 7 for high priority.
The sameforwarding treatment is provided to packets with the same class information and different
treatment to packets withdifferent class information. The class information in the packet can be assigned
by end hosts or byother switches or routers based on a configured policy, detailed examination of the
packet, orboth.
Switches and routers use the class information to limit the amount of resourcesallocated per traffic class.
The behavior of a switch/router when handling traffic in the DiffServarchitecture is called per-hop
behavior. All devices along anetwork path must provide a consistent per-hop behavior in an end-to-end
QoS solution.
Figure QoS-1: QoS Model
The QoS Model can be divided into Ingress packet processing and Egress packet processing.
Actions at the ingress interface include classifying traffic, policing, and marking:
Classifying distinguishes one kind of traffic from another.
Ingress
Egress Processing
Forwards or drops
data based on policy
Modifies DSCP
and/or CoS values
Egress queue
handling for data,
based on CoS
Classifies data based
on ACL
Classification Policing
Marking
Queuing and
Scheduling
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