50 CHAPTER 6: USING TRAFFIC PRIORITIZATION
Figure12 DSCP Service Level Mapping
Figure 12 illustrates how DiffServ code point (DSCP) service levels are
mapped to the two Traffic Queues.
The DSCP service level of the packet is not altered by the Switch 4200.
Traffic Prioritization and your Switch
The traffic should be marked as it enters the network; the marking can be
achieved in two ways:
■The original device can apply the DSCP o r 802.1p markings to the
packet before transmission.
■The edge port on the Switch connecting the originating device can
classify and mark o r re-mark the packets before sending them to the
network. This is not done by the Switch 4200, an intermediate device
in the network is required to do this.
Received packets in the Switch 4200 are checked for DSCP classification
and IEEE 802.1D priority. The Switch 4200 does not set or modify priority
levels within the packet.
The transmitting endstation sets the priority of each packet. When the
packet is received, the Switch places the packet into the appropriate
queue, depending on its priority level, for onward transmission across the
network. The Switch determines which queue to service next through its
Strict Priority queuing mechanism. This method se rvices both traffic
queues, giving priority to the high priority q ueue.
DSCP
Service levels
Classification
DSCP
Low Priority Queue
All
Egress Ports
Best Effort
Business Critical
Video Applications
Voice Applications
Internetwork Control
Network Control
Service Level 7
Service Level 6
Service Level 5
Service Level 4
Service Level 3
Service Level 2
High Priority Queue
IngressPort
StrictPriority
QueueScheduling