Traffic Prioritization And Your Switch - 3Com SuperStack 3C17300 Implementation Manual

54 C 6: U
HAPTER SING
Traffic Prioritization
and your Switch
T P
RAFFIC RIORITIZATION
Figure 14 DSCP Service Level Mapping
Classification
Ingress Port
Figure 14 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
Series.
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 or 802.1p markings to the
packet before transmission.
The edge port on the Switch connecting the originating device can
classify and mark or re-mark the packets before sending them to the
network. This is not done by the Switch 4200 Series, an intermediate
device in the network is required to do this.
Received packets in the Switch 4200 Series are checked for DSCP
classification and IEEE 802.1D priority. The Switch 4200 Series 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 services both traffic
queues, giving priority to the high priority queue.
DSCP
Service levels
Service Level 2
Best Effort
Service Level 3
Business Critical
Service Level 4
Video Applications
DSCP
Service Level 5
Voice Applications
Service Level 6
Internetwork Control
Service Level 7
Network Control
Strict Priority
Queue Scheduling
Low Priority Queue
All
Egress Ports
High Priority Queue