3Com 3 manual Traffic Prioritization, Your Switch

50CHAPTER 6: USING TRAFFIC PRIORITIZATION

Figure 12 DSCP Service Level Mapping

Ingress Port

Classification

DSCP

DSCP

Service levels

Service Level 2

Best Effort

Service Level 3 Business Critical

Service Level 4

Video Applications

Service Level 5

Voice Applications

Service Level 6

Internetwork Control

Service Level 7

Network Control

Strict Priority

Queue Scheduling

Low Priority Queue

High Priority Queue

All

Egress Ports

	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	The traffic should be marked as it enters the network; the marking can be
and your Switch	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, 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 services both traffic
	queues, giving priority to the high priority queue.