3Com 3C17300A Implementation Guide - Page 54

54 CHAPTER 6: USING TRAFFIC PRIORITIZATION Figure 14 DSCP Service Level Mapping Classification Ingress Port 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 All Egress Ports High Priority Queue 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 Family. 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 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 Family, an intermediate device in the network is required to do this. Received packets in the Switch 4200 Family are checked for DSCP classification and IEEE 802.1D priority. The Switch 4200 Family 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.