| Sun Netra CP3240 Switch User’s Guide |    
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| C H A P T E R 23 |
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Configuring Class of Service Queuing |
This chapter describes the Class of Service (CoS) feature and how to configure it.
This chapter contains the following topics:
The Class of Service (CoS) feature lets you give preferential treatment to certain types of traffic over others. To set up this preferential treatment, you can configure the ingress ports, the egress ports, and individual queues on the egress ports to provide customization that suits your environment.
The level of service is determined by the egress port queue to which the traffic is assigned. When traffic is queued for transmission, the rate at which it is serviced depends on how the queue is configured and possibly the amount of traffic present in other queues for that port.
Some traffic is classified for service (i.e., packet marking) before it arrives at the switch. If you decide to use these classifications, you can map this traffic to egress queues by setting up a CoS Mapping table.
Each ingress port on the switch has a default priority value (set by configuring VLAN Port Priority in the Switching sub-menu) that determines the egress queue its traffic gets forwarded to. Packets that arrive without a priority designation, or packets from ports you’ve identified as “untrusted,” get forwarded according to this default.
The first task for ingress port configuration is to specify whether traffic arriving on a given port is “trusted” or “untrusted.”
A trusted port means that the system will accept at face value a priority designation within arriving packets. You can configure the system to trust priority designations based on one of the following fields in the packet header:
You can also configure an ingress port as untrusted, where the system ignores priority designations of incoming packets and sends the packet to a queue based on the ingress port’s default priority.
Mapping is from the designated field values on trusted ports’ incoming packets to a traffic class priority (actually a CoS traffic queue). The trusted port field-to-traffic class configuration entries form the Mapping Table the switch uses to direct ingress packets from trusted ports to egress queues.
For unit/slot/port interfaces, you can specify the traffic shaping rate for the port, which is an upper limit of the transmission bandwidth used, specified as a percentage of the maximum link speed.
For each queue, you can specify:
FASTPATH supports the tail drop method of queue management. This means that any packet forwarded to a full queue is dropped regardless of its importance.
CoS Mapping and Queue Configuration illustrates the network operation as it relates to CoS mapping and queue configuration.
Four packets arrive at the ingress port 1/0/10 in the order A, B, C, and D. You’ve configured port 1/0/10 to trust the 802.1p field of the packet, which serves to direct packets A, B, and D to their respective queues on the egress port. These three packets utilize port 1/0/10’s 802.1p to COS Mapping Table. In this case, the 802.1p user priority 3 was set up to send the packet to queue 5 instead of the default queue 3. Since packet C does not contain a VLAN tag, the 802.1p user priority does not exist, so Port 1/0/10 relies on its default port priority - 2 - to direct packet C to egress queue 1.
FIGURE 23-1 CoS Mapping and Queue Configuration
Continuing this example, you configured the egress Port 1/0/8 for strict priority on queue 6, and a set a weighted scheduling scheme for queues 5-0. Assuming queue 5 has a higher weighting than queue 1 (relative weight values shown as a percentage, with 0% indicating the bandwidth is not guaranteed), the queue service order is 6 followed by 5 followed by 1. Assuming each queue unloads all packets shown in the diagram, the packet transmission order as seen on the network leading out of Port 1/0/8 is B, A, D, C. Thus, packet B, with its higher user precedence than the others, is able to work its way through the device with minimal delay and is transmitted ahead of the other packets at the egress port.
FIGURE 23-2 CoS Configuration Example System Diagram
You will configure the ingress interface uniquely for all cos-queue and VLAN parameters.
You can also set traffic shaping parameters for the interface. If you wish to shape the egress interface for a sustained maximum data rate of 80 Mbps (assuming a 100Mbps link speed), you would add a simple configuration line expressing the shaping rate as a percentage of link speed.
The following web pages are used for the Class of Service feature.
FIGURE 23-3 CoS Trust Mode Configuration Page
FIGURE 23-4 802.1p Priority Mapping Page
FIGURE 23-5 IP Precedence Mapping Configuration Page
FIGURE 23-6 IP DSCP Mapping Configuration Page
| Note - Configure 802.1p Priority Mapping screen from the Switching ---> Class of Service menu. |
FIGURE 23-7 CoS Interface Configuration Page
FIGURE 23-8 CoS Interface Queue Configuration Page
FIGURE 23-9 CoS Interface Queue Status Page
| Sun Netra CP3240 Switch User’s Guide | 820-3252-11 |
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