IBM 8479 User Reference - Page 71

Priority Packet mode: Priority Packet is a traffic-prioritization utility that enables you to set up filters to process high-priority traffic before normal traffic. You can send information from critical nodes or applications with an indicated priority. Because you set this priority at the host or entry point of the network, the network devices can base forwarding decisions on priority information defined in the packet. Priority Packet information is available on the IBM Networking Web site at http://www.ibm.com/networking/support. Priority Packet prioritizes traffic based on priority filters. These are parameters you assign to outgoing (transmit) packets. Using the Priority Filter Wizard, you can set up predefined or custom priority filters based on a node medium access control (MAC) address, Ethernet type, or by various properties of the protocol and connector. Priority Packet provides two different methods for prioritizing traffic: IEEE 802.1p tagging and High Priority Queue. IEEE 802.1p is an IEEE standard for tagging, or adding additional bytes of information to packets with different priority levels. Packets are tagged with 4 additional bytes, which increase the packet size and indicate a priority level. When you send these packets out on the network, the higher priority packets are transferred first. Priority packet tagging (also known as Traffic Class Expediting) enables the adapter to work with other elements of the network (such as switches and routers) to deliver priority packets first. You can assign specific priority levels from 0 (low) to 7 (high). You can assign values to packets based on their priority when you use the IEEE 802.1p standard for packet tagging. This method requires a network infrastructure that supports packet tagging. The routing devices receiving and transferring these packets on your network must support 802.1p for tagging to be effective. After you set up the priority filter in Priority Packet, you must start IBMSet and select 802.1p/802.1Q Tagging on the Advanced tab. Note: IEEE 802.1p tagging increases the size of the packets it tags. Some hubs and switches will not recognize the larger packets and will drop them. Check your hub or switch documentation to see if they support 802.1p. (You can configure the switch to strip the tags from the packets and send it on to the next destination as normal traffic.) If these devices do not support 802.1p, or if you are not sure, use high priority queue (HPQ) to prioritize network traffic. The requirements for effectively using IEEE 802.1p tagging are: • The other devices receiving and routing 802.1p tagged packets must support 802.1p. • The adapters on these devices must support 802.1p. The Ethernet controller in your xSeries 200 and all IBM 10/100 Ethernet Security Adapters support 802.1p. • The adapter cannot be assigned to an adapter team. • If you are setting up virtual local area networks (VLANs) and packet tagging on the same adapter, 802.1p/802.1Q tagging must be enabled on the IBMSet Advanced tab. If your network infrastructure devices do not support IEEE 802.1p or you are not sure, you can still define filters and send packets as high priority. While HPQ does not provide the precise priority levels of 802.1p tagging, it does assign traffic as either high or low priority and sends high priority packets first. Therefore, if there are multiple applications on a system sending packets, the packets from the application with a filter are sent out first. HPQ does not change network routing, nor does it add any information to the packets. Chapter 5. Installing options 57