IBM eServer 200 xSeries User Reference Manual 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