HP ProCurve Series 6120 Blade Switches Advanced Traffic Management Guide

5-37
Quality of Service (QoS): Managing Bandwidth More Effectively
Using QoS Classifiers To Configure Quality of Service for Outbound Traffic
Figure 5-14 shows an example of the ToS byte in the header for an IPv4 packet,
and illustrates the diffserv bits and precedence bits in the ToS byte. (Note that
the Precedence bits are a subset of the Differentiated Services bits.)
Figure 5-14. The ToS Codepoint and Precedence Bits
Table 5-7. How the Switch Uses the ToS Configuration
Outbound Port ToS Option:
802.1p (Value = 0 - 7) Differentiated Services
IP Packet Sent Out
an Untagged Port
in a VLAN
Depending on the value of the IP
Precedence bits in the packet’s ToS
field, the packet will go to one of eight
outbound port queues in the switch.
See table 5-1 on page 5-7.
For a given packet carrying a ToS codepoint that the switch
has been configured to detect:
• Change the codepoint according to the configured policy
and assign the 802.1p priority specified for the new
codepoint in the DSCP Policy Table (page 5-51).
• Do not change the codepoint, but assign the 802.1p priority
specified for the existing codepoint in the DSCP Policy
Table (page 5-51).
Depending on the 802.1p priority used, the packet will leave
the switch through one of the following queues:
1 and 2 = low priority, exits queue 1
0 or 3 = normal priority, exits queue 2
4 and 5 = medium priority, exits queue 3
6 and 7 = high priority, exits queue 4
If No-override (the default) has been configured for a
specified codepoint, then the packet is not prioritized by ToS
and, by default, is sent to the “normal priority” queue.
Field: Destination
MAC Address
Source MAC
Address
802.1Q Field Type &
Version
ToS Byte …
Packet: FF FF FF FF FF FF 08 00 09 00 00 16 08 00 45 E 0 ...
Differentiated Services Codepoint
Rsvd.
Precedence
Bits
1 1100000
E 0