3Com CoreBuilder 3500, Руководство по внедрению, Страница: 478 / 592

478 C
HAPTER
17: Q
O
S
AND
RSVP
Key Concepts
Before configuring QoS, review the following standards and terms.
Related Standards
and Protocols
The system supports IEEE 802.1Q, IEEE 802.1p, and the RSVP protocol.
IEEE 802.1p
This standard, which is part of the IEEE 802.1D MAC Bridges base
standard, focuses on traffic class prioritization as well as dynamic
multicast filtering services in bridged LANs. It uses the same tag format as
the proposed IEEE 802.1Q standard, but it uses three additional bits of
the tag control information for setting a user priority level (for
policy-based services such as QoS). You can classify traffic according to a
specific IEEE 802.1p priority tag value (or several tag values). You can also
define a control that inserts a priority tag value in forwarded frames.
The IEEE 802.1p priority tag values are 0 to 7 decimal. Table 59 shows the
IEEE 802.1p (user-priority) values and the corresponding traffic types. The
value 7 (Network Control) is considered the highest priority and 1
(Background Traffic) is the lowest priority. Note that the value 0 (the
default, Best Effort) has a higher priority than value 2 (Standard).
The IEEE 802.1p standard addresses separate queuing of time-critical
frames to reduce jitter.
Table 59 IEEE 802.1p Priority Tag Values
Tag Value Traffic Type (order of priority)
1 Background
2 Standard (spare)
0 (the default) Best Effort
3 Excellent Effort (Business Critical)
4 Controlled Load (Streaming
Multimedia)
5 Video (Interactive Media), less than
100 milliseconds latency and jitter
6 Voice (Interactive Voice), less than
10 milliseconds latency and jitter
7 Network Control (Reserved Traffic)