3Com 3C16476BS-US - Baseline 2250 Plus Switch, Руководство пользователя, Страница: 42 / 67

42 C
HAPTER
4: C
ONFIGURING THE
S
WITCH
been priority encoded, then the Switch will read the
priority level and determine whether the packet
should be directed through the normal or high prior-
ity channel. This feature can be useful for example
during excessive loads when one type of traffic may
require priority over another.
The Switch is configured to comply with 802.1p,
VLAN tagged frames.
Traffic prioritization ensures that high priority data is
forwarded through the Switch without being delayed
by lower priority data. It differentiates traffic into
classes and prioritizes those classes automatically.
Traffic prioritization uses the multiple traffic queues
that are present in the hardware of the Switch to
ensure that high priority traffic is forwarded on a dif-
ferent queue from lower priority traffic, and is given
preference over that traffic. This ensures that
time-sensitive traffic gets the highest level of service.
The 802.1D standard specifies eight distinct levels of
priority (0 to 7), each of which relates to a particular
type of traffic. The priority levels and their traffic types
are shown in the following table.
Table 10 Priority Levels for Traffic Types
The traffic prioritization feature supported by the
Switch is compatible with the relevant sections of the
IEEE 802.1D standard (incorporating IEEE 802.1p).
This switch uses the Weighted Round Robin (WRR)
algorithm to determine the frequency at which it ser-
vices each priority queue. The Switch allows you to
choose between using IP Precedence or DSCP (Differ-
entiated Services Code Point) priority. When either of
these services is enabled, the priorities are mapped to
a Class of Service value by the Switch, and the traffic
then sent to the corresponding output queue.
Figure 28 802.1p Prioritization Screen
Priority Level Traffic Type
0 Best effort
1 Background
2 Standard (spare)
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 milli-
seconds latency and jitter.
7 Network control reserved traffic