Chapter 12 QoS
XGS1210-12 / XGS1250-12 User’s Guide
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reassigned.
Note: Frames without an explicit priority tag are treated as system traffic and assigned to
Queue0
.
12.2.3 Weighted Round Robin Scheduling (WRR)
Round Robin Scheduling services queues on a rotating basis and is activated only when a port has more
traffic than it can handle. A queue is a given amount of bandwidth irrespective of the incoming traffic
on that port. This queue then moves to the back of the list. The next queue is given an equal amount of
bandwidth, and then moves to the end of the list; and so on, depending on the number of queues
being used. This works in a looping fashion until a queue is empty.
Weighted Round Robin Scheduling (WRR) uses the same algorithm as round robin scheduling, but
services queues based on their priority and queue weight (the number you select in the queue
Weight
field) rather than a fixed amount of bandwidth. WRR is activated only when a port has more traffic than
it can handle. The bandwidth is divided across the different traffic queues according to their weights.
Queues with larger weights get more service than queues with smaller weights. This queuing mechanism
is highly efficient in that it divides any available bandwidth across the different traffic queues and returns
to queues that have not yet emptied.
Figure 38
WRR Application Example
12.3 Port-Based QoS
The Switch’s default settings for Port-Based QoS are shown in the next figure.
Table 15 IEEE Priority to Traffic Type Mapping Recommendations
PCP
PRIORITY
ACRONYM
TRAFFIC TYPES
1
0 (lowest)
BK
Background
0
1 (default)
BE
Best Effort
2
2
EE
Excellent Effort
3
3
CA
Critical Applications
4
4
VI
Video, <100 ms latency and jitter
5
5
VO
Voice, <10 ms latency and jitter
6
6
IC
Internetwork Control
7
7 (highest)
NC
Network Control
