Cisco Systems WSC4500X16SFP Manual De Usuario
27-5
Software Configuration Guide—Release 12.2(25)SG
OL-7659-03
Chapter 27 Configuring Quality of Service
Overview of QoS
•
Classification is the selection of traffic to be marked.
•
Marking, according to RFC 2475, is the process of setting a Layer 3 DSCP value in a packet; in this
publication, the definition of marking is extended to include setting Layer 2 CoS values.
publication, the definition of marking is extended to include setting Layer 2 CoS values.
•
Scheduling is the assignment of Layer 2 frames to a queue. QoS assigns frames to a queue based on
internal DSCP values as shown in
internal DSCP values as shown in
.
•
Policing is limiting bandwidth used by a flow of traffic. Policing can mark or drop traffic.
Basic QoS Model
shows the basic QoS model. Actions at the ingress and egress interfaces include classifying
traffic, policing, and marking:
•
Classifying distinguishes one kind of traffic from another. The process generates an internal DSCP
for a packet, which identifies all the future QoS actions to be performed on this packet. For more
information, see the
for a packet, which identifies all the future QoS actions to be performed on this packet. For more
information, see the
.
•
Policing determines whether a packet is in or out of profile by comparing the traffic rate to the
configured policer, which limits the bandwidth consumed by a flow of traffic. The result of this
determination is passed to the marker. For more information, see the
configured policer, which limits the bandwidth consumed by a flow of traffic. The result of this
determination is passed to the marker. For more information, see the
.
•
Marking evaluates the policer configuration information regarding the action to be taken when a
packet is out of profile and decides what to do with the packet (pass through a packet without
modification, mark down the DSCP value in the packet, or drop the packet). For more information,
see the
packet is out of profile and decides what to do with the packet (pass through a packet without
modification, mark down the DSCP value in the packet, or drop the packet). For more information,
see the
Actions at the egress interface include queueing and scheduling:
•
Queueing evaluates the internal DSCP and determines which of the four egress queues in which to
place the packet.
place the packet.
2
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
1
0
1
0
1
0
1
16
17
18
19
20
21
22
23
17
18
19
20
21
22
23
6
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
1
0
1
0
1
0
1
48
49
50
51
52
53
54
55
49
50
51
52
53
54
55
3
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
1
0
1
0
1
0
1
24
25
26
27
28
29
30
31
25
26
27
28
29
30
31
7
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
1
0
1
0
1
0
1
56
57
58
59
60
61
62
63
57
58
59
60
61
62
63
1.
MSb = most significant bit
Table 27-1
IP Precedence and DSCP Values (continued)
3-bit IP
Precedence
Precedence
6 MSb
1
of ToS
6-bit
DSCP
DSCP
3-bit IP
Precedence
Precedence
6 MSb
1
of ToS
6-bit
DSCP
DSCP
8 7 6
5 4 3
8 7 6
5 4 3