Quality of Service (QoS) is a concept
generally existing in occasions with service supply and demand. It evaluates
the ability to meet the need of the customers in service. Generally, the
evaluation is not to grade precisely. Its purpose is to analyze the conditions where
the service is the best and the conditions where the service still needs
improvement and then to make improvements in the specified aspects.
In an internet, QoS evaluates the ability
of the network to deliver packets. The evaluation on QoS can be based on
different aspects because the network provides various services. Generally
speaking, QoS is the evaluation on the service ability to support the core
requirements such as delay, jitter, and packet loss ratio in the packet
delivery.
Stream refers to traffic, including all
packets that pass through a switch.
This section describes the IP precedence, Type
of Service(TOS) precedence, Differentiated Services Codepoint (DSCP) precedence,
and 802.1p priority.
1)
IP precedence, TOS precedence and DSCP
precedence
Figure 1-1 DS field and ToS byte
As shown in Figure
1-1, the TOS field of an IP header contains eight bits, among which the first three represent the IP precedence, ranging from 0 to 7. Bits 3 to 6 (a total of 4 bits) represent the TOS precedence, ranging from 0 to 15.
The TOS field of an IP packet header is redefined as Differentiated Services (DS)
field in RFC2474, among which the first six bits (bits 0 to 5) represent DSCP
precedence, ranging from 0 to 63, and bits 6 and 7 are reserved.
2)
802.1p priority
Embedded in the header of a Layer 2 packet,
802.1p priority is intended to ensure Layer 2 QoS rather than analysis of a Layer3
header.
Figure 1-2 An Ethernet frame with an 802.1Q
tag header
As shown in Figure
1-2, an 802.1Q-enabled host will include a 4-bit 802.1Q header next to the source address in its outbound Ethernet frames. The 4-bit header is comprised of a 2-bit Tag Protocol Identifier (TPID) with a value of 8100 and
a 2-bit Tag Control Information (TCI). TPID was defined recently by IEEE,
indicating that the packet includes an 802.1Q tag. The detailed make-up of an
802.1Q header is illustrated in Figure 1-3.
Figure 1-3 802.1Q tag header
In Figure 1-3, the Priority field in TCI is 802.1p priority. It consists of three bits with a value range of 0 to 7. The three bits are intended to determine the priority of a given packet. A total of 8 priorities are provided to
help the switch decide which packet to be sent first in case of traffic
congestion.
As it is the 802.1p specifications that have
described in detail the application of these priorities, hence the name. It is
also known as CoS priority.
When congestion occurs, packets contend for
network resources. To address this issue, queue scheduling was introduced. The
following are two ways of implementing it: Weighted Round Robin (WRR) and High
Queue-WRR (HQ-WRR).
1)
WRR
With each port supporting four output
queues, WRR performs a round-robin scheduling to ensure that all queues are
served. Each queue is allocated with a weight value (w3, w2, w1, and w0)
denoting the resource proportions allocated to the corresponding queue. For
example, on a 100M port, allocating its output queues with WRR weight values of
50, 30, 10, and 10 (corresponding to w3, w2, w1,and w0 respectively) will
ensure that even queues with the lowest priority can get at least 10Mbit/s
bandwidth, thus avoiding the scenario where packets with low priority are not
served over a long time. Performing round-robin scheduling, WRR also ensures
that network bandwidth is used efficiently by not allocating a fixed amount of
time to each individual queue. This means that when a queue has nothing to
output, its bandwidth can be given to the next queue with outputs.
2)
HQ-WRR
HQ-WRR is an improvement over WRR. With
queue 3 allocated with the highest priority, the switch will ensure that this
queue get served first and will perform round-robin scheduling to the other
three queues when the traffic has exceeded the bandwidth capacity of a port.
Local port monitoring copies inbound packets
of a given port to the local destination port for network detection and
troubleshooting.
Remote switched port analyzer (RSPAN)
breaks through the limitation that the source port and destination port have to
be located on the same switch, and permits them to reside across multiple
network devices. Therefore, it enhances the way network administrator can
manage remote switches.
Refers to rate limit of a given port. It
limits the rate that a port receives or sends packets.
Table 1-1 QoS functions and related commands
|
QoS functions
|
Specifications
|
Related Command
|
Related section
|
|
Port priority
|
Support
|
priority priority-level
|
Configuring Port Priority
|
|
Packet trust priority
|
Support
|
priority trust
|
Configuring Packet Trust Priority
|
|
Priority to local precedence queue mapping
|
Support
|
qos cos-local-precedence-map
qos ip-precedence-local-precedence-map
qos dscp-local-precedence-map
|
Configuring Priority - Local Precedence Queue Mapping
|
|
Priority options
|
The
following options are available:
l
According to dscp precedence
l
According to ip-precedence
l
According to CoS priority
|
priority-trust { dscp | ip-precedence | cos }
|
Configuring Packet Priority
|
|
Queue scheduler
|
WRR, HQ+WRR
|
queue-scheduler
|
Configuring Queue Scheduling Algorithm
|
|
Local port monitoring
|
One-to-multiple
port monitoring, that is to say, one destination port to multiple source ports.
Packet
monitoring directions can be inbound, outbound or both.
|
System view:
mirroring-group group-id local
mirroring-group group-id mirroring-port mirroring-port-list { inbound | outbound | both }
mirroring-group group-id monitor-port monitor-port
|
Configuring Local Port Monitoring
|
|
Ethernet port view:
monitor-port
mirroring-port
|
|
RSPAN
|
Monitoring
applies to both inbound and outbound packets.
|
mirroring-group group-id { remote-source | remote-destination
}
mirroring-group group-id mirroring-port mirroring-port-list { inbound | outbound }
mirroring-group group-id monitor-port monitor-port
mirroring-group group-id reflector-port reflector-port
mirroring-group group-id remote-probe vlan remote-probe-vlan-id
|
Configuring RSPAN
|
|
Port rate limit
|
Rate limit applies to both inbound
and outbound packets with a rate value of 64 kbps.
|
line-rate
|
Setting Rate Limit on Ports
|
By default, the switch replaces the 802.1p
priorities of the received packets with the priorities of the ports receiving
the packets, and then put the packets into different output queues according to
the new priorities, so as to control service quality.
Table 1-2 Configure port priority
|
Operation
|
Command
|
Description
|
|
Enter
system view
|
system-view
|
—
|
|
Enter Ethernet port view
|
interface interface-type interface-number
|
—
|
|
Configure port priority level
|
priority priority-level
|
Required
Defaults to 0.
|
I. Network requirements
Configure port priority level for
Ethernet1/0/1.
II. Configuration procedure
<H3C> system-view
[H3C] interface Ethernet1/0/1
[H3C-Ethernet1/0/1] priority 7
Users can configure the switch to trust the
priority of inbound packets rather than priority of the receiving port.
Table 1-3 Configure packet trust priority
|
Operation
|
Command
|
Description
|
|
Enter system view
|
system-view
|
—
|
|
Configure packet trust priority
|
priority trust
|
Required
By default, the switch replaces
802.1p priority brought by packets with priority of the receiving port.
|
I. Network requirements
Configure the switch to trust 802.1p
priority of inbound packets.
II. Configuration procedure
<H3C> system-view
[H3C] priority trust
The switch put packets into the proper port
output queue based on the priority - local precedence queue mapping. You can set
the mapping relationship between priority and local precedence queue with the
help of commands.
New mapping relationships have been
established to modify the “802.1p priority - local precedence
queue”, “IP precedence - local precedence queue”, and “DSCP
precedence - local precedence queue” mapping tables.
Table 1-4 Configure the “802.1p priority - local precedence queue”
mapping table
|
Operation
|
Command
|
Description
|
|
Enter system view
|
system-view
|
—
|
|
Set the mapping table
|
qos cos-local-precedence-map
cos0-map-local-prec cos1-map-local-prec cos2-map-local-prec
cos3-map-local-prec cos4-map-local-prec cos5-map-local-prec
cos6-map-local-prec cos7-map-local-prec
|
Required
|
The following table shows the default
“802.1p priority - local precedence queue” mapping table.
Table 1-5 Default “802.1p priority - local precedence queue”
mapping table
|
802.1p priority
|
Local precedence queue
|
|
0
|
1
|
|
1
|
0
|
|
2
|
0
|
|
3
|
1
|
|
4
|
2
|
|
5
|
2
|
|
6
|
3
|
|
7
|
3
|
Table 1-6 Configure the “IP precedence - local precedence queue”
mapping table
|
Operation
|
Command
|
Description
|
|
Enter system view
|
system-view
|
—
|
|
Set the mapping table
|
qos ip-precedence-local-precedence-map
ip0-map-local-prec ip1-map-local-prec ip2-map-local-prec ip3-map-local-prec
ip4-map-local-prec ip5-map-local-prec ip6-map-local-prec ip7-map-local-prec
|
Required
|
The following table shows the default
“IP precedence - local precedence queue” mapping table.
Table 1-7 Default “IP precedence - local precedence queue” mapping
table
|
IP precedence
|
Local precedence queue
|
|
0
|
0
|
|
1
|
0
|
|
2
|
1
|
|
3
|
1
|
|
4
|
2
|
|
5
|
2
|
|
6
|
3
|
|
7
|
3
|
Table 1-8 Configure the “DSCP precedence - local precedence queue”
mapping table
|
Operation
|
Command
|
Description
|
|
Enter system view
|
system-view
|
—
|
|
Configure the mapping table
|
qos dscp-local-precedence-map
dscp-list : local-precedence
|
Required
|
The following table shows the default
“DSCP precedence - local precedence queue” mapping table.
Table 1-9 Default “DSCP precedence - local precedence queue”
mapping table
|
DSCP precedence
|
Local precedence queue
|
|
0–15
|
0
|
|
16–31
|
1
|
|
32–47
|
2
|
|
48–63
|
3
|
I. Network requirements
Modify the “802.1p priority - local precedence
queue” mapping table as follows.
Table 1-10
“802.1p priority - local precedence
queue” mapping table
|
802.1p priority
|
Local precedence queue
|
|
0
|
0
|
|
1
|
0
|
|
2
|
1
|
|
3
|
1
|
|
4
|
2
|
|
5
|
2
|
|
6
|
3
|
|
7
|
3
|
II. Configuration procedure
<H3C> system-view
[H3C] qos cos-local-precedence-map 0 0
1 1 2 2 3 3
[H3C] display qos cos-local-precedence-map
cos-local-precedence-map:
cos(802.1p) :
0 1 2 3 4 5 6 7
----------------------------------------------------------------------
local precedence(queue) :
0 0 1 1 2 2 3 3
l
The mapping relationship between the priority
and local precedence queue has been established. Refer to 1.5 Configuring Priority - Local Precedence Queue Mapping.
l
The kind of priority (chosen from 802.1p
priority, IP precedence and DSCP precedence) to be used for putting packets
into queues is determined.
Table 1-11
Determine the priority
to trust
|
Operation
|
Command
|
Description
|
|
Enter system view
|
system-view
|
—
|
|
Determine the priority to trust
|
priority-trust { cos | dscp | ip-precedence }
|
Required
Default to 802.1p priority.
cos:
Uses the 802.1p priority.
dscp:
Uses the DSCP precedence.
ip-precedence: Uses the IP precedence.
|
I. Network requirements
Users choose to trust 802.1p priority. Table 1-12 shows the mapping relationship.
Table 1-12 “802.1p priority- local
precedence queue” mapping table
|
802.1p priority
|
Local precedence queue
|
|
0
|
0
|
|
1
|
0
|
|
2
|
1
|
|
3
|
1
|
|
4
|
2
|
|
5
|
2
|
|
6
|
3
|
|
7
|
3
|
II. Configuration procedure
<H3C> system-view
[H3C] qos cos-local-precedence-map 0 0
1 1 2 2 3 3
[H3C] display qos cos-local-precedence-map
cos-local-precedence-map:
cos(802.1p) : 0
1 2 3 4 5 6 7
----------------------------------------------------------------------
local precedence(queue) :
0 0 1 1 2 2 3 3
[H3C] priority-trust cos
[H3C] display priority-trust
Priority trust mode: cos
l
Mapping relationships between the priority and
local precedence queue have been established. Refer to 1.5
Configuring Priority - Local Precedence Queue Mapping.
l
The priority to trust has been determined (from
the 802.1p priority, IP precedence, and DSCP precedence). Refer to 1.6 Configuring Packet Priority.
l
The scheduling algorithm (WRR or HQ+WRR) has
been determined, and the weight value for each queue has been allocated.
Table 1-13
Configure the queue scheduling algorithm
|
Operation
|
Command
|
Description
|
|
Enter system view
|
system-view
|
—
|
|
Set the queue scheduling algorithm
|
queue-scheduler { hq-wrr queue0-weight queue1-weight queue2-weight |
wrr queue0-weight queue1-weight queue2-weight queue3-weight }
|
Required
Defaults to WRR algorithm with a
weight ratio of 1:2:3:4.
|
I. Network requirements
l
802.1p priority is in use.
l
WRR algorithm is in use with a weight ratio of
2:3:4:5
l
The “802.1p priority - local precedence
queue” mapping table is shown as follows.
Table 1-14
“802.1p priority - local precedence queue”
mapping table
|
802.1p priority
|
Local precedence queue
|
|
0
|
0
|
|
1
|
0
|
|
2
|
1
|
|
3
|
1
|
|
4
|
2
|
|
5
|
2
|
|
6
|
3
|
|
7
|
3
|
II. Configuration procedure
<H3C> system-view
[H3C] qos cos-local-precedence-map 0 0
1 1 2 2 3 3
[H3C] display qos cos-local-precedence-map
cos-local-precedence-map:
cos(802.1p) :
0 1 2 3 4 5 6 7
----------------------------------------------------------------------
local precedence(queue) :
0 0 1 1 2 2 3 3
[H3C] priority-trust cos
[H3C] display priority-trust
Priority trust mode: cos
[H3C] queue-scheduler wrr 2 3 4 5
[H3C] display queue-scheduler
Queue scheduling mode: weighted
round robin
weight of queue 0: 2
weight of queue 1: 3
weight of queue 2: 4
weight of queue 3: 5
I. Configuration prerequisites
l
The source port is specified and whether the
packets to be mirrored are inbound or outbound is specified: inbound:
only mirrors the packets received via the port; outbound: only
mirrors the packets sent by the port; both: mirrors the packets
received and sent by the port at the same time.
l
The destination port is specified.
l
The group number of the mirroring group is
specified.
II. Configuring Local port
mirroring in Ethernet port view
Table 1-15
Configure Local port mirroring in Ethernet port
view (1)
|
Operation
|
Command
|
Description
|
|
Enter system view
|
system-view
|
—
|
|
Create a port mirroring group
|
mirroring-group group-id local
|
Required
|
|
Enter Ethernet port view of the
destination port
|
interface interface-type interface-number
|
—
|
|
Define the current port as the
destination port
|
monitor-port
|
Required
LACP must be disabled on the
destination port.
|
|
Exit current view
|
quit
|
—
|
|
Enter Ethernet port view of the
source port
|
interface interface-type interface-number
|
—
|
|
Configure the source port and specify
the direction of the packets to be mirrored
|
mirroring-port { inbound | outbound | both }
|
Required
|
Table 1-16
Configure Local port mirroring in Ethernet port
view (2)
|
Operation
|
Command
|
Description
|
|
Enter system view
|
system-view
|
—
|
|
Create a port mirroring group
|
mirroring-group group-id local
|
Required
|
|
Enter Ethernet port view of the
destination port
|
interface interface-type interface-number
|
—
|
|
Define the current port as the
destination port
|
mirroring-group group-id monitor-port
|
Required
LACP must be disabled on the
destination port
|
|
Exit current view
|
quit
|
—
|
|
Enter Ethernet port view of the
source port
|
interface interface-type interface-number
|
—
|
|
Configure the source port and specify
the direction of the packets to be mirrored
|
mirroring-group group-id mirroring-port { both | inbound | outbound }
|
Required
|
III. Configuring Local port
mirroring in system view
Table 1-17
Configure Local port mirroring in system view
