QoS (Quality of Service) 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.
Traffic means
service traffic; that is, all the packets passing the switch.
Traffic classification means identifying
packets that conform to certain characteristics according to certain rules.
A classification rule is a filter rule
configured to meet your management requirements. It can be very simple. For
example, you can use a classification rule to identify traffic with different
priorities according to the ToS field in the IP packet header. It can be very
complicated too. For example, you can use a classification rule to identify the
packets according to the combination of link layer (Layer 2), network layer
(Layer 3), and transport layer (Layer 4) information including MAC addresses,
IP protocols, source addresses, destination addresses, port numbers of
applications, and so on.
Classification is
generally based on the information in the packet header and rarely based on the
packet contents.
1)
IP precedence, ToS precedence, and DSCP
precedence
Figure 1-1 DS field and TOS byte
The TOS field in an IP header contains eight
bits:
l
The first three bits indicate IP precedence in
the range of 0 to 7.
l
Bit 3 to bit 6 indicate ToS precedence in the
range of 0 to 15.
l
RFC2474 re-defines the ToS field in the IP
packet header, which is called the DS field. The first six (bit 0 to bit 5)
bits of the DS field indicate DSCP precedence in the range of 0 to 63. The
first three bits in DSCP precedence are class selector codepoints, bit 4 and
bit 5 indicate drop precedence, and bit 6 is zero indicating that the device
sets the service class with the DS model. The last two bits (bit 6 and bit 7)
are reserved bits.
The precedence
values of the IP packet indicate eight different service classes.
Table 1-1 Description on IP Precedence
|
IP Precedence (decimal)
|
IP Precedence (binary)
|
Description
|
|
0
|
000
|
routine
|
|
1
|
001
|
priority
|
|
2
|
010
|
immediate
|
|
3
|
011
|
flash
|
|
4
|
100
|
flash-override
|
|
5
|
101
|
critical
|
|
6
|
110
|
internet
|
|
7
|
111
|
network
|
The Diff-Serv network defines four traffic
classes:
l
Expedited Forwarding (EF) class: In this class,
packets can be forwarded regardless of link share of other traffic. The class
is suitable for preferential services with low delay, low packet loss ratio,
low jitter, and assured bandwidth (such as virtual leased line);
l
Assured forwarding (AF) class: This class is
further divided into four subclasses (AF1/2/3/4) and a subclass is further
divided into three drop priorities, so the AF service level can be segmented.
The QoS rank of the AF class is lower than that of the EF class;
l
Class selector (CS) class: This class comes from
the IP TOS field and includes eight classes;
l
Best Effort (BE) class: This class is a special
class without any assurance in the CS class. The AF class can be degraded to
the BE class if it exceeds the limit. Current IP network traffic belongs to
this class by default.
Table 1-2 Description on DSCP values
|
DSCP value (decimal)
|
DSCP value (binary)
|
Description
|
|
46
|
101110
|
ef
|
|
10
|
001010
|
af11
|
|
12
|
001100
|
af12
|
|
14
|
001110
|
af13
|
|
18
|
010010
|
af21
|
|
20
|
010100
|
af22
|
|
22
|
010110
|
af23
|
|
26
|
011010
|
af31
|
|
28
|
011100
|
af32
|
|
30
|
011110
|
af33
|
|
34
|
100010
|
af41
|
|
36
|
100100
|
af42
|
|
38
|
100110
|
af43
|
|
8
|
001000
|
cs1
|
|
16
|
010000
|
cs2
|
|
24
|
011000
|
cs3
|
|
32
|
100000
|
cs4
|
|
40
|
101000
|
cs5
|
|
48
|
110000
|
cs6
|
|
56
|
111000
|
cs7
|
|
0
|
000000
|
default (be)
|
2)
802.1p priority
802.1p priority lies in Layer 2 packet
headers and is applicable to occasions where the Layer 3 packet header does not
need analysis but QoS must be assured at Layer 2.
Figure 1-2 An Ethernet frame with an 802.1Q tag header
As shown in the figure above, each host supporting
802.1Q protocol adds a 4-byte 802.1Q tag header after the source address of the
former Ethernet frame header when sending packets.
The 4-byte 802.1Q tag header contains a 2-byte
Tag Protocol Identifier (TPID) whose value is 8100 and a 2-byte Tag Control
Information (TCI). TPID is a new class defined by IEEE to indicate a packet
with an 802.1Q tag. Figure 1-3 describes the detailed contents of an 802.1Q tag header.
Figure 1-3
802.1Q tag headers
In the figure above, the 3-bit priority
field in TCI is 802.1p priority in the range of 0 to 7. These three bits
specify the precedence of the frame. Eight classes of precedence are used to
determine which packet is sent preferentially when congestion occurs.
Table 1-3 Description on 802.1p priority
|
CoS (decimal)
|
CoS (binary)
|
Description
|
|
0
|
000
|
best-effort
|
|
1
|
001
|
background
|
|
2
|
010
|
spare
|
|
3
|
011
|
excellent-effort
|
|
4
|
100
|
controlled-load
|
|
5
|
101
|
video
|
|
6
|
110
|
voice
|
|
7
|
111
|
network-management
|
The precedence is called 802.1p priority because the related
applications of this precedence are defined in detail in the 802.1p
specifications.
Protocol packets carry their own priority.
You can perform QoS actions on protocol packets by setting their priorities.
Port rate limit is port-based rate limit.
It limits the total rate of outbound packets on a port.
The feature of queue scheduling
configuration synchronization on aggregated ports makes the queue scheduling
configuration synchronous on each port of an aggregation group.
l
Supporting the feature of queue scheduling
configuration synchronization on the ports in an aggregation group
When you modify or delete the queue
scheduling mode in Ethernet port view, the queue scheduling modes of all the
ports in the aggregation group are modified or deleted if this port belongs to
an aggregation group; only the queue scheduling mode of this port is modified
or deleted if this port does not belong to any aggregation group.
l
Dynamic aggregation supported by queue
scheduling modes on ports
If the queue scheduling configuration
information of some LACP-enabled ports in up state is the same, these ports can
be aggregated into the same aggregation group.
l
Static aggregation or manual aggregation
supported by queue scheduling modes on ports
You can add a queue-scheduling-enabled port
into a specific static or manual aggregation group. This operation can be
performed not only on the local device but also across devices in an intelligent
resilient framework (IRF).
l
You can use the copy command to copy the
queue scheduling configuration of a port.
For the
introduction to the copy command, refer to the Basic Port Configuration
Module in this manual.
When the network is congested, the problem
that many packets compete for resources must be solved, usually through queue
scheduling.
In the following
section, strict priority (SP) queueing and weighted round robin (WRR) queueing are
introduced.
1)
SP queueing
Figure 1-4 Diagram for SP queueing
SP queue-scheduling algorithm is specially
designed for critical service applications. An important feature of critical
services is that they demand preferential service in congestion in order to
reduce the response delay. Assume that there are eight output queues on the
port and the preferential queue classifies the eight output queues on the port
into eight classes, which are queue7, queue6, queue5, queue4, queue3, queue2,
queue1, and queue0. Their priorities decrease in order.
In queue scheduling, SP sends packets in
the queue with higher priority strictly following the priority order from high
to low. When the queue with higher priority is empty, packets in the queue with
lower priority are sent. You can put critical service packets into the queues
with higher priority and put non-critical service (such as e-mail) packets into
the queues with lower priority. In this case, critical service packets are sent
preferentially and non-critical service packets are sent when critical service
groups are not sent.
The disadvantage of
SP queue is that: if there are packets in the queues with higher priority for a
long time in congestion, the packets in the queues with lower priority will be
“starved” because they are not served.
2)
WRR queueing
Figure 1-5 Diagram for WRR
WRR queue-scheduling algorithm schedules
all the queues in turn and every queue can be assured of a certain service
time. Assume there are eight priority queues on a port. WRR configures a weight
value for each queue, which is w7, w6, w5, w4, w3, w2, w1, and w0. The weight
value indicates the proportion of obtaining resources. On a 100 M port,
configure the weight value of WRR queue-scheduling algorithm to 50, 50, 30, 30,
10, 10, 10, and 10 (corresponding to w7, w6, w5, w4, w3, w2, w1, and w0 in
order). In this way, the queue with the lowest priority can get 5 Mbps
bandwidth at least, and the disadvantage of SP queue-scheduling that the
packets in queues with lower priority may not get service for a long time is
avoided. Another advantage of WRR queue is that: though the queues are
scheduled in order, the service time for each queue is not fixed; that is to
say, if a queue is empty, the next queue will be scheduled. In this way, the
bandwidth resources are made full use.
1.2 QoS Supported by S3100-52P
Table 1-4 QoS functions supported by S3100-52P
and related commands
|
QoS
|
Specification
|
Related command
|
|
Priority mapping
|
Support only the mapping between 802.1p
priority and local queues
|
qos cos-local-precedence-map
|
|
Port priority
|
Supported
|
priority priority-level
priority trust
|
|
Queue scheduling
|
Support SP and WRR
Support queue scheduling configuration
synchronization on aggregated ports
|
queue-scheduler
|
|
Set the priority of protocol packets
|
Supported
|
protocol-priority
|
|
Set port rate limit
|
Supported
|
line-rate
|
The
mapping between the local precedence and the outbound queue is one-to-one. You
can modify the mapping between the 802.1p priority and the outbound queue by modifying
the mapping between the 802.1p priority and the local precedence.
I. Configuration prerequisites
You have understood the mapping between the
802.1p priority and the local precedence and the default mapping table.
II. Configuration procedure
Table 1-5
Configure the mapping table
|
Operation
|
Command
|
Description
|
|
Enter system view
|
system-view
|
—
|
|
Configure the COS-to-local-precedence
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
|
Optional
|
|
Display the mapping table
|
display qos
cos-local-precedence-map
|
Optional
You can execute the display
command in any view
|
III. Configuration example
l
Configure the following 802.1p priority-to-local
precedence mappings: 0 to 2, 1 to 3, 2 to 4, 3 to 1, 4 to 7, 5 to 0, 6 to 5,
and 7 to 6.
l
Display the configuration results.
Configuration procedure:
<H3C> system-view
System View: return to User View with
Ctrl+Z.
[H3C] qos cos-local-precedence-map 2
3 4 1 7 0 5 6
[H3C] dis qos
cos-local-precedence-map
cos-local-precedence-map:
cos(802.1p) : 0
1 2 3 4 5 6 7
--------------------------------------------------------------------------
local precedence(queue) : 2 3
4 1 7 0 5 6
By default, the
switch replaces the 802.1p priority of the received packet with the priority of
the inbound interface, and then assigns local precedence to the packet
according to the priority. In this case, you can set the port priority.
In addition, you can specify the switch to use
the packet priority.
I. Configuration prerequisites
l
The priority trust mode is specified
l
The port whose priority is to be configured is
specified
l
The priority value of the specified port is
specified
II. Configuration procedure
Table 1-6 Set to use the port priority
|
Operation
|
Command
|
Description
|
|
Enter system view
|
system-view
|
—
|
|
Enter Ethernet port view
|
interface interface-type interface-number
|
—
|
|
Set the port priority
|
priority priority-level
|
Optional
By default, the port priority is 0
|
Table 1-7
Set to use the packet priority
|
Operation
|
Command
|
Description
|
|
Enter system view
|
system-view
|
—
|
|
Enter Ethernet port view
|
interface interface-type interface-number
|
—
|
|
Set the switch to use the packet
priority
|
priority trust
|
Through this configuration, the
switch uses the packet priority instead of the port priority
|
III. Configuration example
l
Set to use the port priority and specify the
priority of Ethernet1/0/1 to 7.
Configuration procedure:
<H3C> system-view
System View: return to User View with
Ctrl+Z.
[H3C] interface Ethernet1/0/1
[H3C-Ethernet1/0/1] undo priority
[H3C-Ethernet1/0/1] priority 7
l
Set the switch to use the 802.1p priority
carried in the packet on Ethernet1/0/1.
Configuration procedure:
<H3C> system-view
System View: return to User View with
Ctrl+Z.
[H3C] interface Ethernet1/0/1
[H3C-Ethernet1/0/1] priority trust
The protocol packet carries its own
precedence. You can modify the precedence of the protocol packet by setting its
precedence. And then you can match the precedence with the corresponding QoS
action to perform the corresponding QoS operation on the protocol packet.
l
The type of protocol whose precedence needs
modification is specified
l
The precedence value after modification is
specified
Table 1-8
Set the precedence of the protocol packet
|
Operation
|
Command
|
Description
|
|
Enter system view
|
system-view
|
—
|
|
Set the precedence of the protocol
packet
|
protocol-priority protocol-type protocol-type { ip-precedence ip-precedence
| dscp dscp-value }
|
Required
You can modify the IP precedence or
DSCP precedence of the protocol packet
Only the precedence of TELNET, OSPF,
SNMP, and ICMP protocol packets is supported currently
|
|
Display the precedence of the
protocol packet
|
display protocol-priority
|
Optional
You can execute the display
command in any view
|
l
Set the IP precedence of ICMP protocol packets
to 3.
l
Display the configuration results.
Configuration procedure:
<H3C> system-view
System View: return to User View with
Ctrl+Z.
[H3C] protocol-priority protocol-type
icmp ip-precedence 3
[H3C] display protocol-priority
Protocol: icmp
IP-Precedence: flash(3)
l
The ports on which rate limit is to be performed
is specified
l
The target rate is specified
l
The direction of rate limit is specified
Table 1-9
Configure port rate limit
|
Operation
|
Command
|
Description
|
|
Enter system view
|
system-view
|
—
|
|
Enter Ethernet port view
|
interface interface-type interface-number
|
—
|
|
Configure port-based rate limit
|
line-rate { inbound | outbound } target-rate
|
Required
l
target-rate:
Total rate to limit packet sending and receiving on the port, in Kbps. The
granularity of rate limit is 64 Kbps. If the number you input is in the range
of N*64 to (N+1)*64 (N is a natural number), the switch will set the value to
(N+1)*64 Kbps automatically
l
The rate range of 100 M Ethernet ports is from
64 to 99,968
l
The rate range of Gigabit Ethernet ports is in
from 64 to 1,000,000
|
l
Set rate limit in the outbound direction of
Ethernet1/0/1 on the switch
l
The limit rate is 1 Mbps (1,024 Kbps)
Configuration procedure:
<H3C> system-view
System View: return to User View with
Ctrl+Z.
[H3C] interface Ethernet1/0/1
[H3C-Ethernet1/0/1] line-rate
outbound 1024
Refer to section 1.1.7
"Queue Scheduling" for the introduction to queue scheduling.
The queue-scheduling algorithm is
specified: which queues adopt the WRR queue-scheduling algorithm, and which
queues adopt the SP queue-scheduling algorithm.
Table 1-10 Configure queue scheduling in system view
|
Operation
|
Command
|
Description
|
|
Enter
system view
|
system-view
|
—
|
|
Configure
the queue scheduling mode
|
queue-scheduler
{ strict-priority | wrr queue0-weight
queue1-weight queue2-weight queue3-weight queue4-weight queue5-weight queue6-weight
queue7-weight }
|
Required
In WRR
mode, if the weight value of one or more queues is set to 0, SP algorithm is
used for this or these queues
By
default, all the outbound queues on the port adopt the WRR queue scheduling
algorithm and their default weight values are 1:2:3:4:5:9:13:15.
|
|
Display the queue-scheduling mode and
related parameters on the switch
|
display queue-scheduler
|
Optional
You can execute the display
command in any view.
|
Table
1-11 Configure queue scheduling in Ethernet port
view
|
Operation
|
Command
|
Description
|
|
Enter system view
|
system-view
|
—
|
|
Enter Ethernet port view
|
interface interface-type
interface-number
|
—
|
|
Configure the queue scheduling mode
|
queue-scheduler wrr queue0-weight queue1-weight queue2-weight queue3-weight
queue4-weight queue5-weight queue6-weight queue7-weight
|
Required
In WRR mode, if the weight value of one
or more queues is set to 0, SP algorithm is used for this or these queues
By default, all the outbound queues on
the port adopt the WRR queue scheduling algorithm and their default weight
values are 1:2:3:4:5:9:13:15.
|
l
The queue scheduling algorithm defined by
executing the queue-scheduler command in system view takes effect on all
ports of the switch. The queue scheduling algorithm defined by executing the queue-scheduler
command in Ethernet port view takes effect on the current port only. If the weight
values of the queues in the WRR queue scheduling algorithm defined globally
cannot satisfy the requirement of a port, you can modify the weight values of
the queues in Ethernet port view of this port. A new queue scheduling algorithm
on this port will overwrite the globally defined queue weight value. You cannot
use the display queue-scheduler command to display the queue weight defined
in Ethernet port view.
l
If you have configured link aggregation groups,
the queue scheduling algorithm defined on a port in an aggregation group will
be synchronized to other ports in the aggregation group automatically.
1.7.3 Configuration Example
l
The switch adopts the WRR queue scheduling
algorithm, and the weight values of outbound queues are 2, 2, 3, 3, 4, 4, 5,
and 5, respectively;
l
Disable the applied queue scheduling mode. By
default, all outbound queues on the port adopts the WRR queue scheduling algorithm
and their default weight values are 1:2:3:4:5:9:13:15;
l
Query the configuration information.
Configuration procedure:
<H3C> system-view
System View: return to User View with
Ctrl+Z.
[H3C] queue-scheduler wrr 2 2 3 3 4 4
5 5
[H3C]display queue-scheduler
Queue scheduling mode: weighted
round robin
weight of queue 0: 2
weight of queue 1: 2
weight of queue 2: 3
weight of queue 3: 3
weight of queue 4: 4
weight of queue 5: 4
weight of queue 6: 5
weight of queue 7: 5
[H3C] undo queue-scheduler
[H3C] display queue-scheduler
weight of queue 0: 1
weight of queue 1: 2
weight of queue 2: 3
weight of queue 3: 4
weight of queue 4: 5
weight of queue 5: 9
weight of queue 6: 13
weight of queue 7: 15
1.8 Displaying
QOS Configuration
After finishing the
configurations mentioned above, you can execute the display command in
any view to check the running state of the QoS profile after the configuration.
You can verify the effect of the configuration by checking the information on
display.
Table 1-12 Display the QoS configuration
|
Operation
|
Command
|
Description
|
|
Display the configuration of protocol
packet precedence
|
display protocol-priority
|
You can execute the display
command in any view
|
|
Display the Mapping between 802.1p
Priority and Queues
|
display qos cos-local-precedence-map
|
|
Display all QoS configurations on a port
or all ports
|
display qos-interface {interface-type interface-number | unit-id } all
|
