Table of Contents

1 QoS Overview·· 1-1

Introduction to QoS· 1-1

Introduction to QoS Service Models· 1-1

Best-Effort Service Model 1-1

IntServ Service Model 1-2

DiffServ Service Model 1-2

QoS Techniques Overview· 1-2

Applying QoS Techniques in a Network· 1-3

QoS Processing Flow in an AP· 1-4

2 QoS Policy Configuration· 2-1

QoS Configuration Approach Overview· 2-1

Non-Policy Approach· 2-1

Policy Approach· 2-1

Configuring a QoS Policy· 2-1

Defining a Class· 2-2

Defining a Traffic Behavior 2-2

Defining a QoS Policy and Applying the QoS Policy to an Interface· 2-3

Displaying and Maintaining QoS Policies· 2-3

3 Priority Mapping Configuration· 3-1

Introduction to Packet Precedences· 3-1

IP Precedence and DSCP Values· 3-1

802.1p Priority· 3-2

802.11e Priority· 3-3

Priority Mapping Overview· 3-3

Introduction to Priority Mapping· 3-3

Introduction to Priority Mapping Tables· 3-4

Priority Mapping Configuration Task List 3-5

Configuring Priority Mapping· 3-6

Configuring a Priority Mapping Table· 3-6

Configuring a Port to Trust Packet Priority for Priority Mapping· 3-6

Changing the Port Priority of an Interface· 3-7

Displaying and Maintaining Priority Mapping· 3-7

Priority Mapping Configuration Example· 3-7

 

 

This chapter includes these sections:

l          Introduction to QoS

l          Introduction to QoS Service Models

l          QoS Techniques Overview

Introduction to QoS

In data communications, Quality of Service (QoS) is the ability of a network to provide differentiated service guarantees for diversified traffic in terms of bandwidth, delay, jitter, and drop rate.

Network resources are always scarce. The contention for resources demands that QoS prioritize important traffic flows over trivial traffic flows. When making a QoS scheme, a network administrator must consider the characteristics of various applications to balance the interests of diversified users and fully utilize network resources.

The subsequent section describes some typical QoS service models and widely-used mature QoS techniques. By appropriately using these techniques, you can improve QoS effectively.

Introduction to QoS Service Models

This section covers three typical QoS service models:

l          Best-Effort Service Model

l          IntServ Service Model

l          DiffServ Service Model

Best-Effort Service Model

Best effort is a single service model and also the simplest service model. In the best effort service model, the network does its best to deliver packets but does not guarantee delay or reliability.

The best-effort service model is the default model in the Internet and applies to most network applications. It uses the first in first out (FIFO) queuing mechanism.

IntServ Service Model

The integrated service (IntServ) model is a multiple-service model that can accommodate diverse QoS requirements. It provides the most granularly differentiated QoS by identifying and guaranteeing definite QoS for each data flow.

In the IntServ model, an application must request service from the network before it sends data. IntServ signals the service request with the Resource Reservation Protocol (RSVP). All nodes that receive the request reserve resources as requested and maintain state information for the application flow.

The IntServ model demands high storage and processing capabilities, because it requires that all nodes along the transmission path maintain resource state information for each flow. The model is suitable for small-sized or edge networks, but not large-sized networks, for example, the core layer of the Internet, where billions of flows are present.

 

 

DiffServ Service Model

The differentiated service (DiffServ) model is a multiple-service model that can satisfy diverse QoS requirements. Unlike IntServ, DiffServ does not require an application to signal the network to reserve resources before sending data. DiffServ is easy to implement and extend.

All QoS techniques in this document are based on the Diff-Serv model.

QoS Techniques Overview

The QoS techniques fall into traffic classification, traffic policing, traffic shaping, line rate, congestion management, and congestion avoidance. The following part briefly introduces these QoS techniques.

Applying QoS Techniques in a Network

Figure 1-1 Positions of the QoS techniques in a network

 

As shown in Figure 1-1, traffic classification, traffic shaping, traffic policing, congestion management, and congestion avoidance mainly implement the following functions:

l          Traffic classification uses certain match criteria to assign packets with the same characteristics to a class. Based on classes, you can provide differentiated services.

l          Traffic policing polices flows entering or leaving an AP, and imposes penalties on traffic flows that exceed the pre-set threshold to prevent aggressive use of network resources. You can apply traffic policing to both incoming and outgoing traffic of a port.

l          Traffic shaping proactively adapts the output rate of traffic to the network resources available on the downstream AP to eliminate packet drops. Traffic shaping usually applies to the outgoing traffic of a port.

l          Congestion management provides a resource scheduling policy to determine the packet forwarding sequence when congestion occurs. Congestion management usually applies to the outgoing traffic of a port.

l          Congestion avoidance monitors the network resource usage and is usually applied to the outgoing traffic of a port. When congestion worsens, congestion avoidance actively reduces the queue length by dropping packets.

QoS Processing Flow in an AP

Figure 1-2 QoS processing flow

 

Figure 1-2 briefly describes how the QoS module processes traffic:

1)        Traffic classifier identifies and classifies traffic for subsequent QoS actions.

2)        The QoS module takes various QoS actions on classified traffic as configured, depending on the traffic processing phase and network status. For example, you may configure the QoS module to perform traffic policing for incoming traffic, traffic shaping for outgoing traffic, congestion avoidance before congestion occurs, and congestion management when congestion occurs.

 

This chapter includes these sections:

l          QoS Configuration Approach Overview

l          Configuring a QoS Policy

l          Displaying and Maintaining QoS Policies

QoS Configuration Approach Overview

Two approaches are available for configuring QoS: Non-Policy Approach and Policy Approach.

Some features support both approaches, but some support only one.

Non-Policy Approach

In non-policy approach, you configure QoS service parameters directly without using a QoS policy. For example, you can use the line rate feature to set a rate limit on an interface without using a QoS policy.

Policy Approach

In policy approach, you configure QoS service parameters by using QoS policies. A QoS policy defines the shaping, policing, or other QoS actions to take on different classes of traffic. It is a set of class-behavior associations.

A class is a set of match criteria for identifying traffic. It uses the AND or OR operator:

l          If the operator is AND, a packet must match all the criteria to match the class.

l          If the operator is OR, a packet matches the class if it matches any of the criteria in the class.

A traffic behavior defines a set of QoS actions to take on packets, such as priority marking and redirect.

By associating a traffic behavior with a class in a QoS policy, you apply the specific set of QoS actions to the class of traffic.

Configuring a QoS Policy

Figure 2-1 shows how to configure a QoS policy.

Figure 2-1 QoS policy configuration procedure

 

Defining a Class

To define a class, specify its name and then configure the match criteria in class view.

Follow these steps to define a class:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Create a class and enter class view	traffic classifier tcl-name [ operator { and | or } ]	Required By default, the operator of a class is AND. The operator of a class can be AND or OR. l      AND: A packet is considered belonging to a class only when the packet matches all the criteria in the class. l      OR: A packet is considered belonging to a class if it matches any of the criteria in the class.
Configure match criteria	if-match match-criteria	Required For more information, see the if-match command in QoS in the ACL and QoS Command Reference.

 

Defining a Traffic Behavior

A traffic behavior is a set of QoS actions (such as traffic filtering, traffic policing, and priority mapping) to take on a class of traffic. To define a traffic behavior, first create it and then configure QoS actions (such as priority mapping and traffic policing) in traffic behavior view.

Follow these steps to define a traffic behavior:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Create a traffic behavior and enter traffic behavior view	traffic behavior behavior-name	Required
Configure a CAR action	car cir committed-information-rate [ cbs committed-burst-size [ ebs excess-burst-size ] ] [ pir peak-information-rate ] [ red action ]	Optional
Drop or send packets	filter { deny | permit }	Optional To drop matching packets, select the deny keyword. To permit matching packets to pass through, select the permit keyword.
Set the local precedence for packets	remark local-precedence local-precedence	Optional
Set the 802.1p priority for packets	remark dot1p 8021p	Optional
Display traffic behavior configuration information	display traffic behavior user-defined [ behavior-name ]	Optional Available in any view

 

Defining a QoS Policy and Applying the QoS Policy to an Interface

A policy applied to an interface takes effect on the traffic sent or received by the interface.

A policy can be applied to multiple interfaces, but only one policy can be applied in one direction (inbound or outbound) of an interface.

Follow these steps to apply the QoS policy to an interface:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Define a QoS policy and enter QoS policy view	qos policy policy-name	Required
Associate a class with a behavior in the QoS policy	classifier tcl-name behavior behavior-name	Required Repeat this step to create more class-behavior associations.
Enter interface view	interface interface-type interface-number	—
Apply the policy to the interface	qos apply policy policy-name { inbound | outbound }	Required

 

 

Displaying and Maintaining QoS Policies

To do...	Use the command...	Remarks
Display traffic class information	display traffic classifier user-defined [ tcl-name ]	Available in any view
Display traffic behavior configuration information	display traffic behavior user-defined [ behavior-name ]	Available in any view
Display the configuration of one or all classes in one or all QoS policies and the associated behaviors of the classes	display qos policy user-defined [ policy-name [ classifier tcl-name ] ]	Available in any view
Display QoS policy configuration on the specified or all interfaces	display qos policy interface [ interface-type interface-number ] [ inbound | outbound ]	Available in any view

 

This chapter includes these sections:

l          Introduction to Packet Precedences

l          Priority Mapping Overview

l          Priority Mapping Configuration Task List

l          Configuring Priority Mapping

l          Displaying and Maintaining Priority Mapping

l          Priority Mapping Configuration Example

Introduction to Packet Precedences

IP Precedence and DSCP Values

Figure 3-1 ToS and DS fields

 

As shown in Figure 3-1, the ToS field of the IP header contains eight bits, and the first three bits (0 to 2) represent IP precedence from 0 to 7. According to RFC 2474, the ToS field of the IP header is redefined as the differentiated services (DS) field, where a DSCP value is represented by the first six bits (0 to 5) and is in the range 0 to 63. The remaining two bits (6 and 7) are reserved.

Table 3-1 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

 

Table 3-2 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	be (default)

 

802.1p Priority

802.1p priority lies in the Layer 2 header and is applicable to occasions where Layer 3 header analysis is not needed and QoS must be assured at Layer 2.

Figure 3-2 An Ethernet frame with an 802.1Q tag header

 

As shown in Figure 3-2, the 4-byte 802.1Q tag header consists of the tag protocol identifier (TPID, two bytes in length), whose value is 0x8100, and the tag control information (TCI, two bytes in length). Figure 3-3 presents the format of the 802.1Q tag header. The Priority field in the 802.1Q tag header is called the 802.1p priority, because its use is defined in IEEE 802.1p. Table 3-3 presents the values for 802.1p priority.

Figure 3-3 802.1Q tag header

 

Table 3-3 Description on 802.1p priority

802.1p priority (decimal)	802.1p priority (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

 

802.11e Priority

To provide QoS services on WLAN, the 802.11e standard was developed. IEEE 802.11e is a MAC-layer enhancement to IEEE 802.11. IEEE 802.11e adds a 2-byte QoS Control field to the 802.11e MAC frame header. Three bits of the QoS control field represents the 802.11e priority, which ranges from 0 to 7.

Figure 3-4 802.11e frame structure

 

Priority Mapping Overview

Introduction to Priority Mapping

When a packet enters an AP, the AP assigns a set of QoS priority parameters to the packet based on a certain priority field carried in the packet and sometimes may modify its priority, according to certain rules depending on AP status. This process is called priority mapping. The set of QoS priority parameters decides the scheduling priority and forwarding priority of the packet.

Priority mapping is implemented with priority mapping tables and involves priorities such as 802.11e priority and 802.1p priority.

Introduction to Priority Mapping Tables

The AP provides various types of priority mapping table, as listed below.

l          dot11e-lp: 802.11e-to-local priority mapping table.

l          dot1p-lp: 802.1p-to-local priority mapping table.

l          dscp-lp: DSCP-to-local priority mapping table, which applies to only IP packets.

l          lp-dot11e: Local-to-802.11e priority mapping table.

l          lp-dot1p: Local-to-802.1p priority mapping table.

l          lp-dscp: Local-to-DSCP priority mapping table.

Table 3-4 through Table 3-7 list the default priority mapping tables.

Table 3-4 The default dot1p-lp mapping

802.1p priority	Local precedence
0	2
1	0
2	1
3	3
4	4
5	5
6	6
7	7

 

Table 3-5 The default dscp-lp mapping

DSCP	Local precedence
0 to 7	0
8 to 15	1
16 to 23	2
24 to 31	3
32 to 39	4
40 to 47	5
48 to 55	6
56 to 63	7

 

Table 3-6 The default lp-dot1p and lp-dscp mappings

Local precedence	802.1p priority	DSCP
0	1	0
1	2	8
2	0	16
3	3	24
4	4	32
5	5	40
6	6	48
7	7	56

 

Table 3-7 The default port priority-local precedence mapping

Port priority	Local precedence
0	0
1	1
2	2
3	3
4	4
5	5
6	6
7	7

 

 

Priority Mapping Configuration Task List

You can configure priority mapping in two approaches:

l          Configuring priority trust mode. In this approach, you can configure a port to look up the priority mapping tables based on a certain priority such as 802.1p carried in incoming packets. If no packet priority is trusted, the port priority of the incoming port is used.

l          Changing port priority. By default, all ports are assigned the port priority of zero. By changing the port priority of a port, you can change the priority of the incoming packets on the port.

It is recommended that you plan QoS throughout the network before making QoS configuration.

Complete the following task to configure priority mapping:

Task	Remarks
Configuring a Priority Mapping Table	Optional
Configuring a Port to Trust Packet Priority for Priority Mapping	Optional
Changing the Port Priority of an Interface	Optional

 

Configuring Priority Mapping

Configuring a Priority Mapping Table

Follow these steps to configure a priority mapping table:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter priority mapping table view	qos map-table  { dot11e-lp | dot1p-lp | dscp-lp | lp-dot11e | lp-dot1p | lp-dscp }	Required You can enter the corresponding priority mapping table view as required.
Configure the priority mapping table	import import-value-list export export-value	Required Newly configured mappings overwrite the previous ones.
Display the configuration of the priority mapping table	display qos map-table [ dot11e-lp | dot1p-lp | dscp-lp | lp-dot11e | lp-dot1p | lp-dscp ]	Optional Available in any view

 

Configuring a Port to Trust Packet Priority for Priority Mapping

You can configure the AP to trust a particular priority field carried in packets for priority mapping on ports or globally.

When configuring the priority trust mode for a port, you can select the following keywords:

l          dot11e: Uses the 802.11e priority of the received packets for mapping.

l          dot1p: Uses the 802.1p priority of the received packets for mapping.

l          dscp: Uses the DSCP value of the received packets for mapping.

Follow these steps to configure the priority trust mode for a port:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter interface view	interface interface-type interface-number	—
Configure the priority trust mode	qos trust { dot11e | dot1p | dscp }	Required
Display the priority trust mode and port priority information of the specified interface or all interfaces	display qos trust interface [ interface-type interface-number ]	Optional Available in any view

 

Changing the Port Priority of an Interface

If an interface does not trust any packet priority, the AP uses its port priority to look for the set of priority parameters for the incoming packets. By changing port priority, you can prioritize traffic received on different interfaces.

Follow these steps to change the port priority of an interface:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter interface view	interface interface-type interface-number	—
Set the port priority of the port	qos priority priority-value	Required By default, the port priority is 0.

 

Displaying and Maintaining Priority Mapping

To do...	Use the command...	Remarks
Display priority mapping table configuration information	display qos map-table [ dot11e-lp | dot1p-lp | lp-dot11e | lp-dot1p ]	Available in any view
Display the priority trust mode and port priority of the specified interface or all interfaces	display qos trust interface [ interface-type interface-number ]	Available in any view

 

Priority Mapping Configuration Example

Network requirements

As shown in Figure 3-5:

l          All departments access the Intranet through the same AP. Each department is configured with an independent WLAN name. These departments are assigned to different VLANs based on WLAN-BSS interface.

l          It is required that the AP assigns local precedence to incoming packets by mapping the priority of the receiving port.

l          The default priority mapping table of the AP is used.

Figure 3-5 Network diagram for priority mapping configuration

 

Configuration procedure

1)        Configure the switch

# Create VLAN 2 and VLAN 3.

<Switch> system-view

[Switch] vlan 2

[Switch-vlan2] port ethernet 1/0/2

[Switch-vlan2] vlan 3

[Switch-vlan3] port ethernet 1/0/3

[Switch-vlan3] quit

[Switch] interface ethernet1/0/1

[Switch-Ethernet1/0/1] port link-type trunk

[Switch-Ethernet1/0/1] port trunk permit vlan all

[Switch-Ethernet1/0/1] quit

[Switch]

2)        Configure the AP

# Enter system view.

<AP> system-view

# Configure a WLAN network for each of the two departments, with the SSID being PART1 and PART2 respectively. Bind the two WLAN networks to WLAN-BSS 1 and WLAN-BSS 2 respectively.

[AP] wlan service-template 1 clear

[AP-wlan-st-1] ssid PART1

[AP-wlan-st-1] service-template enable

[AP-wlan-st-1]quit

# Create interface WLAN-BSS1, and configure its port priority as 5.

[AP] interface wlan-bss 1

[AP-WLAN-BSS1] qos priority 5

[AP-WLAN-BSS1] quit

[AP] interface wlan-radio 1/0/2

[AP-WLAN-Radio1/0/2] service-template 1 interface WLAN-BSS 1

[AP-wlan-st-1] quit

[AP] wlan service-template 2 clear

[AP-wlan-st-2] ssid PART2

[AP-wlan-st-2] service-template enable

[AP-wlan-st-2]quit

# Create interface WLAN-BSS2, and configure its port priority as 7.

[AP] interface wlan-bss 2

[AP-WLAN-BSS2] qos priority 7

[AP-WLAN-BSS2] quit

[AP] interface wlan-radio 1/0/2

[AP-WLAN-Radio1/0/2] service-template 2 interface WLAN-BSS 2

[AP-wlan-st-2] quit

# Assign interfaces WLAN-BSS 1 and WLAN-BSS 2 to different VLANs, such as VLAN 2 and VLAN 3 respectively.

[AP] vlan 2

[AP-vlan2]quit

[AP] interface WLAN-BSS 1

[AP-WLAN-BSS1] port access vlan 2

[AP-WLAN-BSS1] quit

[AP] vlan 3

[AP-vlan3]quit

[AP] interface WLAN-BSS 2

[AP-WLAN-BSS2]port access vlan 3

[AP-WLAN-BSS2] quit

# Configure port Ethernet 1/0/1 to use the 802.1p priority of received packets for priority mapping, and configure port Ethernet 1/0/1 as a trunk port.

[AP] interface ethernet 1/0/1

[AP-Ethernet1/0/1] qos trust dot1p

[AP-Ethernet1/0/1]port link-type trunk

# Assign port Ethernet 1/0/1 to VLAN 1 through VLAN 3.

[AP-Ethernet1/0/1] port trunk permit vlan 1 to 3

[AP-Ethernet1/0/1] quit

With these configurations completed, when you copy files to Host A and Host B or load files to Host A and Host B through the two wireless users connecting to BSS1 and BSS2 respectively, you will find that the loading rate of the wireless user connecting to BSS2 is faster than the loading rate of the wireless user connecting to BSS1.