QoS Design and Deployment for - …d2zmdbbm9feqrf.cloudfront.net/2014/eur/pdf/BRKEWN-3003.pdf · QoS Design and Deployment for Wireless LANs BRKEWN-3003 Robert Barton, P. Eng

QoS Design and Deployment for Wireless LANs BRKEWN-3003

Robert Barton, P. Eng

Systems Engineer

CCIE #6660

CCDE #2013::6

© 2014 Cisco and/or its affiliates. All rights reserved. BRKEWN-3003 Cisco Public

Presentation Source Material

End-to-End QoS Network Design, 2nd Edition

First Edition is one of better selling Cisco Press books of all time, but . . .

– It was time for a 2nd edition!

Book is organized around PINs (Places in the Network), e.g. Data Center, WAN, Wireless LANs, VPN, Campus

Content in this session primarily based on the “WLAN QoS Design” section

3

Now Available!


• Wireless QoS Building Blocks

• IEEE 802.11e and Wireless Multimedia (WMM)

• Wireless QoS Design Considerations

• Cisco WLC 5500 QoS Design Strategies

• Developing a Unified QoS Strategy for the WLAN

• Wrap-up and Final Thoughts

QoS Design and Deployment For Wireless LANs AGENDA

Wireless QoS Building Blocks


Comparing Wired and Wireless QoS

Wired environments are Full Duplex, Wireless is Half Duplex

– Half duplex environments are very susceptible to collisions

Thus, wired QoS is mostly concerned with managing packet loss due to congestion problems (queuing), however . . .

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Wireless QoS is focused on a much bigger problem:

1. WLAN QoS mostly revolves around reducing the probability of a collision for high-priority traffic, based on it’s QoS classification

2. Managing congestion is a secondary concern

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Carrier Sense Multiple Access / Collision Avoidance

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Wired Hubs use CSMA/CD (collision detection)

– A transmitting station will first listen to the medium to see if it is idle before sending it’s frame. When it seems idle, it sends the frame.

– After sending, it listens to see if a collision occurred (the waveform is reflected back)

802.11 networks use CSMA/CA (collision

avoidance)

– Wireless networks have no way to detect that a collision even occurred!

– CSMA/CA accepts collisions will occur, but has a system for dealing with then once they do occur.

– What do you do on a conference call when more than one person speaks at the same time?


The Distributed Coordination Function (DCF) Algorithm for Media Access

Using CSMA/CA, DCF Does the Following:

1. Listen first to see if any other transmissions are in progress

2. After the WLAN is idle, wait for a set period before trying to transmit (called DIFS)

3. If the medium is still idle, sends the frame

4. If a collision occurs (because it hears another station transmit at the exact same time, or because you didn’t get an ACK from the station your are sending to, wait another random backoff period and retry

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Who Get the Higher Transmission Priority?

1. Access Point

2. Wireless Client

3. They all get equal access

9

Other channel access models have been proposed. These models allow the AP to organizes channel access in a structured way, but these have never been widely adopted

1. Legacy Point Coordination Function (PCF)

2. 802.11e Hybrid Controlled Channel Access (HCCA)


Backoff Timers and Contention Windows

10

Random Contention Window (CW)

Time (t)

Medium is Busy

Begin Transmission

DIFS ……….

After the medium is idle, all stations must wait the DCF Interframe space (DIFS) – This is a pre-established wait time that all stations must wait (they all wait the same

DIFS period)

Once DIFS has expired, a random countdown timer, called the Contention Window (CWmin) begins

– Once CWmin expires, the station tries to resend

– If the medium is still busy double the CW up to a value of CWmax until you can send

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The DCF Decision Process

11

Once the medium is free, countdown the DIFS period

Transmit the Frame

YES

NO

Is the medium available for Transmission?

NO

YES

Wait the random backoff period between 0 and

CWmin

If the medium still busy after another attempt, wait another random backoff

period between 0 and CWmax

Is the medium free?


DCF In Action: Consider an Example of Five Stations Trying to Unicast all at Once

12

Station A

Station B

Station C

Station D

Station E

Frame

Defer

Defer

Defer

Frame

DIFS DIFS

Defer

Frame

DIFS

Frame

Backoff time

Backoff time remaining

Defer

Defer

Defer

Defer

IEEE 802.11e and Wireless Multimedia (WMM)


DCF Needed an Update

QoS is not possible with DCF:

1. No method of classification (all traffic is treated equally)

2. The DIFS and Contention Window values are the same for all traffic

IEEE 802.11e was formed and finally ratified in the 802.11e-2007 standard (which is now part of the 802.11e-2012 “rollup”)

– 802.11e set out to make tweaks to DCF that would allows priority handling of high priority traffic

– The Goal: Improve the probability that high priority traffic will always be transmitted first

By the way, what is the difference between IEEE 802.11e and WMM??

14


Enhanced Distributed Channel Access (EDCA)

1. Establishment of four priority queues (known as Access Categories, ACs)

2. Instead of a single DIFS timer, give timers to each class of service (AC)

3. For each class (AC), give a different range of contention window size – preferential CWmin and CWmax for each AC

4. Transmission Opportunity (TXOP)

5. Call Admission Control (CAC) with TSpec

– Other enhancements were also introduced, including: Power Save mode

15


Access Categories Act like Transmit Queues

16

Background Best Effort Video Voice

Application Data


Summarizing the Four Access Categories

EDCA / WMM AC Name Description Cisco WLC Profile Name

Voice Highest Priority Platinum

Video Video, Medium Priority Gold

Best Effort Most Other Traffic Silver

Background Low Priority Traffic Bronze

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When 802.11 frames are transmitted, a QoS value known as the User Priority (UP) is written into the L2 frame

– This is used to distinguish traffic types and place them in the correct AC

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Understanding WLAN QoS Markings Surprising Differences Emerge . . .

Traffic Type DSCP 802.11e UP 802.1p CoS WLC Profile

Network Control

56 (CS7) 7 7 Platinum

CAPWAP 48 (CS6) 7 6 Platinum

Voice 46 (EF) 6 5 Platinum

Interactive Video

34 (AF41) 5 4 Gold

Streaming 26 (AF31) 4 3 Gold

X-Data 18 (AF21) 3 2 Silver

Bulk Data 10 (AF11) 2 1 Bronze

Best Effort 0 (BE) 0 0 Silver


How Backoff Timers Affect QoS

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EDCA / WMM AC AIFS CWmin CWmax

Legacy DCF DIFS > 2 15 1023

Voice 2 3 7

Video 2 7 15

Best Effort 3 15 1023

Background 7 15 1023

EDCF does the following:

– Variable Arbitration Interframe Spacing (AIFS)

– Variable CWmin and CWmax values depending on traffic type


Understanding the Effect of EDCA Timers

20

By combining these timers, the theoretical probability of higher priority frames is greatly improved, but is not guaranteed


QoS Enhancements for Voice Applications

EDCA provides two key key optimizations for voice over wireless:

1. Transmission Opportunity (TXOP)

2. Transmission Specification (TSpec)

TXOP is a set period of time when a wireless station may send as many frames as possible without having to contend with other stations. – In DCF once a client has access to the medium, it just keeps sending as long as it wants (bad)

– TXOP gives a specified period of time per client to access the medium (good)

TSpec allows real-time applications, such as voice calls that are in progress, to be prioritized over requests for new calls.

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Wireless QoS Design Considerations


0 EF

Classification

Marking/Mutation

Shaping/Policing

Queueing

Trust

What Make up Wireless Qos?

http://images.google.fr/imgres?imgurl=http://4.bp.blogspot.com/_UZImdYAiry8/Sb9qYmN0llI/AAAAAAAAPtc/a_qXEx69CB0/s400/oracle_logo.jpg&imgrefurl=http://vectorlogo.blogspot.com/2009/03/oracle-logo-eps.html&usg=__TTg6bQ4L8aDCa2kKWUD3Q4YWewM=&h=161&w=400&sz=7&hl=fr&start=3&sig2=xj4d94noyf1kS0Adw6tzJA&um=1&tbnid=LLEUA6II6jNxiM:&tbnh=50&tbnw=124&prev=/images?q=oracle+logo&hl=fr&safe=off&rlz=1T4GGLL_frFR328FR328&um=1&ei=FeHBSvDVKsjKjAeGsfDoBQ


0 EF

Classification

Marking/Mutation

Shaping/Policing

Queueing

Trust

SET MUTATE



Classification

Marking/Mutation

Shaping/Policing

Queueing

Trust


Line Rate

Shaped Rate

Traffic shaping limits the transmit rate to a value lower than line rate

with Traffic

Shaping

without

Traffic Shaping

Line Rate

Policed Rate

Policing discards traffic which exceeds policed rate

without Policing

with Policing


Classification

Marking/Mutation

Shaping/Policing

Queueing

Trust


Queue 2 (Access Category 2)

Queue 1 (Access Category 1)


Classification

Marking/Mutation

Shaping/Policing

Queueing

Trust


DSCP 46


QoS Remarking: Upstream vs. Downstream

Upstream means traffic originating at the client, headed towards the WLC

Downstream means traffic destined for the WLAN clients

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CAPWAP Tunnel

WLC AP Client

Radio Upstream Network Upstream

Network Downstream Radio Downstream

Ethernet

Switch

802.1q/p 802.11e UP CAPWAP DSCP DSCP


The Downstream QoS Marking Model

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CAPWAP Tunnels Si Si Si Si Si Si

WLAN Controller

AP

Ethernet Switch

CAPWAP Encapsulated DSCP 802.1p DSCP Payload

AP

AP

802.1q Trunk

1 The Ethernet frame is received over an 802.1q trunk by the WLC. The WLC uses the

DSCP value of the IP packet and maps it to the outer DSCP of the CAPWAP tunnel.

802.11 DSCP Payload

1


The Downstream QoS Marking Model

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WLAN Controller

AP

Ethernet Switch

802.1p DSCP Payload 11e UP DSCP Payload

2 2

AP

AP

802.1q Trunk

1 The Ethernet frame is received over an 802.1q trunk by the WLC. The WLC uses the

DSCP value of the IP packet and maps it to the outer DSCP of the CAPWAP tunnel.

2 Once the Ethernet frame is received by the AP, it maps the DSCP value of the IP packet

to the 802.11e CoS value on the wireless frame. The frame is then sent to the client.

CAPWAP Encapsulated DSCP

802.11 DSCP Payload


The Upstream QoS Marking Model

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CAPWAP Encapsulated


WLAN Controller

AP

Ethernet Switch

11e UP DSCP Payload DSCP

3 1

AP

AP

802.1q Trunk

3 1 The client 802.11e frame is received by the AP. The AP copies the 802.11e

frame header to the outer CAPWAP IP DSCP header

802.11 DSCP Payload


The Upstream QoS Marking Model

32


WLAN Controller

AP

Ethernet Switch

DSCP

3 1

802.1p DSCP Payload

AP

AP

802.1q Trunk

3 1 The client 802.11e frame is received by the AP. The AP copies the 802.11e

frame header to the outer CAPWAP IP DSCP header

At the WLC side of the CAPWAP tunnel, the 802.11e bridged to the Ethernet switch.

The original packet’s DSCP value is mapped to a CoS value on the 802.1q trunk. 2

2

11e UP DSCP Payload

CAPWAP Encapsulated

802.11 DSCP Payload

Cisco WLC 5500 QoS Design Strategies


Cisco WLC 5500 QoS Profiles

As a “best practice” Cisco recommends to have a separate WLAN (SSID) for voice.

– Not exactly practical any more

– What do you do if you are using MS Lync for Unified Communications on a laptop??

This is the most misunderstood concept in Cisco WLAN QoS

34

Cisco WLC Profile Name

Maximum DSCP Value for the Profile

Platinum EF (46)

Gold AF41 (34)

Silver DF (0)

Bronze AF11 (10)

The main feature of the profile is to set a ceiling on the DSCP value that is allowed.

This only impacts the DSCP value that is set on the CAPWAP header and the downstream UP value.


Step 1: Configure the QoS Profile in the WLC

35

These four pre-configured QoS profiles may be used and applied to each WLAN (SSID) you create.

Recommendations: 1. For enterprise class, mixed-use WLANs,

use the Platinum Profile

2. For guest SSIDs use the Silver Profile


Step 2: Configure the QoS Profile

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Create default bandwidth contracts for each user or each SSID

Bandwidth contracts are

bidirectional

Set the maximum priority

Set the 802.1p CoS value


Customization Feature (AireOS 7.2): Alloy QoS

37

Maximum Priority allows you to customize the upper limit QoS marking for a QoS policy

Non-WMM client packets are defaulted to the maximum priority of the WLAN. – Can introduce significant problems for multicast traffic – flooded to all clients in the

Voice queue, which degrades performance.

These fields set the default QoS marking for non-WMM clients


Step 3: Apply the QoS Profile to Your WLAN (SSID)

38

Choose the QoS profile you want to apply for this WLAN

In this example, the “Voice” profile is selected.

This sets the ceiling on all traffic to DSCP 46 and UP value to 6.

You can also set the per-user and per-SSID bandwidth contracts from this screen.


Example 1 – Downstream QoS Marking

39


WLAN Controller

AP

Ethernet Switch


UP DSCP Payload

AP

AP

802.1q Trunk

802.11 DSCP Payload

Mixed use WLAN (tablets, phones, etc.) configured for the Platinum Profile

6 46 46

5

46


Example 2 – Using the Gold QoS Profile

40


WLAN Controller

AP

Ethernet Switch


UP DSCP Payload

AP

AP

802.1q Trunk

802.11 DSCP Payload

Mixed use WLAN (tablets, phones, etc.) configured for the Gold Profile

DSCP 46 gets Marked down to 34, UP is 5

5 34

46 5

46


What to do With Non-WMM Clients?

41

WMM is critical for QoS – it enables 802.11e UP

Best to use “Required” for a QoS enabled WLAN

“Allowed” will mix QoS capable and non-QoS capable devices on same WLAN

802.11n and 802.11ac enforce WMM support


Example 3 – A WMM Client Using Lync

42

CAPWAP Encapsulated


WLAN Controller

AP

Ethernet Switch

11e UP DSCP Payload DSCP 802.1p DSCP Payload

AP

AP

802.1q Trunk

802.11 DSCP Payload

The AP Recognizes

the WMM UP value

and maps it

automatically to

DSCP 34

5 34

34

34 4

34


Example 4 – A Non-WMM Client on the Platinum Profile

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CAPWAP Encapsulated


WLAN Controller

AP

Ethernet Switch

802.11 DSCP Payload DSCP 802.1p DSCP Payload

AP

AP

802.1q Trunk

802.11 DSCP Payload

The Client is Not WMM Capable.

AP automatically maps the

CAPWAP DSCP to EF (46)

The Controller unpacks the CAPWAP

packet and only uses the inner DSCP

value from here

46

x 34 4

34

34


Tweaking the EDCA Parameters for Voice

Choose “WMM” for networks without voice

Choose “Voice Optimized” or “Voice & Video Optimized” when using multimedia

Values that the Profile influences:

– CWmin

– CWmax

– TXOP values

– Slot Time Values

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Call Admission Control (CAC)

CAC refers to the WLC’s capability to limit the number of voice calls on a per-AP basis CAC limits the number of voice clients which can associate to the Access Point.

Configuration:

1. CAC is a subset of WMM, thus first step is to configure WMM “allowed” or “required”

2. Navigate to this page, enable and configure CAC

45


Introducing Application Visibility & Control (AVC)

Introduced in AireOS 7.4, limited capabilities in IOS-based controllers

Leverages the IOS NBAR2 Engine – same list of traffic signatures as IOS & XE

46

• Discover which applications are running on your

corporate and guest WLANs

• Prioritize critical wireless apps and de-prioritize

non-business apps

• Monitor voice and video performance on the

WLAN

AVC In The Wireless LAN Controller


Key Points to Know About AVC

47

CAPWAP Tunnels

WLC AP

Client

Ethernet

Switch

AVC Policy only

functions here

AVC Does Not

Function Here

AVC feature has no

concept of direction –

modifies DSCP in both

directions

AVC Modifies the inner DSCP value,

thus influencing the CAPWAP DHCP

and wireless UP values


AVC Example: Build a Multimedia AVC Policy

48

More Key Points To Know:

Applications are grouped by class (such as “voice-and-video” shown here)

From AireOS 7.6 Protocol Packs are used for signature updates


AVC Example: Mobile Applications AVC Profile

49

AVC has two basic capabilities:

1. Modify the inner packet’s DSCP to a custom value

2. Drop the packet

Select the application you want to remark (in this case MS Lync)

Decide what DSCP value you would like it remarked to.

In this case, let’s mark it to Gold (DSCP 34)


AVC Example Cont’d:

50

The “Mobile Applications” AVC Policy is now created and ready to be applied.


AVC Example Cont’d: Apply the AVC Policy

51

Navigate to your QoS policy for the WLAN you want to apply this to.

Enable AVC

Apply the AVC policy you created to this QoS policy.


AVC Provides Exceptional Application Visibility

52

Developing a Unified QoS Strategy for the WLAN


QoS Features are Nice, but a QoS Design is Critical

How Does this fit with the Classic Four-Class QoS Model?

54

Transactional

Data

Realtime

Classes

Best Effort

Control

AF21

EF

DSCP

DF

CS3

Database Apps,

Email, FTP, Backups

CRM Apps,

Broadcast Video

Multimedia Streaming

IP Phones,

TelePresense,

WebEx,

Jabber

Application Examples

Everything Else

OAM, Routing Protocols

35% BW Guarantee

WRED

33% of BW,

Strict Priority

QoS Handling

25% BW Guarantee

WRED

7% of BW Guarantee


A Desired Design Might Look Like This:

55

Transactional Data

Realtime

4-Class Strategic

Enterprise Model

Best Effort

Control

Platinum

WMM Model +

802.11e User Priority

Silver

Gold

Bronze

UP 7

UP 5

UP 3

UP 2

UP 6

UP 4

UP 0

UP 1

AF21

EF

DSCP

DF

CS3

Packets (frames) go into the EDCA / WMM ACs based on their UP Value.

This model looks reasonable and desirable, but is it realistic?


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But It Doesn’t Always Work - Remember This Table?

Traffic Type DSCP 802.11e UP

Network Control

56 (CS7) 7

CAPWAP 48 (CS6) 7

Voice 46 (EF) 6

Interactive Video

34 (AF41) 5

Streaming 26 (AF31) 4

X-Data 18 (AF21) 3

Bulk Data 10 (AF11) 2

Best Effort 0 (BE) 0

Consider: In upstream direction, most wireless applications use UP 4 for signalling/control

– (Even if the inner DSCP is CS3)

Since UP 4 = AF31, this gets marked to AF31 on the CAPWAP header.

But, the network is looking to handle DSCP CS3 for signaling – meaning signaling gets put into the wrong queue across the IP transport network!


57 57

The Impact of UP DSCP Mappings on the Network

57

CAPWAP Encapsulated


WLAN Controller

AP

Ethernet Switch

11e UP DSCP Payload DSCP 802.1p DSCP Payload

AP

AP

802.1q Trunk

802.11 DSCP Payload

AP Maps UP 3 to a

CAPWAP Header

DSCP Value of 18

24

24 3

4 24 26


The Default DSCP UP Mappings Are Surprising

58

Transactional Data

Realtime

4-Class Strategic

Enterprise Model

Best Effort

Control

Platinum

WMM Model +


Silver

Gold

Bronze

UP 7

UP 5

UP 3

UP 2

UP 6

UP 4

UP 0

UP 1

AF21

EF

DSCP

DF

CS3

Thus, in the downstream direction, Voice Signaling ends up in the same AC as X-Data and Best Effort (ouch)

The inconsistent mapping mechanism used by 802.11e means only two queues get used

This can negatively impact wireless performance


Solution: Use Mutation on Access Switch

Example: On Upstream, mutate the incorrect DSCP signaling value back to CS3

59

C3750-X(config)# mls qos map dscp-mutation UPSTREAM-MUTATION 26 to 24

! Mutates the DSCP from AF31 back to CS3 to it is correct on the CAPWAP tunnel header

C3750-X(config)# interface GigabitEthernet1/1/10

! The interface that connects to the AP

C3750-X(config-if)# mls qos trust dscp

! Configures the port to statically trust DSCP on ingress

C3750-X(config-if)# mls qos dscp-mutation UPSTREAM-MUTATION

! Attaches the Upstream DSCP mutation map to the interface on ingress


Through Manual Mutation, You Can Achieve This

60

Transactional Data

Realtime

4-Class Strategic

Enterprise Model

Best Effort

Control

Platinum

WMM Model +


Silver

Gold

Bronze

UP 7

UP 5

UP 3

UP 2

UP 6

UP 4

UP 0

UP 1

AF21

EF

DSCP

DF

CS3

Wrap-up and Final Thoughts


Key Takeaways

Wireless QoS has matured, and is well supported by the standards bodies, particularly the IEEE 802.11e-2012 specification

The WLC 5500 Series offers a wide variety of QoS capabilities

– Per-user, per-SSID bandwidth contracts

– Policy control per WLAN

– Call Admission Control

– Application Visibility & Control

The use of Mixed-use WLANs is now the standard

AVC policies can be used to set a trust boundary and remark traffic

If the standard 4-Class QoS model us used in your network, it results in a 2-Class system over the wireless portion.

– Mutating DSCP values on the access switch can change this behavior.

62


Call to Action…

Visit the World of Solutions:-

Cisco Campus

Walk-in Labs

Technical Solutions Clinics

Meet the Engineer

Lunch Time Table Topics, held in the main Catering Hall

Recommended Reading: For reading material and further resources for this session, please visit www.pearson-books.com/CLMilan2014

63

http://www.pearson-books.com/CLMilan2014




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Documents

QoS Design and Deployment for - …d2zmdbbm9feqrf.cloudfront.net/2014/eur/pdf/BRKEWN-3003.pdf · QoS Design and Deployment for Wireless LANs BRKEWN-3003 Robert Barton, P. Eng