BRKEWN-3012

© 2012 Cisco and/or its affiliates. All rights reserved. BRKEWN-3012 Cisco Public

Troubleshooting Voice over Wireless LAN

Deployments BRKEWN-3012 Patrick Croak ([email protected]) Wireless TAC Escalation CCIE Wireless #34712

2


Agenda

Voice over WLAN 101

VoWLAN RF Design

VoWLAN Configuration

Identifying the Problem

Troubleshooting Tools

‒ WLCCA

‒ WCS/NCS

Data Analysis

Debug Analysis

Summary

Troubleshooting Voice over Wireless LAN Deployments

3


Agenda

Call Manager configuration

Gateway issues and solutions

What Will Not Be Covered

4


Agenda

Voice over WLAN 101

VoWLAN RF Design




‒ WLCCA

‒ WCS/NCS

Data Analysis

Debug Analysis

Summary


5


VoWLAN 101

Voice over WLAN would be similar to any other VoIP technology with the added issues of a wireless media

‒ Signaling: SCCP/SIP

‒ Voice transport: RTP

Wireless adds some important differences

‒ Media is shared

‒ Physical coverage is an issue

‒ Security concerns

‒ Battery life

‒ Roaming

Key Concepts

6


VoWLAN 101

WiFi is unlicensed spectrum so has to operate on lower power

‒ Coverage is lower than other radio technologies

As the transmit media is shared we can expect:

‒ Interference (other WiFi)

‒ Noise

‒ Capacity issues

Access points have a limited area they can cover

‒ Power restrictions

‒ Antenna used

‒ Physical environment

Wireless as Media

7


VoWLAN 101

Voice is one of the most critical applications to have over Wireless

Users have high expectations for voice, derived from GSM, DECT, and fixed line “real-life experience”

The main objective on a VoWLAN project, is to provide end users with a service level as close as possible to what they expect

Wireless Networks are mostly designed for data services, so it is usually not possible to “ just drop” voice on top, and expect any positive results

Wireless as Media

8


VoWLAN 101

Voice has very strict requirements as “application”

• Packet Error Rate (PER) <=1%

• As low jitter as possible, less than 100ms

• Retries should be < 20%

• This translates to coverage needs

Normally data services can tolerate loss of connectivity or high packet loss. Users will not accept a clipping voice, or unidirectional voice flow.

In general it is better to prevent a call, than to place a call over a congested media

• This is where “Call Admission Control” takes place

Wireless as Media

9


VoWLAN 101

Roaming means that the Phone has to find new AP before the current parent quality has gone below what is needed to maintain good voice

‒ Has to be Secure

‒ Not too aggressive, but not conservative

‒ May use multiple triggers: Beacon, retries, packet loss, RSSI, SNR, QBSS

Roaming

(792X

10


VoWLAN 101

How to accept a new client association quickly in a secure way?

Each roaming may need full reauth

‒ Key caching mechanisms are needed: CCKM, PMKID, Sticky roaming

A key caching will remove the need to complete 802.1x, which is slow

Voice requirement: max 150ms of traffic drop, 300ms at most

Secure Roaming

11


VoWLAN 101 Association + 802.1x

Probe Request

Probe Response

Auth Request

Auth Response

Association Request

Association Response

EAP Start

EAP ID Request

EAP ID Response

EAP Method

EAP Success

EAPoL 4 way Exchange

DATA

AP WLC Radius

Between 4 and 20+ frames

12


VoWLAN 101 WPA(2)-PSK

Probe Request

Probe Response

Auth Request

Auth Response

Association Request

Association Response

EAPoL 4 way Exchange

DATA

AP WLC Radius

Hey looks

better!

13


VoWLAN 101 CCKM

Probe Request

Probe Response

Auth Request

Auth Response

Reassociation Request

Reassociation Response

DATA

AP WLC Radius

Much better!

14


VoWLAN 101

Devices are battery operated, so they must have power saving mechanisms

‒ U-APSD

‒ PSP/Legacy

Power Save

15


VoWLAN 101

1. QoS and Availability on your wired network is your foundation

2. Security requirements for voice applications are different than from data

3. Start with user consultation and education

4. Address VoWLAN availability requirements in planning and design

5. Maximize your WLAN Capacity by using the 5GHz spectrum

6. Choose the right VoWLAN handset, based on user requirement and features, and availability in Cisco Compatible

Extension Program

7. Follow the VoWLAN handset guidance in planning and design

8. Use Radio Resource Management for deployment, monitoring, and troubleshooting your WLAN

9. Perform a post installation site-survey to confirm you have met your

VoWLAN goals

10. Plan for the future and the addition of more services such as Location

Top Ten Recommendations

16


Agenda

Voice over WLAN 101

VoWLAN RF Design




‒ WLCCA

‒ WCS/NCS

Data Analysis

Debug Analysis

Summary


17


VoWLAN RF Design

In order to determine if VoWLAN can be deployed, the environment must be evaluated to ensure the following items meet Cisco guidelines.

Many different tools and applications can be used to evaluate these items in order to certify the deployment.

Signal

Channel Utilization

Noise

Packet Loss / Delay

Retries

Multipath

What Should Be Covered

18


VoWLAN RF Design

The cell edge should be designed to -67 dBm, where there is a 20-30% overlap of adjacent access points at that signal level.

This ensures the phone always has adequate signal and can roam seamlessly.

Coverage

19


VoWLAN RF Design

Channel Utilization levels should be kept under 50%.

If using the phone, this is provided via the QoS Basic Service Set (QBSS), which equates to a value around 105.

Noise levels should not exceed -92 dBm, which allows for a Signal to Noise Ratio (SNR) of 25 dB where a -67 dBm signal should be maintained.

Channel Utilization and Noise

20


VoWLAN RF Design

Highly reflective environments

Multipath distortion/fade is a consideration

802.11b most prone

802.11g/a better

Things that reflect RF:

‒ Irregular metal surfaces

‒ Large glass enclosures/walls

‒ Lots of polished stone

What Should or Should Not Be Done

21


VoWLAN RF Design

Multipath. Multipath should be kept minimal as this can create nulls and reduce signal levels.

What Should or Should Not Be Done

Temptation is to mount on beams or ceiling rails

This reflects transmitted as well as received packets

Dramatic reduction in SNR due to high-strength, multipath signals

Minimize Reflections When Choosing Locations

22


VoWLAN RF Design What Should or Should Not Be Done

User

Mount the box and antennas downward Please

23


VoWLAN RF Design More Examples

24


Ceiling mount AP up against pipe A little ICE to keep the packets cool


25



26


VoWLAN RF Design

Every site is unique, do not assume two installations would be the same

Think of the AP coverage area as a “reading light”: you want to illuminate where

the devices will be. Avoid long run AP placement

Use the appropriate equipment for the need: 1130/1140/3500i/3600i for

carpeted areas, 1240/1260/3500e/3600e for specific applications, antenna

orientations

Avoid using internal antennas AP in vertical placements. RF planning is more

difficult

Validate that the coverage is “as expected” after installation

A Few Tips

27


VoWLAN RF Design

Use 5 GHz whenever possible (a lot of smartphones are 2.4 GHz only)

Try to isolate sources of interference, rogues, etc, as part of initial survey

More needed in 2.4: clean air would provide continuous monitoring of possible

common interferers

For high ceiling: do not use omni antennas on high placed APs. Either move

APs closer to clients, or use patch/directional

Always do the design for APs at power level 3, so there is power budget

available

Always allow diversity on AP, or MIMO if 11n

A Few More Tips

28


VoWLAN RF Design

A huge percentage of problems come from incorrectly defined coverage areas

Coverage areas: where the voice service should be offered

Typical errors: “not needed in the bathrooms”, “not in the elevators”, “not in the

stairs”, “not in the outdoor smoking area”

Talk to end-users. Think what they will need and when

Coverage Areas

29


VoWLAN RF Design

Cell overlap coverage is not always the only concern

Roaming can fail if the client device does not have enough time to properly

scan for neighboring access points

‒ Imagine turning the corner around a metal or high attenuation barrier – the RF

environment changes very rapidly

Challenging RF obstacles need to be considered during AP placement

A “Transition” AP that is placed at the intersection of hallways can alleviate

some scenarios

The “Transition” AP

30


VoWLAN RF Design

At point A the phone is connected to AP 1

At point B the phone has AP 2 in the

neighbor list, AP 3 has not yet been

scanned due to the RF shadow caused

by the elevator bank

At point C the phone needs to roam, but

AP 2 is the only AP in the neighbor list

The phone then needs to rescan and

connect to AP 3

31

1

3

2 A B

C

Scanning Problems


VoWLAN RF Design

At point A the phone is connected to AP 1

At point B the phone has AP 2 in the

neighbor list as it was able to scan it while

moving down the hall

At point C the phone needs to roam and

successfully selects AP 2

The phone has sufficient time to scan for

AP 3 ahead of time

32

A B

C

1

2

3

Transition AP Placement


VoWLAN RF Design

Pico-cells: signal fade too quickly, not giving time for device to do a controlled

roam

792x 1.4.2 firmware helps here. CCKM timestamp of 5 may alleviate a bit.

‒ config wlan security wpa akm cckm timestamp-tolerance 5000 <WLAN ID>

Avoid Pico-cells When Possible

33


Agenda

Voice over WLAN 101

VoWLAN RF Design




‒ WLCCA

‒ WCS/NCS

Data Analysis

Debug Analysis

Summary


34



Disabled

‒ DHCP required

‒ P2P blocking

‒ MFP client

‒ Band select

‒ Load balancing

‒ Low data rates

Use Design Guide

Enabled - Aironet extensions

- DTPC is enabled

- Platinum + 802.1p “6”

- Long session timeout

- Fast roaming (CCKM/Open/PSK)

- WMM (optional/required)

- DTIM “2”

- AES

- EDCA for Voice or mixed

- CAC

Optional

Client Exclusion

35



Use long DCA period: 8/12/24 hours to prevent frequent channel changes

Set the Maximum Power Level to match your clients

Set the Minimum Power Level to avoid pico-cell issues

Power Threshold can be increased to increase overall power assignments, or

decreased to reduce power assignments

‒ Default value is -70, remember it is a negative number!

RRM Advanced Settings

36



UNII-1 Channels are intended for indoor use, typically have lower max transmit

power of 14 dB*

UNII-2 Channels require use of DFS (Dynamic Frequency Selection), typically

have max transmit power of 17 dB*

UNII-3 Channels do not require DFS, and have a max transmit power of 17 dB*

*Maximum transmit power may vary by AP model

Channel and Power Levels

37



Trust DSCP on APs

Trust COS on WLC trunks

‒ Note that COS value requires 802.1q tag, so it will not work for the native vlan!

Set 802.1p Wired Protocol to 6 for the Platinum QoS Profile

Ensure cos-dscp map on switched network is properly defined

- COS 3 to DSCP 24 (CS3) for SCCP traffic

- COS 5 to DSCP 46 (EF) for RTP traffic

‒ mls qos map cos-dscp 0 8 16 24 32 46 48 56

DSCP and COS

38



Mismatched transmit powers on AP and client can cause one-way audio and

poor performance

792x phone has max tx power of 40 mW (16 dBm)

AP 2.4 GHz can be up to 100 mW (20 dBm)

AP 5.0 GHz can be up to 50 mW (17 dBm) (varies by channel)

Other benefits include reduced co-channel interference radius and power

saving on clients

Requires CCXv2

DTPC

39


Agenda

Voice over WLAN 101

VoWLAN RF Design




‒ WLCCA

‒ WCS/NCS

Data Analysis

Debug Analysis

Summary


40



Avoid jumping into conclusions

Troubleshooting is a process

Do NOT change things without understanding root cause first

Find patterns: where, when, how, the problem is reproducible.

“Random” problems are the worst to troubleshoot

Troubleshooting 101

41



It is critical that the proper problem is described

‒ One way voice

‒ Two way failure (no voice)

‒ “Robotic” or choppy voice quality

‒ Network Busy

‒ Out of coverage

‒ Length of failure

‒ Location when failure occurred

Proper Definition is Important

42



One way voice

‒ Only one side can hear the other

‒ Typical Triggers

Asymmetrical RF (different power levels for example, antenna types)

Failed ARP resolution

No way voice

‒ No voice in both directions


Very bad RF

Failed Roaming

Example Scenarios

43



Robotic/Choppy Voice

‒ High packet drops affecting voice quality


Bad RF/Coverage: lots of retries, low signal levels, no good candidate to roam

Bad Roaming decision: phone may be too conservative

Interference/Noise

QoS configuration

Network Busy

‒ CAC rejected call, high QBSS


High client count

High energy on channel/Interference/Noise

Example Scenarios

44



Out of Coverage/Leaving service area

‒ Phone reports no wireless network


Bad RF/Coverage

Bugs (either phone side, AP side for radio lockups)

Example Scenarios

45



Is the problem affecting only one area? All the building?

Does it happen while walking from X to Y?

Does it occur while stationary at the desk?

Happens for all phones? Specific phones? Specific users?

Any time pattern? All day long? Lunch time?

For pervasive issues, work on contained areas: one floor, one wing, etc.

There are no “real” random problems: a pattern must exist, and that normally

points to root cause

Isolate the Issue

46


Agenda

Voice over WLAN 101

VoWLAN RF Design




‒ WLCCA

‒ WCS/NCS

Data Analysis

Debug Analysis

Summary


47



Wireless sniffer

‒ Omnipeek/AirPcap

‒ Mac with OS X 10.6 and above

‒ Windows 7 with Netmon 3.4

‒ Multichannel, for roaming issues

‒ AP in Sniffer mode

L1 analysis: SpectrumExpert, 3500/3600 Ap, etc

WLCCA (WLC Configuration Analyzer)

Wireless Captures, RF Analysis, Configuration Analysis

48



WLC debug client

‒ Single client on 7.0, Two clients on 7.2

‒ Other debugs may be needed on AP side for radio issues -> only with TAC support

Phone debug

‒ Do not overuse, as it will disrupt voice

WCS/NCS

‒ Roaming history

‒ SNR levels

‒ TSM

Time sync is very helpful!

Debugs, Logs, Reports

49


Troubleshooting Tools Data Capturing

Wireless Capture

Wired Capture

•Time sync •Wireless capture done at phone side. Multichannel if roaming issue is suspected •Call placed to fixed phone to isolate one wireless path only

USB logs

50



Get proper problem description and area isolation

Check your config: WLCCA

Check RF groups, RF neighborhood: WLCCA

Check Historical data, SNR/RSSI, TSM: WCS/NCS

Check Coverage: survey data, WCS/NCS map (if correctly done)

If suspecting a RF issue, get pictures, or go onsite to see the deployment

Try to know how to reproduce

Steps to Resolution

51


Agenda

Voice over WLAN 101

VoWLAN RF Design




‒ WLCCA

‒ WCS/NCS

Data Analysis

Debug Analysis

Summary


52


WLCCA

Basic things first

Direct Troubleshooting

Bad!

53


WLCCA

Power levels and channel distribution: looking for anomalies

RF First View

54


WLCCA

Power levels and channel distribution: looking for anomalies

RF First View

55


WLCCA

May indicate bad coverage.

Only relevant for APs on same physical area

RF Groups

Bad! Good

56


WLCCA

Quick isolation of suspicious areas

No “hard cut” number on what is bad

RF Problem Finder

Why?

57


WLCCA

Lots of information

Neighbor relationships, co-channel interference, isolated APs

AP RF Summary

Bad!

58


WLCCA

In depth analysis on how the APs see each other

RF Neighbors

59


Agenda

Voice over WLAN 101

VoWLAN RF Design




‒ WLCCA

‒ WCS/NCS

Data Analysis

Debug Analysis

Summary


60


WCS/NCS

WCS/NCS can show you where, and how the client has been over time

History to the Rescue

Bad!

61


WCS/NCS

TSM reports can have valuable information

History to the Rescue

Bad!

62


Agenda

Voice over WLAN 101

VoWLAN RF Design




‒ WLCCA

‒ WCS/NCS

Data Analysis

Debug Analysis

Summary


63


Data Analysis

The problem description normally indicates what to look for

RTP analysis can help a lot

PSK can be decoded if EAPoL 4 way is captured + shared key is available

Needle in a Haystack?

64


Data Analysis

Learn how to filter properly

Filters…

Good

Bad

Bad

65


Data Analysis

Filter + IO Graph=Eagle view on activity

Filters…

Why?

66


Data Analysis One Way Voice

67


Data Analysis Robotic/Choppy Voice

68


Data Analysis Slow Roaming

69


Data Analysis

On the 792x phone, while on a call

navigate to Settings > Status >

Network Statistics

Check that the “DataRcvVO” counter is

incrementing

Packet Capture

QoS Verification

70


Data Analysis

Per voice guidelines, PER should not exceed 1% packet loss.

If there is > 1% packet loss, then voice quality can be degraded significantly.

All Cisco IP Phones have the ability to display “receiver lost packets” as well as the total # of receiver packets in the stream (call) statistics.

Simply divide the receiver lost packets by the total # of receiver packets.

Jitter should also be kept at a minimum (< 100 ms).

Packet Loss and Delay

71


Agenda

Voice over WLAN 101

VoWLAN RF Design




‒ WLCCA

‒ WCS/NCS

Data Analysis

Debug Analysis

Summary


72


Debug Analysis

Understanding debug client, doc ID:

100260

http://www.cisco.com/en/US/products/h

w/wireless/ps430/products_tech_note09

186a008091b08b.shtml

On mobility scenarios (multiple

controllers), always debug client +

debug mobility on all WLC where client

may roam to

The controller will give a view of what is

going on, and can close a lot the

spectrum of issues to investigate

Few Pointers…

73

http://www.cisco.com/en/US/partner/products/hw/wireless/ps430/products_tech_note09186a008091b08b.shtml





Debug Analysis

Most common tool used by TAC

‒ debug client xx:xx:xx:xx:xx:xx

Proper roams will be Reassociations, if you see “Associations” then there are

roaming failures that should be investigated

You can trace the roaming path of the phone by looking up the AP radio mac

addresses at each (re)association

*apfMsConnTask_0: Apr 13 16:10:27.014: cc:08:e0:2e:10:2b Association received

from mobile on AP b4:a4:e3:b5:bc:60

WLC Client Debug

74


Debug Analysis

Set phone trace logs from Error to Info (or Debug, but this can impact

performance of the phone)

‒ Kernel

‒ WLAN Driver

‒ WLAN Manager

The phone log will show the neighbor list and roaming trigger for each roam

WLAN_DRVR: 3845.629757: Roam trigger = ROAMING_TRIGGER_MAX_TX_RETRIES

WLAN_DRVR: 3845.643734: Candidate 0, BSSID=c4:7d:4f:3b:02:e2, RSSI =-60

WLAN_DRVR: 3845.650550: Candidate 1, BSSID=00:19:30:76:52:dc, RSSI =-63

WLAN_DRVR: 3845.657382: Candidate 2, BSSID=00:19:56:b0:79:f0, RSSI =-72

WLAN_DRVR: 3845.664203: Candidate 3, BSSID=1c:df:0f:b5:47:b2, RSSI =-74

792x Phone Debugs

75


Debug Analysis

Idle timeout from AP, shortly after roam, CSCto73361 fixed in 7.0.220.0 *pemReceiveTask: Nov 23 15:34:44.946: 00:15:f9:93:42:9e 192.168.32.32 Added NPU entry of type 1, dtlFlags 0x0

*spamApTask0: Nov 23 15:34:44.948: 00:15:f9:93:42:9e Received Idle-Timeout from AP 00:24:14:31:ce:70, slot 0 for STA 00:15:f9:93:42:9e *spamApTask0: Nov 23 15:34:44.948: 00:15:f9:93:42:9e apfMsDeleteByMscb Scheduling mobile for deletion with deleteReason 4, reasonCode 4

Bad PSK configuration, also shows in logs. *dot1xMsgTask: Sep 06 18:37:11.341: 00:0b:6b:b3:d6:e7 Sending EAPOL-Key Messageto mobile 00:0b:6b:b3:d6:e7 state INITPMK

(message 1), replay counter 00.00.00.00.00.00.00.00 *Dot1x_NW_MsgTask_7: Sep 06 18:37:11.378: 00:0b:6b:b3:d6:e7 Received EAPOL-Key from mobile 00:0b:6b:b3:d6:e7 *Dot1x_NW_MsgTask_7: Sep 06 18:37:11.378: 00:0b:6b:b3:d6:e7 Received EAPOL-key in PTK_START state (message 2) from mobile 00:0b:6b:b3:d6:e7 *Dot1x_NW_MsgTask_7: Sep 06 18:37:11.378: 00:0b:6b:b3:d6:e7 Received EAPOL-key M2 with invalid MIC from mobile 00:0b:6b:b3:d6:e7

Some Examples

76

http://cdets.cisco.com/apps/dumpcr?&content=summary&format=html&identifier=CSCto73361


Debug Analysis

CCKM time validation errors *apfMsConnTask_5: Apr 04 12:55:54.402: 00:01:e3:bb:e5:23 Processing WPA IE type 221, length 22 for mobile 00:01:e3:bb:e5:23

*apfMsConnTask_5: Apr 04 12:55:54.402: 00:01:e3:bb:e5:23 CCKM: Mobile is using CCKM *apfMsConnTask_5: Apr 04 12:55:54.402: 00:01:e3:bb:e5:23 CCKM: Processing REASSOC REQ IE *apfMsConnTask_5: Apr 04 12:55:54.402: 00:01:e3:bb:e5:23 CCKM: Received Timestamp deviation in REASSOC REQ IE from mobile *apfMsConnTask_5: Apr 04 12:55:54.402: 00:01:e3:bb:e5:23 CCKM: Failed to validate REASSOC REQ IE

In logs *apfMsConnTask_5: Mar 22 14:49:36.109: %APF-3-VALIDATE_CCKM_REASS_REQ_ELEMENT: apf_ut:2122 Could not validate the CCKM Reassociation

request element.Received Timestamp deviation > 1sec in CCKM Info Element from mobile. Mobile:00:01:e3:bb:e5:23,

Either pico-cells, or roaming issues

Use: config wlan security wpa akm cckm timestamp-tolerance 5000 X

Some Examples

77


Debug Analysis

*Dot1x_NW_MsgTask_2: Aug 30 16:39:06.201: 00:1e:4a:3f:af:4f Sending EAPOL-Key Message to mobile 00:1e:4a:3f:af:4f state

PTKINITNEGOTIATING (message 3), replay counter 00.00.00.00.00.00.00.02

*osapiBsnTimer: Aug 30 16:39:06.801: 00:1e:4a:3f:af:4f 802.1x 'timeoutEvt' Timer expired for station 00:1e:4a:3f:af:4f and for

message = M3

*dot1xMsgTask: Aug 30 16:39:06.801: 00:1e:4a:3f:af:4f Retransmit 1 of EAPOL-Key M3 (length 155) for mobile 00:1e:4a:3f:af:4f


message = M3

*dot1xMsgTask: Aug 30 16:39:07.201: 00:1e:4a:3f:af:4f Retransmit 2 of EAPOL-Key M3 (length 155) for mobile 00:1e:4a:3f:af:4f


message = M3

*dot1xMsgTask: Aug 30 16:39:07.601: 00:1e:4a:3f:af:4f Retransmit failure for EAPOL-Key M3 to mobile 00:1e:4a:3f:af:4f,

retransmit count 3, mscb deauth count 0

*dot1xMsgTask: Aug 30 16:39:07.601: 00:1e:4a:3f:af:4f Sent Deauthenticate to mobile on BSSID c4:7d:4f:3b:02:e0 slot 1(caller

1x_ptsm.c:534)

EAPoL Key Failure

78


Debug Analysis

config advanced eap eapol-key-timeout <200-5000 ms>

‒ Default is 1 second (1000 ms)

‒ Recommendation for 792x Phones is 200 ms

config advanced eap eapol-key-retries <0-4>

‒ Default is 2 retries

‒ Lowering this value may reduce audio loss on roaming failure

“show advanced eap” to verify settings

Mitigating EAPoL Failure Impact

79


Agenda

Voice over WLAN 101

VoWLAN RF Design




‒ WLCCA

‒ WCS/NCS

Data Analysis

Debug Analysis

Summary


80


Summary

RF: survey, survey, survey

Proper problem description, area isolation

Check basic things first

Data capturing on site can be difficult, and you need the proper tools

You can’t just drop voice on a WiFi deployment and expect it to work

Key Take Aways

81


Recommended Reading

82


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Documents

BRKEWN-3012