ASCOM I62 - User manual

Troubleshooting Guide
Ascom i62 VoWiFi Handset
TD 92685EN
28 June 2012 / Ver. A

TD 92685EN
28 June 2012 / Ver. A
Troubleshooting Guide
Ascom i62 VoWiFi Handset
About this document
This guide describes how to investigate and remedy Quality of Service problems experienced
by handset users when accessing a WLAN and making calls using the Voice over IP Protocol
(VoIP).
Cross-references in the document
Throughout this document you will find cross-references in the text which indicate further
details that can be found in other sections of this document. The cross-references are
colored blue and linked to the relevant place in the document. For example: see chapter 9.
Document History on page 61. Positioning your cursor over the cross-reference text and
clicking the left mouse button will take you to the relevant section.
To return to the original page after viewing a cross-referred page in Adobe Acrobat or Adobe
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TD 92685EN
28 June 2012 / Ver. A
Troubleshooting Guide
Ascom i62 VoWiFi Handset
Contents
1. Introduction ................................................................................................................... 3
1.1 Target Group ........................................................................................................... 3
1.2 Prerequisite ............................................................................................................. 3
1.3 Material Needed ...................................................................................................... 3
1.4 Software Version ..................................................................................................... 4
1.5 Abbreviations and Glossary .................................................................................... 4
1.6 Information Required by TAC.................................................................................. 5
2. WLAN Overview ............................................................................................................. 6
2.1 The Problem of Legacy WLANs ............................................................................... 6
2.2 WLAN Planning and Provisioning............................................................................ 7
2.3 The Importance of Pre- and Post-Site Surveys ....................................................... 8
2.4 WLAN Dynamics ...................................................................................................... 8
2.5 Troubleshooting Implications and WLAN Design.................................................... 8
3. The VoWiFi Handset as a Wireless Client .................................................................. 10
3.1 VoWiFi Handset Protocol Layers ........................................................................... 10
3.1.1 Troubleshooting the Layers.......................................................................... 12
3.2 Voice Transmission over a VoWiFi System............................................................ 12
3.3 Handset Startup Procedure................................................................................... 12
3.4 AP Scanning........................................................................................................... 13
3.4.1 Active Scanning ............................................................................................ 13
3.4.2 Passive Scanning .......................................................................................... 13
3.4.3 Configured Channels and Scanning Intervals ............................................... 13
3.5 Power Management .............................................................................................. 14
3.5.1 Overview ....................................................................................................... 14
3.5.2 U-APSD PS Mode Operation.......................................................................... 15
3.5.3 Recommended Values .................................................................................. 17
3.5.4 Screen Saver ................................................................................................. 17
3.6 Roaming ................................................................................................................ 17
3.6.1 Idle Mode ...................................................................................................... 18
3.6.2 Call Mode....................................................................................................... 18
3.6.3 System-Aided Roaming................................................................................ 19
3.7 DFS Channel Probing ............................................................................................. 19
3.8 SIP.......................................................................................................................... 20
3.8.1 SIP Components ............................................................................................ 21
3.8.2 SIP Call Setup ................................................................................................ 23
3.8.3 Redirect Servers............................................................................................ 26
3.8.4 Call Completion ............................................................................................. 26
3.8.5 Message Content .......................................................................................... 27

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Troubleshooting Guide
Ascom i62 VoWiFi Handset
3.8.6 Troubleshooting Implications ....................................................................... 28
4. Factors Affecting RF Propagation.............................................................................. 29
4.1 Jitter, Latency and Packet Loss ............................................................................. 29
4.1.1 Signal Loss .................................................................................................... 29
4.2 Troubleshooting Methodology.............................................................................. 30
4.3 Isolate Problem Areas ........................................................................................... 31
5. The VoWiFi Handset as a Troubleshooting Tool ....................................................... 33
5.1 Handset Device Information.................................................................................. 33
5.2 Site Survey Tool..................................................................................................... 33
5.2.1 Show RSSI ..................................................................................................... 33
5.2.2 Creating Heatmaps ...................................................................................... 34
5.2.3 Evaluate the Radio Environment .................................................................. 34
5.2.4 Range Beep ................................................................................................... 35
5.2.5 Coverage and Roaming Test......................................................................... 35
5.3 The Admin Menu ................................................................................................... 36
5.4 Handset Web Interface ......................................................................................... 36
5.4.1 Logs Tab....................................................................................................... 36
5.4.2 Statistics Tab ................................................................................................ 36
5.4.3 Tools Tab...................................................................................................... 38
5.4.4 Quality of Service (QoS) Test........................................................................ 39
6. Troubleshooting Scenarios ......................................................................................... 40
6.1 SIP.......................................................................................................................... 40
6.1.1 Attended Transfer Example.......................................................................... 40
6.1.2 PBX Basic Call Analysis.................................................................................. 44
6.1.3 Identifying Problems .................................................................................... 46
6.1.4 Name Presentation Problems ...................................................................... 47
6.2 WLAN Troubleshooting Scenarios......................................................................... 47
6.2.1 Voice Problems while Roaming..................................................................... 47
7. VoWiFi Handset Problem Solving Scenarios ............................................................. 50
7.1 Handset Errors....................................................................................................... 50
7.1.1 Startup Problems.......................................................................................... 50
7.1.2 Errors Displayed on the Handset ................................................................. 50
7.1.3 No Access ...................................................................................................... 52
7.1.4 Messaging or Voice Only............................................................................... 53
7.1.5 No Channel.................................................................................................... 54
7.1.6 Battery Power is Low .................................................................................... 54
7.1.7 Connected Call but No Sound or One-way Sound......................................... 55
7.2 U-APSD Troubleshooting....................................................................................... 55
7.2.1 Determining if the AP Supports U-APSD ...................................................... 55
7.2.2 Determining if Handset Signals its use of U-APSD....................................... 56

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7.2.3 Packet Classification of U-APSD in the AP.................................................... 56
8. Related Documents ..................................................................................................... 60
9. Document History ....................................................................................................... 61
Appendix A: Making Air Traces of 802.11 Traffic......................................................... 62
Appendix B: Handset Parameters.................................................................................. 63
Appendix C: Digital Certificates...................................................................................... 69
Appendix D: External Troubleshooting Tools................................................................ 71
Appendix E: Ascom i62 Ports.......................................................................................... 74
Index ................................................................................................................................77

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1. Introduction
1. Introduction
This guide describes procedures to validate and perform troubleshooting on a WLAN that
supports a VoWiFi system. It identifies some of the more common problem areas associated
with the operation of VoWiFi networks and suggests approaches to troubleshooting and the
use of internal and external tools for investigating these problems. The guide contains
detailed information about the behavior of the Ascom i62 VoWiFi Handset under faulty or
problematic conditions. This behavior may be different for different hardware and software
versions of the handset.
1.1 Target Group
This guide is written for support engineers responsible for troubleshooting customer site
Voice over Wireless Fidelity (VoWiFi) systems and the WLANs that support such systems.
The guide may also be of considerable use to system administrators and network planners
intending to design, implement, deploy and commission a new WLAN designed for VoWiFi
access or upgrade an existing WLAN to support a new VoWiFi system. To this latter group,
the importance of careful planning and provisioning through an exhaustive, rigorous and
detailed site survey cannot be over emphasized. Many of the problems described in this
guide arise because of poor provisioning and planning. In this respect, system
administrators and network planners are recommended to read the document System
Planning, Ascom VoWiFi System.
1.2 Prerequisite
To gain the maximum benefit from this guide, readers should have experience in and
knowledge of the following areas:
• Configuring a factory delivered handset and performing a handset software upgrade.
• How WLAN networks function up to the level of Certified Wireless Network
Administrator (CWNA) certification or similar level.
• Sufficient knowledge in networking concepts and an understanding of the TCP/IP
protocol suite.
• A basic understanding of Voice over Internet Protocol (VoIP) and the VoIP Session
Initiation Protocol (SIP).
• Have read the configuration manual for the corresponding handset.
• Have read other documents related to the installation, for example WLAN specification
and documents pertaining to the interoperability of the handset with the WLAN
infrastructure.
1.3 Material Needed
To assist in troubleshooting, it is recommended that the support engineer is able to have at
his or her disposal:
• The Portable Device Manager (PDM) application “WinPDM”. The support engineer should
be familiar with using the application for setting and modifying handset parameter
values. Many error symptoms are related to a inappropriate configuration parameters
values. Troubleshooting the PDM application itself is not covered in this guide.
• One or more handsets.
• A fixed phone, that is, a phone connected to the wired LAN.
• A tool that plays a continuous audio stream such as music, for example a radio or an MP3
player.

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1. Introduction
• An air trace tool or protocol analyzer such as Omnipeek or Wireshark for capturing traces
on the LAN and WLAN. These require a WLAN adapter and network card respectively.
• A spectrum analyzer for detecting non 802.11 RF interference.
1.4 Software Version
This guide refers to a handset running software version 3.4.x or later.
1.5 Abbreviations and Glossary
The following acronyms and terms are used throughout this guide:
AP Access Point.
B2BUA Back-to-Back User Agent
BSS Basic Service Set.
BSSID Basic Service Set Identifier.
CAC Call Admission Control
CCI Co Channel Interference
DFS Dynamic Frequency Selection
DHCP Dynamic Host Configuration Protocol.
DNS Domain Name Server.
DSCP Differentiated Services Code Point. QoS on the Internet Layer.
Used both for WLANs and LANs.
DTIM Delivery Traffic Indication Message.
DTMF Dual-Tone Multi-Frequency
EDCA Enhanced Distributed Channel Access
ESS Extended Service Set.
ESSID Extended Service Set Identifier
IEEE Institute of Electrical and Electronics Engineers
IMS3 Integrated Message Server
ITU-T International Telecommunication Union-Telecommunication
MAC Media Access Control.
PCAP Packet Capture
PDL Portable Device Logger. A troubleshooting tool.
PDM Portable Device Manager.
PSTN Public Switched Telephone Network
QoS Quality of Service.
RFC Request for Comments
RPCAP Remote Packet Capture
RSSI Received Signal Strength Indication.
RTP Real-time Transport Protocol
SIP Session Initiation Protocol
SNR Signal-to-noise ratio

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1. Introduction
1.6 Information Required by TAC
If an issue remains unresolved and a request needs to be opened with the Technical
Assistance Centre (TAC) team, the following information should be forwarded:
• A detailed description of the problem and what tests have been performed. Trace files
should be attached and appended with descriptions of the tests and the MAC and IP
addresses of the equipment used in the tests, for example, the handset, proxy and WLAN
information.
• The values of parameters that have been configured, such as SSID, security setting and
DTIM values.
• The frequency of the occurrence of the error and information about how to reproduce
the error, if possible.
• The WLAN hardware and software versions of both the controller and APs.
• SIP proxy hardware and software.
• The handset software version.
SSID Service Set Identifier.
TAC Technical Assistance Centre
TCP Transmission Control Protocol
TFTP Trivial File Transfer Protocol (TFTP)
TIM Traffic Indication Map
TSpec Traffic Specification
TU Time Unit
U-APSD Unscheduled Automatic Power Save Delivery. Also referred to
as WMM-PS.
UDP User Datagram Protocol
Unite Name of Ascom IP based protocol for handling, events,
messages and alarms.
UP 6 User Priority (value between 0-7). Wireless QoS at the MAC
Layer.
URI Uniform Resource Identifier
VoIP Voice over IP.
VoWiFi Voice over WiFi. Refers to a system running VoIP over WLAN.
WPA/WPA2 WiFi Protected Access 2.
WEP Wired Equivalent Privacy.
WiFi A Wireless Local Area Network based on the IEEE 802.11
standard.
WLAN Wireless Local Area Network.
WMM WiFi Multimedia.
WMM-PS WMM Power Save. Also referred to as U-APSD.

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2. WLAN Overview
2. WLAN Overview
A WLAN enables various devices, or WLAN clients, to communicate across RF channels
through Access Points (APs). APs provide RF coverage throughout the site covered by the
WLAN and this enables users, and their devices, to move around the site without being
disconnected from the network. Each AP is identified by a hard-coded MAC address.
Initially, WLANs were designed to allow users to send and receive data from devices such as
laptop computers but increasingly WLANs are being required to support different and more
demanding types of traffic such as voice and multimedia. A VoWiFi system is illustrated in
figure 1:
Figure 1. VoWiFi Overview
IMS3 / Unite CM
LAN
Access Point
VoWiFi Handsets
IP-PBX
Presence
Management
System
Location Server
Unite System
Controller
optional equipment
required equipment
2.1 The Problem of Legacy WLANs
Legacy WLAN systems were designed for transmitting data packets; support for voice and
other multimedia was never envisaged when these systems were designed, deployed and
commissioned. So many traditional cell-based WLAN topologies proved unsuitable for
handling channelization issues, AP-to-AP handoffs, and the unpredictably of system
bandwidth that are introduced when VoWiFi is implemented. Voice is very susceptible to
such issues being addressed satisfactorily. A WLAN that does not support VoWiFi but is
being upgraded to do so therefore requires very careful planning, design, provisioning and
hardware deployment to get the level of performance to adequately support voice. These
problems are multiplied when different traffic types such as voice, video and data all
contend for the same airspace. Adding voice to a WLAN may require radical changes of the
APs placement and the amount of APs needed. If this is not considered feasible to undertake
in a current installation VoWiFi may never perform as expected.
It follows that if a legacy WLAN is to support VoWiFi then an assessment of how suitable the
WLAN is to support VoWiFi must be made. The number and deployment of additional
devices involved in the WiFi solution must be carefully assessed. For example, the
assessment should consider the adequacy of the current deployment in meeting cell
boundary requirements because adequate cell overlap is a fundamental requirement for a
voice system. The assessment should conclude with a readiness report documenting the
suitability of the WLAN for both the wired and the wireless part of the network. The

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2. WLAN Overview
required parameter settings of the devices supporting the WiFi system should also be
documented.
The following table lists some of the topics that should be included in an assessment
document:
Topic Comments
Are voice settings correctly set in the
infrastructure, both LAN and WLAN
devices?
Voice packet must have precedence over
other types of traffic.
The assessment must check for the ability to
create an QoS solution across the entire
network.
Voice settings must be set according to
vendor's recommendation and Ascom inter-
working reports.
Note: These reports provide important
information for ensuring interoperability
between Ascom handsets and vendor
equipment. The reports are published as
Application Partner Program, Ascom Inter-
Operability Reports on the Ascom Partner
web site.
Is the right software version installed on
thedevices?
Devices may need newer software or hotfixes
to be able to support new devices.
This is important when new features are
added to current protocols. For example,
when 802.11n is added to a WLAN.
Is there sufficient RF coverage? Cell boundaries, cell overlap, and channel
planning are extremely important for mobile
devices which need to roam during usage.
RF coverage must be checked using Site
Survey tools.
2.2 WLAN Planning and Provisioning
To summarize, both a legacy WLAN that is to be upgraded to support VoWiFi and an entirely
new WLAN purpose build to support VoWiFi and probably other kinds of media require:
• Comprehensive site surveys and detailed maps and floor plans of the areas where the
WLAN is to provide coverage.
• Adequate provisioning of hardware, in other words, the deployment of sufficient APs in
suitable locations to meet the coverage requirements of the WLAN
• Extensive and accurate documentation of the AP deployment using site maps and floor
plans to illustrate the deployment
• A proper, well documented commissioning sequence including comprehensive testing
• A rigorous acceptance procedure before the commissioning is signed off as meeting the
voice, and other, requirements, of the new or upgraded WLAN.
In addition, a legacy WLAN:
• Should have been documented properly to provide the basis and understanding
implications of adding voice.
• May require a complete reassessment of its existing infrastructure before voice is added.