ASCOM VOWIFI SYSTEM - User guide

TD 92313GB
13 December 2010 / Ver. F
System Description
Ascom VoWiFi System

TD 92313GB
13 December 2010 / Ver. F
System Description
Ascom VoWiFi System
Contents
1 Introduction .................................................................................................................... 1
1.1 Abbreviations and Glossary................................................................................................... 1
2 WLAN............................................................................................................................... 5
2.1 WLAN Infrastructure ............................................................................................................... 5
2.1.1 Autonomous Access Points ......................................................................................... 5
2.1.2 Controller-Based Access Points .................................................................................. 6
2.2 RF Modulation Standard......................................................................................................... 6
2.2.1 802.11b/g RF Modulation Standard......................................................................... 6
2.2.2 802.11a RF Modulation Standard ............................................................................. 7
2.2.3 802.11n RF Modulation Standard ............................................................................. 8
2.3 Access Control and Security ............................................................................................... 11
2.3.1 ESSID (Extended Service Set Identifier)................................................................. 11
2.3.2 MAC Address Filtering................................................................................................ 11
2.3.3 WEP................................................................................................................................. 12
2.3.4 WPA™............................................................................................................................. 12
2.3.5 WPA2™ .......................................................................................................................... 12
2.3.6 Proactive Key Caching (Opportunistic Key Caching) .......................................... 13
2.3.7 Certificate-based authentication ............................................................................ 13
2.4 Quality of Service (QoS)....................................................................................................... 14
2.4.1 802.11e......................................................................................................................... 14
2.4.2 WMM™ (WME™).......................................................................................................... 14
2.4.3 TSPEC Call Admission Control ................................................................................... 15
2.4.4 WMM™ Power Save .................................................................................................... 15
2.5 Cisco Compatible Extensions (CCX)................................................................................... 15
2.6 802.11h................................................................................................................................... 15
3 VoWiFi ........................................................................................................................... 16
3.1 VoIP Signalling Protocols..................................................................................................... 16
3.1.1 H.323.............................................................................................................................. 16
3.1.2 H.450 Supplementary Services for H.323 ............................................................ 16
3.1.3 Session Initiation Protocol (SIP) .............................................................................. 16
3.2 VoWiFi Standards.................................................................................................................. 17
4 Ascom VoWiFi System Overview................................................................................. 18
4.1 Supported Standards ........................................................................................................... 20
4.1.1 Ascom i62 VoWiFi Handset ...................................................................................... 20
4.1.2 Ascom i75 VoWiFi Handset ...................................................................................... 20
4.2 System Functions.................................................................................................................. 21
4.3 WLAN Functions .................................................................................................................... 21
4.3.1 Roaming......................................................................................................................... 21

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System Description
Ascom VoWiFi System
4.3.2 Association.................................................................................................................... 22
4.3.3 User Authentication ................................................................................................... 22
4.4 Network Parameter Download .......................................................................................... 23
4.5 Supported Third-Party Products ....................................................................................... 23
4.6 WLAN Planning and Deployment for Ascom VoWiFi System .................................... 23
5 Ascom VoWiFi System Components ........................................................................... 24
5.1 Ascom VoWiFi Handsets...................................................................................................... 24
5.1.1 Ascom i62 VoWiFi Handset ...................................................................................... 24
5.1.2 Ascom i75 VoWiFi Handset ...................................................................................... 24
5.2 Access Point (AP).................................................................................................................. 25
5.3 Controller................................................................................................................................. 25
5.4 RADIUS Server ........................................................................................................................ 25
5.5 Integrated Wireless Messaging and Services (IMS2)................................................... 25
5.6 Unite Connectivity Manager (UniteCM)........................................................................... 27
5.7 Portable Device Manager Windows Version (WinPDM) .............................................. 27
5.8 VoIP Gateway/Gatekeeper.................................................................................................. 28
5.9 SIP Proxy Server..................................................................................................................... 28
6 Administration Tools ................................................................................................... 29
7 Connection to Other Systems...................................................................................... 30
7.1 System Solution when connected to IP-PBX .................................................................. 30
7.2 System Solution when connected to Traditional PBX.................................................. 31
8 Related Documents ...................................................................................................... 32
9 Document History ........................................................................................................ 33
Appendix A: Ascom Technical Documentation ............................................................. 34

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System Description
Ascom VoWiFi System
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1 Introduction
The Ascom Voice over Wireless Fidelity (VoWiFi) system provides wireless IP telephony,
messaging and alarm functions to enterprise LANs. Using third-party WLAN products as well
as in-house developed hardware and software, the system enables data and voice
transmission together with seamless roaming.
This document gives a general description of the Ascom VoWiFi solution. It briefly describes
WLAN and VoWiFi technologies and standards.
Figure 1. VoWIFI overview
1.1 Abbreviations and Glossary
Figure1.
AES Advanced Encryption Standard
AP Access Point:
a radio transceiver providing LAN connection to wireless devices.
BPSK Binary Phase-Shift Keying
BSS Basic Service Set
CAC Call Admission Control
CCKM Cisco Centralized Key Management
CCMP Counter Mode Cipher Block Chaining-Message Authentication Code
(CBC-MAC) protocol
CCX Cisco Compatible Extensions
Controller a Controller delivers Wireless LAN services over an existing Ethernet or
IP infrastructure.
DFS Dynamic Frequency Selection
DTIM Delivery Traffic Indication Message
EAP Extensible Authentication Protocol
EAP-FAST EAP-Flexible Authentication via Secured Tunnel
IMS2/
Unite CM
LAN
Access Point
VoWiFi Handsets
IP-PBX
Presence
Management
System
Location Server
Unite System
Controller
optional equipment
required equipment

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EAP-TLS EAP-Transport Layer Security
ESS Enhanced System Service:
Unite modules that handle centralised number planning, remote
connection, system supervision, fault handling, group handling,
message routing, centralised logging, activity logging, and user access
administration.
ESSID Extended Service Set Identifier
ETSI European Telecommunications Standards Institute:
a European standards organization charged with defining standards
for EC countries.
FCC Federal Communications Commission (FCC):
the primary interstate regulatory authority for telecommunications
and radio systems for the US.
FEC Forward Error Correction
GI Guard Interval
Handover The process of moving a handset from one AP to another during an
ongoing call.
IEEE Institute of Electrical and Electronics Engineers
IETF Internet Engineering Task Force
IMS2 Integrated Wireless Messaging and Services:
Unite module that enables wireless services to and from the VoWiFi
handsets in a WLAN system. It also includes the Device Manager.
IP Internet Protocol:
a global standard that defines how to send data from one device to
another over the wired and wireless media.
ISM Industrial Scientific Medical
ITU International Telecommunications Union
Jitter Variation in latency among a group of packets sent between two
nodes.
Latency The total time for a data frame to travel from a sender to a receiver.
MAC address Medium Access Control address:
a unique identifier attached to most forms of computer networking
equipment.
MCS Modulation and Coding Scheme
MIMO Multiple-Input, Multiple-Output
Multipath The receiver does not only contain a direct line-of-sight radio wave, but
also a larger number of reflected radio waves.
PEAP-MSCHAP Protected Extensible Authentication Protocol-Microsoft Challenge
Handshake Authentication Protocol.
PBX Private Branch Exchange:
telephone system within an enterprise.
PRI Primary Rate Interface
PTT Push-To-Talk
QAM Quadrature Amplitude Modulation:
16-QAM has 16 possible signal states with each symbol representing
4 bits. 64-QAM has 64 possible signal states with each symbol
representing 6 bits.

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QoS Quality of Service:
defines to what extent transmission rates, error rates etc. are
guaranteed in advance.
QPSK Quadrature Phase-Shift Keying
RADIUS Remote Authentication Dial-In User Service:
a standard protocol for authentication servers.
RF Radio Frequency
Roaming The process of moving a handset from one AP to another when moving
within the network.
RSVP Resource Reservation Protocol:
a QoS signalling protocol that nails down a channel through an IP
network based on the session ID.
RTCP Real-Time Control Protocol
RTP Real-Time Protocol
RTSP Real-Time Streaming Protocol
SAP Session Announcement Protocol,
SDP Session Description Protocol
SIP Session Initiation Protocol
SOHO Small Office/Home Office
TDMA Time Division Multiple Access
TPC Transmit Power Control
TSPEC Traffic Specification
UNII Unlicensed National Information Infrastructure
Unite Ascom messaging platform. A generic term for a messaging system
that unites different systems, for example System 900, System 9d, and
VoWiFi.
Unite CM Unite Connectivity Manager:
Unite module that enables messaging and alarm handling in a WLAN
system. It also includes the Device Manager.
VoIP Voice over Internet Protocol:
the technology used to transmit voice conversations over IP.
VoWiFi Voice over Wireless Fidelity:
a wireless version of VoIP and refers to IEEE 802.11a, 802.11b,
802.11g, or 802.11n network.
WEP Wired Equivalent Privacy encryption keys:
the original security standard used in wireless networks to encrypt the
wireless network traffic.
WiFi WiFi is a term developed by the Wi-Fi Alliance®ato describe wireless
local area network (WLAN) products that are based on the Institute of
Electrical and Electronics Engineers' (IEEE) 802.11 standards. Today,
most people use WiFi as a reference to wireless connectivity.
WinPDM Portable Device Manager Windows Version:
a software application for initial configuration of the VoWiFi handsets.
WLAN Wireless Local Area Network (LAN):
a type of LAN in which data is sent and received via high-frequency
radio waves rather than cables or wires.

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WMM™ Wi-Fi Multimedia™:
offers QoS functionality for WiFi networks.
WPA™ Wi-Fi Protected Access™:
a set of security features for wireless networks based on IEEE 802.11i.
WPA2™ Wi-Fi Protected Access 2™:
adds additional security features, the most important of which are pre-
authentication, which enables secure fast roaming, and AES, which is
the new FIPS standard for data encryption.
a.) The Wi-Fi Alliance® develops universal specifications, facilitates testing, and grants
interoperability certification for Wi-Fi equipment from a wide range of manufacturers across
product lines.

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2WLAN
A Wireless Local Area Network (WLAN) uses radio frequency (RF) technology to transmit
and receive data over the air. To enable transmission of such different types of
communication as data and voice, it is essential that hardware and software comply to
specified standards. The Institute of Electrical and Electronics Engineers (IEEE) have
established the IEEE 802.11 standard, which is the most used WLAN standard of today. The
original version was released in 1997 and over the years several amendments have been
added, for example, IEEE 802.11a, IEEE 802.11b, IEEE 802.11g, and IEEE 802.11n. Most of
these were merged with the base standard in 2007 except IEEE 802.11n, which is a more
recent amendment.
See section 4.1 Supported Standards for a description of the 802.11 amendments
supported by the Ascom VoWiFi system.
2.1 WLAN Infrastructure
There are two types of WLAN topologies: the Ad-Hoc mode and the Infrastructure Mode. The
Ad-Hoc mode provides peer-to-peer connectivity where two clients communicate directly
with each other via their WLAN cards. The Infrastructure Mode, on the other hand, is used to
incorporate the wireless clients into an existing wired LAN infrastructure.
In the Infrastructure Mode all communication is passed through the Access Points (APs) that
are connected to the wired LAN. A single AP communicating with a number of clients is
called a Basic Service Set (BSS). A number of interconnected APs with the same network
name is called an Extended Service Set.
The AP is basically a radio transmitter/receiver but, depending on hardware and software, it
can be more or less intelligent. An AP that holds information about the mobile clients
authorized to enter the system is called an autonomous AP (or “fat” AP), whereas an AP
that only is responsible for forwarding received data, is called a controller-based AP (or
“thin” AP). While the autonomous APs carry out all wired to wireless packet format
conversion, encryption, QoS application, and RF statistics monitoring, the very thinnest APs
pass all of this to their central controller, and act basically just as a media converter.
2.1.1 Autonomous Access Points
Figure 2. Autonomous APs connected directly to the LAN.
The example in figure 2 shows a system with autonomous APs. This is the most basic type
of a WLAN in Infrastructure Mode. The individual autonomous APs handle all traffic
handling, authentication, RF management, and mobility functions. They are entirely
independent of each other, and have to be configured separately.
Figure2.
LAN
AP AP AP

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2.1.2 Controller-Based Access Points
Figure 3. Controller-based APs with centralized management.
The example in figure 3 shows a system with controller-based APs. With this approach, APs
can share the features that enhance wireless communications. Much of the configuration is
centralized in the Controller. The Controller handles switching functionality to the WLAN,
security functionality, RF management, QoS, and extended roaming features. It is physically
connected to the LAN and not to the APs.
It is also possible to use a Controller that incorporates a switch. The APs are then directly
connected to the Controller and are basically just a radio and an antenna. The Controller
handles most of the MAC layer all by itself.
The use of controller-based APs enhances operation of the VoWiFi system, makes
centralized administration over the WLAN possible, and makes it easy to expand the
network. If several Controllers are used in a system, a centralized intelligent server
(Centralized Wireless Management) can be used for administration and management.
2.2 RF Modulation Standard
2.2.1 802.11b/g RF Modulation Standard
WLAN products based on the 802.11b/g standards operate in the 2.400 to 2.497 GHz
frequency range, which is one of the Industrial Scientific Medical (ISM) bands.This is an un-
licensed frequency band also used by Bluetooth devices, medical equipment, and many
other devices that do not require a license.
The frequency band is divided into channels on which data packets are sent in parallel. It is
important that the channels do not overlap each other as this would decrease the
performance of the network.
APs supporting the 802.11b/g standard have up to 14 channels with centre frequencies
that are 5 MHz apart (applies to channel 1 to 13)1. Since the bandwidth of each channel is
either 22 MHz (802.11b) or 20 MHz (802.11g), the centre frequencies for non-overlapping
channels must be at least 25 MHz apart. This gives us three non-overlapping channels at the
most, see the example with 11 channels in figure 4. These channels are reused and allocated
to APs in different regions, one channel per AP.
Use of other channels than 1, 6 and 11 will have a major negative impact on performance in
the system since those channels will interfere with each other. Not only due to RF
interference, but also due to the 802.11 protocol specification, a selection of channels other
than 1, 6 and 11 will cause a performance reduction.
Figure3.
1.The centre frequency in channel 14 differs from the other (12 MHz apart). It was previously used only in Japan.
Controller Controller
001
LAN
AP AP AP
Centralized Wireless Management

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The 802.11b and 802.11g specifications include the following restrictions:
Figure 4. The 2.4 GHz band with three non-overlapping channels (1, 6 and 11).
The standard specifies data rates up to 11 Mbps for 802.11b and 54 Mbps for 802.11g, but
this must be considered as a theoretical maximum, only available within a limited distance
from an AP. More resilient coding schemes are needed to decode signals with lower strength
at the expense of data rate. Also, note that this is the maximum data rate, which means that
the maximum throughput is more likely to be half of that because of data headers etc.
As a client moves away from the AP, data rate is reduced, and consequently the throughput.
The average throughput is, as a rule of thumb, half of the data rate. Therefore it is important
that APs are not placed too far apart.
2.2.2 802.11a RF Modulation Standard
WLAN products based on the 802.11a standard operate in the 5 GHz frequency range. This
is an unlicensed frequency band called the Unlicensed National Information Infrastructure
(UNII) band. It is divided into the UNII-1 band (5.15–5.25 GHz), the UNII-2 band (5.25–
5.35 GHz), the UNII-2 Extended band (5.47–5.710 GHz), and the UNII-3 band (5.725–
5.825 GHz) (depending on country regulations).
The UNII band is divided into 23 non-overlapping channels (depending on country
regulations) with a bandwidth of 20 MHz. The centre frequencies are 20 MHz apart.
Originally the UNII-1 band was intended for indoor operation, the UNII-3 band for outdoor
operation, and the UNII-2 and UNII-2 Extended band for both indoor and outdoor operation.
This distinction has been removed for FCC. For ETSI the UNII-1 and UNII-2 bands are still
intended for indoor operation, and the UNII-2 Extended band for both indoor and outdoor
operation. Also, the maximum power levels are lower for ETSI than FCC. The UNII-2 band’s
primary users are radar and satellite systems. To avoid interference, all unlicensed
transmitters operating in the UNII-2 band must be able to detect the presence of radar
signals and to dynamically and automatically change to a different transmit frequency if
radar is discovered, see section 2.6 802.11h on page 15.Therefore, it is not recommended to
use these bands for voice traffic.
Above the UNII band there is a small part of the ISM band that can be used by 802.11a
products as well (5.825–5.875 GHz).
Radio Band: 2.4 GHz
Maximum Data Rate: 11 Mbps (802.11b)
54 Mbps (802.11g)
Operating channels: 1–14 (depending on country
regulations)
ETSI: 1–13
FCC: 1–11
Maximum number of non-overlapping channels: 3
Typical Indoor Rangea:
a.With basic antenna and maximum power level.
30 m / 100 ft
Typical Outdoor Range (Line of Sight)a:120m/400ft