Polycom SpectraLink 8020 Quick reference guide

DEPLOYMENT GUIDE
Best Practices Guide for Deploying
SpectraLink 8020/8030 Wireless
Telephones
July 2009
Version H

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©2009 Polycom, Inc. All rights reserved.
Polycom and the Polycom logo are registered trademarks of Polycom, Inc. All other trademarks are the property of Polycom, Inc. or their respective companies.
Deploying SpectraLink 8020/8030
Wireless Telephones
July 2009 Best Practices Guide
Table of Contents
1Introduction........................................................................................................................ 3
1.1 SpectraLink Wi-Fi Release 3.0......................................................................................................4
1.2 SpectraLink 8020/8030 Wireless Telephones...............................................................................4
1.3 SpectraLink Infrastructure .............................................................................................................4
1.4 VIEW Certification Program...........................................................................................................4
2Wireless LAN Layout Considerations .............................................................................. 6
2.1 Coverage .......................................................................................................................................6
2.1.1 Overlapping Coverage...............................................................................................................6
2.1.2 Signal Strength ..........................................................................................................................8
2.2 802.11b/g Deployment Considerations .........................................................................................9
2.3 802.11a Deployment Considerations ......................................................................................... 10
2.4 Access Point Configuration Considerations ............................................................................... 10
2.4.1 Channel Selection................................................................................................................... 10
2.4.2 AP Transmission Power and Capacity................................................................................... 13
2.4.3 Interference............................................................................................................................. 14
2.4.4 Multipath and Signal Distortion............................................................................................... 14
2.4.5 Site Surveys............................................................................................................................ 15
2.5 Wireless Telephone Capacity..................................................................................................... 16
2.5.1 Access Point Bandwidth Considerations................................................................................ 16
2.5.2 Push-to-Talk Multicasting Considerations.............................................................................. 17
2.5.3 Telephone Usage ................................................................................................................... 18
2.5.4 Telephony Gateway Capacity................................................................................................. 19
3Network Infrastructure Considerations.......................................................................... 20
3.1 Physical Connections.................................................................................................................. 20
3.2 Assigning IP Addresses .............................................................................................................. 21
3.3 Software Updates Using TFTP................................................................................................... 22
3.4 RADIUS AAA Servers –Authentication, Authorization, and Accounting ................................... 22
3.5 NTP Server................................................................................................................................. 23
4Quality Of Service (QoS) ................................................................................................. 24
4.1 SpectraLink Voice Priority (SVP)................................................................................................ 24
4.1.1 SVP Infrastructure .................................................................................................................. 24
4.1.2 SVP Server Capacity.............................................................................................................. 24
4.1.3 Multiple SVP Servers.............................................................................................................. 25
4.1.3.1 Scenario One.................................................................................................................. 27
4.1.3.2 Scenario Two.................................................................................................................. 28
4.1.4 DSCP for SVP Deployments .................................................................................................. 29
4.2 Wi-Fi Standard QoS.................................................................................................................... 29
4.2.1 WMM....................................................................................................................................... 30
4.2.2 WMM Power Save.................................................................................................................. 31
4.2.3 WMM Admission Control........................................................................................................ 32
4.2.4 DSCP for Wi-Fi Standard QoS Deployments......................................................................... 33
4.3 Cisco Client Extensions, Version 4 (CCXv4).............................................................................. 34
5Security ............................................................................................................................ 35
5.1 VoWLAN and Security................................................................................................................ 35
5.2 Wired Equivalent Privacy (WEP)................................................................................................ 35
5.3 Wi-Fi Protected Access (WPA)................................................................................................... 35

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©2009 Polycom, Inc. All rights reserved.
Polycom and the Polycom logo are registered trademarks of Polycom, Inc. All other trademarks are the property of Polycom, Inc. or their respective companies.
Deploying SpectraLink 8020/8030
Wireless Telephones
July 2009 Best Practices Guide
5.3.1 WPA Personal, WPA2 Personal............................................................................................. 36
5.3.2 WPA2 Enterprise.................................................................................................................... 36
5.3.2.1 PEAPv0/MSCHAPv2...................................................................................................... 36
5.3.2.2 EAP-FAST ...................................................................................................................... 37
5.3.2.3 OKC................................................................................................................................ 37
5.3.2.4 CCKM ............................................................................................................................. 37
5.3.3 Cisco Fast Secure Roaming (FSR) ........................................................................................ 38
5.4 Using Virtual LANs...................................................................................................................... 38
5.5 MAC Filtering and Authentication............................................................................................... 38
5.6 Firewalls and Traffic Filtering...................................................................................................... 38
5.7 Virtual Private Networks (VPNs)................................................................................................. 39
5.8 Diagnostic Tools......................................................................................................................... 39
6Cisco Compatible Extensions (CCX).............................................................................. 41
7Subnets, Network Performance and DHCP.................................................................... 42
7.1 Subnets and Telephony Gateway Interfaces ............................................................................. 42
7.2 Subnets and IP Telephony Server Interfaces............................................................................. 42
7.3 Network Performance Requirements When Using SVP ............................................................ 43
7.4 DHCP Requirements.................................................................................................................. 44
8Conclusion....................................................................................................................... 46
1Introduction
Wi-Fi telephony, also known as Voice over Wireless LAN (VoWLAN), delivers the capabilities and
functionality of the enterprise telephone system in a mobile handset. The Wi-Fi handset is a WLAN client
device, sharing the same wireless network as laptops and PDAs. For enterprise use, the handset is
functionally equivalent to a wired desk phone, giving end-users all the features they are used to having in
a wired office telephone. The benefits of VoWLAN can result in substantial cost savings over other
wireless technologies by leveraging the Wi-Fi infrastructure and by eliminating recurring charges
associated with the use of public cellular networks. For end users, VoWLAN can significantly improve
employee mobility, resulting in increased responsiveness and productivity.
Delivering enterprise-grade VoWLAN means that wireless networks must be designed to provide the
highest audio quality throughout the facility. Because voice and data applications have different attributes
and performance requirements, thoughtful WLAN deployment planning is a must. A Wi-Fi handset
requires a continuous, reliable connection as a user moves throughout the coverage area. In addition,
voice applications have a low tolerance for network errors and delays. Whereas data applications are
able to accept frequent packet delays and retransmissions, voice quality will deteriorate with just a few
hundred milliseconds of delay or a very small percentage of lost packets. Whereas data applications are
typically bursty in terms of bandwidth utilization, voice conversations use a consistent and a relatively
small amount of network bandwidth.
Using a Wi-Fi network for voice is not complex, but there are some aspects that must be considered. A
critical objective in deploying enterprise-grade Wi-Fi telephony is to maintain similar voice quality,
reliability and functionality as is expected from a wired telephone. Some key issues in deploying Wi-Fi
telephony include WLAN coverage, capacity, quality of service (QoS) and security.
Polycom pioneered the use of VoWLAN in a wide variety of applications and environments, making the
SpectraLink 8020/8030 Wireless Telephone the market leader in this category. Based on our experience
with enterprise-grade deployments, this guide provides recommendations for ensuring that a network
environment is optimized for use with SpectraLink 8020/8030 Wireless Telephones.

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©2009 Polycom, Inc. All rights reserved.
Polycom and the Polycom logo are registered trademarks of Polycom, Inc. All other trademarks are the property of Polycom, Inc. or their respective companies.
Deploying SpectraLink 8020/8030
Wireless Telephones
July 2009 Best Practices Guide
1.1 SpectraLink Wi-Fi Release 3.0
In May 2009, Polycom delivered a major software upgrade that provided significant feature
enhancements to the SpectraLink 8020/8030 Wireless Telephone when using end-to-end VoIP. Release
3.0 (R3.0) adds WLAN QoS and security features that provide IT administrators greater flexibility by
increasing deployment and configuration options. The corresponding features must be supported and
properly configured on the WLAN. Consult the VIEW Certified Products Guide on the Polycom web site
for WLAN infrastructure products certified with Release 3.0. The VIEW Configuration Guides for
approved products must be closely followed to ensure proper operation of the handset with the WLAN.
To take advantages of the R3.0 features described in this guide, SpectraLink handset software must be
upgraded. Release 3.0 features are available in handset version 131.019 or above. The administrator
can recognize R3.0 features from the handset administration menu or the Handset Administration Tool
(HAT), which will show the following menu structure: Network Config (level 1), WLAN Settings (level 2),
Custom or CCX (level 3).
Release 3.0 is available on Polycom handsets using SIP. A future release will support connections to
traditional PBXs using the SpectraLink Telephony Gateway.
1.2 SpectraLink 8020/8030 Wireless Telephones
The information contained in this guide applies only to SpectraLink 8020/8030 Wireless Telephones
(generically referred to as „handsets‟ throughout this document) and their OEM derivatives. Detailed
product information for the SpectraLink 8020/8030 Wireless Telephones can be found at Polycom‟s web
site. For information on other Polycom Wi-Fi handsets, including the SpectraLink e340/h340/i640 or 8002
Wireless Telephones, visit the appropriate product page at Polycom‟s web site.
1.3 SpectraLink Infrastructure
Throughout this guide references are made to SpectraLink infrastructure equipment including the SVP
Server, Telephony Gateway and OAI Gateway.These LAN-based devices are sold by Polycom for use
with the SpectraLink 8020/8030 Wireless Telephone:
When SVP is selected as the QoS mechanism, an SVP Server must be used.
Telephony Gateways allow the handset to operate as an extension off of a PBX. For systems
with four or fewer Telephony Gateways, the integrated SVP Server capability can be used and a
separate SVP Server is not required. For systems with more than four Telephony Gateways, a
separate SVP Server is required.
The OAI Gateway enables third-party applications to send and respond to real-time text
messages and alerts using SpectraLink handsets.
For additional details on any of these products visit the Polycom web site.
1.4 VIEW Certification Program
The VIEW Certification Program is a partner program designed to ensure interoperability and maximum
performance for enterprise-grade Wi-Fi infrastructure products that support Polycom‟s SpectraLink
8020/8030 Wireless Telephones and their OEM derivatives. The Program is open to manufacturers of
802.11a/b/g/n infrastructure products that incorporate the requirements described in the VIEW Technical
Specification and pass VIEW Certification testing. VIEW certification requirements focus on implementing
industry standards for Wi-Fi networks along with meeting the specific quality of service (QoS) and
performance characteristics that are necessary for supporting Polycom handsets.
For each certified product, Polycom provides a VIEW Configuration Guide that details the tested
hardware models and software versions; radio modes and expected calls per AP; and specific AP

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©2009 Polycom, Inc. All rights reserved.
Polycom and the Polycom logo are registered trademarks of Polycom, Inc. All other trademarks are the property of Polycom, Inc. or their respective companies.
Deploying SpectraLink 8020/8030
Wireless Telephones
July 2009 Best Practices Guide
configuration steps. VIEW Configuration Guides are available on Polycom website and should be
followed closely to ensure a proper deployment.

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©2009 Polycom, Inc. All rights reserved.
Polycom and the Polycom logo are registered trademarks of Polycom, Inc. All other trademarks are the property of Polycom, Inc. or their respective companies.
Deploying SpectraLink 8020/8030
Wireless Telephones
July 2009 Best Practices Guide
2Wireless LAN Layout Considerations
SpectraLink handsets utilize a Wi-Fi network consisting of WLAN access points (APs) distributed
throughout a building or campus. The required number and placement of APs in a given environment is
driven by multiple factors, including intended coverage area, system capacity, access point type, power
output, physical environment, and radio types.
2.1 Coverage
One of the most critical considerations in deployment of SpectraLink handsets is to ensure sufficient
wireless signaling coverage. Enterprise Wi-Fi networks are often initially laid out for data applications and
may not provide adequate coverage for voice users. Such networks may be designed to only cover areas
where data devices are commonly used, and may not include coverage in other areas such as stairwells,
break rooms or building entrances –all places where telephone conversations are likely to occur.
The overall quality of coverage is more important for telephony applications. Coverage that may be
suitable for data applications may not be seamless enough to support the requirements of VoWLAN. Most
data communication protocols provide a mechanism for retransmission of lost or corrupted packets.
Delays caused by retransmissions are not harmful, or even discernable, for most data applications.
However, the real-time nature of a full-duplex telephone conversation requires that voice packets be
received correctly within tens of milliseconds of their transmission. There is little time for retransmission,
and lost or corrupted packets must be discarded after limited retries. In areas of poor wireless coverage,
the performance of data applications may be acceptable due to retransmission of data packets, but for
real-time voice, audio quality will likely suffer.
Another factor to consider when determining the coverage area is the device usage. Wireless telephones
are used differently than wireless data devices. Handset users tend to walk as they talk, while data users
are usually stationary or periodically nomadic. Wireless voice requires full mobility while data generally
requires simple portability. Wireless handsets are typically held close to the user‟s body, introducing
additional radio signal attenuation. Data devices are usually set on a surface or held away from the body.
The usage factor may result in reduced range for a wireless telephone as compared with a data device.
Therefore, the WLAN layout should account for some reduction of radio signal propagation.
2.1.1 Overlapping Coverage
Wi-Fi cell overlap must be considered when planning your VoWLAN deployment. Handsets make a
determination to roam in less than half the overlapping coverage area. Therefore, the coverage area must
be adequate enough so that when a voice user is moving, the handset has time to discover the next AP
before signal on the existing AP becomes too weak.
A properly designed Wi-Fi network will position APs with sufficient overlapping coverage to ensure there
are no coverage gaps, or “dead spots”, between them. The result is seamless handoff between APs and
excellent voice quality throughout the facility. Sufficient overlapping coverage is usually considered 15%
to 20% signal overlap between AP cells in a deployment utilizing maximum transmit power for both
handsets and APs. Smaller cells will need larger overlaps due to the potential for much smaller cell size
which causes a decrease in overall overlap from a maximum transmit power deployment. The 15% to
20% of signal overlap between AP cells generally works well with a typical walking speed of the user (the
average walking speed of an individual is 3 mph). If the speed of the moving user is greater (such as a
golf cart, fork lift or running/jogging) then a different overlap strategy may be necessary for successful
handoff between APs.

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©2009 Polycom, Inc. All rights reserved.
Polycom and the Polycom logo are registered trademarks of Polycom, Inc. All other trademarks are the property of Polycom, Inc. or their respective companies.
Deploying SpectraLink 8020/8030
Wireless Telephones
July 2009 Best Practices Guide
The WLAN layout must factor in the transmission settings that are configured within the APs. The
transmission of voice requires relatively low data rates and a small amount of bandwidth compared to
other applications. The 802.11 standard includes automatic rate switching capabilities so that as a user
moves away from the AP, the radio adapts and uses a less complex and slower transmission scheme to
send the data. The result is increased range when operating at reduced transmission data rates. When
voice is an application on the WLAN, APs should be configured to allow lower transmission rates in order
to maximize coverage area. If a site requires configuring the APs to only negotiate at the higher rates, the
layout of the WLAN must account for the reduced coverage and additional APs will be required to ensure
seamless overlapping coverage.
SpectraLink handsets perform Dynamic Channel Assessment (DCA) in between the transmission of
packets to learn about neighboring APs. It takes about two seconds for a DCA cycle to complete in an
802.11a eight channel deployment and approximately one second for a standard three channel
deployment for 802.11b/g. In order to ensure a DCA cycle can complete within the assessment area (see
Figure 1), a person moving through the assessment area must be within the area for at least 4-5 seconds
to make sure the DCA starts and ends within the assessment area. Failure to complete the DCA cycle
within the assessment area can lead to lost network connectivity resulting in a hard handoff, lost audio,
choppy audio or potentially a dropped call.
Figure 1 - Dynamic Channel Assessment (DCA)
The handset compares the signal strength of neighboring APs to determine whether to roam from the
current AP. In order to roam, the handset has to determine whether other APs are either five decibels
(dB) (for any first attempt associating with an AP) or ten decibels stronger (to roam back to the previous
AP) than the current AP‟s signal. In most cases the handset only needs five decibels of signal difference

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©2009 Polycom, Inc. All rights reserved.
Polycom and the Polycom logo are registered trademarks of Polycom, Inc. All other trademarks are the property of Polycom, Inc. or their respective companies.
Deploying SpectraLink 8020/8030
Wireless Telephones
July 2009 Best Practices Guide
2.4GHz
802.11b/802.11g
(CCK)
2.4GHz 802.11g (OFDM)
Rate
(Mb/s)
1
2
5.5
11
6
9
12
18
24
36
48
54
Best
Practices
(dBm)
-75
-70
-69
-65
-67
-66
-64
-62
-60
-56
-52
-47
between APs to make a decision to roam. But to prevent „ping-pong‟behavior the separation needs to be
ten decibels higher for the handset to return to the previously associated AP. This behavior requires that
the assessment area must have at least a ten decibel difference to enable good roaming behavior for all
cases.
Corners and doorways pose a particular design issue. The shadowing of corners can cause steep drop-
offs in signal coverage. This is particularly true of 802.11a. Make sure to have adequate cell overlap at
and around corners so that the audio stream is not impacted by a user going around corners. This may
require placement of an AP at corner locations to ensure appropriate cover and prevent RF shadows.
2.1.2 Signal Strength
To provide reliable service, wireless networks should be engineered to deliver adequate signal strength in
all areas where the wireless telephones will be used. The required minimum signal strength for all
SpectraLink handsets depends on the 802.11 frequency band it is operating in, modulation used, data
rates enabled on the AP, and data rate used by the handset at any particular time.
Recommended signal strength characteristics are summarized in Table 1 and Table 2. Use these values
to determine RF signal strength at the „limit of AP A‟ or „limit of AP B‟, illustrated in Figure 1. The handset
should be in the assessment area for 4–5 seconds to allow for smooth roaming handoffs.
Table 1 –2.4GHz
Table 2 –5GHz
The critical factor is the highest data rate set to “Required”or “Mandatory”1. Other data rates can be set to
“Supported”. The highest AP data rate set Mandatory determines the RF power required by the wireless
1Access Point (AP) vendors refer to this configuration setting differently but the value indicates a data rate that clients must be
capable of utilizing in order to associate with the access point. These data rates are also used for different data traffic types by
clients and APs that should be considered when designing for coverage requirements.
5GHz 802.11a (OFDM)
Rate
(Mb/s)
6
9
12
18
24
36
48
54
Best
Practices
(dBm)
-60
-59
-58
-56
-53
-49
-47
-45

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©2009 Polycom, Inc. All rights reserved.
Polycom and the Polycom logo are registered trademarks of Polycom, Inc. All other trademarks are the property of Polycom, Inc. or their respective companies.
Deploying SpectraLink 8020/8030
Wireless Telephones
July 2009 Best Practices Guide
telephone for proper operation. Broadcast frames (beacons) utilize the highest “Basic”2data rate and
multicast frames (used for the SpectraLink 8030‟s push-to-talk feature and SRP handset check-ins) also
use the highest data rate set Mandatory. Unicast frames (data) utilize the „best or highest‟ data rate which
supports low frame errors and low retry rates but rate scale up or down to use the „best‟ rate of all
available rates.
Referencing Table 1 and Table 2, the highest rate set Mandatory (Required) determines the signaling
requirements for the wireless telephone in all areas (limit of AP) where they are used.
For example, if an 802.11b/g access point has 1Mbps, 2Mbps, 5.5Mbps and 11Mbps all set
Mandatory, the handset requires -65dBm in all areas.
For example, if an 802.11b/g access point has 1Mbps Mandatory and other rates set Supported (or
“Enabled”) the handset requires -75dBm in all areas.
For example, if an 802.11a access point has 6Mbps, 12Mbps & 24Mbps set Mandatory and all other
data rates set to Supported the handset requires -53dBm in all areas.
SpectraLink handsets have a Site Survey mode that can be used to validate the signal strength it is
receiving from the AP. The handset also has a Diagnostics mode which can show AP signal strength, as
well as other details, as received during a call. See the SpectraLink 8020/8030 Wireless Telephone
Administration Guide for details on using the Site Survey and Diagnostics mode features.
Although it is possible that SpectraLink handsets may operate at signal strengths which are weaker than
those provided in Table 1 and Table 2; real world deployments involve many RF propagation challenges
such as physical obstructions, interference, and multipath effects that impact both signal strength and
quality. Designing RF coverage to the required levels will provide an adequate buffer for these
propagation challenges, enabling a more reliable and consistent level of performance with low retry rates.
2.2 802.11b/g Deployment Considerations
The 802.11b and 802.11g standards utilize the 2.4 GHz frequency spectrum. 802.11g networks that
support 802.11b-only clients must run in protected mode to enable backward compatibility. Protected
mode adds considerable overhead to each transmission which ultimately translates into significantly
reduced overall throughput. SpectraLink 8020/8030 Wireless Telephones, which support 802.11a, b and
g radio types, do not operate in protected mode when operating in 802.11g-only mode. The overhead
associated with performing protected mode transmissions largely negates any benefits of transmitting
relatively small voice packets at higher 802.11g data rates. For this reason, when SpectraLink handsets
are installed on a mixed 802.11b/g network which is already running in protected mode, the handset must
be configured for 802.11b & b/g mixed mode. In an 802.11b/g mixed environment a handset that is
configured for the 802.11b and b/g mixed mode will only utilize 802.11b data rates and has no 802.11g
functionality while this mode is enabled.
The handset operating in 802.11g-only mode must use a WLAN with data rates set so only 802.11g
clients can associate. There must be no 802.11b client connected to and using the WLAN. The way to
ensure only 802.11g clients use the WLAN is to set to disable all 802.11b data rates (1, 2, 5.5, and
11Mbps). It is important to include these settings for all SSIDs in the handset coverage area and not just
the voice SSID, since this impacts the spectrum for the entire area.
2The 802.11-2007 Standard defines any data rate set as required to be basic rates. See 802.11-2007 for additional details.
(http://www.ieee.org)

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©2009 Polycom, Inc. All rights reserved.
Polycom and the Polycom logo are registered trademarks of Polycom, Inc. All other trademarks are the property of Polycom, Inc. or their respective companies.
Deploying SpectraLink 8020/8030
Wireless Telephones
July 2009 Best Practices Guide
2.3 802.11a Deployment Considerations
The 802.11a standard utilizes the 5.1 GHz to 5.8 GHz Unlicensed National Information Infrastructure
(UNII) frequency spectrum. Although having the same maximum throughput as 802.11g (54 Mb/s), the
increased frequency spectrum at 5 GHz offers up to 23 channels, providing the potential for higher AP
density and increased aggregate throughput. There is significant variation in channel availability and use
between countries, however, which must be considered for any particular 802.11a deployment.
As compared with the 2.4 GHz frequency of 802.11b/g radio deployments, higher frequency RF signals
utilized by the 802.11a 5GHz band do not propagate as well through air or obstacles. This typically
means that an 802.11a network will require more APs than an 802.11b/g network to provide the same
level of coverage. This should be taken as a guideline however, as signal propagation may also be
impacted by the output power settings of the AP and the antenna type. A comprehensive wireless site
survey focusing on VoWLAN deployments should be conducted to identify the specific needs for each
environment.
2.4 Access Point Configuration Considerations
There are several fundamental access point configuration options that must be considered prior to
performing a site survey and deploying a voice-capable WLAN infrastructure. SpectraLink handsets
provide support for 802.11b, 802.11g and 801.11a radio types. The selection of radio type has significant
impact on the overall configuration and layout of the WLAN infrastructure. This fundamental selection
determines most other configuration considerations. In general, however adjacent APs in three
dimensions (above, below and beside) must use different non-overlapping radio channels to prevent
interference between them regardless of 802.11 radio type.
This document does not cover all issues or considerations for WLAN deployment. It is strongly
recommended that Polycom Professional Services, or another suitable professional services
organization, with wireless voice deployment experience be engaged to answer additional questions
about configurations that may affect voice quality or wireless telephone performance. In addition, VIEW
Configuration Guides for WLAN infrastructure, which are available from the Polycom web site, should be
followed closely.
2.4.1 Channel Selection
The 802.11b/g standard provides for three non-interfering, non-overlapping frequency channels -
channels one, six and eleven in North America. Access points within range of each other should always
be set to non-interfering channels to maximize the capacity and performance of the wireless
infrastructure. Figure 2 illustrates the correct deployment methodology for 802.11b/g deployments.

11
©2009 Polycom, Inc. All rights reserved.
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Deploying SpectraLink 8020/8030
Wireless Telephones
July 2009 Best Practices Guide
Figure 2 - 802.11b/g Non-interfering Channels with Overlapping Cell Coverage
If adjacent access points in three dimensions (above, below or beside) are set to the same channel, or
utilize channels with overlapping frequency bands, the resulting interference will cause a significant
reduction in the network performance and throughput, and will degrade overall voice quality. A channel
space of twenty five MHz, five channels or greater should be used to configure neighbor APs for non-
interfering channels Figure 3 represents the 2.4 GHz frequency range, indicating the overlap in channel
frequencies.
2400 MHz 2483 MHz
2412 2417 2422 2427 2432 2437 2442 2447 2452 2457 2464
1 6 11
2
3
4
5
7
8
9
10
22 MHz
Figure 3 - 802.11b/g Channels
With more available channel options, the 802.11a standard has improved the flexibility of WLAN layouts,
and enabled the possibility for greater density of APs. In an 802.11a deployment, all 23 channels are
technically considered non-overlapping, since there is 20 MHz of separation between the center
frequencies of each channel. However, because there is some frequency overlap on adjacent 802.11a
channel sidebands, there should always be at least one cell separating adjacent channels and two cells
separating the same channel. This methodology is depicted in Figure 4.

12
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Deploying SpectraLink 8020/8030
Wireless Telephones
July 2009 Best Practices Guide
Figure 4 - 802.11a Non-interfering Channels with Overlapping Cell Coverage
There are some deployment scenarios that require limiting the number of 802.11a channels. A key
reason is to improve roaming performance. With 802.11a there are four channel bands available to
choose from. These channel bands comprise a number of individual channels over a specific range of
frequencies in the 5GHz range. These bands include UNII-1 (5.15 –5.25GHz), UNII-2 (5.25 –5.35GHz),
UNII-2 Extended (5.47 –5.725GHz) and UNII-3 (5.725 –5.825GHz). The two UNII-2 bands are DFS
(Dynamic Frequency Selection) bands. The 802.11a specification identifies DFS bands as overlapping
with the frequencies utilized globally by radar systems. Because of this shared use for these two
frequency ranges the 802.11a standard calls for a zero contention behavior from wireless devices on the
channels in these bands. This means that a DFS channel can possibly become unavailable due to the
detection of radar signals by an access point on one of the DFS channels as required by the standard.
Also, the full set of channels available in the U.S. may not be available outside the U.S. Refer to your
local RF governing body for specific channel availability. In some cases where use of DFS channels is
either not allow due to legal restrictions or use of DFS channels is not desired, an eight-channel plan is
recommended as depicted in Figure 5. As illustrated, there is still separation of adjacent channels by at
least 1 cell. Same channel separation can now be a minimum 1 cell in a single plane, rather than in three
dimensions, because only eight channels are being utilized instead of all 23. Many sites use this pattern
with no reported issues.

13
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Deploying SpectraLink 8020/8030
Wireless Telephones
July 2009 Best Practices Guide
Figure 5 - Eight 802.11a Non-interfering Channels with Overlapping Cell Coverage
(52/149, 64/161, etc. shows 1st DFS range channel or upper non-DFS range)
To deploy an eight channel plan for North America, 802.11a networks use channels 36, 40, 44, 48, 149,
153, 157 and 161. This will avoid the DFS channels. In Europe 149, 153, 157, and 161 are not available
so the DFS channels 52, 56, 60, and 64 should be used instead. Note that the handsets were FCC
certified before channel 165 was available and have not been re-certified to allow for use of this channel.
Therefore WLAN deployments must avoid using this channel.
Try to design your AP cell layout so that walls can help divide the cell plane where single cell spacing is
used in a single plane to help attenuate the signal when possible which will help to prevent co-channel
interference. Doing so will provide optimal cell co-channel separation, as depicted in Figure 5.
Use of the eight-channel plan is highly recommended, as the handset will complete the DCA cycle in
about two seconds. In contrast, using all 23 channels causes the DCA cycle time to increase to about six
seconds. This increases the assessment area time, as described in Figure 1, from four seconds to twelve
seconds, thus tripling the distance of overlap.
2.4.2 AP Transmission Power and Capacity
The AP transmit power should be set so that the handsets receive the required minimum signal strength,
as defined in Section 2.1.2 of this document. For deployments with higher AP density, lower transmit
power settings are typically required to prevent channel interference. Maximum AP power settings vary by
band and by channel, and can vary between countries. Local regulations should always be checked for
regulatory compliance considerations. In addition, maximum power output levels may vary by AP
manufacturer. Where possible, all APs should be set to the same transmit power level within a given radio
type. For example, set all 802.11a radios to 50 mW and set all 802.11b and 802.11g radios to 30 mW.
It is crucial to then set the transmit power of the handset to match the transmit power of the APs for that
band. This will ensure a symmetrical communication link. Mismatched transmit power outputs will result
in reduced range, poor handoff, one-way audio and other quality of service or packet delivery issues.
SpectraLink Wireless Telephones support transmission power settings in the range from 5mW to 100mW
(in the United States).
Handsets using Release 3.0 will automatically use Transmit Power Control (TPC) and will learn from the
access point the maximum transmit power they should use, ensuring that the handset coverage radius

14
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Deploying SpectraLink 8020/8030
Wireless Telephones
July 2009 Best Practices Guide
matches that of the AP. However the handset will never exceed the power limit statically set in its handset
administration menus or HAT.
For SpectraLink handsets running pre-R3.0 code, the transmission power setting must be the same for all
APs in a facility, and match the handset‟s statically configured transmit power setting. The transmit power
setting on the phone should be based on the AP‟s configured transmit power setting, not the EIRP
(Effective Isotropic Radiated Power) of the AP. Any AP antenna gain will increase signal gain in both
directions.
When running pre-R3.0 code, regardless of the selected power level settings, all APs and handsets must
be configured with the same transmit settings to avoid channel conflicts or unwanted cross-channel
interference. For access points that support automatic transmission power adjustments, Polycom
recommends using only static power settings to ensure optimal performance of SpectraLink Wireless
Telephones pre-R3.0.
In mixed 802.11b/g environments, Polycom recommends configuring the transmit power of the 802.11b
and 802.11g radios to the same setting, if they are separately configurable. For example, set both radios
to 30mW to ensure identical coverage on both radios. For mixed 802.11a/b/g environments, where the
AP utilizes all three radios types, AP placement should first be determined by modeling for the
characteristics of 802.11a, since this environment will typically have the shortest range. Then, the
transmit power of the 802.11b and 802.11g radios should be adjusted to provide the required coverage
levels and cell overlap for those networks, within the already established AP locations.
2.4.3 Interference
Interference on a wireless network may originate from many sources. Microwave ovens, Bluetooth
devices, cordless phones, wireless video cameras, wireless motion detectors, and rogue APs are among
the many potential interfering RF (radio frequency) sources. In general, devices that employ or emit radio
frequency signals within a given radio coverage area will have the potential to cause unwanted signal
interference.
Radio frequency spectrum analyzers can be used to help identify the sources of such interference. Once
identified, interference is best mitigated by removing the interfering device(s) from the network area.
Otherwise, it may be possible to change the channel setting of the interfering device to avoid conflict with
the surrounding APs. If this is also not possible, then it may be possible to change the channel of the
surrounding APs to avoid as much radio frequency overlap with the interfering device.
A documented facility-wide radio frequency usage policy will help control sources of RF energy. Ideally,
any RF generating device should have prior approval before introduction onto the property or installation
in any building or structures.
2.4.4 Multipath and Signal Distortion
For 802.11a/b/g environments, multipath distortion is a form of RF interference that occurs when a radio
signal has more than one path between the transmitter and the receiver causing multiple signals to be
detected by the receiver. This is typically caused by the radio signal reflecting off physical barriers such
as metal walls, ceilings and other structures and is a very common problem in factories and storage
environments. Multiple converging wave fronts may be received as either an attenuated or amplified
signal by the receiver. In some instances, if the signals arrive exactly out of phase, the result is a
complete cancellation of any RF signal. In 802.11n networks multipath is an exploited feature, rather than
a potential interference problem. The multiple radios used for 802.11n (up to three in an AP) provide
increased throughput. The resulting multipath effects of the multiple radios are used to obtain increased

15
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Deploying SpectraLink 8020/8030
Wireless Telephones
July 2009 Best Practices Guide
range and overall throughput. The remainder of this section focuses on 802.11a/b/g deployments in
which it is favorable to mitigate multipath.
Multipath can cause severe network throughput degradation because of high error rates and packet
retries. This in turn can lead to severe voice quality impairment with SpectraLink Wireless Telephones.
Correctly locating antennas and choosing the right type of antenna can help reduce the effects of
multipath interference.
AP diversity antennas should always be used to help improve performance in a multipath environment. A
diversity solution uses two antennas for each AP radio, and will send and receive signals on the antenna
which is receiving the best signal from the wireless client. Diversity in an AP with two antennas, which
provide signaling to the same geographic area, provides a unique signal path from each antenna to the
handset. This greatly increases the probability that both the AP and the handset will receive better signal
quality in multipath environments. Most access points support receive diversity in that they accept the
received transmission on the antenna that is getting the best signal. Some also support full transmit
diversity where the transmission is made on the same antenna that was last used to receive a signal from
that specific client. In order to provide optimal voice quality, Polycom recommends the use of APs
supporting both receive and full transmit diversity in environments where multipath is an issue. This will
help optimize the WLAN for all wireless clients. External antennas provide additional flexibility in type
(omni or directional), mounting options and gain. External antennas can be separated from 4.5 inches to
5 feet at each AP radio.
Access point antennas should not be placed near a metal roof, wall, beam or other metal obstruction in
any environment, as this will amplify the reflection effects. Additionally, antennas should be positioned so
that they have line of sight (LoS) to most of the clients that they service. Additional instructions from the
wireless network infrastructure vendor should be followed with regard to antenna selection and placement
to provide correct AP diversity operation.
2.4.5 Site Surveys
A wireless RF site survey is highly recommended for any wireless network deployment. However, it is
especially critical for VoWLAN and is essential for large or complex facilities. An RF site survey can
ensure that the wireless network is optimally designed and configured to support voice by confirming RF
placement, cell overlap, channel allocation/reuse, packet transmission quality, packet retry rates, and
other deployment considerations. While many tools exist that allow customers to perform their own
assessment, Polycom recommends a professional site survey to ensure optimum coverage and minimum
interference. Polycom offers a full suite of site-survey services that will ensure a WLAN is properly
configured to support wireless voice.
To verify coverage of an installed Wi-Fi network, Polycom handsets offer a site-survey mode that can be
used to validate the AP locations and configurations are both correct and adequate. This mode detects
the four strongest AP signals and displays the signal strength along with the AP channel assignments.
The site survey mode may be used to detect areas with poor coverage or interfering channels; check for
rogue APs; confirm the Service Set Identification (SSID) and data rates of each AP and include the
security and QoS mechanisms supported by the AP; and detect some AP configuration problems. With
SpectraLink handsets, the entire coverage area must be checked to ensure that at least one access
point‟s output meets the signal strength requirements summarized in Section 2.1.2 of this document. If
the site-survey mode indicates that two APs are using the same channel within range of the handset, it is
important to adjust the channelization to avoid channel conflicts.

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Deploying SpectraLink 8020/8030
Wireless Telephones
July 2009 Best Practices Guide
After a site survey is complete, coverage issues can be resolved by adding and/or relocating APs if
necessary. Overlap issues may be resolved by reassigning channels or by relocating some access
points. When adjustments are made to the WLAN configuration an additional site survey or site
verification should be performed to ensure that the changes are satisfactory and have not had an adverse
impact in other areas of coverage.
2.5 Wireless Telephone Capacity
Network capacity requirements factor into the number of APs required, although in most cases the
coverage area is the primary factor. Data traffic is often very “bursty”and sporadic. This is typically
acceptable because data applications can tolerate network congestion with reduced throughput and
slower response times. Voice traffic cannot tolerate unpredictable delays, where the bandwidth
requirements are much more constant and consistent. Voice traffic can also be predicted using
probabilistic usage models, allowing a network to be designed with high confidence in meeting anticipated
voice capacity requirements. Beyond the standard IP telephony design guidelines, there are several
additional considerations that should be addressed for VoWLAN with SpectraLink handsets.
When SVP is the selected QoS method for the handset, the SVP Server prevents oversubscription of an
AP and improved load balancing by limiting the maximum number of active calls per AP. Recommended
settings are AP specific and can be found in the VIEW Configuration Guides on the Polycom web site.
The maximum number of active calls must be defined for each of the three possible handset radio types –
802.11b, 802.11g and 802.11a. The SVP Server determines the maximum number of wireless
telephones in-call on a given AP and forces handsets to handoff when capacity maximums are reached.
Although 802.11g and 802.11a networks theoretically provide increased available bandwidth for support
of additional simultaneous call volume, the practical call volume limitations will depend on many factors
such as data rates used, competing network traffic, and network performance. Overall, the calls per AP
specified is often lower than the maximum number an individual AP may be able to support. This allows
some handsets to work at lower rates (802.11b at 1Mbps and 2Mbps) and some at the highest data rates.
For Wi-Fi Standard QoS or CCX, WLAN admission control techniques are used for AP bandwidth
management. When the handset is configured to use WMM it will be necessary to ensure the access
point also supports WMM Admission Control. This mechanism is responsible for ensuring the AP does
not become overloaded with any particular type of traffic. Depending on the AP manufacturer it may be
possible to adjust the settings for individual WMM traffic classifications. Details for making these sorts of
changes to APs are available in the VIEW Configuration Guides or from the AP manufacturer. See
Section 4.2.3 for additional details.
2.5.1 Access Point Bandwidth Considerations
There are several factors which determine the AP bandwidth utilization during a telephone call. The first is
the VoIP protocol used and its characteristics. The type of codec utilized combined with the packet rate
will determine the size of the voice packets along with any additional overhead information required for
the protocol. Payload data will generally account for 30-50%of a typical voice packet, with 802.11 and IP
protocol overhead filling the rest. The 802.11 protocols include timing gaps for collision avoidance, which
means bandwidth utilization is more accurately quantified as a percentage of available throughput rather
than actual data throughput.
The percentage of bandwidth required is greater for lower 802.11a/b/g data rates; however it is not a
linear function because of the bandwidth consumed by the timing gaps and overhead. For example, a call
using standard 64 Kbps voice encoding (G.711) utilizes about 4.5 percent of the AP bandwidth at 11
Mbps, and about 12 percent at 2 Mbps. In this example, four simultaneous calls on an AP would consume

17
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Deploying SpectraLink 8020/8030
Wireless Telephones
July 2009 Best Practices Guide
about 18 percent of the available bandwidth at 11 Mbps or about 48 percent at 2 Mbps or about 90
percent at 1Mbps.
The maximum number of simultaneous telephone calls an AP can support is determined by dividing the
maximum recommended bandwidth usage by the percentage of bandwidth used for each individual call.
Note that approximately 20 to 35 percent of the AP bandwidth must be reserved for channel negotiation
and association algorithms, occasional retries, and the possibility of occasional transmission rate
reductions caused by interference or other factors. Therefore, 65 to 80 percent of the total available
bandwidth should be used for calculating the maximum call capacity per AP. For example, if all calls on
an AP are using a theoretical 5.4 percent of the bandwidth at 11 Mbps, the actual number of calls
expected at that rate would be about 12 (65 percent of bandwidth available / 5.4 percent theoretical
bandwidth utilized per call). Lower overall bandwidth is available when there are a greater number of
devices associated with an AP or when lower data rates are used for the telephone call or calls.
Even with all of the known variables, there are many other vendor-specific characteristics associated with
individual APs that make it difficult to quantify the precise number of concurrent calls per AP, without
thorough testing of specific configurations. Polycom‟s VIEW Configuration Guides identify the maximum
number of calls per AP for specific models that have been tested to be compatible with the SpectraLink
handset.
When using SVP for QoS, Polycom provides the ability to limit the number of calls per AP with a
configurable setting in the SVP Server. The “Calls per Access Point” setting limits the number of active
calls on each AP and can be used to set aside bandwidth for data traffic. Wireless Telephones in-call are
free to associate with other APs within range that have not reached the set maximum number of calls.
Polycom requires this setting to be equal to or below the maximum number of calls recommended in
VIEW Configuration Guides. It is still possible for the number of phones associated to an AP to exceed
the maximum number of calls as would be the case with any additional clients associating to the same
AP. The maximum number of calls per AP will simply control how many of those associated phones will
be able to enter into a call. Additional phones beyond the maximum number specified will be forced by
the SVP Server to roam to a new AP that has not reached the maximum calls per AP. If no APs are
available any phones beyond the maximum will display an error message indicating there is insufficient
bandwidth to complete the call.
For systems configured to use Wi-Fi Standard QoS, the calls per AP are managed by the AP using
standards based methods. WMM Admission Control will ensure that AP capacity and bandwidth are
reserved for wireless clients based on the TSPEC (Transmission Specification) each device submits to
the AP to reserve bandwidth for that device‟s communications. The AP will keep track of the total
available bandwidth and will restrict access to network resources for clients if bandwidth becomes
unavailable.
2.5.2 Push-to-Talk Multicasting Considerations
SpectraLink 8030 handsets provide push-to-talk (PTT) functionality using the Polycom-proprietary
SpectraLink Radio Protocol (SRP) ADPCM encoding. Because the PTT mode uses IP multicasting, all
APs on the subnet will transmit a PTT broadcast. This can be limited to only the APs that are handling
one or more PTT-enabled handsets by enabling the Internet Group Management Protocol (IGMP) on the
wired infrastructure network.
When 8030 handsets are deployed on a network with previous versions of SpectraLink handsets, some
interoperability considerations must be observed. The SpectraLink 8030 handsets have 24 PTT channels
plus one priority channel available. Earlier models enabled only eight PTT channels with no priority
channel. When PTT is activated on a network using a mix of handset versions, only the eight common
channels will be available for the older handsets.

18
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Deploying SpectraLink 8020/8030
Wireless Telephones
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2.5.3 Telephone Usage
When the handset is used with traditional PBXs through a Telephony Gateway, the PBX interface will
assemble audio, packetize it, and release these packets at a preset interval (20ms with no SVP Server).
The PBX release interval is generally 20ms or 30ms. If SVP is the selected QoS method, the SVP Server
will receive these audio packets and release them to the network for delivery to the handset every 30ms.
With a PBX release interval of 20ms, packets delivered to the handset by the SVP Server will have one
audio payload followed by a packet with two audio payloads. This pattern, one audio payload then two
audio payloads, will continue during the call. With a PBX release interval of 30ms, packets sent to the
handset will have one audio payload each. In rare occasions, a PBX may use a 40ms release interval.
With this audio payload release interval, packets delivered to the wireless telephone will have one large
audio payload or no audio payload per packet sent to the handset. The no audio payload packets and
long time between audio (two SVP packets –60ms) payload aggravates any weakness (multi-path, retry
packets, etc.) in the WLAN and will cause poor audio. Therefore, whenever possible the PBX should be
configured to use release intervals of 30ms or 20ms.
Because data rate and packet rates are constant with voice applications, wireless telephone calls may be
modeled in a manner very similar to circuit-switched calls. Telephone users (whether wired or wireless)
generally tend to make calls at random times and of random durations. Because of this, mathematical
models can be applied to calculate the probability of calls being blocked based on the number of call
resources available.
Telephone usage is measured in units of Erlangs. One Erlang is equivalent to the traffic generated by a
single telephone call in continuous use. A typical office telephone user will generate 0.10 to 0.15 Erlangs
of usage during normal work hours, which equates to six to nine minutes on the telephone during an
average one-hour period. Heavy telephone users may generate 0.20 to 0.30 Erlangs, or an average of 12
to 18 minutes of phone usage in an hour. Note that traffic analysis is based on the aggregate traffic for all
users, so users with higher or lower usage are included in these averages.
The traffic engineering decisions are a tradeoff between additional call resources and an increased
probability of call blocking. Call blocking is the failure of calls due to an insufficient number of call
resources being available. Typical systems are designed to a blocking level (or grade of service) of 0.5
percent to two percent at the busiest times. Traffic model equations use the aggregate traffic load,
number of users and number of call resources to determine the blocking probability. The blocking
probability can also be used along with the aggregate traffic load to determine the number of call
resources required. Traffic model equations and calculators are available at www.erlang.com.
Consider a system with APs that can support six active telephone calls. If a blocking probability of one
percent or less is desired, each AP can support approximately 13 moderate wireless telephones users. If
the AP coverage supports 12 simultaneous calls per AP, each AP can then support approximately 39
moderate users. This allows some users to be in-call and others in standby.
The Table 3 shows maximum users per AP based on the AP‟s ability to handle simultaneous calls:

19
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Deploying SpectraLink 8020/8030
Wireless Telephones
July 2009 Best Practices Guide
Table 3 - Users Supported per Access Point
Areas where heavier wireless telephone usage is expected, such as cafeterias, staff lounges, and
auditoriums, can obtain higher call capacity and handle more users by installing additional APs. For most
enterprise applications however, the table above should be sufficient in demonstrating the number of
wireless handsets supported within each AP‟s coverage area.
2.5.4 Telephony Gateway Capacity
Telephone system administrators should consider the user distribution on SpectraLink 8000 Telephony
Gateways much in the same way as they do PBX line cards. Telephony Gateways incorporate a physical
connection to a PBX line card. The phone system administrator should spread departments or functional
areas across multiple PBX line cards and across multiple Telephony Gateways so that a failure of either
component does not cause a complete wireless handset outage in one department or area. In addition,
system administrators must consider that one Telephony Gateway can support a maximum of eight
handsets in an active call state. While the Telephony Gateway can manage 16 wireless telephones total
only eight can be in call at any one time. Therefore, heavy users should be spread across Telephony
Gateways to reduce the chance of call blocking.
User Calling Intensity
Light
Moderate
Heavy
Erlangs per User
0.10
0.15
0.20
Max Active Calls per
AP
Users Supported per AP
(1% Blocking Probability)
1
1
1
1
2
2
2
2
3
4
3
3
4
8
6
4
5
13
9
7
6
19
13
10
7
25
17
13
8
31
21
16
9
37
25
19
10
44
30
22
11
51
34
26
12
58
39
29

20
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Deploying SpectraLink 8020/8030
Wireless Telephones
July 2009 Best Practices Guide
3Network Infrastructure Considerations
3.1 Physical Connections
SpectraLink infrastructure components, including the SVP Server(s), Telephony Gateways and OAI
Gateway, must connect to a facility‟s LAN using enterprise-grade Ethernet switches rather than Ethernet
hubs or consumer-grade SOHO switches in order to provide adequate bandwidth and limit traffic collisions
and bottlenecks (see Figure 6 for reference).
Ethernet switches should be configured to statically set the speed and duplex values as appropriate for the
device being connected to that port. The SVP Server should be set to the 100Base-T/Full Full-duplex
transmission setting. This is required to support the maximum simultaneous voice calls and for optimal
system performance. The SpectraLink Telephony Gateway and OAI Gateway products utilize a 10Base-T,
half-duplex Ethernet interface and the Ethernet switch ports should be set accordingly.
Network wiring is an important component of any Ethernet-based system and is subject to local and state
building code specifications. Cat 5 or better, 4-pair 10/100 Base-T Ethernet cabling must be used for
SpectraLink infrastructure equipment.
Wireless bridges are sometimes used to interconnect geographically isolated Ethernet LANs or to extend
the range of existing WLANs. Such devices create bottlenecks for network capacity and add delay to the
overall network, which are generally not tolerable for real-time voice connections. Polycom does not
support a configuration that includes wireless bridges and does not recommend using wireless bridges
with any wireless network supporting voice.