Wireless VoIP --
BY RICHARD WATSON
In previous articles, the challenges of security, reliability, VoIP
protocol robustness, and voice quality have been discussed in relation to
the implementation of VoIP on 802.11/WiFi wireless networks. Despite the
technical complexities that may exist, it is possible to purchase wireless
VoIP devices that provide excellent voice quality in todayï¿½s market. These
offerings, often requiring vendor specific adjunct components, are being
deployed in an increasing number in commercial and enterprise environments.
But do the current wireless VoIP products meet all the requirements of the
As technology advances, so do the demands and requirements of those
customers that want to integrate such technologies into their corporate
infrastructures. As with most things in life -- there are many ï¿½changesï¿½ on
the horizon for wireless VoIP products. In this article, we try to look into
the future (as best as possible) and identify some key elements of the
evolving and changing wireless VoIP landscape.
Todayï¿½s WLAN products are mostly 802.11b or WiFi. The 11Mbps data rate
supported by this standard meets most of the data rate needs of todayï¿½s
applications -- as did 10Mbps Ethernet. However, the demand for increased
bandwidth is never-ending as customers see applications for wireless video
and the like. These bandwidth hogs require higher total available bandwidth
-- thus new high-bandwidth standards are emerging that are targeted to meet
How does this impact ï¿½voiceï¿½ applications? To understand these dynamics, you
have to learn your ï¿½A, B, Gï¿½s.ï¿½ IEEE 802.11b (WiFi) supports raw data rates
up to 11Mpbs, but the new ï¿½Aï¿½ and ï¿½Gï¿½ standards support 54Mbps (and higher).
While Access Point proximity dictates the exact effective data transfer
rate, these newer standards easily meet the demands of the new, bandwidth
hungry mobile applications. So, whatï¿½s the difference between these
standards and what are the major consideration regarding voice applications?
The major difference between the ï¿½Aï¿½ and ï¿½Gï¿½ standards is the operating
spectrum frequency utilized. The ï¿½Gï¿½ standard utilizes the 2.4GHz ISM band
(like ï¿½Bï¿½) while ï¿½Aï¿½ utilizes the 5.2GHz band. One rationale for using the
5.2GHz band is that the ISM band may become too crowded and introduces a
possibility of interference problems (e.g., Bluetooth, RFID tags, cordless
phones, microwave ovens and other 2.4GHz applications). Deployment of an
ï¿½A-onlyï¿½ network will, of course, require deployment of 802.11a wireless
voice devices which are, as of yet, not readily available on the market.
A ï¿½Gï¿½ network may have the potential drawback of operating in the 2.4GHz
band, but it can also provide the extended capability of supporting ï¿½Bï¿½
devices. This feature is a real asset to those companies that have already
deployed ï¿½Bï¿½ WLAN infrastructures with ï¿½Bï¿½ mobile devices. With a ï¿½Gï¿½ WLAN,
older ï¿½Bï¿½ mobile units can continue to be used along with any new ï¿½Gï¿½ mobile
Since bandwidth is not a major issue with regards to supporting good
wireless voice quality (this can be done well with just 1Mbps), the issue of
deploying new wireless technology will be an issue of retaining existing
investments in mobile devices or purchasing new devices. To date, however,
there have only been a few vendors that have announced support of 802.11a or
802.11g for a wireless VoIP application; most are still 802.11b compliant.
Even when these do become available, there is a potential of greater power
management demands in both ï¿½Aï¿½ and ï¿½Gï¿½ devices that may impact the length of
So, how might ï¿½Gï¿½ and ï¿½Aï¿½ impact voice applications? The biggest issues
would be (1) the availability of a specific RF conformant device (e.g., an
ï¿½A-phoneï¿½); and (2) potentially shorter battery life which may reduce
standby time or talk time.
RF SERVICE CHANGES
Unfortunately, the ï¿½standardsï¿½ are still evolving, forcing future changes.
The two major functional elements that will be impacted by the impending
standards changes are:
ï¿½ QoS ï¿½ Quality of Service or voice prioritization.
ï¿½ Security ï¿½ authentication and encryption.
The 802.11e standard attempts to address the issue of QoS. Supplanting the
current proprietary voice QoS offerings, this standard would provide a
vendor independent QoS serviceï¿½maybe. As currently drafted, the standard
allows for some latitude in implementation options. A fully conformant WLAN
product would potentially impose an AP capacity limit on access to the WLAN
and lower the overall system call capacity. For this reason, deploying a QoS
supported wireless voice application may remain a somewhat vendor specific
consideration. Make sure to look at your options carefully.
The 802.11i standard addresses the security weakness in the original 802.11
standard. Articulating two approaches to solve this problem:
ï¿½ Enhanced encryption that can be utilized on existing hardware.
ï¿½ Enhanced encryption that may require hardware upgrades This standard
specifies use of the Advanced Encryption Standard (AES).
As vendors make standards-compliant products available, it will be important
to understand the impact of these standards with regard to the required
voice quality of the wireless voice application. Applying the ï¿½software
onlyï¿½ enhancements may impose additional latency burdens that will
negatively impact the observed voice quality. In addition, conformance to
the higher encryption standards may also require replacement of existing
mobile devices with new, security compliant hardware.
TELEPHONY SERVICE OPTION CHANGES
Once you have a WLAN VoIP device, one of the other major considerations is
the service that will be needed to supply the telephony services. There are
basically two generic connection options:
ï¿½ Telephony services derived from a Telephony Internet Service Provider (TISP)
or IP-Centrex vendor.
ï¿½ Telephony services derived from corporate PBX services.
Either option requires cooperation with the group that is
supplying/supporting the service and the two options are typically mutually
If the WLAN-VoIP initiative is a corporate driven program, selection of
which option to follow will be dictated. Interfacing to a corporate
wireless-VoIP service may evolve over time as paced by the corporation
adoption of VoIP as a backbone voice service. Deployment of a corporate
wireless VoIP solution that integrates into a PBX vendorï¿½s system may
require vendor-specific client VoIP firmware. However, if Wireless-VoIP is
an independent requirement, there are a number of ISP/TISP services that are
becoming available to support SOHO or home/hotspot wireless VoIP access.
TISPs and IP-Centrex services will become a crowded, competitive landscape
in the future, much like the competitive landscape for long-distance calling
services and wide-area telephony services.
VoIP PROTOCOL CHANGES
In todayï¿½s wireless VoIP market, vendor proprietary protocols dominate.
These protocols were developed and deployed out of necessity because the
international VoIP standards were not sufficiently mature. In addition, none
of the ï¿½standardï¿½ VoIP call control protocols address hardware specific
device controls that are important for support of vendor specific value-add.
Will this always be the case? No.
The IETF Session Initiation Protocol (SIP) is challenging the status of ITU
H.323 as the most popular standards-based call control. However, even SIP
does not meet the requirements of many corporate customers and is still in
the process of evolving to a richer set of features. Specifically, a working
group has been formed and is defining an optimal expression of SIP for the
wireless deployments (ITU T-41), but this effort has not been completed.
The maturing of any of the protocols, from a wireless perspective, will
continue to provide more robust and feature rich choices to companies
interested in deploying wireless VoIP solutions.
FORM FACTOR CHANGES
To date, all commercial WiFi voice devices have been voice-only ï¿½phones.ï¿½
Appearing on the horizon is the option of using a PDA as a phone. In theory,
any wireless-enabled PDA can become a phone by loading a ï¿½softphoneï¿½
application. There are a number of ï¿½softphoneï¿½ products available on the
market, but many of them have not been fully optimized for the wireless LAN
and donï¿½t provide the same voice quality or reliability of commercially
available wireless handsets. This situation, however, will change. As market
demand increases, the reliability of these offerings will also increase. To
meet these higher requirement levels, you may see softphone offerings that
are ï¿½tunedï¿½ to specific hardware platforms and/or vendor specific wireless
LAN infrastructures. Having a PDA with telephony capability can be a real
asset for the mobile worker.
The holy grail of the mobile workforce, however, is the dual-mode phone. The
ability to use the same device while in WLAN coverage and in WAN (GSM or
CDMA) coverage is extremely appealing to a vast number of mobile workers.
Sales/support people, doctors, lawyers and the like often carry two devices
to get maximum accessibility and desire a single dual-mode device. To this
end, there have been announcements by several major corporations of
dual-mode phone availability beginning in mid/late 2004. While this single
device approach may appear the ultimate solution, it is more likely that
these initial offerings will not be as ï¿½seamlessï¿½ in service or
functionality as the consumer would like. Most likely, phased releases of
increasing functional support will be made available to the market. Even
these offerings will still have to address all the other complex challenges
that have been previously identified for a simple WLAN phone.
So, what does the future hold? Change. Changes on many fronts will impact
the delivery of a wireless VoIP solution. In order to successfully manage
the expected changes and navigate the churning vendor ï¿½waters,ï¿½ it will be
important to focus on the following areas:
ï¿½ Define the exact wireless telephony requirements within your company.
These become the baseline from which evaluation and selection of various
wireless VoIP options are made.
ï¿½ Understand and incorporate any corporate wireless LAN strategies/polices
into selection of a final solution option (security and QoS).
ï¿½ Identify and focus on any specific PBX (or PSTN) connectivity features
that are required, as they will impact any final solution configuration.
ï¿½ Fully understand the current and future support plans from the selected
vendor to supply the wireless VoIP components. This will allow for making
future transition plans for expected changes that impact either firmware or
The market demand is heating up for support of wireless VoIP applications
and the population of commercial offerings increases almost daily. There are
solid solutions available in todayï¿½s market but there is also a need to
understand the ï¿½changesï¿½ on the horizon, which may shape todayï¿½s decisions
for tomorrowï¿½s use.
Richard Watson is director of telephony product marketing for
Symbol Technologiesï¿½ Wireless Systems
Division in San Jose, CA. Prior to taking on the marketing role for Symbolï¿½s
NetVision family of WiFi Telephony products, he managed the software
engineering team for three years and was responsible for developing Symbolï¿½s
WiFi Telephony products.
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