March 2004
Wireless VoIP - Corporate & Commercial
Hotspot Access
BY RICHARD WATSON
Imagine the following serene image. A
businessman sits at a coffeehouse table, sipping a Latte, and surfing the
�net in complete peace. None of the hustle and bustle from the office. Time
to read, reflect, and compose one�s thoughts. What about making those
important phone calls too? Use wireless access to the Internet to invoke a
VoIP call to that key associate or customer. Too good to be true? This scene
may be coming to a coffee shop near you in the next 12�24 months.
But, what are the promises? What are the
challenges?
THE PROMISE
In the same manner that users execute data applications in a WiFi hotspot
(e.g., surf the net or other applications), the use of VoIP applications
holds promise with the simple addition of an IP enabled softphone
application (there are a growing number of �softphones� that are on the
market to enable laptops and PDA devices to support VoIP applications). The
assumption is that once users are in a hotspot, their system has detected
the proper RF standards-based service (e.g., �b�, �a�, or �g�), the proper
WLAN ESSID, and the proper level of security has been invoked (e.g., VPN,
WEP, or other). With this level of RF/network access, there should be little
that would prevent launching a VoIP client and start making calls � right?
Not so fast! You are only halfway there. There are some technical and
operational challenges that need to be addressed in order to provide
full-featured, toll-quality phone calls from WiFi hotspots.
THE CHALLENGES
Much like being able to ensure the best voice quality on a WiFi network
within the corporate network fabric, providing such a level of service
within a publicly accessible network is also a challenge. Operating from
within a hotspot usually presumes that there is at least one router �hop,�
which can pose some potential latency problems that may degrade the voice
quality. This, however, may only be a minor concern when compared to other
issues that need to be addressed.
The first application hurdle to be met is the resolution of the VoIP service
point address. Such a requirement involves the resolution and validation of
an IP address of either the target VoIP callee (such as in a peer-to-peer
call) or network level access to a VoIP call server that may provide access
to the PSTN. The former situation is typically resolved by using DNS
services, an architecture that is used in SIP applications. The latter often
requires that your mobile client be pre-configured with the service point IP
address that is reachable across the network.
QoS CHALLENGES
Managing the end-to-end QoS (Quality of Service) is key to ensuring the very
best voice quality. Making sure that the voice traffic gains priority over
data traffic is currently not mandated by any exiting wireless standard, so
only vendor proprietary solutions can currently be applied. The IEEE 802.11e
(or WiFi Alliance�s WME) holds promise for a standard dictating wireless QoS,
but that may be a number of quarters away and support may vary somewhat from
vendor to vendor.
Applying proper QoS to the wireless domain is only half of the QoS
challenge. It will be equally important to support toll quality voice. To do
this, IEEE 802.1p must be applied when the voice traffic is transmitted on
the Ethernet network. However, not all WiFi access point vendors will
provide �seamless� QoS management by supporting some kind of QoS on the WiFi
domain AND also supporting IEEE 802.1p frame �tagging� on the Ethernet
components. Without robust and complete support of QoS mechanisms, voice
quality from hotspots may be �iffy.� End-to-end bandwidth allocation and
management is yet another discussion.
FIREWALL CHALLENGES
Traversing the corporate Intranet also raises an additional challenge �
firewall management. Depending on the network architecture, one network
component that needs to be considered in designing a wireless VoIP solution
is the firewall configuration. Most VoIP applications utilize UDP (User
Datagram Protocol) frames to transmit the audio payload. This is transport
unreliable and is often blocked by firewalls. A potential security breach,
most network administrators guard their firewalls jealously, and only
approve the use of UDP traffic that is highly filtered by some
identification scheme and restrict publishing of the UDP ports under guarded
conditions. At best, resolution of this network configuration problem will
be addressed through a client configuration operation.
APPLICATION CHALLENGES
The final technical challenge relates to matching the application VoIP
protocols and functions accessed. Once access to the network is achieved,
placing that end-to-end phone call involves making sure that the mobile
application employs a peer VoIP call control protocol to the gating
telephony service. There are many different �softphones� on the market today
and it seems that each one of them uses different VoIP call control
protocols. Each protocol is promoted as being the �best� at some
feature/function and may be bound to specific vendor products. ITU H.323,
IETF SIP, or proprietary call control protocols can all provide you with a
quality audio experience, but lack of inter-vendor or inter-service provider
interoperability can frustrate the average user. Support of a commercial
future wireless VoIP service will be very similar to current hardware-based
services, such as those offered today from the desktop through a network
gateway/bridge product by Vonage, VocalTec, and Net2Phone, all of which
require specific client modules.
How, then, are these challenges addressed? Today, all of the above
challenges are most easily overcome when you purchase your wireless VoIP
service from a single vendor. Any successful service provider will define
your network access requirements (security and other elements) and the
specific softphone application (e.g., call control protocol) to be employed.
OPERATIONAL CHALLENGES
Once you can make phone calls from hotspots, are there feature restrictions
or limitations? Does telephony access from a hotspot make sense to corporate
associates? Does it make sense for the average personal phone user?
Corporate Operational Challenges
Corporate utilization of WiFi telephony is closer to reality because a
corporation has more control over the telephony components within their
network. Deployments of such services require corporate network managers to
mitigate or eliminate any network intrusion access from such hotspots. Any
remote wireless access to a corporate network will include requirement for
high security (VPN or another high security scheme). Once the security/risk
aspects of a corporate hot spot have been resolved, full usability of such a
wireless configuration will have to support basic telephony functions, such
as:
� Placing an outbound call through the PSTN.
� Receiving an inbound call through the PSTN.
� Accessing voice mail from the �home� office.
Placing an outbound call through a corporate network should be as simple as
dialing the phone number, but may be further simplified if the softphone can
access a corporate personnel directory. This precludes having to carry a
large corporate phone book, but such a feature may require the use of a
custom enterprise softphone. Operational questions arise from such
configurations as to what �caller ID� is to be displayed at the receiving
end. There may be no traditional PSTN phone number assigned to the
originating phone, where only an IP address or UserID is associated with the
device. While this is not a major problem, it might cause some confusion to
users who have grown dependent on caller ID information that accompanies the
call. This also brings up the question of being able to support the �redial�
feature for received phone calls. A standards-based approach to addressing
this problem is the ITU ENUM (RFC2916), which defines how to map standard
PSTN phone numbers (E.164 numbers) to VoIP URL identifiers.
Receipt of inbound calls is more difficult because it requires the
management of a �registration� authority. Some early market services
supporting such technologies will only support outbound calls with inbound
calling to be supported as a feature to be released later. The ability to
receive an inbound call requires that the remote client register itself by
informing the telephony server �I�m here� and provide the acquired IP
address and user ID information. This kind of function may also employ the
use of a custom softphone, unless this function is supported by the native
call control protocol.
Presuming you can make a PSTN class phone call, access to one�s personal
voice mail may be as simple as making a phone call. This is straightforward
enough, but won�t provide the �message waiting� indication that would be
found on their desktop phone. So, the experience will not be exactly like
what you have at the desktop because you won�t be informed when you have
voice mail queued to be read. Corporate telephony users also expect more
sophisticated functions such as conferencing and call transfers that may not
be supported by a generic WiFi VoIP application.
Above and beyond the basic challenges of making quality calls across
hotspots, any corporate implementation may require development of some
enterprise enhancements of a selected softphone.
Commercial Operational Challenges
The promise of using a WiFi phone in any commercial hotspot is a little more
elusive because there is no entity that has total control over all the
components within the network fabric. Certainly any good Telephony Internet
Service Provider (TISP) will provide the necessary VoIP service and
softphone. More importantly, such a provider will negotiate or provide the
hotspot access at popular locations (e.g., coffee shops), but are there
limitations to this class of service? What about Intranet QoS and security
options?
Perhaps the biggest limitation to a commercial WiFi telephony service is the
ability to receive an inbound phone call. How does anyone know how to reach
me if my phone has a different IP address in each hotspot? The one call
control protocol that holds out the best promise to solve this difficulty is
Session Initiation Protocol (SIP). Built into the SIP architecture is the
ability to support a DNS registration and address resolution capability.
Therefore, powering up in a hotspot, obtaining an IP address, and
successfully registering with a DNS service provides the promise of being
able to receive an inbound call. The ability to receive an inbound call will
still rely on the presence of some system-wide address/extension ENUM
mapping service.
Use of cell phones and enterprise telephony systems have conditioned most
users to rely on voice mail if a person is not available. Simply having a
robust registration capability to announce a presence in a hotspot will not
resolve the problem of what to do with call attempts that are made when that
user is not in a hot spot? Addressing this problem will be made by the TISP,
which will either provide its own voice mail (much like WAN carriers) or
forward the call to a designated voice mail address/extension. Early VoIP
service providers are now deploying such sophisticated services.
THE ULTIMATE PROMISE:
DUAL MODE PHONES
Is there a possibility to ensure almost nationwide continuous wireless
coverage for telephony services? What about a dual-mode phone? A WAN and
WLAN device that would provide telephony coverage both outdoors and within
hotspots is possible using today�s technology. Conceptually, a national (or
international) carrier would provide such a device and the necessary wide
area and local area wireless coverage for almost ubiquitous wireless
coverage. This promise may not be that far off in the future, as several
major companies (phone manufacturers and carriers) have announced strategic
partnerships to provide such products and services sometime in 2004. Such
almost miraculous devices, however, will still have to address the
challenges detailed in the earlier paragraphs to fulfill the promises
expected by the consumer.
SUMMARY
Hotspot services are springing up everyday across North America and while
the primary use of these services are for data applications, it won�t be
very long before offerings of low cost and flexible VoIP services will be
made available through these networks. Most likely, corporate hotspot
services will be on the vanguard of these product rollouts, but not far
behind will be wireless VoIP offerings for the masses. However, the biggest
challenges � finding the hotspot locations and the right service provider �
will remain. c
Richard Watson is director of telephony product marketing for
Symbol Technologies� Wireless Systems
Division in San Jose, CA. Prior to taking on the marketing role for Symbol�s
NetVision family of WiFi Telephony products, he managed the software
engineering team for three years and was responsible for developing Symbol�s
WiFi Telephony products.
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