ITEXPO begins in:   New Coverage :  Asterisk  |  Fax Software  |  SIP Phones  |  Small Cells

Feature Article
March 2004

Wireless VoIP - Corporate & Commercial Hotspot Access


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?

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.

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.

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.

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.

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.

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.


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.

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.

If you are interested in purchasing reprints of this article (in either print or HTML format), please visit Reprint Management Services online or contact a representative via e-mail at [email protected] or by phone at 800-290-5460.

[ Return To The March 2003 Table Of Contents ]

Today @ TMC
Upcoming Events
ITEXPO West 2012
October 2- 5, 2012
The Austin Convention Center
Austin, Texas
The World's Premier Managed Services and Cloud Computing Event
Click for Dates and Locations
Mobility Tech Conference & Expo
October 3- 5, 2012
The Austin Convention Center
Austin, Texas
Cloud Communications Summit
October 3- 5, 2012
The Austin Convention Center
Austin, Texas