The industry regularly produces new wireless technologies such as 2.5 and 3G mobile, 802.11, and UWB, so its ironic that enterprise IT administrators often hope that just one of them will solve all of their problems. Take WiFi, for example. As enterprises deploy WiFi to support data network access, many IT administrators are looking at voice over WiFi (VoWLAN) as a way to put all voice and data traffic on the same IP-based network. Theoretically, this strategy should reduce management costs and enable free voice calls over the corporate network. But today, VoWLAN leaves a lot to be desired when it comes to scalability, QoS, and cost reduction. The reality is that certain wireless technologies are simply better for specific applications, and trying to make one technology suit every application can be a costly and time-consuming exercise in frustration.
To evaluate the pros and cons of VoWLAN (define - news -alerts) and 2.5/3G mobile wireless technologies when it comes to meeting corporate mobility needs, its important first to understand that WiFi and 2.5/3G cellular are two fundamentally different technologies with fundamentally different design goals.
WiFi and VoWLAN Technology
WiFi (802.11) was designed to support IP data connections within a limited area. To cover large areas, its necessary to deploy multiple WiFi access points (APs). Multi-AP networks theoretically deliver up to 54Mbps of bandwidth and have centralized management that simplifies AP configuration and security, but WiFi remains a fairly primitive technology as radio networks go, and VoWLAN is in its infancy. Consider:
Although an 802.11g AP has a proclaimed data rate of 54Mbps, this is only achieved for a single user close to the antenna. As the user gets farther away, the AP rapidly drops to lower rates. At the fringe of a coverage area, bandwidth is typically limited to two to six Mbps.
Multiple users in the same cell contend for the same bandwidth. Some packets collide and have to be retransmitted, so real throughput rarely exceeds 10 percent of the proclaimed rate.
While IP data packets can be easily delayed a short period without affecting performance, IP voice is a very time-sensitive application, and packet delivery delays will reduce quality of service.
To support voice, the AP must be deloaded to minimize packet collisions. Most APs cannot handle more than seven simultaneous IP voice calls with reasonable quality, and they achieve this level only when there is no other IP data traffic present.
Using vendor-recommended engineering rules, a mixed voice/data network of APs in a typical office requires approximately four times the number of APs as a data-only network.
APs cannot distinguish between IP voice packets and regular IP data packets today, and cannot independently control the quality of service (QoS) for each type of traffic. Although the industry anxiously awaits the ratification of the 802.11e standard (which will introduce QoS capabilities), current QoS mechanisms are primitive and proprietary.
WiFi uses the public USM band, which is shared with cordless phones, microwave ovens, other unregulated devices, and even the WiFi network in the neighboring office. Any of these can interfere with your own WiFi network and lower its performance (and the first service affected is IP voice, because its the most sensitive to disruption).
Although WiFi-only phones are available for as low as $100, users are reluctant to carry an extra handset along with their cellphone. The optimum solution is a dual-mode (VoWLAN/cellular) handset, but today there are only a couple of these on the market and prices are around $600. These prices arent expected to reach the same range as high-quality cellular phones for two years.
Even if the previous challenges were all resolved, theres still the problem of interconnecting WiFi and cellular networks. Most industry analysts dont expect seamless WiFi cellular interconnection until at least 2008.
2.5 and 3G Mobile Technology
In contrast, todays 2.5 and 3G mobile networks were designed to support data rates from 300400Kbps to two Mbps, along with voice traffic for millions of users over very large geographical regions. Because of these requirements, these cellular networks handle voice and data traffic much differently.
All base stations are connected to a base station controller, which knows about each active user and coordinates client access among them to balance the overall client load. If a base station is unable to handle a client request, it hands that client off to the next nearby base station.
Base stations control QoS in both directions to every client.
One 3G base station radio can handle anywhere from 30 to 85 simultaneous users without QoS degradation, and base stations are engineered to support multiple radios, allowing hundreds of simultaneous voice calls and data sessions.
Base station controllers automatically coordinate channels among their connected base stations to avoid interference. Cellular frequencies are dedicated to each wireless carrier, so there is no interference between networks. In fact, such interference is prohibited by FCC regulation.
Voice and data traffic are handled separately, rather than contending for the same bandwidth.
Despite these advantages, in-building cellular coverage is often poor. Steel, concrete, and other building materials block or absorb the radio energy, causing lower QoS or bandwidth and even dropped calls as users move throughout a facility. However, theres an easy remedy for this problem: mobile wireless extension technology.
Mobile wireless extension technology has been around for years, and many companies already use it to improve cellular service within their facilities. In-building wireless extension gear includes a rooftop antenna (if necessary), a micro base station in the wiring closet or communications room, expansion hubs on each floor (if needed), and distributed remote antennas to extend radio coverage. By extending in-building cellular coverage, companies can immediately provide high-quality mobile voice services to any number of users. In addition, costs for this solution can often be shared with the cellular carrier.
Enterprise Wireless Goals and Requirements
With these technical differences in mind, lets look at the goals and requirements for enterprise wireless deployments. Basically, enterprise IT managers want wireless systems to:
Provide seamless voice and data coverage throughout their facilities.
As the wireless user population grows and companies adopt applications such as voice or RFID, companies must enable access anywhere.
Ensure the highest possible quality of service.
Voice users, in particular, are sensitive to poor connections, and QoS is more difficult for voice because users are often moving.
Minimize IT administration and equipment costs.
Any wireless network requires additional equipment purchases, but it is far less expensive to deploy WiFi for data applications than for voice applications, because wireless data requires fewer APs and less QoS management.
Minimize network services and per-minute costs.
WiFi networks avoid carrier network usage charges, but any costs involved with deploying, configuring, managing, and maintaining a WiFi network must be factored into the total cost. Along with APs and controllers, it may be necessary to purchase new wireless LAN cards or client devices that support higher data rates (802.11g or a).
VoWLAN Versus In-building Cellular
Considering the business requirements, its relatively easy to evaluate the effectiveness of an all-in-one (i.e., WiFi data and VoWLAN) solution against a combined WiFi data network and 2.5/3G mobile voice solution.
Seamless voice and data coverage.
Since data users will likely be seated someplace, WiFi data can be used to provide access for this application. But for voice, in-building 2.5 or 3G cellular provides more pervasive coverage at a lower cost.
Ensure the highest possible quality of service.
WiFi delivers higher bandwidth for data applications for stationary users, while cellular offers far higher QoS for voice users. In addition, enterprises are increasingly adopting mobile applications for todays smartphones, and the applications are designed to function well under the constraints of 2.5 or 3G cellular data bandwidth. For instance, Salesforce.com (one of the most popular CRM applications on the market) allows the mobile salesperson to see critical data on a RIM Blackberry (news - alerts).
Minimize IT administration and equipment costs.
WiFi data networking equipment is relatively inexpensive and easy to manage, while problems with QoS, interference, scalability, and handset costs make VoWLAN very expensive to deploy and manage. By extending cellular coverage indoors, companies can leverage existing infrastructure and client devices, which are largely managed by the carrier at no cost to the enterprise.
Minimize network service and per-minute charges.
For VoWLAN, the company must bear the cost of replacing cellular handsets with dual-mode handsets, and the WiFi network must be upgraded with up to four times as many APs to support even modest levels of voice coverage. But in-building wireless equipment costs can usually be shared with the carrier or building owner, and most cellular carriers now have rates as low as $39.95 per month for corporate users with unlimited mobile-to-mobile calls within the same network.
In summary, its clear that VoWLAN today is a lot more complex and costly than simply extending cellular wireless with an in-building system. At the same time, VoWLAN cant deliver anywhere near the quality of service that voice callers demand. In-building mobile wireless extension allows companies to offer quality voice services throughout their facilities without major equipment expenditures, and to support the growing array of mobile applications designed for todays smartphones. When it comes to supporting mobile data and voice services, one technology does not meet all application requirements. IT
By John Spindler, vice president of marketing, LGC Wireless. For more information, please visit www.lgcwireless.com (news - alerts).
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