Home North AmericaNorth America 2006 Voice over Wireless LANs

Voice over Wireless LANs

by david.nunes
Dan SimoneIssue:North America 2006
Article no.:14
Topic:Voice over Wireless LANs
Author:Dan Simone
Title:Co-Founder and Chief Technology Officer
Organisation:Trapeze Networks
PDF size:60KB



About author

Dan Simone is the Co-Founder and Chief Technology Officer of Trapeze Networks. Before Trapeze, Mr Simone was vice president of Product Management for Redback Networks. A 20-year veteran of the networking and communications industries, Mr Simone has worked in engineering, product management and marketing at several prominent companies. At Bay Networks (now Nortel Networks), he drove the development of hubs, switches and net management products. At Motorola, he headed up design, installation and management of the corporate LAN. Mr Simone co-authored the point-to-point protocol over Ethernet (PPPoE) and holds several patents. Dan Simone earned a MBA from the University of Chicago and BSEE and MSEE degrees from Marquette University.


Article abstract

Voice-over-wireless LAN (VoWLAN) is an outgrowth of the growing use of WiFi-based wireless local area networks (WLANs) by businesses. Voice networks, a basic necessity in any company, are increasingly based upon VoIP (voice over IP). VoIP-based enterprise phone systems are rapidly replacing traditional PBX networks. VoWLAN adds mobility and accessibility to the list of VoIP benefits, greatly reduces the cost of voice and data communications, simplifies maintenance and eases integration with call centres and other IP-enabled voice solutions.


Full Article

WiFi networks provide inexpensive and convenient access to the Internet, email and business-critical applications. As organizations widely deploy wireless LANs (WLANs), adding voice to the wireless data network is a logical productivity improvement. Voice networks are fundamental to the success of most businesses, but before you deploy a voice-over-wireless-LAN (VoWLAN) system in your business, you must understand the critical technical issues to delivering a reliable, high-quality voice service to your users. Careful planning of the converged wireless LAN is essential to ensure adequate capacity, coverage, quality of service (QoS) and traffic management. Resiliency and security are vital when business-critical voice services are added to the network. Efficient management of the converged network and mobile devices are needed to keep operating costs under control. A fast-growing market VoWLAN systems are based on voice over IP (VoIP), a technology that is being widely deployed in enterprise markets. According to a recent report by Merrill Lynch, sales of VoIP systems in the year ending June 2005 were higher than those for traditional voice systems. Traditional voice systems dropped by 20 per cent while VoIP systems sales grew 31 per cent. This trend will likely continue. Enterprise IT is moving to VoIP for several reasons, including savings in toll costs, reductions in operating costs, simplification of moves, additions and changes, and the relative ease of integration with call centres and other IP-enabled voice solutions. High adoption rates for VoIP are driving the VoWLAN market. VoWLAN adds complete mobility and accessibility of employees to the list of VoIP benefits. Voice and data over WiFi opens up the possibility of eliminating building wiring, which produces additional savings. The number of enterprise VoWLAN handset suppliers is increasing, with at least seven vendors currently in this space. A great many soft clients, most notably Skype, work over WiFi. Market research firm Synergy Research forecast that about 400,000 WiFi handsets would be sold in 2005, increasing to more than 16 million by 2009. Dual-mode phones that work over WiFi and cellular networks take the voice evolution one step further. Dual-mode phones reduce toll costs, offer greater mobility and improve in-building coverage in one convenient handset. There are already more than ten manufacturers of dual-mode phones. This market is also forecast to grow rapidly. Infonetics Research predicts that sales will rise from a few million dollars in 2005 to nearly US$3 billion in 2009. Deploying voice over your wireless LAN Architecting your WLAN to support the needs of a sensitive application like voice – as well as the more steadfast data applications – requires a thorough understanding of the issues at hand. Many of these issues with VoWLAN are not unique to wireless, but apply to any well-engineered VoIP network. • Planning and management – Carefully plan your WLAN so adequate coverage and capacity exists anywhere a user might initiate a call or roam. You could potentially manage thousands of VoIP phones, laptops and other mobile devices, so be sure your WLAN offers comprehensive management and reporting capabilities to lower the cost of ownership. • QoS and traffic management – Make sure your WLAN minimizes latency and jitter to ensure voice quality. The hand-off time between access points (APs) must also be quick to maintain calls as users roam. QoS and traffic management techniques will make the most of the limited WLAN bandwidth. • Security and resiliency – Secure your voice traffic with strong authentication and encryption to protect against network- and VoIP-specific threats. Make sure that the WLAN infrastructure is highly resilient to deliver services when they are needed. Ease planning and management chores Robust VoWLAN starts with defining coverage areas and calculating capacity requirements to ensure that voice services are ubiquitous and available, especially when user densities are high. You must ensure coverage anywhere a user might initiate a call or roam. Automated planning and configuration tools can significantly simplify this detailed process and speed deployment. Resource-strapped IT departments cannot bear the burden of deploying and managing, potentially, thousands of mobile devices. WLANs must make it easy to plan, configure, deploy and manage the wireless elements. That means you must be able to manage WLAN switches and APs remotely. You must be able to identify and locate mobile devices immediately. Your WLAN should also offer comprehensive reporting to track and understand utilization trends. Use quality of service and traffic management Minimizing latency and jitter requires supporting QoS mechanisms that classify, prioritize and queue traffic so that voice packets incur minimal delays when the network is experiencing a heavy load. Since WiFi is a shared medium, supporting QoS at the AP is especially important. Several options exist for implementing QoS. IEEE 802.11e and WiFi Multimedia (WMM) define four priority levels to support different kinds of traffic: voice, video, best effort (usually data) and background. 802.11e specifies enhancements to the 802.11 MAC (media access control) that arbitrates access to the wireless medium. These enhancements are backward compatible with existing 802.11 devices. SpectraLink Voice Priority (SVP) is a QoS mechanism that is implemented in wireless handsets and APs. It gives controlled preference to voice packets over data packets on the WiFi network. An open specification, SVP is compatible with the IEEE 802.11b standard and has been widely adopted in the industry. Call admission control (CAC) is a traffic management technique that regulates the number of voice calls handled by the network. It prevents oversubscribed resources from impairing voice quality. CAC is usually employed where resource contention might occur – at the PBX, across a wide area network (WAN) link or in an AP. TSPEC describes traffic streams in terms of their data rate, packet size, delay requirements and service interval needs. Stations using TSPEC submit parameterized reservation requests to an AP, which then assigns them transmit opportunities, effectively scheduling access to the AP. If an AP cannot, for example, accept a call due to loading, the client can try another AP. Be secure and resilient Security is always a top concern when deploying a WLAN, but consider the implications of adding VoIP to your wireless infrastructure. Viruses and worms are being unleashed against cell phones, so VoIP-specific attacks cannot be far behind. Phones are also subject to network-based attacks, service theft, replay attacks and eavesdropping. VoWLAN security originally consisted of simple MAC authentication and encryption implemented as WEP (Wired Equivalent Privacy) with pre-shared keys. Because of WEP’s vulnerabilities, the Temporal Key Integrity Protocol (TKIP) was introduced as an intermediate fix while the 802.11i standard was developed. The WiFi Alliance specified TKIP as WiFi Protected Access (WPA). Although WPA is better than WEP, it is not considered best practice, even though it may be the best option for legacy handset support. In the future, all wireless voice conversations will be authenticated and encrypted using standards defined by IEEE 802.11i and WPA2, the companion specification from the WiFi Alliance. 802.11i/WPA2 is a vast improvement over the original 802.11 standard for WEP encryption. 802.11i/WPA2 uses the Advanced Encryption Standard (AES), which is not susceptible to known attacks. WLAN systems need to handle the demands of voice roaming. Voice roaming is potentially incompatible with 802.11i, since when users traverse a network, they negotiate new encryption keys at each AP they encounter. If this does not happen quickly, voice quality is adversely affected. The 802.11i specification on fast roaming is designed to solve this problem. Voice greatly increases the importance of the WLAN and intensifies the need to protect it. This means introducing facility-wide intrusion prevention capabilities that include: • Detection of rogue devices with the option to disable them remotely; • Location of unauthorized devices; • Detection of wireless denial-of-service attacks and RF jamming; • Detection of security attacks such as spoofed devices and man-in-the-middle; • Detection of unauthorized network monitoring activity; • Remote packet capture anywhere in the network. The power of strong industry partnerships The improved productivity that results from mobility and anywhere/anytime connectivity has motivated many organizations to install WLANs. A new generation of dual-mode phones substantially extends that value proposition. Dual-mode phones will reduce toll charges by substituting the enterprise WLAN for carrier-owned cellular infrastructures to support voice calls on premise. Control over coverage, capacity and other factors that impact call volume and quality will also shift from the cellular provider to enterprise IT. A single handset, phone number and voice mailbox for employees reduces infrastructure and management costs. Delivering on the promise of dual-mode technology will require partnerships among key industry players. Many requisite features are embedded in handsets and require integration with APs to deliver uninterrupted voice connectivity with full mobility and to support capabilities like advanced power management. Up to the challenge? With the move to VoIP (voice over Wireless LAN) are poised for rapid growth. Standards-based QoS, traffic management and fast-roaming features ensure VoWLAN quality with full mobility. A full range of security capabilities protects the corporate network, wireless data in transit, and the airwaves that carry the data. Infrastructure resiliency ensures high availability and maintains user satisfaction. Scalable, centralized network management covers the full lifecycle to minimize operational expenses.

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