1. WHITE PAPERPreparing your WLANinfrastructure for voice
2. IntroductionAdding mobility to enterprise voice communications can be the key to unlockingbusiness productivity and responsiveness. Whether addressing productionproblems, planning promotions or responding to customer requests, enterprisesrequire that associates be able to move about freely and still be accessible at amoments notice. Those communications links must extend from the office tothe shop floor and out to the loading dock.The Webtorials 2008 State of the WLAN Report indicates that 36% of enterprisewireless LANs support voice today, and an additional 33% plan to add itwithin the next 12 months. Organizations of all types are using their wirelessLANs to support mobile workers with both connection-based and push-to-talkvoice services in a wide range of applications. From healthcare to retail andwarehouse management, users are discovering the benefits of cost-effectivecontinuous access. However, that flexibility and responsiveness will depend onhaving a reliable mobile network that allows employees to remain productivewhile they move through their daily activities.A sound and reliable wireless infrastructure is needed to ensure the qualityand availability of a mobile voice service. At the outset, it is imperative that thenetworking group recognize the requirements of a WLAN voice network, assessthe capabilities of their existing infrastructure and take the necessary steps tobring the network capacity and coverage up to the levels needed to supportenterprise-quality voice services. Mobility will not lead to improved productivityif the network is unreliable or unable to provide good voice quality.
3. Defining requirements Getting your wired networkfor WLAN voice ready for WLAN voiceThe first step in a voice over WLAN (VoWLAN) The backbone for your WLAN voice service willproject will be to develop a definition of service you be the wired LAN. Whether your wired voicelook to provide, and that starts with an adequate system is based on an IP PBX, a traditionaldefinition of requirements. The first step is to TDM model or a hybrid configuration, you willspecify the number of users to be served, the type have to interconnect calls between the wiredof voice service you will provide (i.e., traditional and wireless systems. Further, if you will bevoice calling or push-to-talk), the areas where the supporting push-to-talk (PTT) devices, theyservice will be available and the expected traffic should be able to interconnect to any other PTTvolumes. Having a handle on traffic volumes and systems or services you already have in place.usage patterns will not only help in planning yourinfrastructure requirements, it will also be key in The requirements for the wired network intercon-determining other parameters such as battery nection will vary based on the nature of therequirements. wired telephone system and the signaling that is used on the wireless LAN voice devices. AsIn contrast to data users who typically operate shown in Figure 1, if the wireless LAN handsetsfrom a stationary location, voice users are highly use a signaling protocol that is compatible withmobile, so it will be difficult to predict accurately the telephony server on the wired IP PBX, youwhere they will be when they need to make or should be able to pass calls directly throughreceive calls. That means you will also require a to the wired LAN. On the other hand, if yousound network management system that allows are using a TDM PBX or a WLAN handset thatyou to identify capacity and coverage problems, employs a proprietary signaling system, you willand plan for expansion. Further, mobility is highly require a gateway between the wireless LANappealing, and as other employees see that the devices and the wired PBX. In the longer term itservice is available, you can anticipate more is expected that all voice services will migrate torequests, more mobile handsets and hence more IP technology and the Session Initiation ProtocolWLAN voice traffic. (SIP) will be adopted as the signaling standard, which should greatly ease the integration ofIn defining your requirements it will also be wired and wireless users.important to categorize the various types of usersto be supported (e.g., general office, tech support, If you are using an IP PBX or a hybridsecurity, production, etc.), the criticality of their configuration that supports LAN-connected IP/communications (e.g., general business calls Ethernet handsets, there are several features andversus security or emergency services) and the configurations that are universally recommendedtypes of handsets or other mobile voice-enabled for the wired LAN infrastructure. Those woulddevices they will be using. Classifying users can include:help to quantify the volume and location of callingand will also be useful in predicting the amount A fully-switched LAN configurationof traffic additional users of that type will likely (i.e., no hubs)generate. Finally, you should identify the types Use of 802.1p QoS for prioritizing voiceand models of the WLAN voice devices you will frames over the LANsupport, and the systems for maintaining them. Power over Ethernet (PoE) to power wiredNew WLAN voice devices are introduced regularly, IP handsets and WLAN access pointsso you should define the procedure by which All voice devices should be configured on anew devices are tested before they are added to separate virtual LAN (VLAN) for improvedthat list. security capabilities3 WHITE PAPER: Preparing your WLAN infrastructure for voice
4. Figure 1: If the wireless LAN handsets use a signaling protocol that is compatible with the telephony server on the wired IP PBX, youshould be able to pass calls directly through to the wired LAN. On the other hand, if you are using a TDM PBX or a WLAN handset thatemploys a proprietary signaling system, you will require a gateway between the wireless LAN devices and the wired PBX.These features must be coordinated with the 54 Mbps 802.1a or g radio links require a 100 MbpsWLAN voice implementation. The WLAN is a connection to the wired LAN. If you plan to upgradeshared media configuration, but the use of a fully- to 802.11n, the access points will require 1 Gbpsswitched wired infrastructure will minimize wired connections. WLAN voice handsets supportingthe delay for delivery of voice frames over the 802.11n are not likely to appear for the next fewwired network. The 802.1p QoS standard is years, but n-capable access points might still beimportant to minimize delay in forwarding voice used to provide higher capacity data services, soframes, and that implementation will have to be choosing a vendor with a strong 802.11n portfoliocoordinated with the WLANs 802.11e QoS; those will be key.issues will be described later. To associate WLANvoice devices with the voice VLAN in the wired Finally, the network management capabilities ofnetwork, you will have to define separate wireless the wired LAN network should be investigated withVLANs with different network names (i.e., SSIDs) regard to their ability to provide information that willfor the voice and data traffic. Those wireless voice be useful in supporting voice applications.and data users may be sharing the same WLANchannel, but each group can still be associatedwith the appropriate wired VLAN. The WLAN infrastructure The basic requirement for a WLAN infrastructure toThe WLAN access points will be connected over support voice is dense, pervasive coverage. Densitythe wired infrastructure. For that, it is important refers to the signal strength and pervasivenessthat the LAN switches be capable of supporting refers to the coverage. Signal strength impacts thethe required number of IEEE 802.3af Power over transmission rate users receive on the networkEthernet (PoE) ports. Both wireless LAN access and hence the number of simultaneous calls thatpoints and wired IP voice handsets use PoE, so if can be supported on an access point. The generallyyou are using or planning to migrate to an IP PBX, accepted design parameter is a received signalyou will want to ensure there is sufficient PoE strength floor of -67 dBm, though better designedcap