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Feature Article
March 2004

Six Steps To Deploying A Successful Wi-Fi Telephony Network


Wi-Fi Networks are becoming increasingly popular in today�s enterprises in fact, a recent NOP study shows that mid-size and large companies have rolled Wi-Fi to almost a quarter of their users and predict 50 percent of their users will have Wi-Fi access in the next two years.

As companies look to maximize WLAN ROI, the overlaying of enhanced IP services such as IP telephony is also taking hold. The logic being, extend the costs savings of traditional wired IP telephony to the new wireless infrastructure.
Wi-Fi telephony is an umbrella term that describes various methods of IP telephony over wireless networks. It also goes by many names such as Voice over WiFi (VoWiFi) Voice over Wireless LAN (VoWLAN) and even Wireless voice over IP (WVoIP). Nonetheless they all describe the same technology. These range from dedicated Wi-Fi handset such as Spectralink�s NetLink, or Cisco�s 7920 IP Phone, to softphone software for laptops and pocket PCs with Wi-Fi connections such as, Xten�s X-Pro, Cisco�s IP softphone, and Polypix�s Netphone PDA.
Most organizations with a mobile workforce can reap huge productivity gains when outfitting their users with one handheld device (handset or PDA) to carry, which can also double as a network access terminal. For example, hospitals that deployed Wi-Fi telephony, not only created a unified telephony and messaging system but, have given their staff the ability to receive critical patient data right to their handsets. Next to user mobility, the strongest argument for Wi-Fi telephony as compared to its wired counterpart is the ability to take all the same mini-Web browsing and application access that can come with wired telephony to anywhere in your organization.
As with any new service rollout, proper planning will pay off generously during implementation.
Organizations should take a logical and structured approach to Wi-Fi telephony deployment; their goal should be a reliable and secure service with satisfied users. The following steps will put your organization on track to successful Wi-Fi telephony deployment.

� Step 1. Research your needs.
� Step 2. Know your network.
� Step 3. Choose your solution.
� Step 4. Pilot rollout.
� Step 5. Service rollout.
� Step 6. Document your work.

Research Your Needs
When approaching a Wi-Fi telephony rollout, knowing your organization needs will make choosing a solution much easier. Ask yourself questions such as: How many users will require Wi-Fi telephony? Where will the users be while accessing the Wi-Fi telephony network? What other services or applications would you like to integrate with Wi-Fi telephony access device? The answers to these questions should come from your IT Staff/Management and your prospective users.

Know Your Network
A properly documented network allows for easier decisions to be made regarding the addition of new services. However with IT staff being forced to do more with less, the resources to properly document your network may not exist. The first consideration for planning your Wi-Fi telephony service is what IP telephony infrastructure does your organization use? Each vendor offers a different solution that has its challenges and benefits whether you are using an Avaya Definity Sever, Alcatel�s Omni PCX, or a Cisco Call Manager.
Since Wi-Fi telephony shares the same network performance requirements as traditional wired IP telephony, it is just as susceptible to packet loss and delay. Before deploying any additional services you should have a proper baseline of your Wi-Fi and wired network utilization patterns, hourly, daily, and weekly. Using tools such as WildPackets Airo Peek NX or TamoSoft�s Commview for WiFi will give you better picture of your channel and bandwidth utilization (both have useable demos you can try). You will also want to look at your network�s geographic coverage; does your Wi-Fi network�s usable range cover all the areas needed for the Wi-Fi telephony deployment? Do dead zones exist in areas your mobile telephony users need to be? Think about E-911 locating services; for instance Cisco recommends trying to limit any access point�s coverage to a single floor. This will help keep your Wi-Fi telephony device from attaching to access points on other floors and reduce confusion for emergency personal.
Understanding your network also means knowing what QoS policies you network supports. Too often planners forget that the Wi-Fi network is an extension of the wired network. Prior to rolling out Wi-Fi telephony, your company�s wired QoS policy should be optimized for voice and critical data. In terms of your network�s access points, firmware upgrades may be required to get newer functionality and interoperability required for IP telephony. Knowing your network is complete when you have a map of your office space with an overlay of your Wi-Fi network, including access points and RF coverage with charts and graphs detailing utilization patterns over time and a firm understanding of your working QoS policy.

Choose Your Solution
One of the biggest factors in deciding which solution to deploy is your current IP telephony infrastructure. Your Wi-Fi deployment is an extension of your existing IP telephony and Wi-Fi infrastructure. Keep in mind interoperability and upgradeability; choose a solution that leverages the investment your company has already made. If your organization has not deployed any IP telephony infrastructure, you should choose a vendor that has a product portfolio to suit your organizations needs and leverages existing skill sets.
Wi-Fi telephony is a relatively new variation of Wi-Fi technology, and it builds on the 802.11a/b/g standards and comes complete with their limitations. The upcoming 802.11e standard (expected sometime in 2004) will add QoS to wireless networks and address problems associated with packet loss and prioritization. The upcoming 802.11i will add increased security and move from WEP to WPA.
Citing a lack of approved standards most Wi-Fi telephony vendors have created their own solutions for the traditional IP telephony challenges such as QoS. Spectralink�s NetLink utilizes a proprietary QoS network appliance for both upstream (towards the AP) and downstream (towards the Wi-Fi Telephony device) QoS called the NetLink SVP server. SVP supported by numerous AP Vendors such as Avaya, Cisco, Enterasys, Proxim, and Symbol. SVP specifies a back-off time of 0 for any packet identified as voice. If a contention occurs the voice packet will always get retransmitted because the data packet will have a back-off value higher than 0.
The Cisco 7920 utilizes separate mechanisms for controlling upstream and downstream QoS. For upstream it uses a shorter random back-off time than data traffic in the event of a collision, and downstream CDP (Cisco Discovery Protocol) is used to identify voice devices so that AP with release 12.0+ will route traffic to them into a higher priority queue than the voice. Cisco Wi-Fi telephony deployments also encourage the use of wireless VLANs with different SSIDs to separate voice and data traffic. (See Table 1 for comparison.)

Pilot Rollout
Here is where your solution will encounter its first real test. User feedback is the most valuable commodity when deploying your new services. During the pilot you have an opportunity to experiment with your solution while still in a relatively controlled environment. The best results from a pilot group come from selecting the broadest range of potential users. Try to include some representation from all groups who will use the new Wi-Fi telephony service. Set up a formal method of collecting their feedback with specific criteria to be evaluated, and encourage any improvement suggestions they may have. Ask them about audio quality, use of advanced features such conference calling, call hold, and call transfer. Have them try the phone in all possible places they may use the services. Monitor the network utilization and log the effects of your users Wi-Fi telephony usage. A smooth pilot rollout will greatly improve your chances of smooth service deployment increases productivity from user�s acceptance.

Service Rollout
Your service rollout should be carried out with a logical and structured approach. Deploy the service in physical or logical based units. For instance, if your company occupies four floors of an office building, try to do one floor at a time, or if you have an administrative office and large factory, try to deploy to one logical group at a time. Depending on your time requirements and rollout resources you may opt for a more aggressive schedule. With Wi-Fi telephony you have the luxury of not having to cut over the service right away. Depending on your overall plan and goals, users may get to keep their legacy wired/wireless phone or IP phones for a short period time or permanently after the deployment. Always go back after each �mini� deployment and look for faults and ways to improve your process.

Document Your Work
Documentation of your deployment is very important step, and should be carried out as a concurrent task during the rollout. Your documentation will help with troubleshooting and can be used as a metric to define your deployment�s success. Your documentation is a public notice of your team�s success and professionalism; many fantastic rollouts are not recognized as such due to a lack of final documentation.
The productivity gains and resource saved by offering a unified voice & data network are well documented. The introduction of Wi-Fi telephony is an opportunity for enterprises to extend those benefits and increase ROI on their Wi-Fi networks. Ultimately the Wi-Fi telephony device will become much more than a phone in the traditional sense, it will become a integrated tool enabling users to access company resources and applications wirelessly from anywhere in their office in real-time.

Lawrence Imeish is the founder of Imeix, a network consulting company specializing in VoIP planning and deployment. He has over 10 years experience with IP networks and holds a Cisco CCIE (#12000). For more information please visit www.Imeix.com.

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