This information is also available as a PDF download.
Voice over IP (VoIP) can provide substantial savings on your telephone service by allowing you to use an IP network to make phone calls instead of the traditional telephone companies' public switched telephone network (PSTN). Many organizations today run IP networks over wireless technology, and it's possible to run VoIP applications over Wi-Fi, too. But you need to be aware of a number of issues when planning a VoIP over wireless (often called VoW, VoFi, or wVoIP) deployment.
With the advent of WiMAX for longer range Wi-Fi communications, wireless phone companies (cellular carriers) are gearing up to offer hybrid phones that will use VoIP over Wi-Fi when a Wi-Fi network is available and switch to cellular when one is not. So VoIP over wireless encompasses different things, depending on the context.
Here are some things you need to know about wVoIP.
#1: Wireless VoIP offers advantages over cellular service
A big advantage of wireless VoIP is that IP phones that work on Wi-Fi networks can be used in place of cell phones in many cases. Public 802.11 hotspots are often free or available at a low daily cost. If you're connecting to the Wi-Fi network anyway for Web and e-mail access, there's no additional cost to make VoIP calls other than the cost of your VoIP service, which is usually far less than the cost of cell phone service and may offer free unlimited international calling, something you don't get with most cellular plans.
#2: VoIP over wireless LAN has many uses
VoIP over a wireless LAN can provide easy internal calling for corporations, educational campuses, hospitals, hotels, government buildings, and multiple-tenant units such as dorms, with the ability to roam freely and advanced calling features such as voicemail and caller ID. Users can also use the LAN's Internet connection and an account with a VoIP provider to make calls outside the site, including domestic long distance and international calls, often at no extra charge.
#3: WiMAX extends the reach of VoIP
WiMAX is a long range microwave-based wireless technology based on the 802.16 standards. It can provide wireless broadband coverage to an entire metropolitan area or a large rural area, since WiMAX transmissions can span up to 75 kilometers (46 miles). With theoretical throughputs of up to 288 Mbps and practical throughput up to 70 Mbps, WiMAX has the bandwidth to support VoIP.
#4: Voice transmission is more sensitive than data transmission
VoIP is a real-time application, making it particularly sensitive to packet loss that can be caused in a wireless network by weak signals, range limitations, and interference from other devices that use the same frequency. To support VoIP, your wireless network must be reliable because users expect more dependability from their phone systems than from their computers. They expect a dial tone every time, no dropped calls, and high voice quality.
#5: Mixing VoIP and data can degrade call quality
Because of the sensitivity of VoIP applications to any disruption or delay, competing with data transmissions on the same wireless network can cause degradation of voice quality. It's important to implement quality of service (QoS) features to ensure that VoIP packets get priority.
#6: Security is a bigger concern over wireless
Security is already a major concern for VoIP, as sending telephone calls over a public IP network presents more security risks than using the proprietary "closed" networks of the telcos. Wireless adds another layer of security concerns, with transmissions going over the airwaves instead of cables and thus subject to easier interception. Common VoIP protocols such as SIP have their own security vulnerabilities.
Any Wi-Fi network that will carry VoIP traffic must be secured, and such traffic should always be protected by authentication and encryption.
On the other hand, many of today's telephone calls already travel over the airwaves, on cellular phones.
#7: Older wireless LAN equipment isn't ready for VoIP
If your plan is to roll out VoIP over your existing data Wi-Fi network, you may be in for a disappointment. For good performance, especially in the enterprise space, you need wireless LAN hardware and software specifically designed to work with voice traffic and address the prioritization and security issues.
Look for integrated support for SIP and policy-based management that allows you to block unauthorized voice traffic.
#8: Wireless VoIP equipment is available at consumer and enterprise levels
Many popular vendors of consumer-level networking equipment (LinkSys, D-Link, Netgear) now make IP phones that work with their wireless routers. For example, D-Link's DPH-540 IP phone supports all SIP-based VoIP providers and works with 802.11b or g Wi-Fi networks. It supports WEP, WPA, and WPA2 encryption.
At the same time, vendors of enterprise-level hardware, such as Cisco, are offering IP phones that work with IP PBX systems. For example, Cisco's Unified Wireless IP phone 7920 works with the Cisco Unified Communications Manager and supports EAP-FAST authentication for increased security.
#9: VoIP over wireless smart phones can save companies money
Today, many business people carry smart phones or handheld computer phones that run the Windows Mobile operating system, such as the Samsung i730 and Treo. These phones are provided by cell phone carriers, and using the telephone capability costs precious minutes. International calls call extra.
However, by installing Skype for Mobile on these devices, users can make free or very low cost phone calls while bypassing the cellular plan and using the phone's Internet connection or in the case of Wi-Fi enabled devices, like the Samsung, using a wireless hotspot.
#10: Future phones will combine cellular and Wi-Fi VoIP
Industry pundits predict that the next generation of cell phones will all include built-in Wi-Fi. With these hybrid or dual-mode phones, you'll be able to seamlessly switch between cellular and VoIP over Wi-Fi when you come into range of a Wi-Fi hotspot, even within the same phone call.
Landlines are expected to all but disappear as the hybrid phones become a single solution for telephony, operating off the user's Wi-Fi network at home and using cellular technology when there is no Wi-Fi network within range. This is predicted to lower the total cost of telephone service.