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 …
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
DEBRA LITTLEJOHN SHINDER is a technology consultant, trainer and writer who has authored a number of books on computer operating systems, networking, and security. These include Scene of the Cybercrime: Computer Forensics Handbook, published by Syngress, and Computer Networking Essentials, published by Cisco Press. She is co-author, with her husband, Dr. Thomas Shinder, of Troubleshooting Windows 2000 TCP/IP and the best-selling Configuring ISA Server 2000, ISA Server and Beyond and Configuring ISA Server 2004. \ \ Deb is also a tech editor, developmental editor and writer to over twenty additional books on subjects such as the Windows 2000 and Windows 2003 MCSE exams, CompTIA Security+ exam and TruSecure?s ICSA certification. She formerly edited the Brainbuzz A+ Hardware News and currently edits Sunbelt Software?s WinXP News (www.winxpnews.com) and Element K's Inside Windows Server Security journal. Her articles are regularly published on TechRepublic?s TechProGuild site and Windowsecurity.com, and have appeared in print magazines such as Windows IT Pro (Windows & .NET) Magazine. She has authored training material, corporate whitepapers, marketing material, and product documentation for Microsoft Corporation, GFI Software, Hewlett-Packard, DigitalThink, Sunbelt Software, CNET and other technology companies. \ \ Deb currently specializes in security issues and Microsoft products; she has been an MCSE since 1998 and has been awarded Microsoft?s Most Valuable Professional (MVP) status in Windows Server Security. A former police officer and police academy instructor, she lives and works in the Dallas-Ft Worth area and teaches computer networking and security and occasional criminal justice courses at Eastfield College in Mesquite, TX.
