The 802.11 standards make VoIP and IP telephony possible with nothing more than your laptop armed with a wireless interface card, perhaps a set of headphones, and IP telephony software from your VoIP provider. Theoretically, you can walk into any coffee shop or hotel that provides wireless Internet access and make a telephone call while you’re surfing the Web. There are many more scenarios for using wireless VoIP, but I think you get the picture.
The following sections provide an overview of some of the VoIP telephony devices you can use with a wireless network.
IP soft phones for pocket PCs
You already know that VoIP uses packets to transport phone calls from sender to receiver. Thus, any computer that uses IP protocols can theoretically connect to a VoIP network and make or receive telephone calls. This includes pocket PCs.
Many pocket PCs running the Windows operating system can connect to local area networks and exchange data. Provided the data rate for your pocket PC is high enough, you can use the device for your phone calls. The software used on the wireless pocket computer to make and receive phone calls is referred to as an IP soft phone for pocket PC. In most cases, the pocket PC can also operate as a cellular phone. This makes the device versatile in a mobile, wireless environment.
Wireless extension to cellular
When using a land line, the caller pays the regulated recurring per-minute charges involved with the call. The caller has to pay these charges whether the call is answered or goes into voice mail. Wireless extension to cellular (WEC) is a technique that enables an incoming call to ring at your hardwired telephone (land line) and your cell phone at the same time. It enables you to take the incoming call or send it to voice mail wherever you are at the time of the call. Plus, the call does not get billed to your cell phone plan. It is treated as an inbound call to your office number.
WEC requires the PRI transport service, as discussed in topic 5. The PRI transport line has proven to be a cost-effective way to support WEC because
it is directly compatible with the PSTN. The PRI line terminates on a PRI interface card, which is installed in the customer’s premise equipment, such as a PBX. (topic 11 provides more detail on PBX telephone systems.) When implementing WEC, all desk phones and cell phones must be digital, not analog.
The network administrator sets up each internal extension that has the WEC feature operating on it. Each WEC user has the ability to turn WEC on and off. WEC is not a feature that a company should give to every extension because the PRI has a limited number of channels. Typically WEC is given to critical personnel who need to be reached anywhere, anytime.
After the administrator sets up an extension to have WEC, he or she provides the user with an access code for enabling or disabling the WEC application via the desktop phone. Calls coming into the company’s telephone system ring at the internal desktop extension and simultaneously go out through the PRI to the PSTN. From there, they are switched to the wireless cellular network. The cell phone rings. All standard cellular phone features such as caller ID, call waiting, and voice mail are available. The cell phone is treated as a local extension of the in-house telephony system, even though the call is routed off-net through the PSTN and wireless CSIs.
