Wireless Home Networking - Index of

Chapter 13: Using Your Wireless Network for Phone Calls
And, of course, there are services that aren’t just instant messaging services
(such as AOL IM) but are explicitly built around the concept of providing
individuals with VoIP calling capabilities. Skype (www.skype.com), for example,
offers both computer-to-computer and computer-to-phone calling, and
companies such as Vonage (www.vonage.com) incorporate special hardware
in your home that lets you plug regular phones (wired or cordless) into your
broadband connection for making VoIP calls.
Understanding VoIP terminology
Like any self-respecting Internet technology, VoIP is laden with acronyms and
jargon. Heck, even the name (VoIP) is an acronym! For the most part, you don’t
need to understand all these acronyms, but you may run across them as you
shop for VoIP equipment for your wireless network (or just plain old wired
VoIP equipment). So here are a few we think you should know:
� SIP: SIP, or Session Initiation Protocol, is the predominant signaling and
control mechanism for VoIP calls. SIP is a standardized way for Internet
clients (such as VoIP phones and networks) to create a session (or call)
and to control that call (for example, to hang up). The other signaling and
control mechanism for VoIP phone calls is called H.323.
Some VoIP systems, such as Skype, use their own proprietary protocols
to control VoIP calls.
� RTP: RTP, or Real-time Transport Protocol, is the underlying IP protocol
used for carrying voice calls over IP networks. RTP is used with another
protocol called RTCP (Real-time Transport Control Protocol) to provide
Quality of Service (QoS) support to help prioritize real-time applications
(such as voice calls) over other traffic on the network which isn’t time
or delay sensitive (such as e-mail).
� Codec: VoIP calls digitize and compress the analog signal created by the
microphone in your phone. The specific encoder/decoder used to do
this is known as the codec. The amount (and type) of compression used
in a VoIP codec affects the sound quality of the call — many VoIP systems
use codecs that offer a higher quality of sound than the analog phone
calls you’re used to!
� Telephone adapter: Most VoIP implementations use standard analog
POTS telephones. The device that sits between these phones and the
broadband Internet connection is known as a telephone adapter (or
sometimes an analog telephone adapter, or ATA). The telephone adapter
digitizes the analog phone signal and handles the SIP (or other protocol)
signaling.
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