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IP Telephony
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IP Telephony

If you've never heard of Internet Telephony, get ready to change the way you think about long-distance phone calls. Internet Telephony, or Voice over Internet Protocol, is a method for taking analog audio signals, like the kind you hear when you talk on the phone, and turning them into digital data that can be transmitted over the Internet.
How is this useful? Internet Telephony can turn a standard Internet connection into a way to place free phone calls. The practical upshot of this is that by using some of the free Internet Telephony software that is available to make Internet phone calls, you are bypassing the phone company (and its charges) entirely.

Internet Telephony is a revolutionary technology that has the potential to completely rework the world's phone systems. Internet Telephony providers like Vonage have already been around for a little while and are growing steadily. Major carriers like AT&T are already setting up Internet Telephony calling plans in several markets around the United States, and the FCC is looking seriously at the potential ramifications of Internet Telephony service.
Above all else, Internet Telephony is basically a clever "reinvention of the wheel." In this article, we'll explore the principles behind Internet Telephony, its applications and the potential of this emerging technology, which will more than likely one day replace the traditional phone system entirely.

The interesting thing about Internet Telephony is that there is not just one way to place a call.

There are three different "flavors" of Internet Telephony service in common use today:
ATA - The simplest and most common way is through the use of a device called an ATA (analog telephone adaptor). The ATA allows you to connect a standard phone to your computer or your Internet connection for use with Internet Telephony.

The ATA is an analog-to-digital converter. It takes the analog signal from your traditional phone and converts it into digital data for transmission over the Internet. Providers like Vonage and AT&T CallVantage are bundling ATAs free with their service. You simply crack the ATA out of the box, plug the cable from your phone that would normally go in the wall socket into the ATA, and you're ready to make Internet Telephony calls. Some ATAs may ship with additional software that is loaded onto the host computer to configure it; but in any case, it is a very straightforward setup.

IP Phones - These specialized phones look just like normal phones with a handset, cradle and buttons. But instead of having the standard RJ-11 phone connectors, IP phones have an RJ-45 Ethernet connector. IP phones connect directly to your router and have all the hardware and software necessary right onboard to handle the IP call. Wi-Fi phones allow subscribing callers to make Internet Telephony calls from any Wi-Fi hot spot.

Computer-to-computer - This is certainly the easiest way to use Internet Telephony. You don't even have to pay for long-distance calls. There are several companies offering free or very low-cost software that you can use for this type of Internet Telephony. All you need is the software, a microphone, speakers, a sound card and an Internet connection, preferably a fast one like you would get through a cable or DSL modem. Except for your normal monthly ISP fee, there is usually no charge for computer-to-computer calls, no matter the distance.

If you're interested in trying Internet Telephony, then you should check out some of the free Internet Telephony software available on the Internet. You should be able to download and set it up in about three to five minutes. Get a friend to download the software, too, and you can start tinkering with Internet Telephony to get a feel for how it works.
Post: #2
please read for IP Telephony seminars report and presentation
Post: #3
can u give me a complete doc presentation of IP Technogy

Post: #4
for more details on IP Telephony , please go through the following thread.
Post: #5

• IP Telephony refers to the transfer of voice over the Internet Protocol (IP) of the TCP/IP protocol suite
• Using IP Telephony we can enhance the traditional PBX (Public Branch Exchange) by combining voice and data services onto a single network.
• Development of this 'IP Telephone' will require the development of a 'system on a chip' which combines digital signal processing (DSP) functions, microcontroller (MCU) functions, analog interface, telephone user interface, network interface
• VocalTec introduced the first IP telephony software product in early 1995. Running a multimedia PC, the VocalTec Internet Phone (and the numerous similar products introduced since) lets users speak into their microphone and listen via their speakers.
• In March of 1996, VocalTec announced it was working with Dialogic Corporation (Intel acquired Dialogic in 1999) to produce the first IP telephony gateway. The original Internet telephone products based on multimedia PCs are tremendous - offering the ability to combine voice and data on one network
 How IP Telephony works?
 Benefits of IP Telephony
 Cost Reduction
 Simplification
 Consolidation
 Advance applications
 Major problems in this operation
 Converting telephone numbers to IP address and vice-versa.
 Compressing and Packetizing Stream of audio and then transmitting.
 Maintaining quality of service.
 Real time transmission of voice with no delay
 H.323 Standard
 The internetworking of telephone service that spans the Internet and the telephone network is addressed by the introduction of gateways as provided by H.323
 Recommendation H.323 consists of a set of standards to provide support for real-time multimedia communications on LAN’s and packet networks
 Gatekeepers
 Gatekeepers perform name-to-address translation and they direct calls to appropriate gateways when necessary. The gatekeepers are responsible for call control for calls within an H.323 network. Gatekeepers grant permission or deny requests for connections. They manage the bandwidth that can be used by calls.
Multipoint control unit
It synchronizes incoming audio streams and video streams and transmits the resulting stream.
Standards around H.323
 H.225 specifies the call control procedures that are used for setting up H.323 calls in the H.323 network.
 H.245 control channel is a reliable channel that carries the control messages to set up logical channels including the exchange of transmits and receives capabilities.
 H.323 terminals are required to support the G.711 voice standard for log-PCM voice compression.
Working of IP Telephony
There can be 4 types of IP telephony calls possible.
Computer to Computer
 Computer to Phone
 Phone to Computer
 Phone to Phone
 Traditional telephones are simple in their design and working where as IP telephones are complex in their design and have their own processing capability.
 Traditional phones are meant for converting incoming electrical signal into sound. But there exists a great processing power in IP telephone.
 Traditional phones connect to PSTN (public switched telephone network) through PBX where as IP Telephones connect to Internet (Packet switched network) via the Ethernet LAN.
 Traditional Telephones get power from PBX where as power should be provided to IP Telephone externally.
 Architecture
User Interface
The User Interface provides the traditional user interface functions of a telephone. At a minimum, this consists of a keypad for dialing numbers (0-9, *, #) and an audible indicator for announcing incoming calls to the user.
Voice Interface
The Voice Interface provides the conversion of analog voice into digital samples. Speech signals from the microphone are sampled at a rate of 8 KHz to create a digitized 64kbps data stream to the processor
Network Interface
The Network Interface allows transmission and reception of voice packets from/to the telephone
Processor Core
The Processor Core performs the voice processing, call processing, protocol processing, and network management software functions of the telephone
 Lower latency due to an embedded system implementation.
 Familiar user paradigm of using a phone vs. a "PC-enabled phone“
 Greater reliability
 Lower station cost where a PC is not required, e.g., conference room, production floor, etc.
 It allows centralized, bulk administration and quick access reporting tools, to exciting new applications that improve user productivity
 A browser-based interface allows users to set up personalized rules for forwarding and screening calls in advance or in real time. Calls can be forwarded to user-defined locations such as home, office, or mobile phones.
 In addition, the Cisco Unity™ Unified Communications Server manages e-mail, voice mail, and faxes through a single inbox, allowing users to access all messages from their IP phone, cellular phone, or PC
IP telephony provides a means for transmitting voice, video and data on same line enhancing the reliability and reducing the cost. This combined transmission enables vast, robust and effective applications to be developed.

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