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Definition 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. 1 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. 2 An overview of how VoIP works Voice over Internet Protocol (VoIP) is a protocol optimized for the transmission of voice through the Internet or other packet switched networks. VoIP is often used abstractly to refer to the actual transmission of voice (rather than the protocol implementing it). VoIP is also known as IP Telephony, Internet telephony, Broadband telephony, Broadband Phone and Voice over Broadband. “VoIP” is pronounced voyp. Companies providing VoIP service are commonly referred to as providers, and protocols which are used to carry voice signals over the IP network are commonly referred to as Voice over IP or VoIP protocols. They may be viewed as commercial realizations of the experimental Network Voice Protocol (1973) invented for the ARPANET providers. Some cost savings are due to utilizing a single network to carry voice and data, especially where users have existing underutilized network capacity that can carry VoIP at no additional cost. VoIP to VoIP phone calls are sometimes free, while VoIP to public switched telephone networks, PSTN, may have a cost that is borne by the VoIP user. 3 Voice over IP protocols carry telephony signals as digital audio, typically reduced in data rate using speech data compression techniques, encapsulated in a data packet stream over IP. There are two types of PSTN to VoIP services: Direct Inward Dialing (DID) and access numbers. DID will connect the caller directly to the VoIP user while access numbers require the caller to input the extension number of the VoIP user. IP Phone An IP phone uses Voice over IP technologies allowing telephone calls to be made over the internet instead of the ordinary PSTN system. The phones use protocols such as Session Initiation Protocol, Skinny Client Control Protocol or one of various proprietary protocols such as that used by Skype. IP phones can be simple software-based Softphones or purpose-built hardware devices that appear much like an ordinary telephone or cordless phone or an ATA (analog telephony adapter) which allows to reuse ordinary PSTN phones. One of the primary motivations for implementing such a system is the lower calling cost. When calling other IP phones over the internet one only pays for the usually fixed cost internet bandwidth. It may have many features an analog doesn't support, such as e-mail-like IDs for contacts that may be easier to remember than names or phone numbers. Elements of an IP phone 1. Hardware 2. DNS client 3. STUN client 4. DHCP client (not commonly used) 5. Signalling stack (SIP, H323, Skinny, Skype, or others) 6. RTP stack 7. User interface Hardware of a stand alone IP phone 4 Hardware-based IP phone The overall hardware may look like telephone or mobile phone. An IP phone has the following hardware components. • Speaker/ear phone and microphone • Key pad / touch pad to enter phone number and text (not used for ATAs). • Display hardware to feedback user input and show caller-id/messages (not used for ATAs). • General purpose processor (GPP) to process application messages. • A voice engine or a Digital signal processor to process RTP messages. Some IC manufacturers provides GPP and DSP in single chip. • ADC and DAC converters: To convert voice to digital data and vice versa. • Ethernet or wireless network hardware to send and receive messages on data network. • Power source might be a battery or DC source. Some IP phones receive electricity from Power over ethernet. Other devices There are several WiFi enabled mobile phones and PDAs that come pre-loaded with SIP clients or are at least capable of running IP telephony clients. Some IP phones may also support PSTN phone lines directly. Analog telephony adapters These are usually rectangular boxes that are connected to the internet or Local area network using an Ethernet port and have sockets to connect one or more PSTN phones. Such devices are sent out to 5 customers who sign up with various commercial VoIP providers allowing them to continue using their existing PSTN based telephones. Another type of gateway device acts as a simple GSM base station and regular mobile phones can connect to this and make VoIP calls. While a license is required to run one of these in most countries these can be useful on ships or remote areas where a low-powered gateway transmitting on unused frequencies is likely to go unnoticed. Common features of IP phones Caller ID • Dialing using name/ID: This is different from dialing from your mobile call register as user need not to save a number to sip phone. • Locally stored and network-based directories • Conference and multiparty call • Call park • Call transfer and call hold • Preserving user name/ number when choosing a different service provider (not widely supported). • Applications like weather report, Attendance in school and offices, Live news etc. Disadvantages of IP phones • Requires internet access to make calls outside the Local area network unless a compatible local PBX is available to handle calls to and from outside lines. • Non-PoE IP Phones and the routers they connect through need to have their own power supply unlike PSTN phones which are supplied with power from the telephone exchange. • IP networks are often more prone to outages and congestion than analogue phone networks. 6 Contents • 1 History • 2 Functionality • 3 Implementation o 3.1 Reliability o 3.2 Quality of service o 3.3 Difficulty with sending faxes o 3.4 Emergency calls o 3.5 Integration into global telephone number system o 3.6 Single point of calling o 3.8 Security o 3.9 Pre-Paid Phone Cards o 3.10 Caller ID o 3.11 VoIM • 4 Adoption o 4.1 Mass-market telephony o 4.2 Corporate and telco use o 4.3 Use in Amateur Radio o 4.4 Click to call • 5 Legal issues in different countries o 5.1 IP telephony in Japan .
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