Today, as a result of new technological advances, audio, can be transferred across the Internet, and it is this ability which has lead to Internet telephony, or the transfer of voice over Internet protocol (IP) networks, instead of over public switched telephone networks (PSTN). In a basic form, the gateway, a combination of hardware and software that is the key to Voice-over-IP (VoIP), coverts a standard telephone signal to a digital form (if not already digitized), compresses and translates it into IP packets, and sends it to a destination where the process is reversed. Internet telephony utilizes the Internet medium to transfer audio between two or more clients in real time, thus allowing the clients to converse as if they were all on telephones. Economically, IP telephony offers a low-cost long distance "telephone" service by bypassing international costs and even, in some instances, in-country charges.
This technology of transporting voice-over-IP networks will be the focus of this paper and presentation. The primary sub-topics will include a detailed explanation of the communication process from the Internet medium to home or business telephone and vice versa, various economic advantages and disadvantages of Internet telephony, a brief history of voice-over-IP’s origin, some of the technological aspects behind this, and a brief look into the future of Internet telephony.
A primary form of communication today lies within the international network of computer networks, which has evolved to be known as the Internet. Over this communication medium, technology has brought us the ability to transfer a variety of data types and messages from one person to another, the most familiar being email. Now, with new technological advances, audio, too, can be transferred across the Internet, and it is this ability, which has lead to Internet telephony, or the transfer of voice over Internet protocol (IP) networks, rather than over public switched telephone networks (PSTN). Through the utilization of the Internet medium to transfer audio between two or more clients in real time, Internet telephony has economically matured to attribute several advantages with its technology, primary the offering of low-cost long distance "telephone" service, but also still carries several disadvantages with it, only to be improved through future technological advancement.
The Internet telephony technology first became a reality in February, 1995 when VocalTec, Inc. first announced its Internet telephony software product, the VocalTec Internet Phone; an event that became the birthplace of this audio transfer technology which allows for conversation between users over the Internet (dialogic.com). Primitive in comparison with the available technologies today, this software was originally designed to operate on a PC with a 486/33-MHz processor or higher, where a user would be able to utilize the PC's modem, sound card, speakers and microphone to hold a conversation with another user by talking into the microphone and listening via the speakers. In the process of transfer, the software generally functioned by compressing a voice spoken into a microphone and translating this compressed voice into IP packets, the standard transmission form, for deployment across the Internet medium. With this technology, though, a conversation was limited to only two computer users and it was essential that both parties were using the Internet Phone software in order for all to work. Thus, as of this time, Internet telephony was limited to PC-to-PC connection, although PC-to-Phone and Phone-to-Phone connections were spawned about a year later in March of 1996.
During the beginning months of 1996, the same company who had first introduced the Internet telephony software, VocalTec, announced that it would be working with another company, Dialogic, to produce a piece of hardware, known as a gateway, that allows for PC-to-Phone and Phone-to-Phone connections by bridging the Public Switched Telephone Network (PSTN) with the Internet. It was the creation of this gateway that allowed for Internet telephony to become a success as the first technology that combined both the Internet and PSTN worlds. Before the creation of the gateway, several companies had worked and created various forms of Internet telephony software as solutions to place "telephone" calls over the Internet, but it was the functionality of the gateway that was essential to truly make Internet telephony work. The PSTN or network where telephone calls are transferred is a circuit-switched network where a direct single path route is created between the caller and callee and the network resources (e.g. link bandwidth) are allocated to each call for the duration of the call. Thus, no resource sharing occurs between separate calls and a resource piece is idle if it is not being used by its owning call. However, this telephone connection network is different from the Internet connection network in that the Internet connection network follows a packet-switching network scheme. With packet-switching, each data stream to be transferred over the Internet medium is divided into packets, or simply smaller portions of the entire data, where all users connected to the Internet share all of the networks resources, where each packet uses the full link bandwidth, and where the network resources are only used as needed. Thus, the evidence of the differences between these two networks caused a wide array of dilemma as to how to bridge the two very distinct and separate networks and it wasn't until the development of the gateway that this dilemma could be overcame.
The second primary obstacle the gateway overcame lay in the means of addressing, or accessing a user on a PC which could be located anywhere around the world. Prior to the deployment of the gateway, in order to access a remote PC, a user needed to know the PC's IP address, an address that is not easily obtainable if one has not had prior contact to the remote PC. However, the gateway overcame this problem by allowing a user to access a remote PC that was equipped with any gateway by only knowing the contactee's phone number. A phone number is a more easily obtainable piece of information than an IP address, thus the gateway's functionality now overcame two primary obstacles; network bridging and addressing.
The gateway's functionality, in a basic sense, works in the following way, as highlighted in Figure 1 and described below:
Upon receipt of a standard telephone voice signal, the gateway first digitizes the analog voice signal, compresses the new digital signal, packetizes the signal into the standard data transfer blocks of the Internet, known as IP packets, and moves the packets onto the Internet for transport to the destination gateway, where this gateway reverses the process.
With this gateway technology, it is possible to place three different types of calls using Internet telephony; PC-to-PC, PC-to-Phone, and Phone-to-Phone. In order to obtain a sense of how a call is placed using Internet telephony, Figure 2, as seen below, should provide a physical sense of how two parties are connected.
Using the above figure as a general display, the process of making a call using Internet telephony starts with the calling party wanting to contact the called party. Upon registering with a Voice Over IP (VOIP) service provider and obtaining the necessary software, the calling party connects to and provides the called party's telephone number to his/her Internet Service Provider (ISP), who provides the gateway to connect to the Internet. Using a microphone, the calling party then speaks into it and the voice signal is transferred to the gateway, where the digitization (if the signal is not already digital), compression, and packetization takes place, as described above. From here, the IP packets are transferred over the Internet, via a path determined by the ISP gateway, until they reach the destination gateway. This destination gateway converts the IP packets into a voice signal form and transfers the voice over the local PSTN of the called party. From here, the called party's phone will signal an incoming call and upon call establishment, the two parties can hold a full-duplex (two-way) conversation, as signals are transferred back and forth over the networks.
As the above example details a PC-to-Phone connection, data flow examples for both PC-to-PC connections and Phone-to-Phone connections can be easily derived from this example. With a PC-to-PC connection, one would only have to reverse the calling party's process of the above example up to where the data reaches the Internet to create a simulation of the called party reversal process, while, in a similar fashion, with a Phone-to-Phone connection, the called party's data flow would need to be reversed in the above example to create the calling party of the Phone-to-Phone connection.
As with most data transfer methods, such as via the PSTN, standards have been developed for Internet telephony to create a somewhat uniform operation method and for interoperability between the vast number of products that are available. For instance, companies such as Deltathree, Net2Phone, Netspeak Corp., and VocalTec Inc. offer different products and services relating to Internet telephony. To overcome the primary software interoperability problem that existed with VocalTec's Internet Phone, where a VOIP call could only be placed if both users were using this same software, standards were put in place so that one user, using one company's software, could contact another person, who might be using another company's software. Thus, with the H.323 standard and G.723 audio codec standard, users with different software products are able to communicate using Internet telephony. Now, keeping these PC standards in mind, as well as the PSTN standards, gateway producers are able to create a gateway product that adheres to these specified requirements. Below, Figure 3 highlights some of the major standards implemented on both sides of an Internet telephony gateway, in addition to displaying the sequence of a VOIP connection, as discussed earlier.
In addition to the standards that determine Internet telephony software and gateway development, in any connection that will be utilizing a PC, either PC-to-PC or PC-to-Phone connection, in order to run the Internet telephony software, the PC must also adhere to certain minimum system requirements. As VocalTec's original Internet Phone software only required a 486/33 MHz processor, today most software products require at least a minimum of a 166 MHz processor. In addition to this, speakers, a microphone, an Internet connection and a full-duplex sound card are needed. As a user's system specifications increase, so does the quality of the voice within the conversation. Traditional links to carry voice signals require approximately a 64KB/sec. connection to create a full quality conversation. However, as some users still connect with speeds under 56KB/sec., voice quality diminishes as connection speed decreases, but those users connecting via Digital Subscriber Line (DSL) or cable, to name two common examples, connection speeds far surpass that of 64KB/sec. and thus voice quality increases. Diminishing quality, though, even at these speeds may occur due to the shared resource network that Internet telephony runs over, as opposed to the non-shared resource connection the traditional PSTN runs over.
The use of Internet telephony as a means of placing a "telephone call" has two primary advantages which make this means appealing to users. The main advantage of Internet telephony is the reduction in cost of long distance phone calls. In this way, it makes it cheaper to "reach out and touch someone" all over the world. Using some of the free software, such as that of DialPad, makes the cost of long distance phone calls that of only the cost to connect to a local ISP. Thus, taking this path leads users to bypass per minute charges that usually come with making calls over the PSTN, and allows them to pay a flat monthly ISP rate. As one can easily see with this, is that the more long distance calls that are made in one month's time, the cheaper the per call and thus per minute rate comes out to be.
For companies, the use of Internet telephony also allows them to bypass the international and in-country long distances charges they normally incur with using the PSTN. The benefit to large companies is that even by using Internet Telephony Service Providers (ITSP) which require per minute or flat rate charges, the rates are lower than that of PSTN rates and thus the savings becomes great with the large volume of calls companies place. In addition, a company may need to purchase a gateway to bridge its PSTN with the Internet, and despite the current high costs of gateways, with technological advancement, the prices are sure to decrease, and aside from maintenance costs to the gateway, the purchase of a gateway is a one-time fee.
To highlight the per minute long distance call saving, within the continental 48-states of the US, the per minute long distance charge using MCI WorldComm is $0.06, while the VOIP company Deltathree charges a free rate within this calling area. In addition, a call from any of the 48 continental states of the US to Russia using MCI WorldComm is $0.35 per minute while the cost using Deltathree is $0.21 per minute (long-distance-phone-rates.com). As is evident by these two examples, the savings can become very large primarily for companies by using Internet telephony as a calling method.
Another primary advantage of Internet telephony is enhanced customer service. As many people today still use a modem to connect to the Internet, a great portion of these people also only have one phone line, thus one is not able to be online and on the phone at the same time. Thus, by being able to place a call and receive calls while online, a person does not need to worry about two or more phone lines or missed calls while online. The customer service is displayed by using the Federal Express Corporation as an example. FedEx makes use of NetSpeak's WebPhone to enhance package tracking. This allows customers with one phone line to speak with a FedEx representative while they are online. Thus, the customer is able to use the company's existing online package tracking system, while also being able to speak to a customer service representative if needed to answer questions without having to switch back and forth between the telephone and online.
The main disadvantage of using Internet telephony is seen within the sound quality of a conversation between users. Using the Internet medium as a transport for voice, such sound quality problems as dropouts, echoes, delay, and unwanted distortion can occur. As the Internet itself is a packet-switched network, as highlighted above, information that travels across it can take any number of paths to reach its destination. Thus, with congestion and flow problems that exist within the Internet, packet loss and delay can occur, which result in the voice quality problems mentioned above.
In addition to the Internet structure as a cause, Internet connection speeds also pose similar problems. As connection speeds increase, the possibilities for delay decrease, thus sound quality becomes better. However, with the decrease of Internet connection speeds, large delay can occur, resulting in a choppy conversation. When users want to speak with each other, as humans they expect to speak and listen in real time, or the seemly instantaneous amount of time to hear someone's voice if that person were right next to you, and thus the delay caused by slow connection speeds leads to frustration. Also, related to this, as mentioned an IP Telephony Basics document by the Dialogic Corp. "latency affects the pace of the conversation (and) humans can tolerate about 250 msec of latency before it has a noticeable affect. Today's IP telephony products exceed this latency, so most connections sound like traditional calls routed over a satellite circuit (which are usable, but require some getting used to)" (dialogic.com). Thus, as seen from the above statement, latency and delay still pose problems, but will continue to be improved with technology advancements in gateway development and Internet infrastructure.
Other disadvantages of Internet telephony include interoperability between products and security issues. As all companies recognize the H.323 standard, that defines technology of Voice over Internet applications, and adopt them for their Internet telephony products, the problem of interoperability will be eliminated. In terms of security, as with any data transfer over the Internet, security is an issue, and specifically for voice data, companies are worried about eavesdropping, or unwanted people listening in on conversations. However, with today's current extensive technologies in cryptography and encryption of data transferred over the Internet, security issues should be minimized as important voice data becomes encrypted.
The future of Internet telephony still remains a question that is primarily dependent on certain factors. Using what is known today, the adoption of Internet telephony as an alternative to using the PSTN to place calls, should increase mainly within companies and corporations to decrease the costs of long distance calls. As technology advancements are made within this area, such as with the gateways, sound quality and interoperability between products will continue to improve, thus making Internet telephony a more appealing switch. In addition, as technological advancement is made, the prices of gateways should decrease, thus making Internet telephony a much more economical switch for companies. In terms of the average home user, dependent on the services of their local ISP, people may begin to see Internet telephony as an alternative for them to place long distance calls. For each individual home user, it may be more beneficial to pay a flat monthly rate over a per minute rate and thus a rise in Internet telephony will occur within the average user spectrum.
Internet telephony is still an emerging technology, but it continues to gain large amounts of interest. It is seen as a possible money saving solution to long distance calls, and as Internet connection speeds increase, the sound quality of Internet telephony increase, and if government regulations do not hinder its potential, it is expected to catch interest and grow throughout the world.
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