About Internet Telephony (IP-Telephony)

About Internet Telephony

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Differences Between Internet Telephony and Telephone Network

What is internet calling

Internet calling is an exciting, new technology, which makes it possible to place domestic and international calls from a personal computer to any telephone in the world. Using a sound-equipped PC, you can place a call through one of the growing number of call providers, commonly referred to as InternetService Telephony Providers (ITSP).

When you place an Internet call from your pc, your call is then transmitted over the Internet into local telephone networks and finally, passed on to the regular telephone you are calling. The result is real time, uninterrupted, full duplex voice communication, generally as good as traditional phone calls, and in some cases, even better.

Differences Between Internet Telephony and Telephone Network

The underlying technology for Internet telephony is dramatically different from traditional telephone calling on the public switched telephone network (PSTN).

The Internet is a packet switched network, while the telephone network is fundamentally circuit switched. In packet switched networks, the data packets each have their own address, and the network routes individual packets to the destination address. A simple analogy is that data packets are like pieces of mail. For both the Internet and real mail, the envelope or packet contains the destination address. The "data" inside the envelope or packet can be virtually anything: documents, notes, pictures, software, or even recorded voice. For Internet telephony, the recorded voice is transmitted practically real time.

The personal computer digitizes the speaker's voice and assembles the data into Internet protocol packets. These data packets are transmitted at a rate of approximately 30 - 50 packets per second, creating sound that appears to be continuous. There is a small delay (about 1/10th of a second) between the time a word is spoken on one end and when that word is heard on the other end. This delay is usually less than the delay to transmit international telephone calls over satellite. Carrying a telephone conversation over the Internet is not new, and the precursors to today's Internet telephony were demonstrated as early as the mid 1970s. In contrast with the Internet, the telephone network is primarily circuit switched. Under circuit switching, telephone switches establish dedicated connections from end-to-end for the entire duration of the call. The concepts of circuit switching extend from the very roots of connecting telephones in the late 19th century, where telephones had to be in electrical contact, or a "circuit" in order to communicate. As calls were placed, operators manually pulled and inserted cables to connect two telephones for each call. Although today's telephone switches are entirely digital and can handle thousands of calls simultaneously, the fundamental principle of building a dedicated circuit for the duration of the call has not changed since the late 19th century. Even the designers of today's telephone network realized the power of packet switching, and today the control element of the telephone network (the SS7 network) is packet switched. This network links telephone switches and instructs them on the control features of phone calls such as beginning, end, or number dialed.

Advantages of Internet Telephony

Although circuit switching guarantees high reliability and quality of sound, packet switched networks are beginning to offer comparable service at a much lower cost. The higher quality sound available today on the telephone network is achieved through an inefficient use of bandwidth. Packet switched networks are an order of magnitude more efficient at handling voice communication. This means the same DS0 channel or "circuit" handling one traditional telephone call could potentially handle 10 packet switched telephone calls. In addition to better use of bandwidth, the equipment to support packet switched networks is both much lower in cost and much more flexible. Today, a high end router from Cisco or Juniper can process an order of magnitude more bits per second for less than one-tenth the cost of a Class 5 telephone switch from Lucent or Nortel. In addition, the router can fit in one rack in a closet rather than taking up an entire basement with expensive overhead: raised floors, extensive air conditioning, and large banks of batteries for backup power. The other limitation of circuit switching is that all of the intelligence in the network resides in the switches and not in the telephones or edge device. Circuit switches are essentially mainframe computers programmed with over 20 million lines of proprietary software. Compared to packet switched networks with personal computers at the edge, it is very difficult and slow to introduce dramatically new features into the PSTN. This limitation of circuit switching will become even more important as customers demand greater functionality and features. During the past 4 years, Internet telephony with personal computers has been introduced with a robust and rapidly growing feature set that includes caller ID, video, conference calling, chalkboards, encryption, and document sharing. In contrast, the feature set offered by the PSTN is not dramatically different than the features of 5 years ago. Within the past 18 months, an entire new industry of Internet Telephony Service Providers (ITSP) has been introduced. These companies install and operate Internet Gateways, which switch Internet telephone calls onto the PSTN, allowing a person at a PC to call any telephone number served by the gateway. In essence, the PC-to-phone variable cost is simply the cost to place a local call where the Internet Gateway is located. This eliminates one initial limitation of Internet telephony, where callers on a PC could only call others who were logged onto the Internet. Many ITSPs are ISPs seeking to diversify revenue, and the skills required to operate an Internet Gateway are very similar to the skills to operate network servers.

Save Money:The large cost savings offered by Internet telephony is fueling rapid growth in the global consumer market. Prices to call a telephone internationally from a PC are typically 70% lower than the best traditional international long distance rates. The cost of regular international long distance is beyond the reach of most international consumers. For example, a 10-minute phone call from India to the US costs an Indian clerical worker a week's worth of wages. One of the greatest benefits of Internet calling is the savings you can realize when you call long distance - sometimes up to 95% off the cost of traditional long distance calls. Because calls are carried over the Internet, rates are determined by the call destination, and not the origin. To find the best rates for calling any location in the world, try IPTop's Price-Analyser.

Call Anywhere: Another advantage of Internet calling is that any regular telephone can be reached via a PC. Unlike pc-to-pc technology, such as voice-chat, where both caller and receiver must be online, Internet calling offers the freedom to reach any regular telephone, without requiring any extra effort on the part of the receiver.

Toll-Free Access: While US toll-free numbers are generally not accessible from outside the US, Internet calling enables users to reach toll-free numbers (800, 888 or 877), from anywhere in the world.

Call and Surf: If you only have a single phone line for your calls and your computer's Internet access, Internet calling allows you to enjoy both at the same time. Because Internet calling uses your online connection, you can talk and still surf the net.