Telephone over Internet. A brief technical explanation

	Telephone over Internet. A brief technical explanation

This page will deal with the technicalities of Internet-connected telephoning. While the ordinary telephone service has improved greatly over the last twenty years, not the least of which is the availability of mobile or cellular phone services, there are still two main advantages to using the Internet as telephone carrier: It´s a lot cheaper, particularly over long distances. It can be readily integrated with other computerized local equipment which the user might have, enabling switchboards, local call logging and local digital storage of conversations to be controlled locally. We would not need any phone companies and their (expensive) services in the future. One can also note that using the Internet for phone services would make it a lot more difficult for "Big Brother" to tap our phones and listen in to our conversations. Whether this is good or bad depends on one´s point of view. As can be seen from figure 1, the phone network is much more ubiquitous than the Internet (the orange lines in the illustration). In the developed countries it reaches into every home and every workplace, there are even phone booths in the streets. Not so the Internet. Which is hardly surprising, considering that the phone network got a 100-year head start. So, to get at the Internet from where you are, you have, first, to enlist the services of an ISP (= Internet Service Provider), and, second, use the phone service from your place to the ISP, using modems at both ends.	Figure 1

This page will deal with the technicalities of Internet-connected telephoning. While the ordinary telephone service has improved greatly over the last twenty years, not the least of which is the availability of mobile or cellular phone services, there are still two main advantages to using the Internet as telephone carrier:

It´s a lot cheaper, particularly over long distances.
It can be readily integrated with other computerized local equipment which the user might have, enabling switchboards, local call logging and local digital storage of conversations to be controlled locally. We would not need any phone companies and their (expensive) services in the future.

One can also note that using the Internet for phone services would make it a lot more difficult for "Big Brother" to tap our phones and listen in to our conversations. Whether this is good or bad depends on one´s point of view.

As can be seen from figure 1, the phone network is much more ubiquitous than the Internet (the orange lines in the illustration). In the developed countries it reaches into every home and every workplace, there are even phone booths in the streets. Not so the Internet. Which is hardly surprising, considering that the phone network got a 100-year head start. So, to get at the Internet from where you are, you have, first, to enlist the services of an ISP (= Internet Service Provider), and, second, use the phone service from your place to the ISP, using modems at both ends.

The phone network is more ubiquitous than the Internet

Figure 1

Replacing the phone network?

Looking at figure 1, we can see that, for instance, houses 1, 2 and 3 use a (more or less) temporary connection over the phone lines to their ISP, and from then on to the Internet. Since the phone network is "circuit switched" (as opposed to Internet, which is "packet switched") this means 3 conditions have to be filled for the connection between the subscriber and the ISP:

There has to be a "session", i.e. the subscriber has to phone the modem pool at the ISP, and thus occupy the phone line for the duration of the call.
The server at the ISP has to assign an IP-address to the subscriber´s computer.
The digital information transmitted has to be modulated on a carrier wave so that the phone network can handle the call in an analog fashion.

There are, nowadays, work-arounds for this. One method is for one or more subscribers (usually living in close proximity of each other) to connect directly to the Internet using a broadband channel of some kind (as apartment house 4 in the illustration). This connection can be of copper, optical fiber or radio link.

The other method is for the phone companies themselves to provide solutions, via existing cables, using methods such as ISDN or ADSL. ADSL is almost as being directly connected; you don´t have to phone in and you have a more-or-less permanent IP-address. So, provided that you are willing to pay for the technology and services that are available, you can have direct access to Internet today, no matter where you live or happen to be.

Can we implement VoIP in our existing network?

Well, I don´t know. Probably not right away. Research has shown that 90% of all existing LANs in small businesses need som kind of upgrading before they can handle VoIP. Things like:

Locally available communications capacity
Server capacity
Broadband connection to the Internet

It is important that the VoIP and other network functions do not interfer, capacity-wise, with each other.

Packaging the call

In 1995, the Israeli company "VocalTec" released the first version of the protocol that came to be known as "VoIP" (Voice over IP). With this protocol, two Internet-computers equipped with soundcards, loudspeakers and microphones could enable their users to converse with each other. The trick was to adapt an information flow which consist of more-or-less continuous waves, into the packets that the Internet handles. To simplify, one can say the continuous conversation is chopped up into equal-size packets. Each packet is labeled with the IP-address of the recipient, a sequence number, plus a few other control parameters, and sent on its way. Now, the way Internet works, the servers always try to find the speediest way to forward packets, so it could well happen that these packets travel on slightly different paths. Consequently, they might not arrive in correct sequence.

Normally, when it comes to data handling, this is no big deal. The receiving computer simply waits until all relevant packets have arrived, and then put them together in the correct order. But people talking to each other are an impatient lot. A delay of just half a second is regarded as annoying. So, transmission channels for talkig over the Internet have to be fast and reliable.

Nowadays, one can use headsets in place of loudspeakers, and there are equipment om the market to attach ordinary telephones to the computer. If the computer is equipped with a Bluetooth-interface, it can convey the conversion wirelessly to one or more persons with Bluetooth-headsets, moving about in the vicinity.

Phone companies have also come up with a solution where they convey the call through their switchboard, to the Internet. You use an ordinary phone, connected to your computer, and use a specific dialing prefix when you make a call, and you want this call to go through the Internet. The phone compant then serves as your ISP, and long-distance calls get a bit cheaper this way.

There is information and downloadable test tools available on the web. Check out for instance:

Utel Systems website,
Brekeke`s website, or the
Technology Evaluation.Com´s website.

The SIP-protocol and IP-addresses

There are two standards in existence for voice communications over the Internet. ITU has produced a document labeled H.323, which has not made a hit, since it is regarded as being unnecessarily complex.

The other standard comes from IETF and is called SIP (= Session Initiation Protocol). Since this is the standard which is likely to be universal, let´s take a look at it. SIP uses an artificial session to keep track of an on-going telephone exchange, thus somewhat imitating a real session on the phone network. SIP is also used in connection with video-conferencing and chat over the Internet. In addition, it uses both UDP and TCP as transmission protocol for signalling information. This protocol provides for using IP-addressing in place of phone numbers, which means that you must know the IP-address of the party you are calling. If this IP-address is known to the DNS-servers as belonging to a domain, it is sufficient to know the domain-name. In either case, domain-names and IP-addresses can be stored in your computer.

There are a host of other services, such as call waiting and number display, that we are used to having on today´s digitized phone service on the PSTN (= Public Switched Telephone Network), that we, at the present, have to do without when phoning over the Internet. But those services will gradually come there, too. In the future, we will all have HMS-units (= Home Media Switch) which is an access unit with switch, gateway, firewall and support for VoIP, video, etc.

The Audio-quality

There has mainly been two problems with phoning over the Internet:

The poor audio-quality
The intermittent delays.

The poor audio-quality nowadays is result of narrow bandwith, as headsets, speakers and soundcards have no problems providing for the quality. Tha narrow sector has been the analog modems. A good quality-conversion requires 64 kbit/sec. But there is some overhead as well, so you must have a transmission capacity of at least 100 kbit/sec. Thus; You need two ISDN-channels, ADSL or better.

As noted above, the intermittent delays are caused by congestion on the Internet, insofar as one or more of the servers has it hands full. In other words, some of the transmitted packets have to wait too long in a buffer area on some server along the way. This can only be remedied by better capacity on the Internet, and this is a problem that, admittedly, does not affect regular phone service on the PSTN.

One can thus see that we need permanent broadband Internet-access for phoning over Internet, both to ensure quality of service and to provide us with a permanent IP-address, so that others may call us.

Last Updated: 2007-01-02	Author: Ove Johnsson