Overview

Internet telephony, or voice over internet protocol (VoIP), refers to any type of voice conversation that is routed through the Internet or other packet-switched networks rather than over a Public Switched Telephone Network (PSTN) used by traditional landline phones.

A PSTN system will dedicate a fixed wire path to transfer a conversation as it occurs, like the image below

whereas a packet-switched network will transmit the conversation in small packets that may travel along many separate paths in order for each packet to take the fastest route currently available. Once the packets are received at the end, they are reassembled in the correct order and played to the end user, as seen in the subsequent image

Types of VoIP

There are several different ways in which VoIP technology may be employed. The only requirement is that at some point along the path of the voice conversation, a packet-switched network is employed. Thus calls may initiate or terminate at a computer station, landline phone, mobile phone, or a landline phone equipped to convert from VoIP. Some examples of the various combinations include:

Computer to Computer

Users can download software such as Skype or AOL Instant Messenger and initiate a "call" to another user of the same software by selecting their screenname. The users then communicate by simply substituting the receiver and transmitter of a standard phone with headphones or speakers and a microphone, respectively.

Computer to Phone

Certain software may also allow computer users to initiate a call from a packet-switched network and eventually merge into a PSTN to terminate the call at a standard telephone. Skype, MSN, and GoogleTalk all offer functionality for computers to dial standard landline numbers and talk to those users as they would on a typical computer to computer call.

Phone to Computer

It is now possible to have a phone number assigned to a computer's IP address. Thus, a standard phone can dial a number like any other originating on a PSTN and terminate the call at the other user's computer. Skype allows users to purchase this service, and, much like cell phones, wherever your computer goes (as long as the IP address is mapped properly to the number given out to other users) it will be able to receive calls from landline phones via the number assigned.

Phone to phone - via Landline Phones

Many phone to phone VoIP services are now arising in the hopes of replacing the typical home telephone. The user simply connects an adapter to their standard home phone and places calls as they normally would. The adapter, however, routes the call over a public-switched network instead of the usual PSTN line for the user's end of the call. Not all of the functionality of a typical home PSTN phone, including 911 emergency calls, are available over these phone to phone VoIP services such as Vonage and Net2Phone.

Phone to Phone - via Cell Phones

Some companies have begun to release services where VoIP calls may be made from a mobile phone. To originate the call, the mobile phone must be able to access a high speed WiFi or 3G connection to make or receive a call. Skype has already offered this service and has even released their own line of cell phones specifically to work with this service. Much like a computer to phone call, the Skype phone access the packet-switched network via the WiFi or 3G connection to place the call.

Phone to Phone - Future Services

Skype also has a new service in the works that has been tested by the British wireless company Vodaphone. Vodaphone plans to allow users of their service to place Skype calls directly from their standard cell phones. This project, codename Starfish, allows users to see their Skype buddy list on their cellphones and place calls as if doing so from the interface of their PC brand software.

Downsides to VoIP

Although VoIP is much cheaper in that it can utilize the already existing infrastructure of the Internet to route calls, there are still several downsides to the service as it stands. Some of these issues vary with the company providing the service, but in general every company faces similar issues.

Loss of Internet = Loss of Phone

Nearly every method of VoIP (except potentially the future Skype Starfish service) relies on a functional Internet connection to be able to place and receive calls. This poses a problem to users who have inconsistent and intermittent Internet access. Additionally, if a large number of the population switch to VoIP only, an attack on the Internet infrastructure would also affect the VoIP service. Currently, though, VoIP is seen mainly as an alternative to landline phones and thus most users would have their cell phones as a backup in the event of loss of Internet service. Another consideration involves the problems with the Digital Divide in that if there simply is no Internet access, users will not be able to take advantage of this inexpensive alternative to landline phones.

Loss of Power = Loss of Phone

A current benefit of the PSTN system is that in the event of a power shortage or outage, the PSTN system still remains functional allowing users to place phone calls. Obviously, a lack of power equates to a lack of Internet access, therefore, loss of power leads to a loss of packet-switched VoIP phone calls. If a situation occurs like the blackouts recently seen in California or New York, users would be left without a way to place VoIP calls.

No 911 Service

The 911 emergency service relies on the PSTN network to route calls to the nearest local emergency call center. Current VoIP service does not have the ability to route VoIP calls to the nearest center, leaving VoIP users without a way to place emergency 911 calls. Especially problematic are computers with IP addresses that have been assigned actual telephone numbers. There is no guarantee that the number will correspond whatsoever with the location of the computer the IP address is assigned to - making identification of the caller's location even more difficult. This consideration will be discussed further in the policy section of our website.

Security

Many VoIP services do not provide encryption for the voice conversations they transmit. There are many services available that allow eavesdropping on conversations even sometimes to the extend of allowing users to change the content being transmitted. Some services like Skype do employ strong encryption on their conversations, but this is not yet the industry standard. Attempts to minimize eavesdropping such as compression of the packets or application of codecs to the audio are the level of security these approaches provide is not a sufficient replacement for true encrypted security.

Caller ID and Spoofing

Although many VoIP services now provide Caller ID functionality, there are still some instances where it can be unreliable, specifically with computer to phone type calls. Additionally, it is easy to alter your Caller ID information during a VoIP call allowing users to make calls appearing to originate from other numbers.

Services Requiring Landline

There are several services aside from telephony that require the use of a landline phone connection for complete operability. Many alarm systems, satellite television, Tivo, and modems will not function over a packet-switched network connection.