- all about Voice Over IP
VoIP Connections bypassing phone network
VoIP connections using phone network
FXS/FXO gateway pairs
VoIP CONNECTIONS BYPASSING THE PHONE NETWORK
Let's first consider how VOIP can be deployed without any
links to the phone network. In this setup, parties connect
using sound capabilities of their Internet-connected computers, but
they won't be able to place or receive telephone calls (telephone
as in "1-212-999-9999").
Sometimes, such variants of VoIP deployment are
The main requirements for the IP-to-IP setup are:
- Computer with a sound card
- Broadband Internet connection
- Communications software
ADVANTAGES AND DISADVANTAGES
The main advantage of IP-to-IP is cost, or the lack of
it. Save for the cost of your computer setup and Internet
connection, there is no cost to making voice calls. In
other words, the connections are virtually FREE.
Disadvantages exist, too:
- IP-to-IP does not integrate with the analog phone
system. In most cases you can not make calls to
phone number or receive calls to a phone number.
- Establishing the connection requires your party to
be using the same protocol.
- IP-to-IP is often difficult to configure, especially
if there are issues with NAT ( 1 ).
The following describes popular VoIP software options at the end of
2003. Note that
such as GnomeMeeting for Linux, utilize standard VoIP protocols
(H.323 and SIP), and some, such as Skype implement their
own protocols. A connection between two parties is established
either by one party "calling" the other directly via their IP address
or by using a public directory.
These software packages are either free or bundled with other
products and they generally allow users to connect to each
other bypassing the phone network
- MSN Messenger (Windows) as well as other
"messenger" clients (AIM, Yahoo, ICQ)1.
A lot of devepment is happening in this area, but
at present, the applications have numerous issues ranging
from NAT incompatibility 1 to confusing interface.
Microsoft is moving toward integrating voice features
into its Office suite.
AIM is presently utilizing Net2Phone
as the "voice" plug-in.
Stay tuned - it's all but inevitable that voice
features of major IM clients will be upgraded in 2004.
- GnomeMeeting (Linux)
1 - one of the most popular
programs for Linux users utilizes the H.323 protocol
and allows to easily add video.
GnomeMeeting is cross-compatible with NetMeeting.
- Skype (Windows). Skype is based on the p2p architecture used in KaZaa
and has managed to avoid most NAT-related problems
1, but at a cost: the protocol
used by this application is non-standard (it's neither
H.323 nor SIP).
As of the time of this writing (December 2003)
Skype is the only major VoIP player utilizing P2P.
Skype is currently free, but says the following about its
What does it cost?
During the beta period Skype is free and helps us to refine and improve our product. Eventually, some features and services of Skype will require a paid subscription or prepayment. Our ambition is to keep the basic functionality of Skype (PC to PC calls) free. More information will be provided once our beta program is complete.
- NetMeeting 1
(Windows) [NOTE: the program being phased out by Microsoft] -
still relatively widespread program utilizing the H.323 standard.
(There are also software packages that allow you to dial
regular phone numbers from your PC. They, however, require you
to subscribe to a service, which is not free. The most
popular piece of software is Net2Phone which is integrated
with some of the most popular messengers. This is
discussed in more detail here).
These programs share the same drawback
which is that
if they are used from behind firewalls using NAT(Network
Address Translation), the firewall needs to be
configured in order to allow for VoIP traffic
to "pass through". More information on
firewall configuraions is available