Voice over IP
What is VoIP and why should you care?
The Internet protocol (IP) was originally designed for sending data packets. VoIP involves sending spoken conversations, in real time, over an IP network. A regular phone line transmits voice as analogue signals, but to be sent over the Internet (or a TCP/IP-based private network), an extra step is added. Sound is converted to analogue signals, then digitised (converted from analogue to digital) and then transmitted over the network. At the receiving end, the conversion process is done in reverse.
VoIP is part of a larger technology category, IP telephony, which encompasses transmission of FAX, video, and any other form of data traditionally transmitted over the public switched telephone network (PSTN). The idea of IP telephony is itself part of a larger trend toward convergence of computer, telephone, television, security monitoring, lighting automation, and related technologies.
Advantages of VoIP over public telephone service
PSTN has worked fine for transmitting voice for many decades -- so if it's not broken, why fix it? The compelling factor behind VoIP is a practical one: cost. Telephone call charges can cost businesses hundreds or thousands of pounds per month. If the business has a fixed cost (unlimited access connection to the Internet) calls transmitted over that connection can be effectively free.
Disadvantages of VoIP
Given the cost advantage, why haven't all businesses rushed to abandon the public telephone network? Why aren't all telephone calls being made over IP? As with any business decision, there are tradeoffs. Some of the disadvantages of using Internet technology for all of your voice calls include:
Initial setup cost:
Although there are low cost and even no-cost ways to transmit voice over IP, an enterprise level company serious about VoIP will have to invest in one or more VoIP devices (such as the Avaya IP Office).
Quality issues:
There are inherent challenges in sending a voice stream over a packet network and voice must be prioritised over data as it has to happen in real time with no delays. Whilst an organistaion can ensure they have a managed network to provide this priority (Quality of Service/QoS), the internet, generally, cannot provide QoS.
However, this is changing rapidly and new technology is allowing providers to be able to gurantee bandwidth for fixed durations, thus ensuring good speech quality
Incompatibility issues:
Some services require that both the caller and the called party be subscribers to their service, and some software programs require that both parties have the same software installed. However, there are other services/programs that allow you to call anyone, including calling from your computer to a regular telephone, or even calling from phone to phone with packets routed over IP in between.
Weighing the pros and cons
Despite these disadvantages, VoIP can still be a viable alternative to PSTN. You should evaluate your workers' telephony needs. You may find that the best solution is to switch some departments or selected users to VoIP while others continue to rely on PSTN for their telephonic needs.
VoIP in a nutshell
Voice over IP can be hardware or software-based. The earliest products worked exclusively via software, and users at both ends of the connection needed a computer running the software, an Internet connection, a sound card, and microphone.
VoIP can also be implemented using gateway devices. These are dedicated hardware devices that create a bridge between analogue telephony equipment (phones, fax machines) and the IP network using one or more of the VoIP protocols.
VoIP protocols and standards
Standards and protocols are necessary for devices to communicate with one another. The protocols used by VoIP include:
H.323
H.323 is a standard that was developed by the International Telecommunication Union (ITU), which includes a group of protocols used for VoIP, video conferencing, and sharing data. These include protocols that manage call setup and termination, negotiate channel usage, and handle authentication and security. Most major VoIP product vendors, such as Avaya and Cisco, make products that rely on H.323.
For more information about H.323 check the IMTC Web site.
SIP is a newer, less complicated protocol that was designed specifically for VoIP. The Internet Engineering Task Force (IETF) developed SIP as an alternative to H.323.
Microsoft includes a SIP stack in Windows XP that is used for real time voice communications by Windows Messenger. Many vendors market SIP-based phones. Click here for more information about SIP.
Some vendors use proprietary VoIP protocols for their devices. Protocols can be (and often are) used in combination; for instance, SIP can be used between the phone and the gateway while H.323 is used between the gateway and the PSTN. Another protocol, the Media Gateway Control Protocol (MGCP) can be used by SIP to create a gateway to the PSTN.
Tip
In selecting which VoIP product to use, you need to consider compatibility with your firewall or NAT product. For example, Microsoft's ISA Server 2000 supports the H.323 gateway, but does not support SIP.
VoIP products and services
There are a large number of VoIP software programs, VoIP-enabled hardware devices, and VoIP services available. Which type of VoIP solution you choose depends on the call quality you need, the amount of VoIP traffic, and how much control you want to have over the technology.
VoIP software products
VoIP software programs range from free to very expensive. NetMeeting, which is included with Windows 2000 and XP, is an H.323-based voice and video conferencing program. Windows XP also includes SIP-based Windows Messenger. Both come with the operating systems.
Tip
NetMeeting is "hidden" in Windows XP; you won't find it in the Start program menus. To open it for the first time, you must type conf at the Run box. When you set it up, you'll be given the option to put an icon on the desktop or in the Quick Launch bar.