VoIP and Internet Telephony

From a technology

standpoint, Internet telephony and modern VoIP are distant

cousins today: They have in common the use of the Internet

protocol for the packetization of the message payload, and

little else. VoIP technologies can interface transparently to

the PSTN, remain exclusively on a private network, and even use

the Internet when no alternatives exist.

The

breadth of access is the distinguishing feature in modern VoIP

products: Will any calls originating on a private,

packet-switched IP network, such as frame relay, terminate on

the circuit switched PSTN or the Internet, or will all calls

remain on one or more private networks? The former is called a

"hybrid network," since it supports calling on one or

more private networks, as well as calling between terminals on

the private networks and those served by PSTN and specialized

Internet access lines.

In contrast, a network in which

calls originate and terminate only on terminals connected to

that closed network is known as an "internal" or

"closed" private network; some companies want the

excellent security a closed network provides.

To the end user, the use of VoIP

technology is transparent. Telephone numbers are dialed in the

same manner as with circuit-switched networks. Dialed numbers

may include a one or two digit prefix, called "steering

digits", in certain implementations of VoIP technology.

Call-routing tables in a PBX or other voice switch determine

whether the call will be completed using a private IP network,

the PSTN, or the Internet.

According to the US-based

consultancy firm, theYankee Group, VoIP gateways found an early

home in multi-site enterprises, particularly multinational

companies looking to reduce long-distance telephone costs.

Corporate interest in IP telephony subsequently spawned interest

from entrepreneurial service providers looking to commercialize

the service, both for businesses and consumers. In medium to

large enterprises, VoIP gateways typically sit between PBXs and

the corporate WANs. The gateways offload voice traffic from a

PBX; packetize and compress it; and place it on the data

network. The PBX is not a



requirement, however, allowing gateways to serve small,
minimally staffed office sites.

Cost savings are the initial

driving force behind enterprise VoIP deployments. But, while the

economic argument is the primary motive for deploying VoIP

gateways, it is not the only one.

The Yankee Group cautions that

VoIP must still overcome some market and technology barriers

before it can provide anything more than cheaper and inferior

(less then toll-quality) voice communications. Poor quality

represents the biggest obstacle to widespread VoIP deployment,

both in the enterprise and in carrier networks. Another

significant bottleneck is the lack of interoperability among the

different gateways. As VoIP gateways achieve a critical mass—and

become more commoditized —interoperability will assume

paramount importance, as organizations look for more purchasing

flexibility and option.