Understanding What VoIP Means

VoIP — which stands for voice over Internet protocol and often pronounced "voyp" — is a new technology that will improve the way we communicate. VoIP basically means voice transmitted over a digital network. The Internet, however, isn't strictly necessary for VoIP. What is necessary for VoIP technology is the use of the same protocols that the Internet uses. (A protocol is a set of rules used to allow orderly communication.) Thus, voice over Internet protocol means voice that travels by way of the same protocols used on the Internet.

VoIP is often referred to as IP telephony (IPT) because it uses Internet protocols to make possible enhanced voice communications. The Internet protocols are the basis of IP networking, which supports corporate, private, public, cable, and even wireless networks. VoIP unites an organization's many locations — including mobile workers — into a single converged communications network and provides an unparalleled range of telephony support services and features .

In the beginning, there was POTS

Before digital networking took off, everyone had to use the one and only POTS (or plain old telephone service — honestly!). POTS runs over a network called the PSTN, or public switched telephone network. These POTS telephone systems use the tried-and-true method of telephone service known as circuit-switched.

For customers, the costs related to the regulated circuit-switched PSTN remain much higher than they need to be. Consumers and companies that rely daily on POTS know what the POTS way of telephony means to the bottom line. The good news is that VoIP is an alternative that can greatly reduce or eliminate POTS-related costs. VoIP also enhances productivity, leaving a bigger budget for things other than paying telephone bills.

From POTS to packets

VoIP technology enables traditional telephony services to operate over computer networks using packet-switched protocols. Packet-switched VoIP puts voice signals into packets, similar to an electronic envelope. Along with the voice signals, the VoIP packet includes both the caller's and the receiver's network addresses. VoIP packets can traverse any VoIP-compatible network. Because VoIP uses packets, much more information can be carried over the network to support and enhance your communication needs when compared to traditional telephony methods.

In a circuit-switched network such as POTS, routing is less dynamic than with a packet-switched network. In the POTS world, if a line is down, the call can't go through. In a packet-switched network, multiple routes can be established, and packets can travel any of the available routes. If one of the lines supporting the network is down, the packet can switch to another working route to keep the call up.

With VoIP, voice signals can travel the same packet-switched network infrastructure that companies already use for their computer data.

Eye for IP telephony

VoIP also makes possible other services that older telephony systems can't provide. VoIP telephony services are interoperable, meaning that they work well over all kinds of networks. They are also highly portable, which means they will work with any IP-enabled device such as an IP telephone, a computer, or even a personal digital assistant (PDA).

IP telephony works by taking traditional voice signals and converting them to a form that can be transmitted easily over a local area network. Thus, the heart of IP telephony is the same as traditional data networking with computers. IP-enabled phones handle the voice-to-data conversion well, but don't be misled — implementing VoIP doesn't mean everyone has to use IP-enabled phones. The best VoIP providers implement IP telephony in a manner that protects your investment in existing telephone equipment, even if you have analog telephone stations.

All IP phones have one important thing in common: a built-in network interface card (NIC), just like a computer uses. The NIC is critical for any network device because it provides the device with a standardized physical, or MAC, address and a way to communicate over the network. (MAC stands for media access control.)

To support IP telephony, a server is typically dedicated to run the software used to manage calls. Servers are just like PCs, except they have more memory, speed, and capacity. The server stores the database that contains all the MAC addresses corresponding to all the IP telephone extensions assigned to users. Depending on the size of the LAN and the number of users, you may use more than one server.

Depending on the size of the LAN, one or more switches are installed. These switches are boxes that have a series of ports into which all LAN-addressable devices (such as computers, printers, and gateways) ultimately connect. Usually, the switches are set up in the communications closets around the LAN, and they operate 24/7. All the switches are interconnected, often with fiber-optic cable.

In a nutshell, all network devices, including your IP telephone, must physically connect to the LAN through a port on a switch.

Boosting VoIP Quality with Dedicated Transports

Transports are the physical lines installed at the company or consumer premises to provide all sorts of network access. Many folks think of T1 or T3 transport lines when they hear the phrase dedicated transport, and with good reason. T1 and T3 lines are the most popular dedicated network transports in the country.

Dedication pays off

VoIP is making dedicated transports even more popular. If you're going to run VoIP on your company's network, dedicated transports give you the best-quality VoIP. Dedicated transports also allow you to connect all the data applications that your company uses at all your locations.

With a dedicated transport, your network can support massive volumes of on-net VoIP calls. Huge networks with multiple locations and hundreds or thousands of callers are best supported with dedicated transports. Dedicated transports enable a quality of service that meets or exceeds the quality found in traditional circuit-switched PSTN telephone calls.

Bandwidth and speed

Bandwidth and speed are the darling twins of data networks. When you compare speeds between dedicated and switched networks, you'll find that a dedicated network transport generally provides far more throughput.

Throughput is the total amount of data that can be passed over a transport line in a given amount of time. Throughput is directly related to bandwidth and is often used synonymously with data speed.

Two factors affect both bandwidth and speed when it comes to dedicated lines:

• Routing on a dedicated line is directly between two points, passing through few routers and switches. Data passing through a switched network, such as the public switched telephone network (PSTN), will go through many routers and switches. The more switching points involved, the less throughput because each switching point adds overhead to track the data.

• Exclusivity refers to the fact that a dedicated transport permits only a single customer's data on the line. In a switched network, data is aggregated and shared with others, reducing the bandwidth available to any single customer. Aggregation also involves resource contention, which can increase delay and signal degradation.

Dedicated networks are often called private networks or private line networks.

Types of dedication

For the corporate sector, dedicated network transports come in two major flavors: the digital service (or digital signal) carrier services infrastructure (CSI) and the optical carrier CSI.

The DS transports

The original digital service (DS) series of standards had five levels of dedicated lines. Each DS standard provided a set number of 64-Kbps channels, or DS0s. For example, a DS1 (T1) transport includes 24 channels, and a DS3 (T3) includes 672 channels.

In the old days, when DS transports were new and costly, the DS0 was leased as a single 64-Kbps transport line. Today, hardly anyone leases a DS0 transport. If you're implementing VoIP on your company's network, don't consider using just a single DS0 channel. Not only does it not provide enough bandwidth, but it also isn't cost effective.

T1 line

The T in the T1 version of transport represents terrestrial, or over land. The tariffs controlled by the government for setting the pricing of DS transports are based on the total terrestrial mileage between point A and point B.

The T1 transport continues to be the most popular transport on the market, and prices continue to drop. A big reason the T1 is so popular is that it permits network configuration folks to divide the total available bandwidth into smaller individual channels. This makes the T1 particularly suitable for VoIP networks that run computer data, telephony voice, and even videoconferencing over the same network transport. T1, however, does not provide adequate bandwidth for large multilocation networks with hundreds of users in each location.

T3 line

If you need more bandwidth than what you can obtain from a T1 or a group of T1s, consider the T3 transport. The T3 transport provides a total aggregate bandwidth of 45 Mbps. This breaks down to about 672 DS0 channels. A growing company can also consider upgrading to T3 transports or some mix of T1 and T3 lines. (The latter is more commonplace for larger companies, which use T1 lines for smaller locations and T3 for the larger locations.)

The OC transports

The advent of fiber-optic cabling in the 1980s changed the way that DS lines were installed. By the 1990s, most dedicated transport lines were going in as fiber-optic cables or being implemented through existing fiber lines. The terminating equipment would then be programmed to deliver the equivalent of however many DS0 channels were needed (1, 24, or 672).

Fiber-optic transports are defined according to the OC (optical carrier) CSI standards. The four most common transports are OC-3 (155 Mbps), OC-12 (622 Mbps), OC-48 (2.5 Gbps), and OC-192 (10 Gbps). These types of dedicated transports are used by only the largest corporations and the carriers themselves. The most popular OC standard is OC-3.

Not surprisingly, most small- and medium-sized companies rarely have the need for even an OC-3. But carrier companies put in a minimum of an OC-3 whenever they install carrier services for multi-tenant buildings and the largest customers. Their rationale is to put in enough fiber bandwidth to cover future customer needs. When those needs arise, the carrier then simply programs its equipment to deliver the necessary bandwidth.