Using VoIP on the Internet

TCP/IP (transmission control protocol Internet protocol) uses a layered approach to networking. When VoIP is the network transport service, UDP is substituted for TCP. UDP (user datagram protocol) is one of the many protocols included in TCP/IP, so VoIP can be made to run on any network type.

The Internet isn't the only network that supports VoIP. Any network — private or public — that runs the TCP/IP suite can run VoIP. Quality of service varies from one network type to another, and the Internet service provider (ISP) you choose can affect the quality of service you experience.

ISPs make the Internet go round

An ISP is a company in the business of providing Internet access to consumers and businesses. It's common to rank the quality of ISPs based on their tier level. Tier-0 is a logical ring formed by all the tier-1 ISPs. Tier-1 ISPs are considered the largest and usually the best type of Internet access providersbecause there is only one "hop" between the tier-1 ISP network and the end-user's network.

In geek-speak, a hop is a connection between networks. Thus, if a packet travels from your network to your ISP's network, that is one hop. If the packet then travels to a larger carrier (perhaps someone from whom your ISP leases lines), that is another hop. It isn't unusual for packets traveling through the Internet to go through 15, 20, or more hops from source to destination.

National and international ISPs are all tier-1 and typically have multiple, ultra-high-bandwidth pipes connecting them into the core of the Internet. Regional ISPs tend to be tier-2. Smaller ISPs that acquire their Internet access through a tier-2 ISP are tier-3 ISPs. A few ISPs operate at the tier-4 and tier-5 levels.

When it comes to VoIP, each hop adds transmission overhead that may diminish the overall throughput of the call. On the one hand, if the network types involved in providing the end-to-end connection are using strictly dedicated bandwidth transports, you may not notice degradation. On the other hand, if you are using an ISP (regardless of its tier) that uses switched transports somewhere in the end-to-end connection, you are going to experience some degradation. This is because switched lines don't pass packets as well as dedicated lines. (That's why VoIP networks are designed using dedicated transports for on-net traffic and use switched lines only when it is necessary to go off-net to the public switched telephone network [PSTN].)

Depending on the number of hops over the Internet and the types of network lines between the VoIP caller's network and the VoIP receiver's network, there may be delay; it's inevitable when using the Internet. Having multiple hops doesn't necessarily equate with a poor connection, but it can be a significant factor.

How you choose to access the Internet and whether you then use the Internet to support VoIP are choices you need to make. In general, for companies with more than four or five locations, the Internet isn't a good choice for VoIP, although it may be a good choice for transferring computer data.

Examining protocol layers

VoIP runs with and requires the use of TCP/IP. The good news is that the way that TCP/IP works for data networking is the same way that it works for VoIP, with the exception that VoIP utilizes UDP instead of TCP and also requires that some additional information be packaged with the data packet.

In the process of being transmitted from source to receiver, VoIP data follows the same process to construct and transmit packets as is followed by other TCP/IP data packets, as shown in Figure 1. The difference is that UDP is used instead of TCP at the transport layer; this is probably the most significant difference between computer data packets and VoIP telephony packets.

Figure 1: Differences in TCP/IP implementation for VoIP and data packets.

Because VoIP packets are constructed pretty much the same way as data packets, VoIP can run on any type of data network that utilizes TCP/IP. Because most corporate networks already handle TCP/IP traffic, the fact that VoIP packets can travel on the same network means that converting to VoIP can be relatively painless.

Understanding VoIP Hard Phones

If you can see it, feel it, and tether it with a network cable, and if it includes a traditional phone keypad, you have a VoIP hard phone. Because there are many makes, models, and manufacturers, competition helps lower the price.

Even though you find much diversity, two things should be common to every VoIP (voice over Internet protocol) hard phone: support of transmission control protocol/Internet protocol (TCP/IP) (mandatory for VoIP) and at least one RJ-45 connection port.

The RJ-45 connector on a hard phone is an Ethernet port used to connect the phone to your network. Through this port, your phone can communicate with any other IP-based device on the network. These devices include servers that keep track of everybody's telephone number and voice mail, other VoIP phones, the gateway to the public switched telephone network (PSTN) (for off-net calling), and the router that takes care of establishing a connection to other VoIP phones on the network (on-net calling).

The RJ-45 port looks like a regular phone jack (RJ-11), but it's a little wider. In Figure 1, the jack on the left is an RJ-11 and the one on the right is an RJ-45. It is the jack on the right that you would use to connect this VoIP hard phone to the network.

Figure 1: Connections on the back of a VoIP hard phone.

Hard-phone categories

The VoIP hard phone looks the most like a traditional desk phones. Hard phones can be broadly categorized as basic, intermediate, and advanced phones, based on their capabilities.

• Basic: Basic VoIP hard phones look like a traditional desk phone. The dialing pad is clearly distinguished. This type of phone is considered a basic, entry-level IP phone that delivers good VoIP telephony service. That is, it makes and receives telephone calls over the VoIP network (on-net) or the PSTN (off-net). You could find such a hard phone on the desk of a staff person or in common areas such as the lobby or hallway of any typical company.

• Intermediate: This type of VoIP phone has a large screen and many more hard buttons compared to the basic hard phone. Intermediate phones can do anything that the basic hard phone can do plus more. This phone can often do Web browsing and access the company phone directory.

• Advanced: Advanced models usually include color video displays and multiple telephony-related applications. These phones have fewer hard buttons than intermediate hard phones because the phone's screen and software can enable many more functions than could be manufactured into the phone's chassis.

Focus on features

Telephony features can be delivered in two ways:

• As a function of your VoIP hard phone

• Through the VoIP network to the phone from another device attached to the network, such as a server or a telephone controller

In the older world of telephony (pre-VoIP), features were known as call features, line features, or system features. You paid for these features each month, sometimes on a per-line basis. This may not seem like much in the grand scheme of things, but if you or your company has multiple lines, feature costs can significantly increase your monthly phone bill. In the VoIP telephony world, all features are free.

The VoIP hard phone itself plays a role in exactly what type of features you receive. Its common features (like those on traditional phones) include call holding, conference call, transfer, redial, volume control, mute, and the other usual stuff.

• The basic VoIP hard phone also provides at least two call appearances, the ability of the phone to bring up and maintain separate telephone calls as if you had separate physical lines. Call appearance buttons are usually located near the Hold button and are labeled 1 and 2.

• Intermediate phones usually include a flat screen. Some of the more expensive ones provide limited Web browsing. These hard phones also come with the ability to receive their electric power from the network. This means that the local area network (LAN) can provide the power the phone needs through its network connection. As a result, you don't need to plug in a power cord at your desk.

Traditional features found on any basic VoIP hard phone are provided by buttons on the phone. The intermediate phone usually includes several buttons, but it also has many other features provided through its software and screen.

• Some people refer to advanced hard phones as appliances because they do more than just allow you to carry on traditional voice conversations. For example, they usually provide Web-related features and may include other applications. Advanced VoIP hard phones include all the features found on basic and intermediate phones, plus the following:

• Phone: Allows the advanced phone to use capabilities offered through a telephony server or other telephone system connected to the VoIP network.

• Directory: Provides access to the corporate LDAP (lightweight directory access protocol) server on the network. With this type of access, you don't have to even dial the number. You can look up the name on the LDAP and press one button; the network takes care of the rest.

• Web access: Advanced hard phones have expanded access that is closer to what you might expect from the browser on your computer. Web access capability often includes support for Java applets (self-contained programs created in the Java language).

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.