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Understanding Voice over IP Technology, First Edition Nick Wittenberg

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C H A P T E R

Objectives

Upon completion of this section, the reader will:

■ Understand that voice over IP (VoIP) is a technology that transmits telephone calls over an IP-based data network.

■ Appreciate that telephone calls can be made over the Internet with a substantial savings in cost but that this technology has problems with voice quality.

■ Know that organizations are slowly embracing VoIP to replace their traditional analog telephone systems and decrease their long distance telephone charges. Objectives

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INTRODUCTION

Voice over IP (VoIP) is the technology used to describe telephone services over a transmission control protocol / Internet protocol (TCP/IP) network. The applications for this technology vary, including making telephone calls over the Internet as well as intra-organizational telephony. However, nothing is simple—VoIP requires modi-fications to network infrastructure and protocols; it requires new hardware, such as IP telephones; it requires new software. This lesson looks at the broad picture of sending voice over a data network.

1.1 WHAT IS VOIP?

VoIP is an application that uses a combination of hardware and software to provide telephony services across an IP-based network.

Hardware and software

At a minimum, the hardware required for VoIP includes network hardware such as network adapters, routers, and switches. Now add gateways and IP PBXs. If a personal computer is being used as a soft phone, the PC also needs a sound card, microphone, and headphone. In a business environment, IP telephone handsets will most likely be used. Software may need to be added to the personal computer, and software in routers, gateways, and PBXs will need to be modified.

Telephony services

A VoIP system provides simple telephone conversations between two persons. This is as expected. It can also provide the additional extended services of a modern tele-phone system such as conference calling, call forwarding, and call display. Some additional services that can be provided by VoIP may be surprising, however. One such is moving the telephone to another location and having the call follow auto-matically. Employees can be reached by just dialing their extension, even if they are working from home that day.

IP-based network

The Internet protocol (IP) is a component of the TCP/IP suite of protocols used to transmit data in a reliable fashion over wide area networks (WANs) and local area networks (LANs). Although there are many protocols, IP is the only protocol al-lowed on the Internet and therefore it has become the overwhelming favorite to move data on modern systems. IP was not designed with voice traffic in mind; however, modifications to the protocol allow it to provide excellent voice quality. These will be examined in upcoming sections of this book.

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People can use the Internet as the transmission medium for telephone calls. For users who have free or fixed-price Internet access, Internet telephony software essentially provides free telephone calls anywhere in the world. To date, however, Internet tele phony does not offer the same quality of telephone service as direct telephone connections. When organizations require the highest voice quality, they may avoid the public Internet, but still use VoIP technology within their company and to their branch offices.

1.2 RESIDENTIAL / SMALL-BUSINESS VOIP

Voice over the Internet

VoIP lets you make long distance calls over the Internet right from your computer. The driving force behind the development of these software tools is the money users can save on long distance charges. The Internet phone was particularly alluring when long distance telephone charges were high. Since the advent of serious price competition in this field, the charges for long distance in North America have dropped extremely low so this exercise may not be worth the effort if your long distance needs are minimal. However, if you often make telephone calls to places outside North America, for busi-ness or family, you may find some serious savings in Internet telephone.

In this section we will explore the different forms that Internet telephone takes—computer to computer and computer to person via an ITSP (Internet tele phony service provider).

Computer to computer

You can use computer-to-computer Internet telephone if the computers at both ends of the conversation are similarly equipped with a sound card, microphone and speakers, a headset, or a USB telephone. Then, all you need is the right software and you can start talking.

This is a relatively new field in software. The first product came on the market in 1994. Pioneered by Vocal Tec, Internet Phone is still a leader in its field. Others soon followed, such as Web Phone and Microsoft’s NetMeeting. Currently the market leader with the most mind share is Skype. Its website claims 173 million downloads as of this writing.

Internet telephone software may be free or cost only a modest amount, and certainly the avoidance of long distance charges is compelling. So what is the catch?

Computer-to-computer Internet telephone is not without its wrinkles

• Both computers have to be similarly equipped with sound cards, speakers, and microphones. So obviously you can’t phone just anyone. You need to know if the other user is equipped to receive your call. • Both computers have to be running the same Internet telephone software.

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• Both machines have to be up and running plus logged onto the Inter-net; otherwise, how will the receiving machine “ring” when the call is coming in?

• The sound quality can range from good to very poor. After all, it is traveling over the Internet and sound quality cannot be guaranteed. Despite these problems, this type of telephone service does have its ardent followers. More users will be attracted once they learn that some of the Internet telephone programs have been enhanced with video. This is a natural fit for these services since once you are already talking, why not add video and see each other as well? As attractive as this sounds, a reality check is in order here; with poor connec-tions or limited bandwidth, the video will be close to useless.

Figure 1-1 illustrates the concept of the computer-to-computer telephone call and the equipment needed to make it. The diagram also illustrates the role of an Internet telephony service provider.

Speakers, headphones, sound card and softphone software

ITSP

The Internet The Internet

ITSP

Figure 1-1: Voice over the Internet

Internet Telephony Service Provider (ITSP)

After looking at the way the computer-to-computer telephone service works, you can see one huge flaw. What if the other party doesn’t have a computer, let alone the hardware and software needed to make the telephone service work? The alternative is to enlist the aid of an ITSP.

An ITSP will take your Internet telephone call and place it onto the national tele-phone system of the person you are calling. As the originator of the call, your computer must be set up just as is required for computer-to-computer telephone; namely you will need the sound card, speakers, and microphone. However, the recipient will receive a real telephone call and can talk to you using his regular telephone handset so you have no worries about computer hardware and software capabilities at the other end.

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The ITSP will take your call either at a local server and send it across a private network to the destination country, or send your call across the Internet to the ITSP’s node in the remote country. In either case, the ITSP must have a server in the remote country that transfers the call to the national telephone system. It is important to know this limitation if you are trying to call someone in a country that is not well served by the Internet. Naturally, the ITSP will expect to be paid for this little service.

Residential VoIP

Residential VoIP makes a regular telephone service available over a broadband In-ternet connection. The InIn-ternet connection can be either DSL, cable, or fiber to the home. The providers of this type of service offer telephone service at very low rates in comparison to the legacy telephone companies. Figure 1-2 illustrates how the resi-dential VoIP service and a family area computer network can share a high-speed Internet connection. DSL/Cable modem Telephone adapter Broadband router Broadband phone company The Internet

Figure 1-2: Residential VoIP

Standard telephone features are included with the service, including voicemail, call waiting, and call forwarding. There are two surprising features that cannot be dupli-cated by the traditional telephone companies.

• Virtual telephone numbers—this option will assign an additional tele-phone number to you from another area code. Anyone calling you from that area code will dial a local number, thereby avoiding all long distance charges.

• Telephone portability—this means that you can take your telephone adapter with you if you travel, and anyone calling your local number will reach you wherever you are. Naturally, you will need to find a high-speed Internet connection at your destination. But since many hotels now offer a high-speed service, this is a practical option.

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1.3 CORPORATE VOIP

Corporate VoIP

Corporate VoIP falls into three distinct types of systems: 1. Analog at the ends, digital IP in the middle 2. Digital IP at the ends, analog in the middle 3. Digital IP end to end

Naturally, the permutations and combinations of digital and analog are endless.

VoIP on managed IP backbones

This is system type one, analog at the ends and digital in the middle. Converting voice to data and sending it across a wide area network to avoid long distance charges (toll bypass) is not a new idea. It is a common ploy used by large organizations to provide telephone services between offices. The current implementation of this idea uses leased lines and technology such as T1 lines, frame relay, or ATM. Figure 1-3 illustrates this technology. Without a leased data line, a call must enter the public system telephone network (PSTN) and long distance charges apply. With a leased line, voice and data can be multiplexed and sent over long distance while avoiding long distance charges. Voice must be digitized by the PBX before it can be sent over the data lines. If the long-haul network is replaced by an IP network, the architecture of the combined voice and data network changes to that illustrated in Figure 1-4.

T1 span line Toll bypass

Data and voiced multiplexed

T1 Multiplexor T1 Multiplexor LAN LAN PSTN Long distance charges apply No long distance charges DSU/ CSU DSU/ CSU Router Router PBX PBX 1 2

Figure 1-3: Traditional long distance—PSTN or toll bypass

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The major change is that VoIP packetizes the digital voice data before trans-mitting it across the wide area network. This is a requirement if the voice traffic is to mingle with the computer data as it traverses the IP backbone network.

LAN

Router Toll bypass _Router

IP Network SIP/ H.323 Voice gateway PBX PBX Voice gateway

Figure 1-4: Voice on a managed IP backbone

Because a traditional voice system is used inside the organization, all the tel-ephone lines are routed to a PBX. To packetize the voice, a VoIP gateway is used. This may be a separate box or it could be a component of the PBX. The digitized voice is then routed over the WAN via routers. The gateway must match the control protocols used by the VoIP system. The most common control protocols used by VoIP are SIP and H.323. The gateway has many functions, just one of which is to look up the address of the person being called and make a connection. A gateway is a machine which connects two different types of systems. Since the machine con-nects an analog and digital system, gateway is the correct term for it. The relation-ship of these components is illustrated in Figure 1-4.

VoIP takes over the company telephone system

The second scenario involves an IP-based telephone system replacing the ana-log telephone system inside the organization. Earlier, this was characterized as the digital at the ends, analog in the middle system. This scenario uses analog in the middle because telephone calls must still funnel into the PSTN to reach outside parties or branch offices that aren’t reached by managed IP backbones. See Figure 1-5.

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LAN LAN PSTN Voice gateway IP phones IP phones Computer with softphone Voice gateway PBX PBX

Figure 1-5: VoIP takes over the company telephone system

Installing an IP-based telephone system may be attractive if the company wants to manage a single unified communication system. For example, only one wire has to be routed to each workstation instead of separate LAN and telephone cables. It is easier to make moves, adds, and changes on an IP-based telephone than a traditional PBX system. The drivers for this technology are explored in greater depth in an upcoming section. In this system, telephones are IP based or the user uses the com-munication software of her computer. Note that the telephones are connected to the LAN and that therefore, the telephone system is dependent on the data network being configured and functioning properly. Since data networks don’t traditionally approach telephone networks in reliability, this could prove a challenge.

VoIP end-to-end

VoIP end-to-end is a combination of the previous two systems and is characterized as being digital at the ends as well as digital in the middle. Not only is the telephone system digital but the network that carries voice to the other offices of an organiza-tion is also digital.

Figure 1-6 illustrates the system. Note that the devices that connect different parts of the pure VoIP system are called VoIP gatekeepers, not gateways. The gate-keeper is used to coordinate voice communications across the IP backbone. Since all portions of the system are digital VoIP, a gatekeeper is used, not a gateway. A gateway is used when connecting different types of systems, such as a digital VoIP system to an analog voice system. Note that even users of a pure VoIP system still need to dial outside the organization and this connection to the public telephone system requires a VoIP gateway.

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LAN LAN PSTN IP backbone VolP gateway VolP gatekeeper IP phones IP phones Computer with softphone VoIP gatekeeper

Figure 1-6: VoIP End-to-End

1.4 VOIP FOR TELEPHONE COMPANIES AND SERVICE PROVIDERS

Telephone companies and VoIP

For telephone companies, VoIP is a major disruptive influence. It requires engineering their voice networks and it allows competitors into their market.

The telephone companies’ voice systems are based on fixed lines with circuit switching. Although voice traffic is already digitized in order to travel over T3 and ATM circuits, these are not packetized. The packet switching services they do offer, X.25 and frame relay, are losing their installed base.

Switching over to an IP-based network fabric will cause disruption and require an expensive upgrade. On the other hand, an IP-based network can provide some efficiencies. Because VoIP can compress telephone conversations, the telephone com-panies can make better use of their lines.

Realistically, the telephone companies will change over to an IP-based infra-structure more because they have to than because they want to. Corporate custom-ers will demand VoIP services, residential customcustom-ers will be seduced into thinking they should have it, and competitors will be offering it.

Converting carriers to VoIP

A superclass softswitch is used to overlay or add VoIP capabilities to the networks of carriers. The superclass softswitch supports multiple core applications on a sin-gle platform, including local, long distance, and tandem. It provides these services with the reliability that carriers are expecting. As Figure 1-7 illustrates, the following

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Figure 1-7: Converting Carriers to VoIP Voice gateway PBX IP network Superclass softswitch ATM network Cable provider FDM network Telco TDM network

carriers or service providers can use a superclass softswitch to convert their core networks to VoIP:

• Carriers that currently provide voice services, the traditional tele-phone companies, typically use a TDM (time domain multiplex-ing) core infrastructure based on SONET and the DS/T services. Their telephone switches are the DMS series from Nortel, the 5ESS switch from Lucent, and the EWSD from Siemens. These systems can be overlaid with VoIP services by adding a super-class softswitch at which point they are known as “hybrids.” • Cable companies use a technology known as FDM (frequency

division multiplexing). VoIP services can be added to these systems, giving cable companies a comprehensive package of services to offer to their customers.

• Service providers that already run an IP or ATM network can also integrate VoIP services by deploying softswitch technology. SUMMARY

This module provides the basic introduction to voice over the IP protocol. Unless you know how traditional analog telephone systems work and how data networks work, VoIP is hard to understand.

Section 1.1: What Is VoIP?

This section defines VoIP as a hardware and software system that provides telephony services over an Internet protocol system.

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Section 1.2: Residential/Small-Business VoIP

This section first looks at telephone services over the Internet. Both computer-to-computer and computer-to-computer-to-ITSP are examined. Since the quality of voice over the Internet is not up to corporate standards, corporations are pursuing VoIP services over leased lines.

Section 1.3: Corporate VoIP

Organizations see VoIP in three areas: toll bypass, replacing the corporate telephone system with an IP-based telephone system, and pure VoIP end to end. This section examines these three areas.

Section 1.4: VoIP for Telephone Companies and Service Providers

VoIP is a double-edged sword for the telephone companies. It is a disruptive tech-nology that will require them to spend a lot of money to overhaul their systems and it will allow new competitors to enter their business. On the other hand, they will be able to run their systems in a more efficient manor. By deploying a superclass softswitch, their networks can be made VoIP ready.

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1. In order to relay a VoIP call from within a company to the public telephone system, __________ is required.

a) a PBX b) a gateway c) a router d) a firewall

2. Which one of the following reasons may prevent computer-to-computer telephone calls?

a) Each computer may have different telephony software.

b) One of the computers may not have an IP telephone attached to it. c) Both of the computers have sound cards, microphones, and

speakers.

d) One of the users hasn’t set up an account with an ITSP yet. 3. In order to achieve cost savings with toll bypass, a company needs

a) an account with an ISP giving it access to the Internet. b) a PBX at both head office and the branch office. c) a special long distance plan.

d) a leased line to its branch office that is located in a different area code.

4. In order for a telephone to be connected directly to the local area network,

a) the PBX must have an IP interface.

b) there must be a jack on the back of the computer to plug the telephone into.

c) it must be an IP telephone.

d) it can be an analog telephone with an IP address.

5. In order for a VoIP telephone call to go from one data network to another, it must be routed through

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