Packet Telephony Primer

8/12/2019 Packet Telephony Primer

1/14

Packet Telephony Primer

3 C o m T e c h n i c a l P a p e r s


2/14

1


Contents

Introduction 2

A New Value Model 2Present and Future Telephony and Computing Models 3

Market Drivers 5

Tariff Arbitrage 5

Freedom of Choice 5

Plummeting Capital Costs 6

Microsofts Application Dominance 6

Intels Planned Obsolescence Strategy 6

Voice Connectivity over Data Applications 6

What Is Packet Telephony? 7

Carrier Applications 7

Enterprise Applications 7

Packet Telephony Standards 8

Packet Telephony Products 8

Toll Bypass Products 8

Internet Phones 8

LAN-Based PBX Systems 8

The UnPBX 9

Related Products and Markets 9

Long-Term Trends 10

Building a Packet Telephony Network 10

The Desktop 10

The Gateway 10

The Gatekeeper 11

IP Fabric 11

Key Market Issues 12

Where Is the Technology Going? 12


3/14


By Chris Lamb

This document describes many of the concepts

underlying packet telephony. Packet telephony isa technology by which voice traffi c is placed on

packet-based networks such as those runni ng the

Internet Protocol (IP). The concepts described

here are suffi ciently general that they also apply

to voice over Frame Relay and voice over

Asynchronous Transfer Mode (ATM). The term

packet telephony encompasses all of these

mani festati ons.

Introduction

3Com Corporation has embarked on a broad

strategic and product initiative to drive theconvergence of data and telephony networksby delivering a wide range of capabilities to

meet the business needs of enterprises world-

wide. By marrying technologies that have tra-ditionally been separate, 3Com is poised to

move the industry to a new paradigm.

The convergence of voice and data net-

works has the potential to drive radicalchanges in collective business behavior by

delivering information more pervasively and

more completely than todays networks. The3Com vision is to create a single fabric to

deliver both voice and data, enhancing the

effectiveness and productivity of individuals incorporations worldwide.

Today, customers can purchase systems

that wed voice and data in limited applica-tions and with confined scope. The auto-

matic call distributor (ACD) is one such

example (Figure 1). ACD systems allow

customer service agents in tele-phone call centers to access cus-

tomer files in conjunction with

incoming telephone calls. Thoughthey have existed for years, ACD call

centers remain costly and difficult to

deploy, requiring a great deal of cus-tomized systems integration for each site.

Another example is the voice logging/

auditing system used by emergency call centers

(e.g., 911) and by financial institutions. Again,the deployment of these systems has been

limited because of the awkwardness and lim-ited scalability of the underlying technology:

voice on one network, data on the other, tied

together by obtuse database linkages. By cre-ating a single unified fabric for both voice and

data, 3Com is laying the groundwork for a

realignment that will allow the easier andbroader deployment of such systems.

The real power of data and telephony

integration is its potential to spawn new appli-

cations. Integral to this opportunity is the useof industry standard architectures upon which

independent third parties can build applica-

tions. Such applications have the power tospark radical shifts in collective business

behavior.

While the potential impact of this conver-

gence is enormous, the size of the separateinstalled bases of data and voice makes migra-

tion a formidable task. Solutions available upto now have generally been limited to point

products with relatively narrow scope and

with no answer to the installed base dilemma.

As a multi-bill ion dollar company, 3Comoffers the breadth of products and the depth

of experience necessary to migrate customers

to this new paradigm. 3Com is committed toprotecting its customers investment and to

migrating their infrastructure in ways thatrespect their current business practices.

A New Value Model

The goal of packet telephony is to provision

voice over packet-switched fabrics in both the

2

Acronyms andAbbreviations

ACDautomatic call distributor

ATMAsynchronous Transfer

Mode

CoSClass of Service

CTIcomputer telephony

integration

ETSIEuropean

Telecommunications

Standards Institute

IEEEInstitute of Electrical and

Electronic Engineers

IETFInternet Engineering Task

Force

IPInternet Protocol

ISDNIntegrated Services Digital

Network

ITSP

Internet telephony serviceprovider

PSTN

Trunks

Ethernet

Station

interface

Databas

e

server

ACD

Figure 1.Automatic Call Distributors TieTelephone Systems and Data Communications

Together


4/14

local area network (LAN) and the wide area

network (WAN). Whereas today voice and

data generally flow over separate infrastruc-tures, the vision is to drive these two commu-

nications methods over a single medium,

allowing users to engage in media-rich com-munication in a natural and straightforward

manner.

3Com is sowing the seeds of a paradigmshift. This shift will turn the telephony industry,

which to date has been highly vertical and

proprietary, into a horizontal industry, openingit to a flood of new vendors and applications.

3Com is uniquely positioned to drive this

shift by providing value to customers for their

next-generation networks.With the move to integrated data and

telephony over packet networks, the commu-

nications industry will emerge into three dis-tinct strata (Figure 2), with vendors providing

value predominantly in one stratum and part-

nering with vendors in other strata.

At the first level reside the infrastructureplayers: vendors who provide the network

foundation upon which the other levels are

built. This level will be 3Coms primary areaof focus. Infrastructure will consist of 3Com

systems products, including switches, routers,

and access devices, all of which will supportmultimedia. To date, 3Com has offered many

multimedia-enabled infrastructure products,

starting with SuperStack II switches with

PACE technology, first introduced in 1995.

3Com continues to introduce multimedia-

enabled products to help migrate users to

next-generation networks supporting media-rich applications such as packet telephony.

The next level consists of services. This

stratum will be dominated mainly by softwarevendors who provide underlying software to

manage transactions. Examples of these ser-

vices include call processing, resource manage-ment, and accounting and settlements. This

technology wil l be generally transparent to

users, much as the network operating systemsrunning on todays LANs are transparent to

network users.

At the top tier are applications. Applica-

tions are visible to end users and provide theservices required to initiate and complete

business transactions. Examples include call

centers, interactive voice response (IVR),conferencing bridges, and private branch

exchanges (PBXs). Today, most application

vendors deliver highly vertical products based

on proprietary hardware and software. Forward-thinking application vendors will migrate to a

software-only business model. This tier will

also see the emergence of large numbers ofstart-up ventures.

Present and Future Telephony and

Computing Models

The transition to this new order will likely

occur gradually, emerging from organizations

back offices and special applications workgroups.

3

Acronyms andAbbreviations

ITUInternational Telecommu

cations Union

IVRinteractive voice respons

MCUMultipoint Controller Uni

PBXprivate branch exchange

PCBprinted circuit board

PRIPrimary Rate Interface

PSTNpublic switched telephon

network

QoSQuality of Service

RSVPResource Reservation

Protocol

TDMTime Division Multiplexin

VOIPvoice-over-IP

xDSL

digital subscriber line

Callprocessing

Infrastructure

Services

Applications

Infrastructure: switches,routers, and gateways needto support QoS

Services: software andmiddleware need to provisionapplications over packet fabric

Applications: processes andtelephony services visible toend users

Accounting &settlements

Conferencebridge

PBX

Voicemail

Callcenters

IVR

API

API

Resourcemanagement

Switches GatewaysRouters

Figure 2. Packet Telephony Will Transform the Communications Industry


5/14

The current paradigm consists of a circuit-

switched fabric for voice networks (Figure 3)

and a completely separate LAN infrastructurefor data. Today, most businesses use a propri-

etary PBX or key system for voice.

The hybrid model (Figure 4) is typical of

todays computer telephony integration (CTI)implementations. While most businesses con-

tinue to run the bulk of their enterprises on

separate networks, some have selectivelydeployed hybrid systems for specific applica-

tions, generally those designed to generate

revenue, such as telemarketing, or minimize

costs, such as after-sale support.In a typical CTI system, the incoming

callers number is transferred to a databaseapplication, which displays information

related to the call, such as the customers

service record. There is loose coordination

over a proprietary link between the telephonyand data traffic. Such applications allow a cus-

tomer service agent to transfer a customers

data records to a specialist along with the call.The key to the hybrid paradigm is that

computers and telephony are loosely inte-

gratedthe I in CTI notwithstanding. The

CTI market is severely restrained because itrelies on proprietary connections between

insular systems. Unlike the world of packet

telephony, which throws the doors open tounfettered competition, CTI relies on an arms-

length relationship, over a proprietary link,

between complementary vendors who haveworked out bilateral business arrangements.

The dynamics of the CTI business are

very different from the LAN industry. As

compared with the brutal free-for-all of theLAN marketplace, the CTI approach makes

for a Tower of Babel in which vendors, by

building competitive moats, have restrictedtheir ownand their competitorsfreedom

of action. While CTI had the potential to be

wide open, due to the closed-system roots ofthe major players, this market became an oli-

gopoly of telephony-computer partnerships.

The new packet telephony paradigm con-sists of telephony and data tightly coupled on

packet-based, switched, multimedia networks(Figure 5). In this new world, data and voice

share a common transport. Designed withnext generation networking equipment, this

fabric is capable of growing to support future

applications such as video conferencing andvideo streaming. The fabric can support mul-

tiple Classes of Service (CoSs) and provide

guaranteed Quality of Service (QoS) to multi-media applications. In this paradigm, the

transport for telephony becomes transparent;

users will be unable to distinguish whether a

call is placed over a packet network, a circuit-switched network, or a combination of the

twonor will they care.

This new paradigm has the power tospark fundamental shifts in collective business

behavior, as people exploit the simultaneous

and joined delivery of voice and data applica-tions over a single, unified fabric. This will

provide unprecedented opportunities for new

enterprises to provide innovative applications.

4

Trunks

Carrier

LAN

Phoneline

s

PBX

Figure 3. Data Networks and Telephone SystemsAre Completely Separate Today

Trunks

Carrier

LAN

Data

base

server

Proprietar

y

control

interface

Phoneline

s

Figure 4. Hybrid Paradigm: Arms-Length

Connection Between Data Networks and

Telephone Systems


6/14

The transition to the new paradigm willtake years to complete. Today, only a small

subset of customers have any compelling busi-

ness need to adopt this new technology.However, as the technology matures and new

applications proliferate, packet telephony will

appeal to a broader market. These customerswill be looking for standards-based solutions

delivered end-to-end by vendors such as 3Com.

Market DriversNew technologies and applications must offer

customers definitive value. The value proposi-

tion for packet telephony will change as themarket emerges, but it is most likely to occur

in the following steps.

Tariff Arbitrage

Todays market drivers for packet telephony

focus around tariff arbitrage across the WAN.

In many international

markets, particularly

highly regulated ones, com-munications carriers have tariff

structures that are artificially high

as compared with deregulated markets.Additionally, these markets generally offer

lower tariff structures for data connections.

A number of startups have begun toexploit tariff disparities and provide users with

significant savings on their long distance

charges. Internet phones and voice-over-IP

(VOIP) gateways, two products designed toexploit these disparities, are discussed later in

this paper. Tariff arbitrage products are purely

tactical infrastructure plays, which will beshort-lived as the international communica-

tions carrier markets embark upon a process of

deregulation over the next two decades. As

artificial tariff disparities evaporate, the valueproposition will implode. Vendors who hope

to survive this transition must be able to re-

articulate their value propositions using a newvocabulary.

Freedom of Choice

In the future, data and voice convergence willfacilitate new business processes, enabling

people to work more effectively. Perhaps most

5

Voice

logging

server

Ethernet

switch

Central

site

Multimedi

a

workflow

server

ACD/PBX

server

Remoteaccess

server

gateway

Remoteac

cess

servergat

eway

Accessswi

tch

orrouter

Ethern

et

switch

Brancho

ffice

Analogorp

roprietary

digitallife

line

Accessswi

tch

orrouter

Corporate

intranet

PSTN

Figure 5. New Paradigm: Voice and Data Mergedin a Single, Open Architecture


7/14

importantly, this technology will release cus-tomers from the limitations of proprietary

solut ions, allowing organizations to develop

integrated voice and data applications tailored

to their own needs, much as PC users todaycan build data applications using Visual

BASIC. Already, a cottage industry has

emerged to deliver object-oriented softwaretools that allow customers to develop their

own IVR applications. These tools are just the

beginning of what customers will be able todo for themselves under the packet telephony

paradigm.

Plummeting Capital Costs

Another market driver is the opportunity to

slash acquisition and operating costs. In 1997,

the capital cost of building a LAN telephonysystem was higher than the cost of building

separate LAN and phone systems. Vendors

who advocate such systems claim that the com-

bined infrastructure can lower maintenancecosts, but there is a decided lack of evidence

on this point. However, the dynamics of this

marketplace are about to change.Many proprietary PBXs are built on

technology that is measured in decades. By

contrast, the data networking industry runs

on a very different metabolism. The LANindustry typically has 18-month product life

cycles, and tradit ional LAN infrastructureequipment costs generally decline by 20

percent per year. Vendors building next-

generation packet telephony products under-

stand where costs are excessive and how todrive them down by employing higher levels

of product integration and by using next-

generation silicon technology. Horizontalplayers, such as 3Com, understand the power

of open systems and how to exploit the dyna-

mics of this new business model to achievemarket dominance.

Microsofts Application Dominance

Microsofts application dominance and itsapplications proliferation strategy are also key

market factors. Microsoft continues to bundle

more capabilities in each new release of

Windows software. One of its recent releasesincludes NetMeeting, a voice and data confer-

encing product, and NetShow, a videostreaming product. These products will be on

tens of millions of desktops over the next few

years, giving users the capability to begin

using voice over packet-based networks.

Intels Planned Obsolescence Strategy

Intel is another determinant in this industry.Ever since the advent of AMDs reverse-

engineered 286 microprocessorwhich

caught Intel napping and forced a violent

migration to 386 technologyIntel hasembarked on a planned obsolescence strategy.

A result of this phenomenon is a biennial

(quickly becoming biannual) wave of new PCswith triple the power of their predecessors.

Intel is also driving new applications, espe-

cially heavy users of microprocessor power,onto its platforms. Intel can be expected to

support the widespread adoption of real-time

voice and video, because it will force a newupgrade cycle using microprocessor tech-

nology that only Intel can provide.

Voice Connectivity over Data Applications

Just as global environmental change has extin-

guished some species and spawned new ones,

the competitive environment in telephony is

driving change. First and foremost is the pro-liferation of Web connectivity, which provides

an alternative patha data pathinto orga-

nizations worldwide. Many organizations areusing Web connectivity as a mechanism to

reach out to their trading partners. Thus far,

Web connectivity has been data oriented, buta few organizations are now experimenting

with Web-based call centers, in which users

can click on a screen object to obtain a voiceconnection to an agent.

Another example of a promising voice-

over-data application is the airline reservationsystem. Today, a travel agent having difficultybooking a reservation must call the airline

over a special toll-free number, provide record

information (such as a record locator) to theairline, and request special service. In the new

model, the agent needing assistance could

click on a help me button, and the applica-tion would bring up a voice connection to the

airline. The airline representative answering

6


8/14

the phone would immediately be linked to therelevant customer record. This application

would save time for both parties while elimi-

nating the cost of a separate telephone call.

This example illustrates the power of joinedand simultaneous delivery of voice and data

communications over an open, standards-

based fabric.

What Is Packet Telephony?

There has been a lot of confusion regarding

packet telephony in two specific areas. First,packet telephony is not Internet telephones.

Internet telephones are software packages sold

predominantly through retail chains for hob-byists to place telephone calls over the Internet.

They are generally awkward to use and offer

poor voice quality. Packet telephony is alsonot the same as computer telephony integra-

tion (CTI). As discussed earlier, CTI is the

loose integration of computer systems withtelephony switches.

Packet or IP telephony is the simulta-

neous and joined delivery of voice and data

communications over a single, unified com-munications fabric based upon the Internet

Protocol (IP). Packet telephony traffic will be

delivered within the enterprise over an organi-

zations intranet and outside the enterprise ini-tially over a circuit-switched fabric. Over time,

as corporations develop extranets with theirtrading partners and as those partners install

interoperable packet telephony systems, cor-

porations will deliver packetized voice end-to-

end outside of the enterprise.

Carrier Applications

In the carriers, packet telephony is emerging

as a key bypass technology. A new class of car-riers, Internet telephony service providers

(ITSPs), is building packet-based WANnetworks to carry voice traffic. Even some tra-ditional long-distance carriers are experi-

menting with packet-based WANs, primarily

for service outside their regulated markets.New partnerships and consortia will emerge as

these carriers attempt to create worldwide

packet-based telephony networks.

Enterprise Applications

In the enterprise, packet telephony willemerge in applications where the value propo-

sition can be clearly articulated. This is likely

to begin with specific applications in large

organizationsapplications utilizing thejoined delivery of data and voice over a single

infrastructure. Examples include next-genera-

tion call centers, new voice logging systems,and unified messaging: the joined receipt of

voice mail and e-mail.

Because of its radical technological depar-ture, packet telephony will emerge at the

fringe of organizations in value-added applica-

tions, not in the core premises telephony

fabric. Given the critical importance of thetelephony infrastructure, telecom managers

will be reluctant to move the core of theirbusiness onto a completely new technologyuntil the technology proves itself.

Much of packet telephonys present

deployment is for toll bypass over WANs.Organizations are purchasing VOIP gateways

to combine their phone and data infrastructures

(or at least selected links in their infrastruc-tures) primarily to high-tariff countries.

Domestically, organizations with large branch

office systems (such as banks) and a capillary

data infrastructure to reach those branches arealso exploiting the WAN data network to

carry voice. In an odd reversal of the metaphor

that sold T1 multiplexers for years (voicepays for the circuit; data rides for free), these

customers have already installed and justified

their data networks and are using spare capa-city to carry intra-corporation voice traffic.

Over time, as the business justification

shifts to increased employee productivity and

effectiveness, packet telephony will infiltratethe LAN fabric. Several events need to occur

to effect this change. Much of the high cost ofinstalling a LAN-based telephony systemtoday lies in the infrastructure components (as

opposed to telephone handsets or other client

equipment). Within one year, these costs willreach a crossover point with traditional PBXs

(Figure 6 on page 8), and within two years

they will be at a 30 percent discount to PBXcosts.

7


9/14

Another key issue is infrastructure relia-

bility. Current LAN telephony systems use PCchassis for common infrastructure compo-

nents. Many of these components lack

redundancy, making the system vulnerable to

component and system failure. However, anew generation of products built upon ful ly

redundant, carrier-grade systems is coming to

market. The 3Com Total Control remoteaccess concentrator is one such platform.

Packet Telephony Standards

Four major organizations are working on var-ious aspects of packet telephony standards: the

International Telecommunications Union

(ITU), the Internet Engineering Task Force(IETF), the European Telecommunications

Standards Insti tute (ETSI), and the Institute

of Electrical and Electronic Engineers (IEEE)under the auspices of its 802 committee.

The ITU has developed the so-called

H.32x family of standards related to videoconferencing. Each H.32x standard pertains

to a specific type of network, and refers to the

appropriate subsidiary ITU standards for callprocessing, capability exchange, channelaggregation, media stream multiplexing, audio

and video codecs, and data conferencing

standards.

Packet Telephony Products

The packet telephony products being deliv-

ered today are largely tactical, self-containedproducts that rely only tangentially on a larger

infrastructure to deliver their value. Thedearth of true systems products in this market

space is attributable to the lack of an end-to-

end, multimedia-ready IP packet infrastructure.

Many 3Com customers are in the process ofupgrading their entire fabric to support

media-rich traffic, including voice and video.

However, in the absence of a sizable installedbased of media-enabled infrastructure, the

packet telephony vendors are blocked from

using the core of the data network and are leftto deliver tactical products at the fringes.

There are several broad categories of packet

telephony products.

Toll Bypass Products

Toll bypass products sit on the edge of the

network between a local PBX and a wide areapacket network (Figure 7). An example is the

VOIP gateway, which provides a VOIP con-

nection between two or more PBXs over a

packet-based network. The VOIP gatewaypacketizes voice and carries it across the pri-

vate corporate intranet. The VOIP gateway is

an outgrowth of voice over Frame Relay prod-ucts, which perform a similar function over a

Frame Relay backbone. 3Coms PathBuilder

S600 access server offers voice over Frame

Relay and voice over ATM support.

Internet Phones

As discussed previously, Internet phones aresoftware packages that run on PCs and pro-

vide connectivity over an Internet connection.

These consumer-oriented products can best bedescribed as toyware or bundleware: free

or nearly free software that delivers less than

business toll quality. Although the hobbyistmay be willing to tolerate these products, they

are generally not business quality today.

LAN-Based PBX Systems

A new product category is emerging that pro-

vides PBX capabilities over the LAN. The

LAN-based PBX, which promises to substitutefor and replace traditional enterprise PBXs, is

a key ingredient to moving to convergence.

Several startups are delivering voice switches

that run on Windows NT. These switchescreate, manage, and tear down voice connec-

8

$800

$600

$400

$200

Present

UnPBX(key system knockoffs)

IP telephony

Traditional PBX

End-userc

ostperseat

2000+

Figure 6. Packet Telephony Costs Will Reach a

Crossover with PBX Costs


10/14

tions between stations on the LAN. The sta-

tions themselves communicate peer-to-peer.The voice traffic between stations is digitized,

placed into data packets, and transmitted

across the packet network directly between thestations, bypassing the LAN-based PBX. For

this class of product, the voice is transmitted

in the packet domain. End stations involve theLAN PBX only when call control is required

for instance, when transferring a call, creating

a conference call, or sending a call to voicemail.

The UnPBX

A fourth product category is the UnPBX.These products are key system and small PBX

knockoffs built around Windows NT servers.

Unlike the LAN PBX, however, they do notuse the data network to transport voice calls.

Rather, they employ station cardsprinted

circuit boards (PCBs) that have connectionsto stations (telephones), and trunk cardsPCBs that attach to the public telephone net-

work. Unlike the LAN PBX, the UnPBX

operates entirely in the circuit-switcheddomain.

The PCBs for these products are built in

a PC Card form factor (usually PCI bus) andconnect to each other using a Time Division

Multiplexing (TDM) bus. The Windows NT

server is used primarily as a housing for thecards and to provide rudimentary connectivity

to software applications, such as basic voicemail and auto-attendant, running on theserver.

The value proposition is aimed at key sys-

tems and low-end PBXs. This new generation

of products is built on a open system thatallows additional software applications to be

written for Windows NT, a standard and easy

environment. The station cards and trunkcards themselves, though built to a standard

form factor, tend to be proprietary in imple-

mentation. However, standards are expectedto emerge here, and costs will drop dramati-

cally as production benefits from economies of

scale.A major drawback of the Windows NT

hybrid is limited scalability. Typically sup-

porting a maximum of 150 users, these sys-

tems cannot easily scale past a single WindowsNT chassis.

Related Products and Markets

The video-conferencing market is a technolog-

ical cousin to packet telephony. To date, mostvideo-conferencing systems have been large

room systems that communicate point-to-point across the WAN. A family of standards

called H.320 allows systems from di fferent

manufacturers to interoperate over Integrated

Services Digital Network (ISDN) links.More recently, the concept of desktop

video conferencing has emerged, allowing

individuals to use this technology directly

9

Ethernet

switch

PBXCentralsit

e

Voiceover

FrameRel

ay

gateway

Voiceover

FrameRel

ay

gateway

FrameRel

ay

link

Router

Router

Ethernetswitc

h

Brancho

ffice

PBX

Figure 7. Toll Bypass Is the First Manifestation of

Packet Telephony


11/14

from their desktops. The latest wrinkle isnetworked desktop video conferencing. When

desktop video conferencing becomes net-

worked, the infrastructure must change to

allow users to dial, transfer, and conferencevideo calls from their desktops.

The networked desktop video-confer-

encing industry has converged on a family ofstandards called H.323. However, existing

LAN infrastructures were not built to handle

the demands of networked video conferencing.

Long-Term Trends

Several long-term trends will drive the growth

in packet telephony. The convergence of voiceand data into open, standards-based platforms

will provide an impetus for independent

software vendors to develop voice- and data-enabled applications for increased effective-

ness. Examples of these services range from

unified messaging (the bundling of voice and

e-mail) to the commoditization of voice mailand personal agent services such as Wildfire.

Another trend is the delivery of telephony

services transparently across packet and cir-cuit-switched networks. As was discussed ear-

lier, some of the early packet telephony players

are exploiting tariff differences between voice

and data for toll bypass, but this market willbe short-lived as carriers become deregulated

and pricing disparities collapse. Ultimately,users will not care how a call is transported,

whether in the packet, circuit, or cell domain,

so long as the call gets to the recipient with

acceptable quality and at a competitive price.In fact, service providers may offer a range of

services, with appropriate cost/quality

tradeoffs.

Finally, broadband access technologiessuch as cable modems and digital subscriber

lines (xDSL) will also enable packet telephony.

The broadband technologies promise todeliver huge amounts of data to the periphery

of networks. They also promise to create a

new category of utili ty providers. For example,Media One, an unregulated subsidiary of US

West, is conducting trials of cable-based

broadband services to the home as a means of

faster Internet access. I f they succeed, they willbe ideally positioned to provide packet-based

telephony services to their customers.

Building a Packet Telephony Network

To build an IP telephony system end-to-end

requires three new types of components: a

modified desktop, a gateway, and a gatekeeper(Figure 8). If multiparty conferencing is

desired, a fourth component called a Multipoint

Controller Unit (MCU) is also needed.

The Desktop

On the desktop, the user has one of two types

of systems. Many users will have an Ethernetphone that plugs into an Ethernet RJ-45 jack.

Other users, often those who use the phone

extensively and in conjunction with a PC, will

have handsets or headsets that plug into theirPCs.

The Gateway

All LAN-based telephony systems today need

to connect to the public switched telephone

10

Ethernet

switch

LANPBXru

nningon

H.323gat

ekeeper

H.323gat

eway

Layer3sw

itch

Corporate

intranet

PSTN

Figure 8. Data and Voice Share a Common LocalInfrastructure


12/14

network (PSTN). Gateways are productsspecifically designed to convert voice from the

packet domain to the circuit-switched

domain. The gateway converts packetized

voice (voice that has been digitized and placedinto an Ethernet frame) to a format that can

be accepted by the PSTN. Gateways support

four types of connections: Analog

T1 or E1

ISDN, generally Primary Rate Interface (PRI) ATM, at OC-3c and higher speeds

Since the digitization format for voice on

the packet network is often different than on

the PSTN, the gateway will also provide thistype of conversion, often called transcoding.

Gateways also pass signaling information,

including dial tone.

The Gatekeeper

The third major component is the gatekeeper.

Although the nomenclature can be somewhatconfusing, gateways and gatekeepers provide

completely separate functions. The gatekeeper

is primarily designed to throttle the originationof additional real-time connections over the

network. Real-time applications register them-

selves with the gatekeeper before attempting

to bring up a session. The gatekeeper mayrebuff a request to bring up a session, or may

grant the request at a diminished data rate.

This is most relevant for video connections,which can consume vast amounts of band-

width for high-quality connection. Packet

telephony call control, call management, andvoice switching intelligence will also reside in

the gatekeeper.

IP Fabric

A robust packet infrastructure is required to

support IP telephony and other real-timeapplications. At a minimum, switched 10Mbps Ethernet to the desktop is required. The

switches themselves must be nonblocking and

support multiple internal queues. Telephonycalls traversing the intranet will go through a

Layer 3 switch, which will need to support

multiple queues and Quality of Service features

such as IEEE 802.1p, 802.1Q and ResourceReservation Protocol (RSVP).

Voice quality is most affected by transmis-sion delays across the fabric, which cause gaps

in the conversation when one party stops

talking and the other begins speaking. Delaysare introduced at a number of points in the

network. One source is the encoding of voice

from analog to digital. This conversion delay

is exacerbated by voice compression algo-rithms, which require large samples of the

voice stream before compressing and packe-

tizing it. A similar delay occurs at the remoteend when the voice is converted back to

analog.

Additional delays are incurred as thepacket propagates through the packet net-

work, though as long as the packet remains on

a LAN with wire-speed switches, the propaga-

tion delay is minimal. At the LAN/WAN edge(the router, Layer 3 switch, or other access

device), however, there can be considerable

queuing delays because of the speed disparitiesbetween LAN and WAN.

A more vexing problem occurs because of

the variability of delay, also called jitter. Jitterdelays occur primarily because of traffic condi-

tions on the backbone network. One particu-

larly troublesome problem is head-of-lineblocking. If all packets arriving in a switch (or

router) are treated with the same priority, avoice packet can get stuck in queue behind

other, less time-critical packets. But the nextvoice packet traversing the network might not

incur the same delay. The result is an accordion

effect, where several packets arrive over a largeinterval or, conversely, in quick succession.

Without appropriate design, this can wreak

havoc on a telephone conversation. A numberof techniques have been developed to address

this problem. One technique is to use jitter

buffers to smooth out the ebb and flow of

packets. However, jitter buffers, which store astring of packets, introduce additional

absolute delay.

A third problem is packet loss. Most endstations using data connections are designed

to accept and recover from an occasional lost

packet. Unfortunately, the human ear is not sotolerant. Unless the network employs specific

countermeasures, such as forward error correc-

tion or error concealment, users will hear

11


13/14

annoying gaps and clicks. The effect on usersdepends upon the packet loss rate and the

compression algorithm used. The higher com-

pression schemes are less forgiving.

Key Market Issues

The packet telephony market today is embry-

onic. Most products have proprietary imple-mentations; very few use VOIP standards,

because the standards themselves are in flux.

As a result, different vendors products are notinteroperable.

The industry is working feverishly to

deliver a business-quality product, and given

the multi-bill ion dollar market opportunity,there is little doubt that such products will

emerge rapidly. 3Com has introduced a busi-

ness quality solution in its Total Controlremote access concentrator, a carrier-class

platform that features high reliabil ity and

redundancy.

Where Is the Technology Going?

Data networking technology is becoming

increasingly pervasive, ubiquitous, and essen-tial. LANs have already spread out from niche

applications in the enterprise, across the enter-

prise, to medium and small businesses. The

next wave of technology promises ubiquity ofdata networks in the home. As this common

transport permeates our society, it will become

a key medium for carrying voice.Another trend is the rapid improvement

in technology. The initial packet telephony

implementations are appropriate for pilot andtrial networks. A new generation, shipping

shortly, will bring the quality and reliability

up to business standards. The capabilities willcontinue to improve rapidly, driven primarily

by rapid improvements in digital signal pro-

cessing technologies, which are key to con-verting voice between the packet- and circuit-switched worlds. Correspondingly, costs will

plummet as manufacturers deliver production

volumes.A third area of improvement is deploy-

ment of QoS and policy-based management

capabilities over the IP fabric. 3Com andother manufacturers are beginning to deliver

next-generation product portfolios that sup-

port bandwidth reservation, multiple classes ofservice, quality of service, and other features

required by telephony and video applications.

Another trend that portends the wide-

spread deployment of packet telephony is thefavorable competitive environment that will

emerge over the next two decades, particularly

for carriers. A recent treaty, driven by theITU, lays the groundwork for deregulating

service in the countries that comprise 95

percent of the worlds long-distance market.That phenomenon, in conjunction with the

telecom free-for-all in the United States and

the desire of alternative service providers to

penetrate all markets including access to thehome, promises to drive a huge market in

packet telephony. In fact, one Dataquest

analyst recently predicted that long-distancecosts would drop from an average of five cents

per minute to one cent per minute for IP

connections.For many businesses, however, real value

will be obtained not by lower long-distance

costs, but by the benefit of delivering voiceand data together, enhancing worker effective-

ness and productivity. Additionally, packettelephony lays the framework for multimedia

communications such as desktop videoconferencing, enhancing the productivity of

collaborating groups of people through rich

communications.We are on the verge of a new era. Packet

telephony will drive an explosion of commu-

nications between individuals and betweencollaborating workgroups worldwide. The

tools, and the tools to build the tools, that are

being created by a unified, open communica-

tions architecture will create an environmentthat fosters competition and encourages inde-

pendent application providers. Driven by

packet telephony, this revolution will lay thefoundation for corporations to work in innov-

ative, productive, and effective ways.

12


14/14

Printed in U.S.A. 500657-001 3/98

1998 3Com Corporation. All rights reserved. 3Com is a publicly owned corporation (NASDAQ.COMS). 3Com and SuperStack are registered trademarks of3Com Corporation or its subsidiaries. PACE, PathBuilder, and Total Control are trademarks of 3Com Corporation or its subsidiaries. Windows and WindowsNT are trademarks of Microsoft. Wildfire is a trademark of Wildfire Communications. Other brand and product names may be trademarks or registered trade-marks of their respective owners. All specifications subject to change without notice.

3Com CorporationP.O. Box 58145

5400 Bayfront Plaza

Santa Clara, CA

95052-8145

Phone: 800-NET-3Com

or 408-764-5000

Fax: 408-764-5001World Wide Web:

http://www.3com.com

3Com ANZASydney, Australia

Phone: 61 2 9937 5000

Fax: 61 2 9956 6247

Melbourne, Australia

Phone: 61 3 9866 8022

Fax: 61 3 9866 8219

3Com Asia LimitedBeijing, China

Phone: 8610 6849 2568

Fax: 8610 6849 2789Shanghai, China

Phone: 86 21 63501581

Fax: 86 21 63501531

Hong Kong

Phone: 852 2501 1111

Fax: 852 2537 1149

India

Phone: 91 11 644 3974

Fax: 91 11 623 3192

Indonesia

Phone: 6221 572 2088

Fax: 6221 572 2089

Korea

Phone: 82 2 319 4711

Fax: 82 2 319 4710

Malaysia

Phone: 60 3 732 7910

Fax: 60 3 732 7912

Pakistan

Phone: 92 21 5846240

Fax: 92 21 5840727

Philippines

Phone: 632 892 4476

Fax: 632 811 5493

Singapore

Phone: 65 538 9368

Fax: 65 538 9369

Taiwan

Phone: 886 2 377 5850Fax: 886 2 377 5860

Thailand

Phone: 622 231 8151 5

Fax: 622 231 8158

3Com BelgiumBelgium, Luxembourg

Phone: 32 2 725 0202

Fax: 32 2 720 1211

Netherlands

Phone: 31 30 6029700

Fax: 31 30 6029777

3Com CanadaCalgary

Phone: 403 265 3266

Fax: 403 265 3268

Montreal

Phone: 514 683 3266

Fax: 514 683 5122

Toronto

Phone: 416 498 3266

Fax: 416 498 1262

Vancouver

Phone: 604 434 3266

Fax: 604 434 3264

3Com FrancePhone: 33 1 69 86 68 00

Fax: 33 1 69 07 11 54

3Com GmbHMunich

Phone: 49 89 627 320

Fax: 49 89 627 32 233

Austria

Phone: 43 1 580 17 0

Fax: 43 1 580 17 20

Berlin

Phone: 49 30 34 98790

Fax: 49 30 34 987999

Poland

Phone: 48 22 645 1351

Fax: 48 22 645 1352

Switzerland

Phone: 41 31 996 1414

Fax: 41 31 996 1410

3Com IrelandPhone: 353 1 820 7077

Fax: 353 1 820 7107

3Com JapanPhone: 81 3 3345 7251

Fax: 81 3 3345 7261

3Com Latin AmericaU.S. Headquarters

Phone: 408-326-2093

Fax: 408-764-5730

Argentina

Phone: 541 312 3266Fax: 541 314 3 3329

Brazil

Phone: 55 11 5181 0869

Fax: 55 11 5182 7399

Chile

Phone: 562 633 9242

Fax: 562 633 8935

Mexico

Phone: 525 520 7841

Fax: 525 520 7837

3Com Northern Latin

AmericaMiami, Florida

Phone: 305-261-3266

Fax: 305-261-4901

Colombia

Phone: 571 629 4110

Fax: 571 629 4503

Venezuela

Phone: 582 953 8122

Fax: 582 953 9686

3Com MediterraneoMilano, Italy

Phone: 39 2 253011

Fax: 39 2 27304244

Rome, Italy

Phone: 39 6 5279941

Fax: 39 6 52799423

SpainPhone: 34 1 509 69 00

Fax: 34 1 307 66 63

3Com Middle EastPhone: 971 4 349049

Fax: 971 4 349803

3Com Nordic ABDenmark

Phone: 45 39 27 85 00

Fax: 45 39 27 08 44

Finland

Phone: 358 0 435 420 67

Fax: 358 0 455 51 66

NorwayPhone: 47 22 58 47 00

Fax: 47 22 58 47 01

Sweden

Phone: 46 8 632 56 00

Fax: 46 8 632 09 05

3Com RussiaMoscow

Phone: 007 095 258 09 40

Fax: 007 095 258 09 41

3Com South AfricaPhone: 27 11 807 4397

Fax: 27 11 803 7405

3Com UK Ltd.Marlow

Phone: 44 1628 897000

Fax: 44 1628 897003

Manchester

Phone: 44 161 873 7717

Fax: 44 161 873 8053

Edinburgh

Phone: 44 131 240 2900

Fax: 44 131 240 2903

Date post:	03-Jun-2018
Category:	Documents
Upload:	-
View:	217 times
Download:	0 times

Packet Telephony Primer

Documents