VoIP Architecture Ag 0207

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Entire c onte nts 2002 Vangua rd Co mm unicat ions Corpo ration.

All right s reserved . Sto rage o r reprod uc tion of this public at ion in

any form or media without prior written permission is prohibited.

a White Paper from

Vanguard Communications

Which VoIP Architec ture

Makes Sense For Your Contac t Center?

by

Areg Gharakhanian

Aug ust 2002

Vanguard Communications Corporation

100 Americ an Roa d

Morris Plains, New Jersey 07950+1 (973) 605-8000

www.vanguard.net


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page 12002 Vanguard Communications Corporation. All rights reserved.

Voice

Networks

(800, Local,

Long Distance)

T1

PRI

Analog Call Control Software

TDM Switching matrix

CPU/Common Control

Data

Networks

(WAN, Internet,

etc.)

BusinessApps Server

RouterEthernetSwitch

Voice MailIVR

Which VoIP Architecture Makes Sense For Your Contact Center?By A reg Gharakhanian, V anguard Comm unications

Convergence of voice and da ta is becoming a rea lity, and Voice over Intern et Protocol (VoIP) is

taking center stage. The early momentu m centered on carrier-based VoIP services, with

provider s setting their sights on the $100+ billion long distance services market. Now , theVoIP-based p remises equipment m arket is heating up , with Cisco and oth er data netw orking

compan ies staking claim to this territory. Traditional switch vend ors have respond ed by

shifting their produ ct development focus away from p roprietary systems to software-based

solutions that ru n on converged architectures.

Its time for enterprises to determine when an d how to tran sition their voice comm un ications

infrastructures to the next generation technology. A starting point for migration p lanning is a

solid u nd erstanding of the architectural options. This pap er describes trad itional circuit-

switched, IP-enabled, and IP-centric architectures, and add resses the pros an d cons for each

alternative.

Life In The TDM World

A trad itional Private Branch Exchan ge (PBX) or Automatic Call Distribution (ACD) system is

comprised of a central processing unit running call processing software, a Time Division

Mu ltiplexing (TDM) switching m atrix, network inter face card s (e.g., analog, T1, PRI tru nks),

end u ser telephon es (stations), and associated cabling. The TDM switching matrix is

responsible for establishing conn ections between end poin ts. It uses circuit-switchedtechnology

to allocate p re-defined band width (typically 64 Kbps before comp ression) for the d ura tion of

each call.

Figure 1: TDM Single Site Dep loyment


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VoIP Architectures


User teleph ones, voice mail servers, an d Interactive Voice Response (IVR) systems are

connected to the PBX or ACD. A separate infrastructure sup ports packet-switcheddata

connections to the local area network (LAN) and wide a rea netw ork (WAN) to provide access to

enterprise compu ting resources and the Internet (see Figure 1). Both the voice and data

infrastructures require technical sup port to install, configure an d service all of the end points,

and ad ministrative sup port to maintain the user database.

Figure 2 p rovides an examp le of a virtual call center configuration in wh ich th e headqu artersACD receives the bu lk of the incoming calls and d irects the call routing activities for all

locations in the n etwork. When qu alified agents are ava ilable at headqu arters, the ACD

switches incoming calls to local stations. When calls need to be rou ted to either Site A or Site B,

the head quar ters ACD extend s them out to the sites via dedicated, point-to-point voice

connections, usua lly T-1 circuits. In this configuration, Site A is configured w ith a remote

carrier capable of d irect network access. Calls can be received d irectly into Site A (e.g., local

calls), and routed to the ap prop riate agents as directed by the central processor located at

Head quar ters. Since the p rincipal non -voice business app lications reside on servers at the

head quar ters data center, the sites must also be configured with d ata access over a WAN.

Data

Networks

(WAN, Internet,

etc.)

BusinessApps Server

Router

EthernetSwitch

Router

Voice

Networks

(800, Local,

Long Distance)

Router

Site A

Site B

Headquarters

VoiceMail

IVR

EthernetSwitch

EthernetSwitch

Figure 2: TDM Mu lti-site Deploymen t

In a simple netw ork w ith few sites, the du plication in voice and data infrastructure can be

man aged. But wh at about operations that supp ort a large num ber of sites? Or wh at if all the

locations receive incoming calls and then selectively route them to other sites on a peer-to-peer

basis? This is another common mu lti-site configuration, frequently u sed w hen formerly

autonom ous centers with their own switches are networked into a virtua l operation. In these

scenarios, multi-site connectivity requ irements are often implemented via d edicated point-to-


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VoIP Architectures


point circuits among the sites. The expense an d complexity of this arrangement becomes

significant with a s few as four locations, and grow s drama tically w ith more.

The pros and cons of the traditional TDM world a re summar ized below.

Advantages of TDM Disadvantages of TDM

Proven and reliable technology.

Addresses call queuing and music-on-hold withinthe main chassis. Many TDM systems canprovide announcements and collect callerentered digits using telephony cards.

Scales well for large call centers, especially forcenters requiring call treatment for a largenumber of callers in queue.

Requires significant investment in a single

vendors proprietary technology that is no longerthe focal point of that vendors R&D efforts.

Requires separate infrastructures for voice anddata with separate hardware and softwarecomponents, and increasing administration andmaintenance costs.

Increases connectivity expenses andcomplexities in multi-site configurations.

Life In The VoIP World

VoIP-based PBX and ACD systems conver t voice conversations into packets and stream 1 them

between end points using the Internet Protocol (IP). Voice IP packets traverse the d atainfrastru cture u sing one of a var iety of stand ard VoIP pr otocols (e.g., H.323, SIP, MGCP,

Megaco/ H.248) and vend or-specific protocols. See Sidebar on page 8.

The main challenge with VoIP is implem enting th e app rop riate Quality of Service (QoS) to

ensure that v oice p ackets arrive at their d estinations in an acceptable time frame (within 150

msec) and w ith minimu m jitter (variation in inter-packet delay), so that users hear a continu ous

flow of speech. To accommod ate these requirements, most enterprises use high-speed (10/ 100

Mbp s) Ethernet switches to conn ect end poin ts on their LANs. They also configure Virtua l

LANs (VLANs) to segment v oice end points from d ata end points, thereby minimizing the

potential for d ata p ackets to adv ersely imp act voice packet delivery. In add ition, the IEEE

standa rd 802.1p/ Q allows packet prioritization, giving voice frames higher p riority than data

frames.

The basic building blocks of VoIP-based PBXs and ACDs are ga teway devices that conv ert calls

from TDM to IP, call control processors, IP phones, and the associated data commu nications

infrastru cture (routers, Ethernet switches, and cabling). This basic architecture comes in two

flavors: IP-enabled and IP-centric. The two are primarily differentiated by:

1. Where the TDM to IP conversion takes place

2. Where supp orting call center functions, such as queuing, queue slots, promp ting, mu sic-on-

hold, and an noun cements, take place.

1 Voice packet tran smission is accomp lished using th e Real time Transp ort Protocol (RTP) over IP. This

pr otocol is focused on d elivering packets to the distant end w ithout retran smissions. It conserves time

that m ight otherwise be consumed re-sequencing p ackets that w ere delivered ou t of order, or

retransmitting corrupted data both common occurrences in d ata packet transmission. The continuous

transm ission of voice packets is often referred to as streaming.


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VoIP Architectures


Voice

Networks

(800, Local,

Long Distance)

T1

PRI

Analog

Call Control Software

TDM Switching matrix

CPU/Common Control

IP Gateway

Data

Networks

(WAN, Internet,

etc.)Business

Apps Server

Router

EthernetSwitch

IP Phone

TDM Phone

Voice MailIVR

IP-enabled Architecture

An IP-enabled system has essentially the same core architecture as a TDM system (switching

matrix, common control, call processing software), with the ad ded ability to service both TDM

and IP phones via d ifferent station-side cards, and terminate IP netw ork connections (see Figure

3). The CPU/ common control and call control software may reside in the TDM switching

matr ix, or on an external server.

In an all-IP station d eployment, th e IP-enabled architecture leverages the enterprises d atainfrastructure for both IP phone and PC connectivity. Most IP phon es are equipped with a

mini-Ethernet sw itch that connects the users IP ph one and PC to the Ethernet switch using a

single port. The IP phones min i-switch transm its packets with specific QoS and VLAN settings

such that voice and d ata are given app ropriate transmission priority in the network. Call

queu ing, recorded an noun cements, and mu sic-on-hold are provided on the TDM switch. Since

an IP-enabled architecture can service both TDM an d IP phones an d network connections, it

provid es a low risk transition p lan for businesses that w ant to m igrate users to IP slowly.

Figure 3: IP-enab led Sin gle Site Dep loyment

In a multi-site environ ment, an IP-enabled architecture simp lifies inter-site connectivity. The

separate commu nications paths u sed for voice and da ta in a TDM world a re combined into a

consolidated d ata infrastructure.

Figure 4 show s a VoIP-enabled m ulti-site environment. Here, the head quarters location

equipm ent p rovides all of the routing intelligence, and d irects inbound calls to the appropriate

location over the WAN. Note that in this example, Site Bs equipment is stripped dow n to a

bare minimu m a rou ter, an Ethernet switch, and IP phon es. Calls destined for Site B are

terminated a t the headqu arters switch, converted to IP via gateway cards, and transp orted to

Site B via the da ta infrastructure and WAN.

Site A can receive inboun d calls from head quarters over the WAN (similar to Site B), or d irectly

from the PSTN w ith remote call control performed by the head quar ters IP-enabled sw itch. For

most vend ors, this set-up requ ires the add ition of a media gatew ay at Site B. Some m edia

gateways sup port TDM-based recorded annou ncements and tou ch-tone detection via resource


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VoIP Architectures


cards to allow for localized caller treatment in qu eue. This arran gement requ ires that the med ia

gateway and IP-enabled headqu arters switch be provid ed by the same vendor. Other vendor

solutions han dle caller treatm ent at th e head quarters site by streaming aud io signals associated

with ann ouncements or mu sic over the WAN.

A WAN with adequate QoS performance is critical for a successful multi-site VoIP deployment.

While the pu blic Internet does not su pp ort QoS, most p rivate WAN service providers offer

service level agreements and performan ce guarantees. Some p roviders also allow users toprioritize their packets as they traverse the WAN by using stand ard QoS techniques (examp les

include 802.1 p/ Q, DiffServ, MPLS, RSVP, and WFQ).

Data

Networks

(WAN, w/QoS)

BusinessApps Server

Router

EthernetSwitch

Router

EthernetSwitch

Voice

Networks

(800, Local,

Long Distance)

Router

Site A

Site B

Headquarters

Gateway

Media Gatewaywith announcementresources, etc.

VoiceMail

IVR

EthernetSwitch

Figure 4: IP-enab led M ulti-site Dep loyment

The pros and cons of IP-enabled solutions are summ arized below.

Advantages of IP-enabled Disadvantages of IP-enabled

Includes TDM components and software that areconsidered proven and reliable technology.

IP-enabled switch cabinet handles callertreatment efficiently with queue slots,announcements, music-on-hold, and caller

entered digits using telephony cards. Scales very well for large call centers that must

support large number of callers in queue.

Begins migration to IP while leveraging existinginvestment and minimizing risk.

Requires significant investment in a singlevendors proprietary technology that is no longerthe focal point of that vendors R&D efforts.

Multi-site configurations may require additionalproprietary components (e.g., media gateways),

further increasing investment in a single vendorsolution.

Mixed architecture includes TDM and IP basedcomponents with greater managementcomplexity than IP-centric architectures.


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VoIP Architectures


Voice

Networks

(800, Local,

Long Distance)

Data

Networks(WAN, Internet,

etc.)

BusinessApps Server

Router

Gateway

CallControlServer

Media Server(music on hold,announcements, IVR, etc)

EthernetSwitch

Voice Mail

IP-centric Architecture

IP-centr ic systems comp letely decomp ose the TDM based architecture. The TDM switching

matr ix is rep laced with the enterp rises d ata infrastructure, and call control, call queu ing,

annou ncements, touch tone prom pting, and mu sic-on-hold functionality is provided via

separate server p rocesses that may or m ay n ot reside on sepa rate p hysical servers (see Figure 5).

Figure 5: IP-centr ic Single Site configu ration

In a single site deployment, a rou ter blade acts as the med ia gateway. Thereafter, all call

processing an d switching is don e via packets. Call control fun ctionality is usually performed by

a separate server, and may be configured in a cluster for redu nd ancy. Call queu ing, music-on-

hold, annou ncements, and collection of caller entered digits are performed via a separate m edia

server. Add itional media servers may be required based on the num ber of simultaneoussessions/ connections. Curren tly, each call in queu e whether listening to mu sic or an

annou ncement is allocated a ded icated VoIP stream, which uses server CPU cycles. IP multi-

cast techniques, w hich wou ld allow mu ltiple callers to listen to one resource simu ltaneously,

have not yet been imp lemented.

An IP-centric system ap plies the same decomp osition to a mu lti-site dep loyment. A centralized

call control server contro ls VoIP streams, wh ether they arrive at the main facility or the rem ote

sites (see Figure 6). In this deploym ent, the call control server at head quarters controls all

inbound commu nications indepen dent of location. Call queu ing, mu sic-on-hold,

annou ncements, and prom pting functionality are provided centrally via the headqu arters

media server.

PSTN calls inboun d to th e head quar ters are converted from TDM to IP via the router blad e.

The call control server establishes a VoIP stream with the m edia server for qu eue treatm ent and

prom pting functionality, and then connects the call with the app ropriate IP phone.

Comm un ication between the h eadqu arters and the remote locations is similar to the IP-enabled

solution.


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VoIP Architectures


Data

Networks

(WAN, w/QoS)

BusinessApps Server

EthernetSwitch

Voice

Networks

(800, Local,

Long Distance)

Router

Site A

Site B

Headquarters

Router

Gateway

Call ControlServer

Media Server(Music on hold,announcements)

Router

Gateway

Voice Mail

EthernetSwitch

EthernetSwitch

Figure 6: IP-centric M ulti-Site configu ration

The pros an d cons of IP-centric solutions are sum mar ized below.

Advantages of IP-centric Disadvantages of IP-centric

Provides a flexible and consistent architecture forcall routing.

Completely leverages the data infrastructure, andminimizes investment in TDM components.

Provides greater flexibility in distributedenvironments, especially in configurations withlocal direct calling into multiple smaller sites.

Provides choice in technology elementpurchases, enabling a mixed vendor environment

for routers, servers, software applications, etc.

Decomposed architecture requires multipleserver platforms.

Leading edge technology and newer code set arenot battle tested.

Requires a highly reliable and robust datainfrastructure.

Does not scale well today for providing queuetreatment for large number of callers (e.g., musicon hold, announcements, etc.).

Can be considered less reliable; may not be wellsuited for 24X7 call center operations.


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VoIP Architectures


Summary

VoIP will be the technology of the futu re for contact centers. The string of VoIP-based p rod uct

annou ncements by traditional equipment vend ors fully sup ports this pred iction. Convergence

of voice and data simp lifies the infrastructure, and decoup les the call control fun ction by

transitioning it to an ap plication residen t on an enterpr ise network. The benefits are magnified

in a m ulti-site environm ent.2

IP-enabled and IP-centric app roaches provide similar capabilities w ith some subtle d ifferences.

Although the evolution of these offerings may further blur the d ifferences, buyers should be

aw are of the basic characteristics of each architecture to choose w isely the VoIP approach that

best supp orts their business strategy.

A key deciding factor in determ ining when and how to move to VoIP is the migration strategy.

IP-enabled ap proaches w ill app eal to the m ore conservative and heavily invested call center

environmen t, while IP-centric method s will be the choice of smaller, new er, and more

aggressive centers wh o can bear some reliability risk to move faster to a more adv anced

platform.

Sidebar: VoIP St andards

VoIP standards are still evolving w ithout a clear winner. Many vend ors curr ently supp ort or

plan to sup port several of the standard s. There are also a few p roprietary app roaches that claim

better performance and functionality. Often vendor prod ucts are based on a mixture of

prop rietary and stan dard s-based call control features.

The main VoIP stand ards tod ay are:

H.323 is the most mature and m ost wid ely implemen ted standard to date. H.323 was

developed by the Intern ational Telecommu nications Union (ITU) in 1996, and is now in its

fourth revision (i.e., H.323 version 4). Microsofts NetMeeting is based on H .323.

SIP (Session Initiation Protocol) is a m ore recent stand ard , developed by the Internet

Engineering Task Force (IETF). SIP focuses on call initiation an d termination betw een

end points. It is a simp ler stand ard th an H .323, but not as feature rich. SIP has been adop ted by

some carr iers; a SIP-based softph one is includ ed in Microsofts Windows XP.

MGCP (Media Gateway Con trol Protocol) is another recently developed standard by the IETF.

MGCP was primarily d efined to ad dress how a softswitch (a software-based IP-switch

generally sitting in the p ublic network, such as an IP Central Office switch), can control gatew ay

type equipm ent, including IP phones.

Megaco/H.248 is a standard jointly developed by the ITU and IETF. Megaco/ H.248 improvesup on MGCP, and is intend ed to be its successor.

2 See Vanguard s companion p aper Should Contact Centers Jum p on th e VoIP Bandwagon ? to

un derstan d p ossible app lications and business benefits of migrating your call center to VoIP.


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VoIP Architectures


Vang uard Co mm unic ations is the lea ding indep end ent c onsulting c om pany in the

c ontac t c ente r industry. Found ed in 1980, Vangua rd helps c lients me et b usiness go a ls

by planning, designing, and imp lem enting solutions for custom er co ntac t a nd for

ma naging c ustom er and p artner relationships.

Co re services include stra teg y deve lop me nt, assessme nt a nd design, req uirem ents

planning, and imp lem enta tion mana ge me nt, for bo th traditiona l c all c enters andem erging ec om me rc e tec hnolog y. We wo rk extensively with ACDs, IVR, CTI, Web

ac c ess, network arch itec ture, CRM a nd other software systems, and business p roc ess

design.

Plea se c onta c t us if you ha ve a ny questions about this White Paper, or ab out how som e

of these idea s might a pp ly to your organiza tion. The author, Areg Gha rakhanian, ca n

be rea che d at a reg@vangua rd.net.

And visit our website to read o ther a rticles and White Papers. There, you c an also lea rn

ab out our rec ently pub lished bo ok, Ca ll Cente r Tec hnolog y Demystified .

Vanguard Com munica tions Corp.

100 Americ an Roa d

Morris Plains, New Jersey 07950

+1 (973) 605-8000

www.vanguard.net

Documents

VoIP Architecture Ag 0207