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IntroductionThe desire for cost control, higher userproductivity, and advanced call centerfeatures is leading a growing number ofcompanies to consider IP telephony now.The year 2005 is considered by manyanalysts as the “year of inflection” whenmore IP-PBX ports will ship than legacydigital PBX ports.
This white paper reviews implementationoptions for enterprises that are choosingnetwork and application convergence. Forthese organizations, this is a time for facingreadiness challenges and for “tuning” theirdata network to Voice over IP (VoIP).
Four Voice Readiness OptionsThe following approaches can help determinethe nature and extent of enterprise networkmodifications. Only one, however, providesa systematic plan, involving actual tests ofvoice traffic across a pre-existing network.
Approach 1: Trial and Error FollowingSystem Installation
This approach is based on the assumptionthat a well functioning data network willhandle voice traffic with only minor changes.It assumes that problems will be quicklyidentified and easily fixed. Actual practice,however, shows many risks that can affectvendor brand, reseller relationships, andthe IT department’s reputation.
One highly probable risk is network down-time, an event that can interrupt businessactivities and result in lost productivity. Inaddition, should the trial create networkproblems, post-installation issues can resultin significant non-budgeted expenses—theneed to purchase additional equipment, thecost of IT troubleshooting time, and lostemployee efficiency.
Approach 2: Trial and Error WithSequential Segment Installation
While this approach appears at first glanceto mitigate deployment risks, it fails to
consider the network and the IP telephonyapplication as a complete converged system.As more IP telephony devices are deployed,new problems may arise requiring furthertroubleshooting efforts.
Because this approach is usually laborintensive, it can negatively impact usersatisfaction and inadvertently impact othernetwork segments. The net result can be ahybrid environment that is able to offerlittle more than IP dial tone and a supportenvironment in which staff must continuallyreact to emergencies. The company’s abilityto utilize many of the cost saving featuresand productivity improvements that moti-vated its IP telephony purchase in the firstplace may be compromised.
Approach 3: Trial and Error DeploymentFollowing a Questionnaire
While this approach is somewhat moreproactive, questions are likely based ontypical scenarios. The result is the identifi-cation of possible, but not actual situationsthat may arise. Unidentified problems caneasily surface after the implementation,creating the same risks as the other trial anderror approaches—unanticipated expenses,the need for extensive troubleshooting, and aprolonged period of migration and adjustmentto a fully-functioning converged network.
Approach 4: Measure, Simulate, and Predict
3Com has a proven alternative to these trailand error methods—the 3Com® VoiceReadiness Service. Implemented by trained3Com professionals, this service simulatesvoice traffic (with real VoIP packets) acrossthe data network using state-of-the arttools to capture network performance dataand estimate likely traffic loads. The serviceconsiders key factors such as utilizationrates on specific segments and data packetbehavior under a variety of customizableconditions.
The assessment evaluates the health of thetested network, in terms of power, quality of service, and differentiated service in the
Taking the Guesswork Out of DeployingIP Telephony
C O N T E N T S
Introduction....................................................1
Four Voice Readiness Options .........................1
How Voice Over IP Differs from Data Communications ....................................2
Industry-Standard Voice QualityMeasurement .................................................2
Voice Readiness Testing ..................................3
Summary ........................................................3
About the Author...........................................3
F R E E D O M T O C H O O S E A B E T T E R N E T W O R K
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Wide Area Network. It predicts audio qualityrating based on a statistical sampling of users,helping IT staff determine optimum networkconfiguration within a predefined voice trafficutilization pattern. This type of assessmentcan save an enterprise time and money, andprovide assurance of a high-quality imple-mentation the first time—without a need formultiple trial and error efforts.
How Voice Over IP Differsfrom Data Communications Ethernet and IP networks are engineered toaccommodate data applications that have ahigher tolerance for packet loss than voicetraffic. Lost data packets are merely resentby the source, while voice packets are withoutrecourse when lost in a packet flow. The lossof parts of words during transmission resultsin poor sound quality. Lost packets andtransmission delays are typically due tonetwork congestion, often from poor band-width utilization and/or insufficient WANlink capacity.
Jitter, a natural occurrence in a data network,can also impact the quality of voice traffic.It results from a variance in the time stampsthat are placed on both the sending andreceiving ends of the packet. This variancecan be corrected by adding buffers to storethe packets and “feed” them in a steadystream to the application.
Compression is another voice traffic sensi-tivity. Packets are compressed for sendingand then must be expanded again when theyare received. IT managers who wish to usecompression to manage bandwidth mustbalance the communications impact of usingless than the highest quality packets. Inaddition, multiple passes through compres-sion/decompression cycles can cause pooraudio quality.
IP telephony requires network equipment toprovide traffic identification features. Type ofService (ToS) distinguishes the packet type andtags it for WAN transport. Quality of Service(QoS) enables switches and routers to prioritizevoice packets in order to minimize packet lossand transport delay. Network equipmentpurchased before 2002 typically does not haveQoS capabilities. Yet, adequate traffic priori-tization is critical to avoid lost or delayedpackets and ensure high voice quality.
Because each network is unique in terms of itsconfiguration/use profile, a successful migra-tion to IP telephony requires an evaluationof the amount and type of voice traffic it
carries—as monitored during actual networkactivity periods. A customized series of testsconducted at intervals on a live network andusing a variety of parameters can capturenetwork performance under a range of loadsand conditions. By calibrating these tests toproduce predictors of industry standardscores, enterprises can obtain the most rele-vant information to help assure a successfulIP telephony deployment.
Industry-Standard VoiceQuality MeasurementThere are two industry-standard measure-ments of voice quality. The most commonlyused is the Mean Opinion Score (MOS),described in detail in the InternationalTelecommunication Union (ITU) publication,ITU-T P.800 methods for subjective determi-nation of transmission quality. E-Model, asecond standard, is based on a computationalmodel that uses the R-Value as its output.This method is described in the ITU-publi-cation, ITU-T G.107 The E-Model, acomputational model for use in transmissionplanning.
For the most comprehensive results, 3Comvoice assessment tests provide scores usingboth measurements, since each provides arating of listener-perceived call quality—even though based on different scales.
Delay between speaking and listening existsin traditional telephony systems, but it is notnoticeable; delay over 200 milliseconds isnoticeable and annoying to the user. Becausethere are five types of delay that can impactany telephony system, each type needs to beidentified and measured in order to pinpointpotential problems. The first two types ofdelay—propagation and transit—are foundat the network layer and together are knownas “network delay”. The other three—pack-etization, jitter buffer, and fixed delay—arefound at the application layer.
Additionally, delay should be measuredseparately in each packet direction since thesend and return signals can travel differentpaths in an IP network. Analysis tools toensure a complete and accurate assessmentshould therefore include virtual clocks ateach end point.
Packet transit time is measured to understandjitter. Because transit times vary, packets arenot always received in order and need to beheld until they can be properly sequenced.Since this traffic hold is perceived by thesystem user as “choppy” voice quality, jitter
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TAKING THE GUESSWORK OUT OF DEPLOYING IP TELEPHONY
F R E E D O M T O C H O O S E A B E T T E R N E T W O R K
levels are factored into the MOS calculation.Testing provides information to help determinethe proper size and placement of the jitterbuffers used to alleviate delays and smoothpacket delivery to the voice application.
Voice Readiness TestingDepending on the network size, a thoroughvoice assessment typically takes two to sevendays to complete. An initial interview identifiescurrent and future needs that help determinethe design of custom tests. Network architec-ture and equipment, typical call durationand frequency, and peak usage hours areconsidered in creating a network- and user-specific test.
3Com tests utilize actual voice packets sentto an end point and then returned to theprimary testing computer. The number ofLAN segments with phones determines thenumber of end points required. Each endpoint can take the place of numerous phonesto measure the call volume that a networkcan handle.
Bandwidth testing is an important part ofthe assessment. If the IT manager prefers todo the testing after normal business hours, itcan be simulated to match prime time levels.Based on the data, models are created toshow how the network will respond withanticipated call volumes—useful informa-tion for identifying a need for increases ordecreases in currently available bandwidth.
Compression/decompression (CODEC) testinghelps IT management determine the need forpacket quality improvement and the possi-bility of reducing expensive bandwidthrequirements. This information also helpsdetermine the type of CODEC that should beused in the deployment.
Enterprises use only a certain percentage oftheir network at any given time. Utilizationpatterns, determined by the IT manager, areunique for each network. The voice assessmenttest design must consider these patterns inorder to provide a quantitative display of howadded voice traffic may impact the network.These measurements are critical to ensuringthe highest possible call quality when design-ing additions or making modifications tonetwork infrastructure.
Data Assessment
A crucial part of the voice assessment is theinterpretation of data based on a company’snetwork environment and business objectives.Recommendations will confirm that thenetwork is IP telephony-ready or indicate aplan on how to obtain readiness. Experts,trained in data and voice technology, canidentify and resolve issues at a detailed levelbefore the implementation begins. Predictivetools and experience let them trace delay orjitter causes to a specific piece of equipmenton a single segment. With this type of precisedata, resolution can be as simple as a changein configuration or a software upgrade.
SummaryVoice assessment is a collaborative processthat allows IT management to test possibledeployment scenarios and identify availableoptions. A complete voice assessment caneliminate the risks, cost, and applicationsimpact of a trial and error approach toimplementing converged networking. Itarms IT managers with the information theyneed to create an efficient and economicaltransition to IP telephony services.
About the Author Ed Sturm, a product developer for 3Com Global Services, brings extensive experience to thisdiscussion on how to assure the voice readiness of enterprise networks. During more than adozen years in the telecommunications and networking industies, he has focused on professionalservice offerings. Ed began his 3Com career as a VoIP engineer in customer services taskedwith enhancing support processes for 3Com voice products. He earned a Bachelors Degree inBusiness with a minor in Electronics Engineering following ten years as an electronics technicianwith the U.S. Navy.
For additional information, visit www.3com.com.
By taking the guesswork out of IP telephonydeployments, the 3Com Voice ReadinessService helps businesses painlessly gain thebenefits of advanced networking solutions.This expert-designed-and-delivered assess-ment simulates voice traffic on the datanetwork, interprets findings, and results inrecommendations that can prevent unex-pected costs and post-installation issues.
Supported by experience gained from over19,000 deployed systems and a history ofbringing practical innovations to market,3Com is changing the way business speaks.
3Com Corporation, Corporate Headquarters, 350 Campus Drive, Marlborough, MA 01752-3064
To learn more about 3Com solutions, visit www.3com.com. 3Com is publicly traded on NASDAQ under the symbol COMS.
The information contained in this document represents the current view of 3Com Corporation on the issues discussed as of thedate of publication. Because 3Com must respond to changing market conditions, this paper should not be interpreted to be acommitment on the part of 3Com, and 3Com cannot guarantee the accuracy of any information presented after the date of publication. This document is for informational purposes only; 3Com makes no warranties, express or implied, in this document.
Copyright © 2005 3Com Corporation. All rights reserved. 3Com and the 3Com logo are registered trademarks of 3Com Corporation.Exercise Choice is a trademark of 3Com Corporation. All other company and product names may be trademarks of their respectivecompanies. While every effort is made to ensure the information given is accurate, 3Com does not accept liability for any errorsor mistakes which may arise. Specifications and other information in this document may be subject to change without notice.
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For additional information contact 3Com Global Services
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