managed migration to ip telephony in a pbx … migration to...executive summary although many...

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Managed Migration to IPTelephony in a PBX Environment:Intel® NetStructure™ PBX-IP Media GatewayCan Provide the Critical Link

Whitepaper

ContentsIntroduction 1

Market Research Reveals Trends 2

Connecting IP Phones to the Corporate PBX 3

A Cost-Effective Bridge 3

Basic Features 3

Translates Call Control and Voice Data 4

Understanding How the PBX-IP Media Gateway Works 5

Call Routing 5

Address Translation 6

Gateway Management 7

Monitoring Status and Operation 7

Configuration 7

Deployment 7

Scenario 1: Adding IP at a Corporate Office 8

Scenario 2: Connecting Legacy Phones to an IP-PBX 9

Scenario 3: Connecting to a Remote Office Using IP 10

Scenario 4: Telecommuting 11

Conclusion 12

Managed Migration to IP Telephony in a PBX Environment Whitepaper

Executive SummaryAlthough many enterprises are eager to adoptIP telephony, they see their legacy PBXsystems as a roadblock to the cost savingsand enhanced applications that IP telephonywould bring. This paper will demonstrate thatthis does not need to be the case. LegacyPBX equipment does not have to be replacedfor enterprises to begin a phased migration toIP telephony. The Intel® NetStructure™ PBX-IPmedia gateway makes the implementation ofIP technology in PBX systems possible right now.

The PBX-IP media gateway provides amanaged migration to IP because it enablesthe seamless convergence of voice, data, andfax across IP networks into a single, integrated enterprise network without anyexpensive changes to the circuit-switchednetwork. It easily joins legacy hardware and the latest technology, simultaneously protecting a company’s investment as itaccelerates growth.

The PBX-IP media gateway allows users toreceive both voice and data content in a singlecall over a managed packet network (LAN, WAN, or VPN) that interfaces directly tothe enterprise PBX. Remote users require lessequipment but receive the same content andlevel of access as users in the corporate office,yet the enterprise does not need to invest innew network or PBX equipment. Enterprisescan take a phased approach to a fullyconverged voice and data network whileprolonging the useful life of legacy switchingequipment.

IntroductionThe benefits of a converged network arecompelling. In an article entitled “The shape ofphones to come” (March 2001), TheEconomist reported that “the corporate sectoris beginning to take network convergenceseriously.” One reason for this heightenedinterest is that the technology used topacketize voice communications and transmitthem over a data network, which is known asIP telephony, is readily available and providessubstantial benefits. By comparing IPtelephony with traditional circuit-switchedtelephony, the increased interest in IPtelephony in the enterprise is easy tounderstand: ■ Dramatically reduced bandwidth usage.

IP telephony can use far less bandwidth thancircuit-switched telephony, generally by afactor of eight or more. A standard voicecircuit uses 64 kilobits per second (Kbps),but IP telephony can be configured to use 6to 8 Kbps, and sometimes as little as 2.4 Kbps.

■ Valuable control information transmittedsimultaneously. Many traditional voicecircuits allow for no additional data other thanthe voice transmission. Packet-switchednetworks send voice communications inpackets whose headers can containadditional information about the transmission.

■ Many new services possible. Because IPtelephony technology treats voice and datauniformly and Custom Local Area SignalingServices (CLASS) are easy to implement,many new services are possible, such asWeb-enabled contact centers and unifiedmessaging.

■ Reliable, scalable, easy to use.Deployment is easy, because IP telephonydoes not use a new infrastructure, but ratherthe data communications network that isalready in place. Implementation is achievedthrough dedicated gateways that can bebased on open standards platforms forreliability and scalability.


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Although many enterprises are eager to adoptIP telephony, they see their legacy PBXsystems as a roadblock to the cost savingsand enhanced applications that IP telephonywould bring. This paper will demonstrate thatthis does not need to be the case. LegacyPBX equipment does not have to be replacedfor enterprises to begin a phased migration toIP telephony. The PBX-IP media gatewaymakes the implementation of IP technology inPBX systems possible right now.

The PBX-IP media gateway allows enterprisesto:■ Interface to an existing PBX without replacing

most current equipment

■ Use new value-added productivity applica-tions on their data network

■ Simplify system integration

■ Provide “digital phone” capabilities anywhereon the IP network

With the PBX-IP media gateway, enterprises,Value-Added Resellers (VARs), and developersalike can benefit from IP telephony, and movegradually towards what The Economist calls“the network that connects everything toeverything.”

Market Research Reveals TrendsThe investment in the installed base oftraditional circuit-based PBXs is very large. Inits Infotrack for Enterprise Communications,Second Quarter 2000 report, the PhillipsGroup estimated that the combined installedbase of Lucent, Nortel, and Mitel PBXs wasabout 30 million lines at the end of 2000.However, despite a sluggish economy, Voiceover Internet Protocol (VoIP) gateway andswitching applications are growing.

Synergy predicts that “enterprise IP Telephonysales are on a growth path to displace over 20percent of traditional PBX sales over the nextthree to four years.” Consequently, Synergyalso forecasts a 34.6 percent compoundedannual growth in VoIP gateway and switchingapplications from 2002 to 2006. Products willbe needed to bridge the gap betweentraditional circuit-switched and IP networks forseveral years. See Figure 1.

VoIP gateways and switching applications arepopular because they allow enterprises tocontrol their transition to a converged networkwithout scrapping their legacy telecomequipment. The PBX-IP media gateway is anexcellent example of a gateway that enablesthe transition to IP.

Whitepaper Managed Migration to IP Telephony in a PBX Environment

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900

800

700

600

500

400

300

200

100

02002 2003 2004 2005 2006

Revenue (M$)EnterpriseVoIP Gatewaysand Switches

*Source — Synergy Reseach Q1'02 Forecast (May 24, 2002)

Figure 1. Growth Forecast for VoIP Gateways and Switching Equipment

Connecting IP Phones to theCorporate PBXHow does the PBX-IP media gateway work?What can it do? How is it deployed? All ofthese questions will be answered in thefollowing sections.

A Cost-Effective BridgeThe PBX-IP media gateway is an open,standards-based, purpose-built device (appliance) that provides a cost-effective bridgebetween legacy telecom equipment and amanaged packet network by converting signalsfrom existing digital telecom equipment toindustry-standard IP protocols: ■ Session Initiation Protocol (SIP) from the

Internet Engineering Task Force (IETF)

■ H.323 from the InternationalTelecommunication Union (ITU)

■ T.38 fax from the ITU

These standards, as used by the PBX-IPmedia gateway, allow IP endpoints to mimicthe behavior of traditional telephones. Noexpensive upgrades to PBX software orhardware are required.

Three types of gateway units are available:■ Emulating — Digital network interfaces

connect to legacy PBXs from Mitel, Nortel,Avaya, NEC, or Siemens. IP-enables anexisting PBX cost-effectively, allowingcommunication between a circuit-switchedtelephony network and H.323- or SIP-compatible devices such as IP phones andwireless phones and applications such as softphones and IP-enabled unified messaging.

■ Phone driving — Digital station interfacesconnect to legacy digital telephones fromNortel, Avaya, NEC, or Siemens. Allows IP-PBXs and applications to control legacydigital handsets, thus protecting an invest-ment in these phones while migrating someor all of the core switching architecture to IP.

■ Analog loop start — Allows IP connectionto PBXs that do not have an appropriatedigital interface.

The converted protocols can be transmittedover a company’s local area network (LAN) orwide area network (WAN) to communications

devices such as IP phones, wireless phones,and IP servers in almost any location, includingremote sites or branch offices.

The conversion enabled by the gatewayprovides a mixed circuit-based and IP-basedenvironment, allowing an enterprise to deployIP applications and use IP telephony deviceswithout scrapping its legacy telecomequipment.

Basic Features

Because telephony features are important toguarantee a satisfactory user experience, thePBX-IP media gateway supports a variety ofprimary and supplementary services:■ Silence detection

■ Line echo cancellation

■ Comfort noise generation

■ Call progress tone

■ Simultaneous ring at regular desk extensionand remote phone

■ Use of PBX dial plan to call coworkers withthree- or four-digit extensions

■ Caller Identification

■ Call hold

■ Call transfer

■ Message waiting indicator control

To simplify deployment, the PBX-IP mediagateway also includes the following features:

■ Web browser with context-sensitiveHelp, DHCP for IP address configuration,SNMP to report alarms, and RS-232 con-nection for local access – Allows for easyinstallation, configuration, and managementof the gateway

■ Hot Swap — Add or remove gatewayswithout affecting the operation of other units

It is also important that a gateway be trulystandards-based to protect the investment inall new equipment. For this reason, the PBX-IPmedia gateway supports:

■ VoIP — ITU H.323 v3, H.450 supplementaryservices (including H.450.2/4/7 – calltransfer/call hold/message waiting indicator)and SIP per Draft-IETF-SIP-RFC2543bis-05.


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Uses Real-Time Transport Protocol/Real-Time Control Protocol (RTP/RTCP) fordelivery of voice over the LAN or WAN

■ T.38 Fax over IP – Emulating unitstranscode fax from T.30 fax protocol, sup-porting V.21, V.27, V.29, and V.17 modulationschemes, to T.38 for transmission over apacket network

■ Enhanced signal processing— A variety ofcompression algorithms for high voice quality,including G.711 A-law and µ-law (64 KbpsPCM [standard]), G.723.1, and G.729AB

■ Ethernet connection – 10/100Base-Tsupporting half-duplex and full-duplex

Translates Call Control and Voice DataThe PBX-IP media gateway communicates toeither a legacy PBX or legacy digital telephonevia the manufacturers’ own proprietary stationlink and translates the call control and voicedata from the legacy PBX equipment to amanaged packet network. This gives H.323 orSIP terminal devices or applications access tothe legacy PBX equipment.

The PBX-IP media gateway has eight portsand is positioned between the PBX equipmentand the enterprise LAN or WAN via its 10/100BaseT-Ethernet connection.


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PBX Manufacturer PBX Model

Mitel Networks SX-200, SX-2000

Nortel Networks Meridian* 1, Norstar*

Avaya Communication DEFINITY* G3, Merlin Magix* and Legend*

NEC 2400 IMX, 2400 IMG, NEAX* 2000

Siemens Hicom* 300 series (North American software only)

Analog unit Various models that supportanalog loop start station interfaces

Table 1. PBXs Supported

Phone-driving PBX-IP media gateway units support the digital handsets in Table 2.

PBX Digital Phone Supported DigitalManufacturer Phone Models

Nortel Networks M2000 series, M7000 series

Avaya Communication 6400, 8400, 4400, and MLX series

NEC Dterm* III, Dterm E series

Siemens Optiset* E series

Table 2. Digital Handsets Supported

Emulating PBX-IP media gateway units are compatible with the PBXs in Table 1.

Understanding How the PBX-IPMedia Gateway WorksTo see how the PBX-IP media gateway works,several technical issues must be understood.These include routing and address translation.

Call RoutingThe PBX-IP media gateway must route a callfrom the PBX network to a destination IPaddress on the IP network. Conversely, callsfrom the IP network must be routed on a PBXport to a destination telephone number on thePBX network. The PBX-IP media gateway sup-ports two modes of call routing: point-to-pointand pooled.

Point-To-PointIn point-to-point routing, a PBX-IP media gate-way PBX port is directly assigned to a singlespecific IP terminal address. Most scenariosthat require both inbound and outbound callingwill be configured in point-to-point mode.

■ PBX-to-IP calls are routed from the PBX tothe IP terminal that is assigned to the PBX-IPmedia gateway PBX port on which the callarrived.

■ IP-to-PBX calls are routed onto the PBX-IPmedia gateway PBX port that has beenassigned to the originating IP terminal’saddress.

In point-to-point routing, a PBX-IP media gate-way PBX port is essentially ‘owned’ by itsassigned IP terminal address. Therefore, only

the IP terminals whose IP addresses areassigned on the IP gateway may originate andreceive calls through the IP gateway. SeeFigure 2 for an illustration.

PooledIn pooled routing, the PBX-IP media gatewayPBX ports serve as a pool of telephony ports.Most systems that require only outbound call-ing can use the pooled mode. Inbound callingis also supported, but the caller needs to “dial”the destination through two-stage dialing asdescribed below.■ IP-to-PBX calls are routed onto the first

available PBX-IP media gateway PBX port ina round-robin fashion. IP call informationspecifies the PBX destination telephonenumber to be dialed.

■ PBX-to-IP calls go through two-stage dialingin order to enter the destination IP aliasextension (E.164 number).

Using pooled routing, any IP terminal mayoriginate and receive calls through the PBX-IPmedia gateway. See Figure 3 for an illustration.

Address TranslationAddress translation is the conversion of aliasnames, email addresses, telephone numbers,and dot-com addresses into IP addresses.

In an H.323 environment, the addresstranslator is called a “gatekeeper” while in a


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Port 1 IP Address 1 IP Terminal 1








PBXNetwork

PBX-IP Media Gateway IP Network

Figure 2. Point-To-Point Routing

SIP environment, the address translator iscalled a “proxy server.” Because both anH.323 gatekeeper and a SIP proxy serverperform the same address translation functionas far as the PBX-IP media gateway isconcerned, the term “address translator” isused in this paper to avoid confusion.

In general, an address translator is needed tocreate a good user experience because itenables features such as dial plans and aliastranslation.

Address Translation ModesThe emulating PBX-IP media gatewaysupports two modes of address translation:localized and centralized.

Localized translation is the simpler mode ofaddress translation because the PBX-IP mediagateway configures destination IP addresseslocally and does not require an addresstranslator on the IP network. Each PBX-IPmedia gateway PBX port is directly assigned acorresponding IP address and calls from thePBX network on a given port are routed to theport’s assigned IP address on the IP network.

Calls from the IP network go to the PBX-IPmedia gateway PBX port that corresponds tothe IP address of the calling party. IP callinformation specifies the dialed PBX destina-tion telephone number. When in localizedtranslation mode, only IP terminals whose IPaddresses are assigned on the PBX-IP mediagateway may originate and receive callsthrough the IP gateway.

With centralized translation, the PBX-IPmedia gateway requires an IP network addresstranslator to perform and control all addresstranslation activities. When centralizedtranslation is used, any IP terminal that hasregistered an alias extension with the addresstranslator (E.164 number) can receive callsfrom the PBX-IP media gateway. Similarly anyIP terminal on the network may originate callsthrough the PBX-IP media gateway.

The phone-driving PBX-IP media gatewayalways requires an address translator to mapthe digital telephones connected to the gate-way into IP addresses reachable by other IPdevices on the network.


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Port 1 IP Terminal 1








IP Terminal N

PBXNetwork

PBX-IP Media Gateway IP Network

Figure 3. Pooled Routing

Gateway Management The PBX-IP media gateway is easy to install,configure, and monitor. The following sectionprovides a brief overview of how some of thesemanagement functions work.

Monitoring Status and OperationThe PBX-IP media gateway supports a numberof interfaces and standards for monitoring theunit’s status and operation. ■ Front-panel LEDs – Provide simple unit

status, Ethernet connection status, and PBXport connection states.

■ Web interface – Provides a view of unitstatus, configuration manipulation, and theability to upgrade the unit firmware.

■ SNMPv1 interface – Provides a view of unitstatus and configuration (read only).

■ Serial-port/telnet interface – Providesinterfaces for configuration manipulation andunit diagnostic tracing.

ConfigurationSince the PBX-IP media gateway has a Webbrowser interface, each PBX-IP media gatewayis initially configured with a default IP address.This allows the unit to be configured using aWeb browser by pointing the Web browser tothe default IP address. The unit’s IP addressmust be changed from the default IP addressin order to have multiple gateway units in asystem.

The gateway also supports the dynamic hostconfiguration protocol (DHCP) so that thegateway’s IP address can be configuredautomatically. At power up, the gatewaysends a broadcast message with a vendor IDcode identifying itself as a PBX-IP mediagateway. If a DHCP server is connected to thenetwork and is configured to recognize a PBX-

IP media gateway, the DHCP server will assignthe gateway an IP address. If no DHCP serverresponds, the gateway uses its default IPaddress.

The gateway is initially configured with noselected PBX interface. The PBX interfacemust be chosen through the Webconfiguration.

DeploymentThe PBX-IP media gateway can be used toconnect IP telephones to a legacy PBX,integrate network-hosted applications with thePBX, extend the PBX to branch offices, andintegrate various voice, fax, and call processingcapabilities in an enterprise LAN or WANenvironment.

The PBX-IP media gateway can function inseveral scenarios. Three key scenarios areoutlined in this paper.

Scenario 1 – Emulates digital station sets to adigital PBX. This mode uses H.323 or SIPstandards to interface with H.323 or SIPdevices, such as IP phones or softphones, onthe IP-based network at a main site or a homeoffice.

Scenario 2 – Connects remote offices to amain-office PBX over a managed packet net-work. Basically, the gateway extends PBXfunctionality to digital phones at a remote site.

Scenario 3 – Drives proprietary digital stationsets from an IP device, such as an IP-PBX orIP-server.

Details about deploying the PBX-IP mediagateway in various scenarios are given below.An address translator may be required tohandle call routing as described earlier in thispaper, but for simplicity the address translatoris not shown in the figures accompanying thescenarios below.


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Scenario 1: Adding IP at a CorporateOfficeThe PBX-IP media gateway can be used toconnect H.323 or SIP phones, softphones, orH.323 or SIP applications servers to thecorporate PBX as shown in Figure 4.

Using the PBX-IP media gateway to supply alink between a legacy PBX and new IPtechnology can supply the following benefits:■ Provides a low cost way to add IP

technology to an existing legacy system

■ Protects investment in legacy equipmentbecause the equipment does not have to bereplaced

■ Prevents disruption of service. Because callscan be transferred freely between IP phonesand legacy phones, the addition of IP tech-nology to a legacy environment is largelyseamless

■ Reduces development costs. An applicationsuch as voice mail can be written for an IPenvironment, but used without softwarechanges in a mixed environment enabled bythe PBX-IP media gateway

As can be seen in the diagram above, the typeof system enabled with the PBX-IP mediagateway is very different from a toll bypassgateway setup. To create a toll bypass config-uration, gateways are placed at two differentsites, and the corporate WAN carries callsbetween the two sites to avoid the PSTN andconsequent toll charges.

The PBX-IP media gateway has quite adifferent function. It is an IP-enablement toolthat allows IP technology to be introducedeasily and gradually into a legacy environmentat the pace that the enterprise finds mostcost-effective for its workload and currentinfrastructure.


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H.323 or SIPApplication Server

With Fax

H.323 or SIPSoft Phone

H.323 or SIPTelephone Set

PSTN

Proprietary DigitalTelephone Set

8 Digital Lines

PBX Network InterfaceGateway (Emulating)†

LANCorporate Office

PBX

†Intel® NetStructure™ PBX-IP Media Gateway

Figure 4. Connecting IP to the Corporate PBX

Scenario 2: Connecting Legacy Phones toan IP-PBXJust as IP phones can be used with a circuit-switched PBX because of the PBX-IP mediagateway, legacy phone sets can be used withan IP-PBX with the PBX-IP media gateway.See Figure 5 for an illustration.

Scenario 2 is very common in marketsegments such as retail. Retailers often havedigital phones installed throughout their stores,but need to migrate to an IP-PBX for newapplications to remain competitive. The PBX-IPmedia gateway allows retailers to install an

IP-PBX, but continue to use their legacyphones without rewiring each of their stores.However, all types of organizations can use thePBX-IP media gateway as shown in Figure 5 ifthey wish to install an IP-based PBX and wantto preserve their investment in legacy phoneequipment.

Scenario 1 is an example of an emulating PBX-IP media gateway. Scenario 2 is anexample of a different model called a phone-driving unit.


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Station Lines

PBX StationInterface Gateway(Phone Driving)†

IP-Based PBXDigital

Telephone

PBX

ManagedData

Network

PBX


DigitalTelephone

Branch/Remote Office

SIP or H.323

Figure 5. Connecting Legacy Phones to an IP-PBX

Scenario 3: Connecting to a RemoteOffice Using IPIn scenario 3, the PBX-IP media gateway isused to connect a circuit-switched PBX toH.323 or SIP phones in two or more locations: ■ At a main site using the enterprise LAN

■ At a remote site using the remote officeLAN across the enterprise’s managed packetnetwork

Using the PBX-IP media gateway in this typeof scenario can provide the following benefits:■ Increases flexibility by allowing IP phones and

legacy phones to be used interchangeably toplace local or remote calls using both IP-based and PBX networks

■ Reduces the costs of calls between the mainoffice and remote sites significantly by usingan existing WAN

■ Deploys quickly because no PBX softwareneeds to be upgraded

■ Protects investment because legacy phonescan continue to be used

■ Saves on equipment costs because remotesites may not require their own PBXs


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H.323 or SIPTelephone Sets


8 Digital Lines

PBX NetworkInterface Gateway

(Emulating)†

Branch OfficeCorporate Office H.323 or SIP Telephone Set

LAN

Router Router

LANPBX

PSTN

ManagedPacket

Network

PBX


Figure 6. Connecting to IP Phones at a Remote Site

Scenario 4: Telecommuting Scenario 4 demonstrates how the PBX-IPmedia gateway can provide a cost-effectivesolution for connecting telecommuters to anexisting PBX environment.

Whether remote workers are at an office athome or a customer site, they can receivevoice and data through the same VPNconnection while enjoying access similar tothat of workers in the enterprise’s mainlocation.

Workers can simultaneously browse corporatedata and speak with customers or each other.Because the PBX-IP media gateway workswith the existing network and PBX equipment,packetized technology integrates seamlesslywith the current system and IP softphoneapplications.

In this scenario, an emulating PBX-IP mediagateway is connected to a legacy PBX throughits digital line card. The PBX may also beconnected to adjunct applications such asvoice mail (VM) and interactive voice response(IVR).

The gateway is also connected to a LAN orWAN via a 10/100BaseT Ethernet connection.The user connects to corporate headquartersthrough a broadband VPN connection andaccesses PBX features using either asoftphone client running on a PC or an IPtelephone.

Calls can be placed and received on anytelephone using the VPN connection to carryvoice and the PBX-IP media gateway to bridgethe gap between the IP network or the PBXnetwork.

Using this configuration can enable several keyfeatures for a telecommuter including:■ One-number access because anyone who

calls the telecommuter’s office numbergenerates an IP call to the telecommuter’ssoftphone

■ Message waiting indication so thattelecommuters know if their corporate voicemail boxes contain any messages withouthaving to constantly call to check (Thisfeature may require additional voice mail configuration)


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H.323 or SIPTelephone Sets

PSTN


8 Digital Lines

PBX Network InterfaceGateway (Emulating)✝

VPN

VM/IVR ApplicationServer

Desktop withSoftphone IP Client

Application (H.323 or SIP)

ManagedPacket

Network

PBX/ACD


Remote Desktop withSoftphone IP Client

Application (H.323 or SIP)

Figure 7. Connecting Remote Workers

■ Use of corporate PBX to make outboundcalls, thereby eliminating the hassle ofsubmitting expense reports to be reimbursedfor calls made from home

■ Ability to contact anyone at the corporateoffice by using a three- or four-digit PBXextension

ConclusionThe PBX-IP media gateway is a standalonedevice that converts PBX messages intoInternet Protocol (IP) for transmission over amanaged packet network. The gatewayprovides access to applications running onnetworked servers and extends PBXfunctionality to H.323 and SIP devices locallyor remotely and to softphone clientapplications.

In essence, the gateway is the bridge betweena legacy PBX and the managed packetnetwork. It offers eight ports of digital PBX ordigital phone connectivity.

Enterprises interested in providing IP solutionsand creating new applications without havingto worry about system integration will find thatthe PBX-IP media gateway offers a simplified,cost-effective way to converge voice and dataacross a managed packet network whilepreserving legacy PBX investment and allowing migration to IP technology at acontrolled pace.

More Information and Additional ServicesAdditional information about the IntelNetStructure PBX-IP media gateway, includingordering information, is available athttp://www.intel.com/network/csp/products/7135web.htm.

Practical Telecommuting Solutions, a relatedwhite paper, can be found athttp://www.intel.com/network/csp/pdf/8141.htm.

Intel also offers consulting, education, andsupport through Intel® Net Services. You canfind a description of these services athttp://www.intel.com/design/network/products/telecom/services/index.htm.


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