white paper voice services with ip-msan

8/19/2019 White Paper Voice Services With IP-MSAN

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White Paper

2009-02-26 © KEYMILE 2009

Advantages of Voice-over-IP with IP-based multi-service

access nodes (IP-MSAN)


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White Paper Voice-over-IP with an IP-MSAN

2009-02-26 © KEYMILE 2009 Page 2


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Table of content

1 Abstract 4

2 Operative advantages due to carrier-class properties 4

3 An IP-MSAN’s telephony service 8

3.1 Telephony solutions for private households and SOHO 8

3.2 Telephony solutions for small to medium-sized enterprises (SMEs) 10

3.3 Telephony solutions for large enterprises (LEs) 11

3.4 Access technology for hosted PBX solutions 12

4 Summary and perspectives 14


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1 Abstract

This paper aims to explain to public network

operators the applications and new functions,enabled by an IP-based multi-service accessplatform for telephony services. The whitepaper offers both technical and businessarguments in favour of multi-service accessnetworks, examines some applications and

looks at the past and future of IP-MSAN

technology. We have merely scratched thesurface of other applications, such as IPTV,broadband DSL or fibre-to-the-home (FTTH)that can be implemented with an IP-MSAN, asthey have been explored in other publications.

When procuring network technology in publicnetworks, operators have two major sets ofexpenses to deal with: the purchasing price ofthe solution (capital expenses, CAPEX) and therunning costs (operational expenses, OPEX.)Usually, CAPEX is relatively easy to identify andto compare, OPEX is not. The reason lies in theeffects of using different solutions that areoften not predictable beforehand.

A term often used by systems manufacturers isthe expression carrier class. It signifies productproperties that are specifically required inpublic networks. If network technology onlyfulfils a few carrier class aspects, it is oftenaffordably priced, however high follow-up costscan occur. When using IP-MSANs which areusually applied in triple-play environments asaccess solutions, it is wise to ensure they have

the following carrier class properties:

■ Tough ambient conditions:An IP-MSAN is often used in air-conditionedand almost dust-free rooms, but must also betough enough to function perfectly in ademanding, harsh environment, such asoutdoor housings. Even in mild climates,

when the sun shines directly on the housings,they reach an operating temperature of over50 °C. In this environment, it is even moreimportant that resistance to vibrations andhumidity are higher than in air-conditionedsurroundings.

■ Reliability and stability:all important components in the accesssolution (power unit, central card, gatewayetc) that are vital for maintaining operation,should be designed so that they are redun-dant. The uplink connection should be

redundant via two or more optical gigabit

2 Operative advantages due to carrier-class properties

Figure 1: Overview of the IP-MSAN functionality


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Ethernet links with automatic switching,should the call server (softswitch) or one ofthe paths fail because there is a malfunctionin the line. It must be viable to carry out

software and firmware updates while systemsare operating and to monitor operatingconditions using central sensors and alarms.

■ Providing traditional telephony interfacesAn IP-MSAN supplies the subscriber withPOTS and the ISDN interfaces, terminatesthem and in the network turns them intomore cost efficient Voice-over-IP technology(VoIP.) The advantage is that end users cancontinue to utilise their traditional terminalequipment and the operator saves substan-tial running costs because no TDM is

required (see the following chapters).

■ Using extremely long copper access lines:Modern IP-MSANs can implement symmetri-cal 2 Mbps connections over copper linesthat are 7 km long. In ISDN connections thelines can be over 10 km, in POTS over 20 kmlong.

■ Service quality:When using advanced prioritising, filteringand queuing methods, voice, data and videosignals in differing quality can be transmitted

gradually to ensure end customers obtain thebest service quality.

■ Central network management with measure-ment functions:

An access network, implemented withIP-MSANs, is operated centrally by a networkmanagement system. This provides the fullset of management functions for FCAPS(fault, configuration, alarm, performance andsecurity.) The management system should beintuitive to operate and have a graphicalinterface. However, there should be a com-mand-line interface (CLI) to guaranteeintegration into an existing CLI if required. Itshould also be possible to trigger measure-ment functions from a central operatinglocation in order for example to prepare acopper access line without time-consumingwork on site.

■ Flexibility:an IP-MSAN concept should allow for differ-ent chassis sizes for carrier class applications,so that usage is possible in different installa-

tion environments, i.e. indoor/outdoor,locally where the customer is situated etc. Itshould be possible to put the same cards inall chassis to enhance logistics and storageprocesses.

■ Support of various transmission media:An IP-MSAN platform should support bothcopper wire and fibre optic transmission,because nowadays almost all networks aredesigned heterogeneously. This allows theoperator pervasive use of a single IP-MSANplatform in different network architectures,such as fibre-to-the-exchange (FTTE,) fibre-to-the-curb (FTTC,) fibre-to-the-building(FTTB,) or fibre-to-the-home (FTTH) - as thepicture shows.

■ Supporting migration:When launching a new access platform it isnot absolutely vital to port all traditional TDMservices to packet-based ones. However, itmust remain viable in the future as well tosupply the full range of profitable services,responsible for generating most of the

revenue and profits. In the fixed line network,such services are for example POTS andISDN telephony services, as well as the2 Mbps standard fixed line network connec-tion, so that private branch exchanges can beconnected for example. These servicesshould also be available in an IP-basedaccess network.


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■ Product continuity and support:This entails providing software updates, regu-lar new functions, including full releasedocumentation and long-term provision ofspare parts etc.

■ Ethernet OAM (Operation, Administrationand Maintenance):

As Ethernet was originally not designed foroperation in public networks, variousattributes were missing initially that arerequired to achieve similar levels of opera-tional reliability and manageability to SDHnetworks. As a result, several Ethernet OAMstandards have been developed to introduceend-to-end monitoring and full managementat several logical levels of an all-IP network. Itshould be easy to integrate an IP-MSAN

concept in this type of environment. ■ Pay-as-you-grow access platform concept:in addition to the technical specifications, it isimportant not to forget the business side.The disadvantage of previous multi-serviceconcepts was that the majority of the func-tions were integrated on the network ele-

ment’s central card. There was no scalabilityin smaller sites because chassis types werenot available, or joint usage of plug-in cardswas not possible. The result was relativelyhigh outlay at the beginning. Above all at thestart of the rollout, operators might have

thought that they were being asked to pay inadvance for extended functions that theywould only need to years later (if at all.)

It should be possible to scale a modernIP-MSAN concept for small and large num-bers of subscribers so that it makes commer-cial sense. A pay-as-you-grow effect in theaccess node is for example often imple-mented by including the functions primarilyin the subscriber subracks. As a result, theoperator only pays when new subscribers areconnected and therefore new revenue

generated. The chassis sizes and centralcards of an IP-MSAN should be adjusted tohandle small numbers of subscribers and alsofor very large POPs (points of presence) withseveral thousand subscribers, in order toguarantee commercial success with the rightport density.

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FTTB for large Enterpriseor Unitversity site

Figure 2: Multi-service does not just mean providing the most important service interfaces, but also the flexibility to be able,cost effectively, to use an IP-MSAN in various network scenarios.


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Network operators should check all thesecarrier class attributes very carefully, so that thebusiness case is not rendered obsolete afterselecting the system because of the operating

costs. If operators want to optimise CAPEX,they can consider opting for an access solutionthat fulfils fewer quality attributes than a carrierclass IP-MSAN. However, they should be aware

of potential repercussions: OPEX follow-oncosts, incurred as a result of troubleshooting,network downtimes and damage to image, areusually much higher. In this case, it is important

to make a cost-efficient and future proofdecision.


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The chief aim of an IP-MSAN is to integrate allcommonly-available groups of services in the

fixed line network, i. e. voice, data and videoand provide their services. We will now look attelephony in more detail. On the one handbecause today the majority of sales areachieved with the standard telephony servicesand on the other, because of the potential forimprovement in public networks. This is thearea where operators need to take action.

In the voice exchange, many operators nowa-days still use 64 kbit TDM technology. Use ofthe technology will continue in many areas forsome time to come, due to the high level of

investment and long periods of depreciation.As a result, in addition to state-of-the-art Voice-over-IP technology, modern IP-MSANplatforms will have to continue to use TDMinterfaces – whether towards the subscribers, orto the exchange.

As the name IP-MSAN already suggests, thiscategory of access solutions also includes IPfunctionality. Important are VoIP-gatewayfunctions that convert POTS and ISDN sub-scriber interfaces into RTP (Real Time TransportProtocol) Ethernet packages and exercise

control with H.248/MEGACO or SIP-signallingvia a soft switch or call server. This sophisti-cated type of telephony saves substantialnetwork operating costs, as Ethernet transmis-sion technology is used and the traditionaldigital exchanges can be replaced by just a fewsoft switches. As far as subscribers are con-cerned, the same familiar services (i.e. POTS orISDN) are implemented that the customerrecognises from TDM technology. Ideally,subscribers will notice no difference afternetwork conversion from TDM to IP and can

continue to use their favourite terminal equip-ment (like DECT telephones, ISDN privateexchanges, fax machines etc) without anyproblems.

However, many network operators have not,even today, migrated their TDM voice networkentirely to VoIP technology. There are manyreasons for this. To supply these providers withproblem-free access to modern NGN technol-

ogy, advanced IP-MSAN concepts use a hybridbackplane architecture, which can also provide

POTS and ISDN subscriber interfaces tradition-ally via a V5.2 uplink. The TDM interfaces usethe TDM backplane in this architecture and thepacket-driven interface boards the Ethernetbackplane. Therefore, both TDM and Ethernettechnology can be used without complexemulation technology. With hybrid boards thatcan access both backplanes, migration scenar-ios can be implemented easily and efficiently– without exchanging existing hardware. Thisoption protects both the operators’ investmentand allows them to seamlessly migrate to the

convergent All-IP world.Migration scenarios such as these will beoutlined in more detail in another KEYMILEwhite paper. The rest of this paper will concen-trate on operation scenarios where a VoIP voiceexchange (soft switch, call server etc) is alreadyused exclusively.

3.1 Telephony solutions for privatehouseholds and SOHO

Basically the demands of private households

and the small office/home office (SOHO) asregards telephony services are similar. Residen-tial properties these days usually still havePOTS, but in the business segment, ISDN tendsto be more popular because of the extraattributes it can offer.

Nowadays, both technologies are experiencingincreasing competition due to Voice-over-Inter-net and Voice-over-DSL (VoDSL) because theseservices are usually cheaper, or in some caseseven free of charge (see figure 2, case A.) Insome cases they provide more functions than

traditional telephony (e.g. with several tele-phone lines via one single copper line, videotelephony etc.)

Nevertheless, in the future it will continue to beessential that network operators offer POTSand ISDN interfaces via copper lines in theprivate customer environment: (see Figure 3 atpage 9, case C.):

3 An IP-MSAN’s telephony service


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■ Legal stipulations:The POTS connection is one of the primaryservices that must be provided.

■ Budget stipulations in extending networks:POTS and ISDN ports in the IP-MSAN are

more affordable than DSL ports. ■ Using existing exchange technology:The existing TDM exchanges will continue tobe used.

■ Very long copper paths:The maximum length of ADSL paths isapproximately 7 km. Particularly in ruralregions however, lines of more than 10 kmare standard.

■ Life line service:In the case of telephone connections thatneed to be extremely reliable (emergencytelephones, doctors, police stations, firealarms, other alarms etc), VoDSL or even Voice-over-Internet is no alternative becausethe network terminations or telephones haveto be supplied locally. The risk of malfunction(e. g. the power supply unit breaks) is toohigh in these cases - remote supply is abso-lutely vital.

With IP-MSANs, network operators can evenapply the more attractive VoIP technology inthe network for these difficult cases to savecosts and use a homogenous all-IP networkinfrastructure in the network internally. ThePOTS and ISDN signals are terminated by the

VoIP gateway in the IP-MSAN, turned into SIPor H.248/MEGACO signals and conveyed as IPpackets through the backbone network.

Advantages for the network operator:

■ The backbone can be completely switched toEthernet.

■ SDH backbone technology, with its inefficientuse of bandwidths, can be switched off.

■ TDM exchange technology can be replacedby more powerful and affordable soft switch

technology. ■ Operating costs are reduced significantly.

■ The end customers do not notice the switch;they can continue to use their previousterminal equipment. This reduces the churnrate.

■ Due to the lower operating costs, competi-tive products with the same margin can beachieved.

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Figure 3: An IP-MSAN platform provides POTS, ISDN and VoIP telephony in one platform and turns them within the network into costefficient VoIP technology.


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3.2 Telephony solutions for small tomedium-sized enterprises (SMEs)

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Figure 4: Network connection of two sites belonging to an SME with a private exchange

Many SMEs have a TDM private exchange thatis connected to the public network with n x 2Mbps interfaces. Although nowadays modern VoIP based private exchanges already exist,

there are good reasons why many SMEs stillstick to the existing system. As a result, whenplanning the network, it is advisable to con-sider what the demands will be over the nextfew years.

In TDM networks, the TDM private exchangewas terminated at the exchange or transmittedtransparently to other places where the com-pany is located. As Figure 4 at page 10 shows,modern IP-MSANs must provide severaltransmission alternatives.

Description Advantage Disadvantage

Option 1

Termination ofthe ISDN-PRAsignalling andimplementa-tion into VoIPsignalling (SIPor H.248) in theIP-MSAN. In thecore network, atelephone con-nection is entirelyIP-based, thepayload data isrouted.

■ There is noTDM in thecore network.

■ Less complex-ity.

■ Better usage ofthe bandwidthsin the corenetwork.

■ VoIP gatewayfunctionsnecessary ineach accessnode.

Description Advantage Disadvantage

Option 2:

Transparenttunnelling of

the ISDN-PRAsignalling viaCircuit-Emulation(CESoP). Teleph-ony signalling isonly terminatedin a dedicatedISDN-PRA gate-way centrally andimplemented in VoIP.

■ Only one or afew ISDN-PRA-

gateway(s) arerequired in theexchange.

■ In addition toISDN-PRA,synchronised2 Mbps TDMconnectionscan also becarried put viaCESoP.)

■ CESoPgateway

functionsnecessary ineach accessnode.

■ The bandwidthfor TDMemulation mustbe reserved inthe corenetwork.

Option 3

Transparenttunnelling of

the ISDN-PRAsignalling viaCircuit-Emulation(CESoP) toanother PBX atanother of thecompany’s loca-tions. Telephonysignalling is notconsidered.

■ See option 2

■ If several of the

customer’spremises arelocated on thesameIP-MSAN, nodata traffic hasto take placeon the corenetwork at all.

■ See option 2


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3.3 Telephony solutions for largeenterprises (LEs)

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Figure 5: Example of a telecommunications network in a large enterprise in three different places

Figure 5 at page 11 shows an example of anetwork in a large enterprise in three differentlocations. There are very rarely ready-madenetwork solutions for these types of applica-

tions, so customised solutions are nearly alwaysrequired. Therefore it is advisable for publicnetwork operators to use the most flexibleplatform possible as CPE equipment that doesnot just support one or two services. The CPEsolution must also be as flexible as possible,and as the figure shows, able to be installed inoutdoor housings too, provide remote testingand measurement functions, support copperand fibre optic connections – or in other wordshave carrier class quality.

The following subscriber interfaces are required

on a large company’s premises: ■ POTS/ISDN: as a substitute for privateexchanges (see following chapter.)

■ ADSL2plus: to connect remote places ofwork, or remote measurement or monitoringfunctions, for example video cameras.

■ E1/G.703: to connect 64 kbps or 2 MbpsTDM equipment such as private exchanges,sensors, monitoring technology etc viacopper wire.

■ SHDSL: such as E1/G.703, only for long, linesof 100 m to 8 km.

■ 100BaseTx: To connect 100 Mbps LANsegments, servers or other IT components viaEthernet in-house cabling.

■ VDSL2: such as 100BaseTx, but only forapplications where standard Ethernet cablingis not sufficient because of the distance orthe interference.

■ 100BaseFx: like 100BaseTx, but with a fibreoptic interface.

■ 1000BaseFx: like 100BaseTx, but withmaximum bandwidth of 1 Gbps.


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3.4 Access technology for hosted PBXsolutions

Figure 6: Advantages of using an IP-MSAN in hosted PBX applications

The definition of hosted PBX is that the func-tions of a private exchange are moved to the

public network and are supplied by the serviceprovider via a broadband connection. Techni-cally this is usually implemented by an IP-Cen-trex application that is either integrated in thesoft switch or operated on an applicationserver.

The advantage of this business model tocorporate customers is that no specially trained

personnel is required. Another benefit is thefact that no investments need to be made intechnology (PBX) and the communicationscosts are transferred from CAPEX to OPEX. Theend customer can also enjoy new services thatpreviously did not exist because they were tooexpensive or too complicated to execute. Thefollowing table shows some examples.

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As regards the implementation of hosted PBXapplications in the public network, all of thepreviously mentioned customer applicationsand switching scenarios from the previouschapters can be applied. The key advantagesof integrating an IP-MSAN into such applica-tions are:

■ Integration of traditional POTS and ISDNconnections into IP-Centrex groups (seeFigure 5 at page 11, site A): previously, a majorproblem posed by corporate-wide hostedPBX solutions was that it was not possible tooperate a mixture of the TDM and VoIP

terminal points easily in a single Centrexgroup. As the IP-MSAN makes the TDMsubscriber interface towards an IPS Centrexapplication look like a VoIP subscriber, theold problem of the mixed Centrex groups issolved.

■ Discarding TDM private exchanges in thecorporate network (see Figure 5 at page 11,site C): A major obstacle in launching acompany-wide hosted PBX service was oftenthe fact that customers did not want (forfinancial reasons) or could not (for technical

reasons) discard existing telephones or otherterminal equipment.

By using POTS and ISDN interface cards, anIP-MSAN can replace TDM privateexchanges, existing terminal equipment canbe retained and from the point of view of thenetwork, TDM and VoIP terminal equipmentcan be integrated into IP Centrex groups andtherefore into the hosted PBX solution.

■ Providing a broadband connection (copperand fibre optics) including an ISDN fallbackline for hosted PBX locations (see Figure 5 atpage 11, site B): in addition to providing thebroadband connection (DSL or opticalEthernet) for company premises, which isused to convey both data and the VoIP voicetraffic from the IP-Centrex group, IP-MSAN inthe fixed network can provide one or severalISDN fall back lines. This connectionbecomes active if the broadband path failsand therefore guarantees company voicetraffic. From the point of view of the net-work, the ISDN fallback line is converted bythe IP-MSANs VoIP gateway into VoIPsignalling. This allows integration into theIP-Centrex solution.

Both for the customer and the networkoperator, this method is a win-win situation:

the customer enjoys the advantages of

Examples and possible impact of hosted PBX applications

New services Impact Advantage

Using new media andterminal equipment

for communicationspurposes

■ The PCs or the laptop replaced thetraditional hardware telephone using the

VoIP soft client. ■ The mobile phone plus VoIP client serves asterminal equipment and uses a WiFiconnection.

■ Reduction in costs for terminal equipment

■ Employee flexibility increased

Job mobility increasedin the company

As soon as a subscriber logs into the com-pany LAN or WAN, whether it is from one ofthe company premises or remotely via a VPNconnection, the employee can be reachedworldwide under his extension number.

■ Employees can be reached on the phone moreeasily.

■ Lower costs in comparison to mobile phoneusage, above all abroad.

■ Costs for office moves are reduced (changingthe cabling etc.)

Connecting the IP-Centrex service withOffice applications

■ Presence function: Other employees in abuddy list can see what the current presentstatus of the employees is (for examplelogged in, absent, temporarily absent etc.)

■ Additional communications functions such asvoice/video mailbox as an e-mail attachment,instant messaging, white boarding, applica-tion sharing, conferencing etc.

■ Increase in corporate productivity by raising thelevel of efficiency of each individual employee.

■ Improvement in team working, due to different

conference functions that integrate office andhome workers.

Reliability An IP-Centrex solution based on carrier classtechnology that was designed for use in publicnetworks.

In comparison to private exchanges that requireexpensive and time-consuming servicing ifhardware fails, an IP-Centrex solution is a lot morereliable. It is monitored and maintained centrallyby the service provider and errors can be put rightmuch more quickly.


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IP-Centrex, but also continues to reap thebenefits of reliability from the familiar TDMworld. The network operator can put the

minds of critical customers at rest and stilluse 100 % more efficient VoIP technology inthe network.

4 Summary and perspectives

The outstanding success of VoIP technology inpublic and private networks is unstoppable.Using carrier-class IP-MSANs in the accessnetworks exploits the advantages of twotechnological worlds. The IP-MSAN convertsthe existing POTS and ISDN connections into VoIP and at the same time implements broad-band All-IP connections via copper or fibreoptic lines. This allows operators to migratetheir networks today already to more afford-able, scaleable and future-proof VoIP technol-ogy, without compromising on quality. Forimplementing corporate network solutions,such as hosted PBX telephony, the carrier classdesign of the IP-MSAN platform is perfect.Good arguments can be made to counteractcustomer scepticism re safety, quality andstability. Without doubt, IP Centrex applica-tions, combined with IP-MSAN technology, canbe implemented at the same service levelquality as is the case for TDM services. The

difference is that the new technology hassignificantly more benefits in terms of opera-tion and usage. This is supported by EthernetOAM standards, that (similarly to TDM trafficnetworks) offer end-to-end management andtherefore support carrier class quality in termsof network operation.

During a network migration to IMS networkarchitecture, setting up IP-MSANs is an impor-tant and necessary step and ideally preparesthe access network for future conversion toAll-IP. Thanks to the ETSI TISPAN standard, in

the future an IMS-Media Control Layer will beable to manage IP-MSANs as full networkelements.

Finally, we should mention that many networkoperators worldwide have already recognisedthe benefits of using an IP-MSAN and willcompletely convert their access networks to IPtechnology in the next few years. From market-ing and business standpoints, the potential togain a competitive edge is extremely high. It isparticularly important not to compromise whenselecting the technology for the access net-work. Should the operator back the wronghorse when choosing the interface to thecustomer, the loss of image can be enormous.


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Author

Marc KahabkaProduct Support Switzerland

Publisher

KEYMILE GmbHWohlenbergstraße 330179 Hanover, Germany

Phone +49 511 6747-0Fax +49 511 6747-450Internet www.keymile.comMail [email protected]

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