Voip Over Atm

8/20/2019 Voip Over Atm

1/21

Accelerating the Deployment of VoIP

and VoATM

Overview

The economic advantages of packet voice are driving both the access and corevoice networks away from circuit switching towards packet. The industry

continues to debate whether the future of these packet networks will be based on pure ATM, pure Internet protocol (IP), IP over asynchronous transfer mode(ATM), IP over multiprotocol label switching (MPLS), or a combination thereof.

There are advantages to both ATM and IP and reasons for choosing each. Thistutorial will explore the role of next-generation switches which, as they become

widely adopted for both access and core networking, must be able to handle voicetraffic over both IP and ATM networks for future extensibility as the debatecontinues and must have the features necessary to interwork with existing public

switched telephone network (PSTN).

Topics

1. Introduction

2. Voice over Packet Architecture

3. Why Voice over IP?4. Why Voice over ATM?

5. Designer Considerations for Voice over Packet6. Elements of a Next-Generation Switching Platform

7. Switching Platform/Media Gateway8. Signalling Gateway9. The Softswitch/Media Gateway Controller

10. Application Server (AS) and Services11. Conclusion

Self-TestCorrect Answers


2/21

Web ProForum Tutorialshttp://www.iec.org

Copyright ©The International Engineering Consortium

2/21

Glossary

1. Introduction

Carriers are moving voice services to packet networks both to reduce upfront andoperational costs and to provide more value-added services in an increasinglycompetitive environment. A recent study by a major carrier found that packetequipment was 70 percent less expensive than traditional voice equipment, anddata access lines were 60 percent to 80 percent cheaper than voice lines.Maintenance of packet networks was 50 percent less expensive, whileprovisioning was 72 percent lower. However, consolidation of voice from thePSTN onto packet networks has, in the past, proven difficult and therefore hashappened very slowly. International voice-over–IP call volumes, which providethe most compelling business case for packet telephony, are still a drop in theocean of international telephony traffic but have experienced phenomenal growthsince 1998, according to a recent report by Washington, D.C.–based research

group TeleGeography. According to the "TeleGeography 2001" report, whichcontains results of an exclusive survey of major voice-over-packet (VoP)providers in 1999 and 2000, international Internet telephony traffic volumesreached 1.7 billion minutes in 1999—a growth rate of more than 1,000 percentfrom 1998. IDC projected more than 9 billion minutes of voice traffic to travelover worldwide packet networks in 2000, exceeding 135 billion minutes in 2004.Service revenue is projected at $1.6 billion in 2000 and $18.7 billion in 2004.

While it is clear that VoP is growing, there is still considerable debate about whether the underlying network technology will be ATM or IP. At the edge of thenetwork the choice, driven primarily by the regional Bell operating companies

(RBOCs), is ATM. An ATM–dominated access network is clearly in the works because until recently IP did not provide the quality of service (QoS) guaranteesthat are so important for voice. Although QoS protocols such as DiffServ,resource reservation protocol (RSVP), and MPLS have been implemented, mostof today's IP traffic is actually being carried over ATM. However, in the long term with the recent success of MPLS it appears that pure IP over lambda may be the winner. And certainly, IP at the application layer and the desktop is a more than just a viable near-term situation.

In addition to the challenges in architecting networks with end to end QoS,service providers must ensure that the rollout of such networks cause no

disruption to their existing voice service revenue, which currently representabout 80 percent of their overall revenue source. With more than $650 billion of worldwide revenue generated by traditional voice and fax services and more than$250 billion installed base of traditional equipment infrastructure in the UnitedStates alone, service providers must deploy next-generation packet switches thatseamlessly interconnect and competitively function as time division multiplexing


3/21



3/21

(TDM)–based PSTN switches as well as support voice over ATM (VoATM) and voice over IP (VoIP).

It appears that most carriers, especially the larger incumbent carriers will startthe migration to packet telephony on the trunk side first (Class-4 tandem) andeventually migrate to the access (Class 5). This migration model is similar to themigration from analog switches to digital switches, which started in the late1970s. Carriers first started on the inner network (i.e., tandem) and then movedoutwards to the Class 5.

The architecture for VoP, the reasons for choosing IP or ATM, and considerationsin next-generation system design need to be understood to accelerate VoPdeployments.

2. Voice over Packet Architecture

In principle, two basic technologies are used for building high-capacity networks:circuit switching and packet switching. In circuit-switched networks, networkresources are reserved all the way from sender to receiver before the start of thetransfer, thereby creating a circuit. The resources are dedicated to the circuitduring the whole transfer. Control signaling and payload data transfers areseparated in circuit-switched networks. Processing of control information andcontrol signaling such as routing is performed mainly at circuit setup andtermination. Consequently, the transfer of payload data within the circuit doesnot contain any overhead in the form of headers or the like. Traditional voicetelephone service is an example of circuit switching.

Circuit-Switched Networks

Carrier-class next-generation switches need to be high-capacity fault-tolerantTDM and VoP switches. They must be designed to significantly enhance theeconomics of providing traditional TDM–based voice and data services as well ashelp service providers migrate to a packet-based telecom network (based on VoIPand VoATM) and generate new competitive services. Service providers deployingnext-generation switches can cap their investment in traditional circuit switchesand migrate to a converged switching infrastructure that allows them to reducethe number of overlay network platforms and provide profitable voice and dataservices over packet networks. See Figure 1.


4/21



4/21

Figure 1. A High-Capacity TDM Switch Capable of Packet

Switching

Since most of the core packet networks today are ATM–based, but most likelymigrating to IP–based, the most future-proof investment is in next generationswitches that can be deployed to transport voice on both ATM and IP networkssupporting protocol layers as outlined in Figure 2.

Figure 2.


5/21



5/21

3. Why Voice over IP?

Support for voice communications using IP, which is usually called VoIP, has become especially attractive to consumers given the low-cost, flat-rate pricing ofthe public Internet.

VoIP is the ability to make telephone calls and access service over IP–based datanetworks with a suitable QoS and superior cost/benefit to PSTN–based calls.Today, most of the VoIP implementations are carried over ATM–based transportas shown in the second column of Figure 2.

The benefits of implementing VoIP are mostly consumer-based and can bedivided into the following three categories:

• Cost reduction—IP is everywhere. It is on our desktops and it is what

the Internet is based on. Many people view the Internet as a "freetransport" for data and voice services. With the introduction ofNet2Phone and other similar "free" services, many people are nowmaking phone calls over the Internet. In addition, businesses andindividuals have turned to higher-quality commercial products andservices to make voice calls based on IP. The prevalence of IP nodesand the abundant supply of better IP–based switches and routerscontinue to reduce the cost of providing VoIP.

• Simplification and consolidation—An integrated infrastructurethat supports all forms of communication could allow more

standardization and could reduce the total equipment complement.The differences between the traffic patterns of voice and data offerfurther opportunities for significant efficiency improvements.Universal use of IP for all applications, voice and data, holds out thepromise of both reduced complexity and more flexibility.

• Advanced applications—Even though basic telephony and facsimileare the initial applications for VoIP, the longer-term benefits areexpected to be derived from multimedia and multiservice applications.For example, Internet commerce solutions can combine World Wide Web access to information with a voice call button that allowsimmediate access to a call center agent from a PC. In addition, voice isan integral part of conferencing systems that could also include sharedscreens, white boards, etc. Combining voice and data features into newapplications will provide the greatest returns over the longer term.

Utilizing an IP–based network for voice traffic can offer advantages to consumersof reduced costs, simplification, and consolidation due to the proliferation of IP–


6/21



6/21

based applications and devices at the desktop. These advantages are compellingfor consumers and are driving service providers to consider VoIPimplementations. In contrast, VoP over the ATM–based network offers distinctadvantages directly to service providers and are still much more prevalent today.

4. Why Voice over ATM?

ATM, from the start, was designed to be a multimedia, multiservice technology. Although ATM has been accepted by service providers for its ability to deliverhigh-speed data services, until recently its potential for deploying voice services was overlooked. With the competitiveness of today's market though, networkoperators and service providers have been continuously striving to reduceoperating costs and lift network efficiency and have turned to the ATM networkto achieve these goals.

With hundreds of millions of dollars of ATM equipment infrastructure in the

United States alone, service providers have recognized that significant economiesof scale can be achieved if the data traffic and voice traffic are integrated onto asingle network. In order to achieve this, service providers have started to use thecircuit emulation services (CESs) of ATM switches to carry full or fractional E-1/T-1 circuits between end points. These CES mechanisms treat voice as aconstant stream of traffic encoded as a constant bit rate (CBR) stream. Inactuality though, voice is a combination of bursts of speech and silence and thisincreases the complexity of VoP.

The ATM Forum and International Telecommunications Union (ITU) came up with several advanced mechanisms to improve the efficiencies of transporting

voice traffic, including:

• ATM trunking using AAL–1 for narrowband services

• ATM trunking using AAL–2 for narrowband services

• IP over ATM (AAL–5)

• Loop emulation service using AAL–2


7/21



7/21

Table 1 summarizes the benefits of utilizing the different methods fortransporting VoATM.

Table 1.

StandardsVoiceCompression

SilenceRemoval

ChannelSuppression

SwitchedConcentration

CES No No No No

BD−CES No No Yes No

ATMtrunking

using AAL−1

No No Yes Yes

VoIP over ATM

Yes Yes No No

AAL−2 Yes Yes Yes Yes

5. Design Considerations for Voice overPacket

Adding voice to packet networks requires an understanding of how to deal withsystem level challenges such as interoperability, call control and signaling, voiceencoding, delay, echo, reliability, density, and performance of all the elementsthat make up the next-generation switching platform.

6. Elements of a Next-GenerationSwitching Platform

The vision for a next-generation switching platform is a distributed architecturein which media gateway/bearer transport platform, signaling, call control, andapplication elements are divided into separate logical network components (see Figure 3), communicating with one another through the use of intraswitchprotocols such as Megaco, media gateway control protocol (MGCP), andSCTP/M3UA. This distributed model allows service providers to scale theirnetwork to support hundreds of thousands of subscriber ports per node. In this

concept, voice traffic is directed between the traditional voice network and thenew packet-based networks by the media gateway. The call control is handled bya softswitch, and the features and services are handled by an applicationplatform. In reality, the softswitch (or call control platform) may support some ofthe more popular services without requiring a separate application platform. Anexample of this type of service is 7/10 digit routing, which would be handleddirectly by the call control platform. Other examples of where the application


8/21



8/21

platform may not be involved are caller name delivery, local number portability(LNP), and E-800 service. These services are already implemented in the PSTNusing service control points (SCPs). In these cases, the call control platform willsend intelligent network (IN)/transactional capabilities application part (TCAP)queries over the signaling system 7 (SS7) network to existing SCPs.

Figure 3. Elements of a Next-Generation Switching Platform

Some vendors enable one or more of these logical network elements to bedeployed on the same physical platform. There are some inherent advantages tothis "integrated" model especially with platforms that support up to 100,000subscriber ports (DS–0s) per bearer platform/media gateway, and allow efficientexecution of the softswitch and signaling gateway software. Benefits also includecost savings and deployment and operation simplicity. In the "integrated" model,the need for intraswitch protocols such as Megaco and MGCP are not required;however interswitch protocols such as RTP/UDP/IP (for MG to MG) and BICC(for SG to SG) are always required for interoperability with the other ends. See Figure 4 for relevant inter-switch protocols.


9/21



9/21

Figure 4. Interoperability: Call Control, Signaling, and BearerPlatforms

7. Switching Platform/Media Gateway

Sometimes referred to as a media gateway, the switching/bearer transport

platform is hardware that sits at the edge of a network and takes in a packetand/or circuit containing voice or data traffic and switches it to a voice or datanetwork. Media gateways come in many different flavors depending on the breadth of definition. The most popular consist of Class 4 and Class 5replacement functionality on a voice over digital subscriber line (VoDSL)gateway. Media gateways are part of the physical transport layer and arecontrolled by a call control engine or softswitch (also called a media gatewaycontroller), which provides instructions to direct voice traffic. Media gateways areat the heart of the transformation of the voice network, as they are essential tomigrating voice traffic onto a packetized network. As part of packetizing voicetraffic, a media gateway adapts (by using compression and echo cancellation) thepacketized traffic, creates and attaches an IP header and/or ATM header, andsends the packet through the network according to instructions provided by thesoftswitch.

While a media gateway can be physically located almost anywhere within thenetwork, depending on the network architecture and the features it is intended tosupport, all media gateways share certain features including the following:


10/21



10/21

• Scalability —A media gateway needs to be able to scale to supporthundreds of thousands of telephone calls (called DS–0s, running at 64Kbps per line) to parallel the scalability of the existing PSTN switches.

• Support for several types of access networks—Needed support

includes wireless, fiber, cable, and copper. In addition to electricalinterfaces, a media gateway needs to support a variety of opticalinterfaces (including OC–3, OC–12, OC–48, and OC–192 speeds).

• Carrier-class reliability —Also known as five nines (99.999 percent)reliability (i.e., less than five minutes of downtime per year) andnetwork equipment building standards (NEBS) certification (theTelcordia quality rating for meeting environmental stress tests),reliability is extremely important to service providers because itenables them to fulfill customer contracts. Most carriers cite reliabilityas the impetus to transform their current architecture.

• Interworking functionality —Media gateways are capable ofsupporting multiple voice and data interface protocols andcompatibility between them by converting circuit traffic to packettraffic and vice versa.

• Interoperability —Most networks are a compilation of multivendorsolutions, making interoperability essential for success.

• Control support—To enable communication between the mediagateway and a softswitch. The most common languages (or protocols)emerging for communication between these devices are MGCP and

Megaco.

• Switching—A media gateway must handle switching and mediaprocessing, based on an ATM, IP, or TDM switching fabric.

• Voice transportation—There are 3 transport standards used fortransporting voice traffic: TDM (traditional circuit-switch method), ATM AAL–1/AAL–2, and IP–based RTP/RTCP (over ATM or pure−IPtransport).

A packetized approach to transmitting voice faces a number of technical

challenges that spring from the real-time or interactive nature of the voice traffic.Some of the challenges that need to be addressed include the following:

• Echo—Echo is a phenomenon where a transmitted voice signal getsreflected back due to unavoidable impedance mismatch and four- wire/two-wire conversion between the telephone handset and thecommunication network. Echo can, depending on the severity, disrupt


11/21



11/21

the normal flow of conversation and its severity depends on the round-trip time delay if a round-trip time delay is more than 30 ms the echo becomes significant making normal conversation difficult.

• End-to-end delay —Voice traffic is most sensitive to delay and is

mildly sensitive to variations in delay (jitter). It is critical that end-to-end delay is minimized to hold interactive communications. Delay caninterfere with the dynamics of voice communication, in the absence ofnoticeable echo, whereas in the presence of noticeable echo, increasingdelay makes echo effects worse. When delay reaches above 30 ms, echocanceller circuits are required to control the echo.

• Packetization delay (or cell construction delay)—Packetizationdelay is the time taken to fill in a complete packet/cell before it istransmitted. Normal G.711 pulse code modulation (PCM) encoded voice samples arrive at the rate of 64 Kbps, which means it can takeapproximately 6 ms to fill the entire 48-byte payload of an ATM cell.

The problem can be addressed either with partially filled cells or bymultiplexing several voice calls into a single ATM virtual circuitchannel (VCC).

• Buffering delay —Sometimes, due to delay in transit, some cellsmight arrive late. If this happens the ATM segmentation andreassembling (SAR) function provided by the adaptation layer mighthave to under run with no voice data to process which results in gaps inconversation. To prevent this, the receiving SAR function wouldaccumulate a buffer of information before starting the reconstruction.In order to ensure that no under runs occur the buffer size should

exceed the maximum predicted delay. The size of the buffer translatesinto delay, as each cell must progress through the buffer on arrival atthe emulated circuit's line rate. This implies that the cell delay variation (CDV) has to be controlled within the ATM network.

• Silence suppression—Voice, by its nature, is variable. In fact, atypical conversation has a speech activity factor of about 42 percentdue to pauses between sentences and words where there is no speech ineither direction. Also, voice communication is half-duplex, whichmeans that one person is silent while the other speaks. One can takeadvantage of these two characteristics to save bandwidth by halting the

transmission of cells during these silent periods. This is known assilence suppression.

• Compression algorithms—G.726 adaptive differential pulse codemodulation (ADPCM) and G.729 adaptive code excited linearprediction (ACELP) are the two major compression algorithms that areused. The benefit of compression is efficient use of bandwidth. Most


12/21



12/21

voice packets are transmitted today using G.711 encoding that does nocompression and therefore adds further delay.

8. Signaling Gateway

A signaling gateway is hardware and software that provides the connection froma softswitch and media gateway to the SS7 network. The signaling gatewayreceives/sends the call control instructions needed between the SS7 network andthe softswitch, typically through stream control transmission protocol (SCTP)and MTP Level-3 user adaptation layer (M3UA) protocols. This allows thesoftswitch to process and communicate call control instructions to a mediagateway. A signaling gateway can either stand-alone or be integrated with asoftswitch/media gateway. In the traditional circuit-switched telephone network,a legacy switch provides the interface directly to the SS7 world, essentially actingas a signaling gateway.

9. The Softswitch/Media GatewayController

A softswitch, also referred to as a "call agent" or "media gateway controller," issoftware that provides the call control and signaling for the next-generationnetwork. The softswitch moves the service intelligence out of the switch into adatabase or application server, connects those databases, and ultimately providesthe "brains" or operating system for the next-generation voice network. Asoftswitch ensures that a call is routed through the network to the properdestination and that features from the existing advanced intelligent network(AIN) such as 1-800 and LNP, as well as new multimedia services, are applied tocalls as appropriate. While the softswitch architecture is similar to the AINdatabases in an SCP, a softswitch provides more robust functionality and isdistinguished by providing control to more than one type of switch—includingTDM, ATM, IP, etc.—while today's AIN controls only TDM–based switches. Thisarchitecture is inherently more flexible and scalable than the architecture oftoday's circuit switches.

There is significant debate in the industry about the definition of a softswitch, itsrole within the network, how it should interface with other gateways andsoftswitches, and how it should interface with the IP and SS7 networks. At the

most basic level, a softswitch must contain call-control features and a signalinginterface to the SS7 network. Call control relates to the setup and teardown ofcalls, including service selection ("which services apply to this call?") and callrouting ("where will this call be sent?"). In addition, a softswitch must providecall authentication ("what calls is this line allowed to make?"), authorization, andaccounting services by accessing information available in the existing SS7network. The SS7 signaling interface, which allows the softswitch to


13/21



13/21

communicate with today's SS7 network, is in some cases distributed to a stand-alone hardware system called a signaling gateway. Today's softswitches typicallyoperate on the Sun Solaris operating system and include features such as thefollowing:

•

Media independence—to make the software agnostic regarding theswitching fabric (ATM, IP, TDM, etc.)

• Interoperability —with multiple vendors' media gateway products,the existing PSTN, and off-the-shelf hardware platforms

• Reliability —to carrier standards (five 9s of reliability)

• Support for multiple signaling and control protocols—including emerging and established standards such as ISUP, BICC,SIP, and MEGACO/H.248

• Scalability —to meet carrier network requirements, supportingthousands of call attempts, also known as busy hour call attempts(BHCA) and simultaneous calls

• Open application programming interfaces (APIs)—or "hooks"into third-party software applications and services

10. Application Server (AS) and Services

Finally, without services, next-generation switches would not be able to generate

the voice revenue that currently provides 80 percent of overall service providerrevenue. The following Class-4 and Class-5 services need to be supported bythese switches. As stated before, several of these services may be implemented inthe softswitch (call control platform) without the need for an external AS. Themore complex services such three-way conferencing may require the need for an AS with multimedia support. Until ASs become more capable in terms ofsupporting more complex services and providing robust easy-to-use servicecreation environments (SCEs), the need to deploy these services outside of thesoftswitch environment is less compelling.

Dial tone*Basic dialing*Basic 7/10 routing AnnouncementsBilling record creationCall blocking/allowCall transferCall forward


14/21



14/21

CF busyCF no answer3-way callingToll restrictionOutbound restriction

Calling name deliveryCalling number deliveryInt. Dial: 011Premium rate: 900/976Toll free: 8xxOperator: 0/00E–911LNPPrimary interexchange carrier (PIC)CALEASelective call rejectSelective call acceptRemote call forwardingSpeed dialing 30 Anonymous call rejectCaller ID block Automatic callback Automatic recallCall waitingCalling identity delivery on call waitingCustomer-originated traceDistinctive ringing/call waitingSelective call acceptance

Selective call forwardingSelective call rejection

11. Conclusion

Voice packet telephony is a reality today, although, as an industry, there still is alot of work ahead. The larger incumbent carriers are starting the migration topacket telephony on the trunk side first (Class-4 tandem) and will eventuallymigrate to the access side (Class 5). This migration model is similar to themigration from analog switches to digital switches, which started in the late

1970s, and offers a proven path for migration to new technologies. The fullmigration to packet-based Class 5 systems will happen when the inner network becomes packet-based and when differentiated Class-5 services become available. And the services must go beyond currently available PSTN–based services forpacket telephony to become truly compelling. On this journey, the debates over VoIP and VoATM will continue. While VoATM makes sense today for somecarriers, especially the larger incumbents, VoIP is the longer-term goal especially


15/21



15/21

with MPLS–based QoS becoming available. For some carriers, VoIP is the answertoday as the consumer benefits are persuasive.

Service providers looking to deploy VoP will be best served if they choose asolution that addresses the issues of interoperability, call control and signaling, voice encoding, delay, echo, reliability, density, and performance of all theelements that make up the switching platform. And they should look for solutionsthat deal with these issues for TDM switching, as well as VoIP and VoATM.

Self-Test

1. A recent study by a major carrier found that packet equipment was 70 percentmore expensive than traditional voice equipment.

a. true

b. false

2. Since most of the core packet networks today are ATM–based, but most likelymigrating to IP–based, it only makes sense to deploy next-generationswitches that can be deployed to transport voice on both ATM and IPnetworks supporting protocol layers.

a. true

b. false

3. Support for voice communications using IP, which is usually called

___________, has become especially attractive given the low-cost, flat-ratepricing of the public Internet.

a. VoATM

b. VoP

c. VoDSL

d. VoIP

4. ___________ from the start, was designed to be a multimedia, multiservicetechnology.

a. AAL

b. IP

c. ATM


16/21



16/21

d. PSTN

5. In the new architecture, the call control will be handled by a ____________

a. softswitch

b. Megaco

c. MGCP

d. SCTP

6. ____________ are part of the physical transport layer and are controlled bya call control engine or softswitch (or media gateway controller), whichprovides instructions to direct the traffic.

a. Switches

b. Headers

c. Media gateways

d. Platforms

7. A media gateway can be physically located almost anywhere within thenetwork.

a. true

b. false

8. A ____________ is hardware and software that provides a connection froma softswitch and media gateway into the SS7 network

a. Megaco

b. header

c. signaling gateway

d. transport layer

9. A softswitch moves the service intelligence out of the switch into a database orapplication server, connects to those databases, and ultimately provides the"brains" or operating system for the next-generation voice network.

a. true


17/21



17/21

b. false

10. While VoATM makes sense today for some carriers, especially the largerincumbents, VoIP is the longer-term goal.

a. true

b. false

Correct Answers

1. A recent study by a major carrier found that packet equipment was 70 percentmore expensive than traditional voice equipment.

a. true

b. false

See Topic 1.

2. Since most of the core packet networks today are ATM–based, but most likelymigrating to IP–based, it only makes sense to deploy next-generationswitches that can be deployed to transport voice on both ATM and IPnetworks supporting protocol layers.

a. true

b. false

See Topic 1.

3. Support for voice communications using IP, which is usually called ___________, has become especially attractive given the low-cost, flat-ratepricing of the public Internet.

a. VoATM

b. VoP

c. VoDSL

d. VoIP

See Topic 3.


18/21



18/21

4. ___________ from the start, was designed to be a multimedia, multiservicetechnology.

a. AAL

b. IP

c. ATM

d. PSTN

See Topic 4.

5. In the new architecture, the call control will be handled by a ____________.

a. softswitch

b. Megaco

c. MGCP

d. SCTP

See Topic 6.

6. ____________ are part of the physical transport layer and are controlled bya call control engine or softswitch (or media gateway controller), whichprovides instructions to direct the traffic.

a. Switches

b. Headers

c. Media gateways

d. Platforms

See Topic 7.

7. A media gateway can be physically located almost anywhere within the

network.

a. true

b. false

See Topic 7.


19/21



19/21

8. A ____________ is hardware and software that provides a connection froma softswitch and media gateway into the SS7 network.

a. Megaco

b. header

c. signaling gateway

d. transport layer

See Topic 8.

9. A softswitch moves the service intelligence out of the switch into a database orapplication server, connects to those databases, and ultimately provides the"brains" or operating system for the next-generation voice network.

a. true b. false

See Topic 9.

10. While VoATM makes sense today for some carriers, especially the largerincumbents, VoIP is the longer-term goal.

a. true

b. false

See Topic 11.

Glossary

ACELPadaptive code excited linear prediction

AINadvanced intelligent network

ASapplication server

ATMasynchronous transfer code


20/21



20/21

BHCA busy hour call attempts

CBRconstant bit rate

CDVcell delay variation

CEScircuit emulation services

INintelligent network

IPInternet protocol

ITUInternational Telecommunications Union

LNPlocal number portability

MGCPmedia gateway control protocol

MPLSmultiprotocol label switching

NEBSnetwork equipment building standards

PICprimary interexchange carrier

PSTNpublic switched telephone network

QoSquality of service

RBOCregional Bell operating companies

RSVPresource reservation protocol


21/21



21/21

SARsegmenation and reassembling

SECservice creation environments

SCTPstream control transmission protocol

SS7signaling system 7

TCAPtransactional capabilities application part

TDMtime division multiplexing

VCC virtual circuit channel

VoDSL voice over digital subscriber line

VoP voice over packet

Documents

Voip Over Atm