Accelerating the Deployment of VoIP and VoATM Overview The economic advantages of packet voice are driving both the access and core voice 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 This tutorial 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 voice traffic over both IP and ATM networks for future extensibility as the debate continues and must have the features necessary to interwork with existing public switched telephone network (PSTN) Topics Introduction Voice over Packet Architecture Why Voice over IP? Why Voice over ATM? Designer Considerations for Voice over Packet Elements of a Next-Generation Switching Platform Switching Platform/Media Gateway Signalling Gateway The Softswitch/Media Gateway Controller 10 Application Server (AS) and Services 11 Conclusion Self- Test Correct Answers Glossary Introduction Carriers are moving voice services to packet networks both to reduce upfront and operational costs and to provide more value-added services in an increasingly competitive environment A recent study by a major carrier found that packet equipment was 70 percent less expensive than traditional voice equipment, and data access lines were 60 percent to 80 percent cheaper than voice lines Maintenance of packet networks was 50 percent less expensive, while provisioning was 72 percent lower However, consolidation of voice from the PSTN onto packet networks has, in the past, proven difficult and therefore has happened very slowly International voice-over–IP call volumes, which provide the most compelling business case for packet telephony, are still a drop in the ocean of international telephony traffic but have experienced phenomenal growth since 1998, according to a recent report by Washington, D.C.–based research group TeleGeography According to the "TeleGeography 2001" report, which contains results of an exclusive survey of major voice-over-packet (VoP) providers in 1999 and 2000, international Internet telephony traffic volumes reached 1.7 billion minutes in 1999—a growth rate of more than 1,000 percent from 1998 IDC projected more than billion minutes of voice traffic to travel over 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 the network 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) guarantees that are so important for voice Although QoS protocols such as DiffServ, resource reservation protocol (RSVP), and MPLS have been implemented, most of 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 represent about 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 United States alone, service providers must deploy next-generation packet switches that seamlessly interconnect and competitively function as time division multiplexing Web ProForum Tutorials http://www.iec.org Copyright © The International Engineering Consortium 2/21 (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 start the migration to packet telephony on the trunk side first (Class-4 tandem) and eventually migrate to the access (Class 5) This migration model is similar to the migration from analog switches to digital switches, which started in the late 1970s Carriers first started on the inner network (i.e., tandem) and then moved outwards to the Class The architecture for VoP, the reasons for choosing IP or ATM, and considerations in next-generation system design need to be understood to accelerate VoP deployments 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, network resources are reserved all the way from sender to receiver before the start of the transfer, thereby creating a circuit The resources are dedicated to the circuit during the whole transfer Control signaling and payload data transfers are separated in circuit-switched networks Processing of control information and control signaling such as routing is performed mainly at circuit setup and termination Consequently, the transfer of payload data within the circuit does not contain any overhead in the form of headers or the like Traditional voice telephone service is an example of circuit switching Circuit-Switched Networks Carrier-class next-generation switches need to be high-capacity fault-tolerant TDM and VoP switches They must be designed to significantly enhance the economics of providing traditional TDM–based voice and data services as well as help service providers migrate to a packet-based telecom network (based on VoIP and VoATM) and generate new competitive services Service providers deploying next-generation switches can cap their investment in traditional circuit switches and migrate to a converged switching infrastructure that allows them to reduce the number of overlay network platforms and provide profitable voice and data services over packet networks See Figure Web ProForum Tutorials http://www.iec.org Copyright © The International Engineering Consortium 3/21 Figure A High-Capacity TDM Switch Capable of Packet Switching Since most of the core packet networks today are ATM–based, but most likely migrating to IP–based, the most future-proof investment is in next generation switches that can be deployed to transport voice on both ATM and IP networks supporting protocol layers as outlined in Figure Figure Web ProForum Tutorials http://www.iec.org Copyright © The International Engineering Consortium 4/21 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 of the public Internet VoIP is the ability to make telephone calls and access service over IP–based data networks with a suitable QoS and superior cost/benefit to PSTN–based calls Today, most of the VoIP implementations are carried over ATM–based transport as shown in the second column of Figure The benefits of implementing VoIP are mostly consumer-based and can be divided 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 "free transport" for data and voice services With the introduction of Net2Phone and other similar "free" services, many people are now making phone calls over the Internet In addition, businesses and individuals have turned to higher-quality commercial products and services to make voice calls based on IP The prevalence of IP nodes and the abundant supply of better IP–based switches and routers continue to reduce the cost of providing VoIP • Simplification and consolidation—An integrated infrastructure that 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 offer further opportunities for significant efficiency improvements Universal use of IP for all applications, voice and data, holds out the promise of both reduced complexity and more flexibility • Advanced applications—Even though basic telephony and facsimile are the initial applications for VoIP, the longer-term benefits are expected 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 allows immediate access to a call center agent from a PC In addition, voice is an integral part of conferencing systems that could also include shared screens, white boards, etc Combining voice and data features into new applications will provide the greatest returns over the longer term Utilizing an IP–based network for voice traffic can offer advantages to consumers of reduced costs, simplification, and consolidation due to the proliferation of IP– Web ProForum Tutorials http://www.iec.org Copyright © The International Engineering Consortium 5/21 based applications and devices at the desktop These advantages are compelling for consumers and are driving service providers to consider VoIP implementations In contrast, VoP over the ATM–based network offers distinct advantages directly to service providers and are still much more prevalent today 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 deliver high-speed data services, until recently its potential for deploying voice services was overlooked With the competitiveness of today's market though, network operators and service providers have been continuously striving to reduce operating costs and lift network efficiency and have turned to the ATM network to achieve these goals With hundreds of millions of dollars of ATM equipment infrastructure in the United States alone, service providers have recognized that significant economies of scale can be achieved if the data traffic and voice traffic are integrated onto a single network In order to achieve this, service providers have started to use the circuit emulation services (CESs) of ATM switches to carry full or fractional E1/T-1 circuits between end points These CES mechanisms treat voice as a constant stream of traffic encoded as a constant bit rate (CBR) stream In actuality though, voice is a combination of bursts of speech and silence and this increases 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 Web ProForum Tutorials http://www.iec.org Copyright © The International Engineering Consortium 6/21 Table summarizes the benefits of utilizing the different methods for transporting VoATM Table Standards CES Voice Compression No Silence Removal No Channel Suppression No Switched Concentration No BD−CES No No Yes No ATM trunking using AAL−1 No No Yes Yes VoIP over ATM Yes Yes No No AAL−2 Yes Yes Yes Yes Design Considerations for Voice over Packet Adding voice to packet networks requires an understanding of how to deal with system level challenges such as interoperability, call control and signaling, voice encoding, delay, echo, reliability, density, and performance of all the elements that make up the next-generation switching platform Elements of a Next-Generation Switching Platform The vision for a next-generation switching platform is a distributed architecture in which media gateway/bearer transport platform, signaling, call control, and application elements are divided into separate logical network components (see Figure 3), communicating with one another through the use of intraswitch protocols such as Megaco, media gateway control protocol (MGCP), and SCTP/M3UA This distributed model allows service providers to scale their network to support hundreds of thousands of subscriber ports per node In this concept, voice traffic is directed between the traditional voice network and the new packet-based networks by the media gateway The call control is handled by a softswitch, and the features and services are handled by an application platform In reality, the softswitch (or call control platform) may support some of the more popular services without requiring a separate application platform An example of this type of service is 7/10 digit routing, which would be handled directly by the call control platform Other examples of where the application Web ProForum Tutorials http://www.iec.org Copyright © The International Engineering Consortium 7/21 platform may not be involved are caller name delivery, local number portability (LNP), and E-800 service These services are already implemented in the PSTN using service control points (SCPs) In these cases, the call control platform will send intelligent network (IN)/transactional capabilities application part (TCAP) queries over the signaling system (SS7) network to existing SCPs Figure Elements of a Next-Generation Switching Platform Some vendors enable one or more of these logical network elements to be deployed on the same physical platform There are some inherent advantages to this "integrated" model especially with platforms that support up to 100,000 subscriber ports (DS–0s) per bearer platform/media gateway, and allow efficient execution of the softswitch and signaling gateway software Benefits also include cost 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 for relevant inter-switch protocols Web ProForum Tutorials http://www.iec.org Copyright © The International Engineering Consortium 8/21 Figure Interoperability: Call Control, Signaling, and Bearer Platforms 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 packet and/or circuit containing voice or data traffic and switches it to a voice or data network Media gateways come in many different flavors depending on the breadth of definition The most popular consist of Class and Class replacement functionality on a voice over digital subscriber line (VoDSL) gateway Media gateways are part of the physical transport layer and are controlled by a call control engine or softswitch (also called a media gateway controller), which provides instructions to direct voice traffic Media gateways are at the heart of the transformation of the voice network, as they are essential to migrating voice traffic onto a packetized network As part of packetizing voice traffic, a media gateway adapts (by using compression and echo cancellation) the packetized traffic, creates and attaches an IP header and/or ATM header, and sends the packet through the network according to instructions provided by the softswitch While a media gateway can be physically located almost anywhere within the network, depending on the network architecture and the features it is intended to support, all media gateways share certain features including the following: Web ProForum Tutorials http://www.iec.org Copyright © The International Engineering Consortium 9/21 • Scalability—A media gateway needs to be able to scale to support hundreds of thousands of telephone calls (called DS–0s, running at 64 Kbps 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 electrical interfaces, a media gateway needs to support a variety of optical interfaces (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) and network equipment building standards (NEBS) certification (the Telcordia quality rating for meeting environmental stress tests), reliability is extremely important to service providers because it enables them to fulfill customer contracts Most carriers cite reliability as the impetus to transform their current architecture • Interworking functionality—Media gateways are capable of supporting multiple voice and data interface protocols and compatibility between them by converting circuit traffic to packet traffic and vice versa • Interoperability—Most networks are a compilation of multivendor solutions, making interoperability essential for success • Control support—To enable communication between the media gateway 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 media processing, based on an ATM, IP, or TDM switching fabric • Voice transportation—There are transport standards used for transporting voice traffic: TDM (traditional circuit-switch method), ATM AAL–1/AAL–2, and IP–based RTP/RTCP (over ATM or pure−IP transport) 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 gets reflected back due to unavoidable impedance mismatch and fourwire/two-wire conversion between the telephone handset and the communication network Echo can, depending on the severity, disrupt Web ProForum Tutorials http://www.iec.org Copyright © The International Engineering Consortium 10/21 the normal flow of conversation and its severity depends on the roundtrip 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-toend delay is minimized to hold interactive communications Delay can interfere with the dynamics of voice communication, in the absence of noticeable echo, whereas in the presence of noticeable echo, increasing delay makes echo effects worse When delay reaches above 30 ms, echo canceller circuits are required to control the echo • Packetization delay (or cell construction delay)—Packetization delay is the time taken to fill in a complete packet/cell before it is transmitted Normal G.711 pulse code modulation (PCM) encoded voice samples arrive at the rate of 64 Kbps, which means it can take approximately ms to fill the entire 48-byte payload of an ATM cell The problem can be addressed either with partially filled cells or by multiplexing several voice calls into a single ATM virtual circuit channel (VCC) • Buffering delay—Sometimes, due to delay in transit, some cells might arrive late If this happens the ATM segmentation and reassembling (SAR) function provided by the adaptation layer might have to under run with no voice data to process which results in gaps in conversation To prevent this, the receiving SAR function would accumulate 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 translates into delay, as each cell must progress through the buffer on arrival at the 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, a typical conversation has a speech activity factor of about 42 percent due to pauses between sentences and words where there is no speech in either direction Also, voice communication is half-duplex, which means that one person is silent while the other speaks One can take advantage of these two characteristics to save bandwidth by halting the transmission of cells during these silent periods This is known as silence suppression • Compression algorithms—G.726 adaptive differential pulse code modulation (ADPCM) and G.729 adaptive code excited linear prediction (ACELP) are the two major compression algorithms that are used The benefit of compression is efficient use of bandwidth Most Web ProForum Tutorials http://www.iec.org Copyright © The International Engineering Consortium 11/21 voice packets are transmitted today using G.711 encoding that does no compression and therefore adds further delay Signaling Gateway A signaling gateway is hardware and software that provides the connection from a softswitch and media gateway to the SS7 network The signaling gateway receives/sends the call control instructions needed between the SS7 network and the softswitch, typically through stream control transmission protocol (SCTP) and MTP Level-3 user adaptation layer (M3UA) protocols This allows the softswitch to process and communicate call control instructions to a media gateway A signaling gateway can either stand-alone or be integrated with a softswitch/media gateway In the traditional circuit-switched telephone network, a legacy switch provides the interface directly to the SS7 world, essentially acting as a signaling gateway The Softswitch/Media Gateway Controller A softswitch, also referred to as a "call agent" or "media gateway controller," is software that provides the call control and signaling for the next-generation network The softswitch moves the service intelligence out of the switch into a database or application server, connects those databases, and ultimately provides the "brains" or operating system for the next-generation voice network A softswitch ensures that a call is routed through the network to the proper destination and that features from the existing advanced intelligent network (AIN) such as 1-800 and LNP, as well as new multimedia services, are applied to calls as appropriate While the softswitch architecture is similar to the AIN databases in an SCP, a softswitch provides more robust functionality and is distinguished by providing control to more than one type of switch—including TDM, ATM, IP, etc.—while today's AIN controls only TDM–based switches This architecture is inherently more flexible and scalable than the architecture of today's circuit switches There is significant debate in the industry about the definition of a softswitch, its role within the network, how it should interface with other gateways and softswitches, 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 signaling interface to the SS7 network Call control relates to the setup and teardown of calls, including service selection ("which services apply to this call?") and call routing ("where will this call be sent?") In addition, a softswitch must provide call authentication ("what calls is this line allowed to make?"), authorization, and accounting services by accessing information available in the existing SS7 network The SS7 signaling interface, which allows the softswitch to Web ProForum Tutorials http://www.iec.org Copyright © The International Engineering Consortium 12/21 communicate with today's SS7 network, is in some cases distributed to a standalone hardware system called a signaling gateway Today's softswitches typically operate on the Sun Solaris operating system and include features such as the following: • Media independence—to make the software agnostic regarding the switching 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, supporting thousands 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 provider revenue The following Class-4 and Class-5 services need to be supported by these switches As stated before, several of these services may be implemented in the softswitch (call control platform) without the need for an external AS The more complex services such three-way conferencing may require the need for an AS with multimedia support Until ASs become more capable in terms of supporting more complex services and providing robust easy-to-use service creation environments (SCEs), the need to deploy these services outside of the softswitch environment is less compelling Dial tone* Basic dialing* Basic 7/10 routing Announcements Billing record creation Call blocking/allow Call transfer Call forward Web ProForum Tutorials http://www.iec.org Copyright © The International Engineering Consortium 13/21 CF busy CF no answer 3-way calling Toll restriction Outbound restriction Calling name delivery Calling number delivery Int Dial: 011 Premium rate: 900/976 Toll free: 8xx Operator: 0/00 E–911 LNP Primary interexchange carrier (PIC) CALEA Selective call reject Selective call accept Remote call forwarding Speed dialing 30 Anonymous call reject Caller ID block Automatic callback Automatic recall Call waiting Calling identity delivery on call waiting Customer-originated trace Distinctive ringing/call waiting Selective call acceptance Selective call forwarding Selective call rejection 11 Conclusion Voice packet telephony is a reality today, although, as an industry, there still is a lot of work ahead The larger incumbent carriers are starting the migration to packet telephony on the trunk side first (Class-4 tandem) and will eventually migrate to the access side (Class 5) This migration model is similar to the migration from analog switches to digital switches, which started in the late 1970s, and offers a proven path for migration to new technologies The full migration to packet-based Class 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 for packet telephony to become truly compelling On this journey, the debates over VoIP and VoATM will continue While VoATM makes sense today for some carriers, especially the larger incumbents, VoIP is the longer-term goal especially Web ProForum Tutorials http://www.iec.org Copyright © The International Engineering Consortium 14/21 with MPLS–based QoS becoming available For some carriers, VoIP is the answer today as the consumer benefits are persuasive Service providers looking to deploy VoP will be best served if they choose a solution that addresses the issues of interoperability, call control and signaling, voice encoding, delay, echo, reliability, density, and performance of all the elements that make up the switching platform And they should look for solutions that deal with these issues for TDM switching, as well as VoIP and VoATM Self-Test A recent study by a major carrier found that packet equipment was 70 percent more expensive than traditional voice equipment a true b false Since most of the core packet networks today are ATM–based, but most likely migrating to IP–based, it only makes sense to deploy next-generation switches that can be deployed to transport voice on both ATM and IP networks supporting protocol layers a true b false Support for voice communications using IP, which is usually called _, has become especially attractive given the low-cost, flat-rate pricing of the public Internet a VoATM b VoP c VoDSL d VoIP _ from the start, was designed to be a multimedia, multiservice technology a AAL b IP c ATM Web ProForum Tutorials http://www.iec.org Copyright © The International Engineering Consortium 15/21 d PSTN In the new architecture, the call control will be handled by a a softswitch b Megaco c MGCP d SCTP are part of the physical transport layer and are controlled by a call control engine or softswitch (or media gateway controller), which provides instructions to direct the traffic a Switches b Headers c Media gateways d Platforms A media gateway can be physically located almost anywhere within the network a true b false A is hardware and software that provides a connection from a softswitch and media gateway into the SS7 network a Megaco b header c signaling gateway d transport layer A softswitch moves the service intelligence out of the switch into a database or application server, connects to those databases, and ultimately provides the "brains" or operating system for the next-generation voice network a true Web ProForum Tutorials http://www.iec.org Copyright © The International Engineering Consortium 16/21 b false 10 While VoATM makes sense today for some carriers, especially the larger incumbents, VoIP is the longer-term goal a true b false Correct Answers A recent study by a major carrier found that packet equipment was 70 percent more expensive than traditional voice equipment a true b false See Topic Since most of the core packet networks today are ATM–based, but most likely migrating to IP–based, it only makes sense to deploy next-generation switches that can be deployed to transport voice on both ATM and IP networks supporting protocol layers a true b false See Topic Support for voice communications using IP, which is usually called _, has become especially attractive given the low-cost, flat-rate pricing of the public Internet a VoATM b VoP c VoDSL d VoIP See Topic Web ProForum Tutorials http://www.iec.org Copyright © The International Engineering Consortium 17/21 _ from the start, was designed to be a multimedia, multiservice technology a AAL b IP c ATM d PSTN See Topic In the new architecture, the call control will be handled by a a softswitch b Megaco c MGCP d SCTP See Topic 6 are part of the physical transport layer and are controlled by a call control engine or softswitch (or media gateway controller), which provides instructions to direct the traffic a Switches b Headers c Media gateways d Platforms See Topic 7 A media gateway can be physically located almost anywhere within the network a true b false See Topic Web ProForum Tutorials http://www.iec.org Copyright © The International Engineering Consortium 18/21 A is hardware and software that provides a connection from a softswitch and media gateway into the SS7 network a Megaco b header c signaling gateway d transport layer See Topic A softswitch moves the service intelligence out of the switch into a database or application 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 10 While VoATM makes sense today for some carriers, especially the larger incumbents, VoIP is the longer-term goal a true b false See Topic 11 Glossary ACELP adaptive code excited linear prediction AIN advanced intelligent network AS application server ATM asynchronous transfer code Web ProForum Tutorials http://www.iec.org Copyright © The International Engineering Consortium 19/21 BHCA busy hour call attempts CBR constant bit rate CDV cell delay variation CES circuit emulation services IN intelligent network IP Internet protocol ITU International Telecommunications Union LNP local number portability MGCP media gateway control protocol MPLS multiprotocol label switching NEBS network equipment building standards PIC primary interexchange carrier PSTN public switched telephone network QoS quality of service RBOC regional Bell operating companies RSVP resource reservation protocol Web ProForum Tutorials http://www.iec.org Copyright © The International Engineering Consortium 20/21 ... gateway, and allow efficient execution of the softswitch and signaling gateway software Benefits also include cost savings and deployment and operation simplicity In the "integrated" model, the need... control is handled by a softswitch, and the features and services are handled by an application platform In reality, the softswitch (or call control platform) may support some of the more popular... combination of bursts of speech and silence and this increases the complexity of VoP The ATM Forum and International Telecommunications Union (ITU) came up with several advanced mechanisms to improve the