VoiP
`
`rest moves among the U.S., Asia Pacific, and Western European regions. It is
`important to closely examine who wi.ll be using this and what carriers or operators
`will be deploying these technologies. Probe Research (www.proberesearch.com)
`believes that by 2002, 6% of all voice lines will be VoiP This is still rather minor,
`given the fact that some have been saying that VoiP would have replaced circuit(cid:173)
`switched calling by now. Piper ]affray (www.piperjaffray.com) reports that minutes
`of communication services traveling over lP telephony networks will grow from an
`anticipated 70 billion minutes and 6% of all the PSTN traffic in the year 2003 to
`over a trillion minutes by the year 2006. In the United States alone, the PSTN is
`handling some 3.6 trillion minutes of traffic monthly.
`Although VolP has a very important place in telecommunications, it's impor(cid:173)
`tant to realize that it is not yet taking over the traditional circuit-switched approach
`to accommodating voice teleph9ny. The exciting future of VolP lies in advanced
`and interesting new applications, an environment where voice is but one of the
`information streams comprising a rich media application. Many expect that sales of
`VoiP equipment will grow rapidly in the coming months and years. Part of the rea(cid:173)
`son for this growth is that the network-specific cost for VolP on dedicated net(cid:173)
`works is quite a bit lower than the cost of calls on circuit-switched networks(cid:173)
`about US l.l cents per minute as compared with US 1.7 cents per minute. Using
`VolP to carry telephony traffic greatly reduces the cost of the infrastructure for the
`provider, but at the expense of possibly not being able to maintain QoS. Potential
`savings are even greater if VolP is implemented as an adjunct to data network
`Another factor encouraging customers to examine VoiP is the use of shared net(cid:173)
`works. Because IP emphasizes logical rather than physical connections, it's easier for
`multiple carriers to coexist on a single network. This encourages cooperative shar(cid:173)
`ing of interconnected networks, structured as anything from sale of wholesale cir(cid:173)
`cuits to real-time capacity exchanges. Also , VoiP can reduce the barriers to entry in
`this competitive data communications world. New companies can enter the market
`\vithout the huge fixed costs that are nom1ally associated with the traditional cir(cid:173)
`cuit-switched network models. Furthermore, because IP telephony will enable new
`forms of competition, there will be pressure to better align government-controlled
`prices with underlying service costs. International VoiP services are already priced
`well below the official rates and some of VoiP's appeal is that it eliminates the
`access charges interexchange carriers normally have to pay to interconnect to the
`local exchange carrier. ln the United States, these charges range from US 2 cents to
`US 5 cents per minute.
`
`Advantages of VoiP
`The key benefits of VoiP are cost savings associated with toll calls, enhanced voice
`services, and creative and innovative new applications. The key concerns related to
`
`APPENDIX C
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`Regulations Related to VoiP
`It's one thing to approach telephony on the Internet such that the incumbent is pro(cid:173)
`tected from competition with other voice telephony services on the Internet. But stat(cid:173)
`ing that voice on the Internet should not be allowed would be to cut your own throat.
`All the exciting new applications on the Internet do involve the use of multimedia
`applications, and voice is part of that overall stream. So, we have to be very careful
`about what we're regulating-whether it's voice, which is increasingly part of a larger
`application set, or whether it's traditional voice telephony.
`
`VoiP are voice quality compared to that in today's PSTN; the cost of QoS to ensure
`the same quality as in the PSTN; security; the current lack of compelling applica(cid:173)
`tions; and regulatory issues, such as whether voice wi.ll be allowed on the Internet
`and whether voice will be treated as an altogether different environment- as a con(cid:173)
`verged, integrated application.
`
`VoiP Applications
`VolP includes any set of enabling technologies and infrastructures that digitize
`voice signals and transmit them in packetized format. Three major network archi(cid:173)
`tectures can be used in support of VolP applications:
`
`Voice-over intranets, which could be based on leased lines, Frame Relay,
`ATM, or VPNs
`• Voice-over extranets, which could also be based on leased lines, Frame
`Relay, ATM, or VPNs
`• Voice over the public Internet
`
`The following sections discuss some of the key issues related to VolP applications.
`
`IP Long-Distance Wholesale
`So far, the most compelling business case for VolP has been in IP long-distance
`wholesale, where there are clear financial benefits and low barriers to entry. Early
`pioneers in this area include iBasis, ITXC, and Level 3, which predominantly offer
`lP services to domestic and international carriers, but also offer services to corpo(cid:173)
`rations and other service providers. What the customers gain by doing business in
`this fashion is a reduction in cost associated with carrying their traffic over expen(cid:173)
`sive toll or international transit links.
`ln IP long-distance wholesale, the voice service levels must match those of the
`PSTN. End customers of the international carriers expect to perceive the same voice
`
`APPENDIX C
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`

`

`VoiP
`
`351
`
`D 5oftswitch
`
`'
`
`'
`
`/
`
`557
`Network
`
`P5TN
`
`Broadband
`Packet Network
`
`P5TN
`
`VOIP{Trunking
`Gateway
`
`VOIP/Trunking
`Gateway
`
`VOIP{Trunking
`Gateway
`
`P5TN
`
`---- i
`
`L
`
`Figure 11.11 A converged long-distance network
`
`quality throughout. How can providers guarantee that when it's almost impossible to
`control QoS over the public Internet? Even in the case of IP backbones, QoS depends
`on the underlying architecture used. The solution lies in smart management of
`packet latency, to ensure circuit-like behavior inside the IP network. For example,
`iBasis developed a proprietary routing algorithm that monitors performance on the
`Internet; when it detects that congestion levels may affect the quality of the voice, it
`swi.tches the calls over to the circuit-switched network, thereby ensming that cus(cid:173)
`tomers experience the high quality that they expect end-to-end.
`The lP long-distance wholesale environment takes advantage of a converged
`voice/data backbone by using trunking gateways to leverage the PSTN (see Figure
`11.11). This allows support and processing of voice calls. The trunking gateways
`enable connection of the data network to the PSTN, to support long-haul carrying of
`the switched calls. In addition, svvitching services can be added to the data networks
`through the use of softswitches. (The functions and types of softswitches and gate(cid:173)
`ways that make up the new public network are discussed later in this chapter.)
`These are main issues in selecting providers of IP long-distance wholesale:
`
`Voice quality versus bandwidth- How much bandwidth do you use to
`ensure the best quality?
`Connecting to the customer-How many services need to be supported
`(voice, data, dialup modem, fax, ISDN, xDSL, cable modem)?
`Maintaining voice quality- As bandwidth becomes constrained, how do
`you maintain the voice quality?
`
`APPENDIX C
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`IP Telephony
`There are two main approach es to IP telephony. First, there's IP telephony over the
`Internet. Calls made over the public Internet using IP telephony products provide
`great cost-efficiencies. But the Internet is a large, unmanaged public network, with
`no reliable service guarantee, so the low costs come at a trade-off. International
`long-distance consumer calls are the major application of IP telephony over the
`Internet. Second, the use of private IP telephony networks is rapidly emerging. In
`this approach, calls are made over private WANs, using IP telephony protocols.
`The network owner can control how resources are allocated, thereby providing
`QoS and a managed network. Many private IP telephony networks are being built.
`They enable an enterprise to take advantage of its investments in the IP infrastruc(cid:173)
`ture. Again, because this is a single-owner network, th e QoS issues are much easier
`to contend with; in fact, a single-owner network makes it possible to contend with
`QoS issues!
`Multinational enterprises spend billions of dollars on international voice ser(cid:173)
`vices each year, so the savings that lP telephony offers is compelling. The cost ben(cid:173)
`efit of nmning voice services over a private IP network is on th e order of 20% or
`more savings on international long distance, as compared to using traditional voice
`services. Private IP transport platforms will be increasingly deployed, therefore, as
`an enterprisewide telephony option.
`Recent deployment of IP local exchange products, coupled with low-band(cid:173)
`width, high-quality voice compression , creates a solid foundation for extending
`business telephone service to telecommuters at home or on the road. Th e efficien(cid:173)
`cies of IP packet technology, coupled with the ITU G.723. l voice compression
`standards at 6.4Kbps, enable road warriors and small office/home office workers to
`have a complete virtual office over a standard 56Kbps Internet modem connection
`to the office. The really great feature of this environment is that your current loca(cid:173)
`tion is your office and your IP phone rings wherever you are. However, this
`requires an lP local exchange- a carrier-class product that resides in the service
`provider network and provides PBX-like telephony service to multiple business
`and telecommuter customers. It also requires a softswitch (that is, call-agent soft(cid:173)
`ware) that's used for purposes of managing call processing functions and adminis(cid:173)
`tration. Also, end-user services are delivered via IP Ethernet phones or analog
`telephones that use Ethernet-to-analog adapters.
`There are three major categories of IP phones:
`
`• POTS phone-The advantage of the POTS phone is high availability and
`low price. The disadvantage is that it has no feature buttons and the
`required Ethernet-to-analog adapter is quite costly.
`• Soft phone-A soft phone is software that runs on the user's PC and graphi(cid:173)
`cally resembles a telephone. Its advantage is low price. Its disadvantage is that
`
`APPENDIX C
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`

`

`VoiP
`
`353
`
`•
`
`it relies on the PC sound card, and it can create volume level problems when
`you switch between it and other applications that use the PC sound card.
`IP Ethernet phone-This device looks and works just like a traditional
`multiline business display phone, and it plugs into an Ethernet Rj-45 jack.
`It's priced similarly to PBX phones, at US$300 and up . Emerging "IP phone
`on a chip" technologies promise dramatically lower prices in the near
`future.
`
`The evolution of IP telephony will involve many different types of applica(cid:173)
`tions, including long-distance wholesale voice services; the support of voice appli(cid:173)
`cations for campus or enterprise networks in bringing VolP to the desktop in the
`form of new advanced applications that involve converged streams (such as video
`conferencing or multimedia in the establishment of remote virtual offices); Inter(cid:173)
`net smart phones; IP PBXs; IP centrex service; unified messaging; Internet call
`waiting; and virtual second-line applications.
`
`Vo/P Enhanced Services
`Another approach to supporting voice services is to look toward enhanced ser(cid:173)
`vices. There are two categories of enhanced services:
`
`• Transaction-oriented services-These services include Click-N-Call appli(cid:173)
`cations, interactive chat, Surf-With-Me, videoconferencing, and varieties of
`financial transactions.
`• Productivity-enhancing services-These services include worldwide for(cid:173)
`warding, multiparty calling, a visual second line, unified messaging, collab(cid:173)
`oration, access to online directories, visual assistance, CD-quality sound,
`personal voice response, and video answering machines.
`
`The key to enhanced services is not cost savings, but cost savings are realized
`through toll bypass, QoS differentiation, the capability to support remote access,
`an d the capability to create new forms of messaging. Because of the cost savings
`and features available, the use of enhanced services will grow by leaps and bounds
`over the next several years.
`VolP is part of a larger trend toward innovative voice-enabled Internet applica(cid:173)
`tions and network interactive multimedia. This trend includes various facilities to
`enhance e-commerce, customer service, converged voice and visual applications,
`new intelligent agents and variou s forms of bots, and e-calling campaigns. These
`sorts of advanced services make it possible to gain greater value from the IP invest(cid:173)
`ments that have been made, and at the same time, they create interesting n ew reve(cid:173)
`nue streams with altogether n ew businesses.
`
`APPENDIX C
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`We'll see VolP applications increasingly used in a number of ways. VolP appli(cid:173)
`cations will be included on Web-based call centers as automatic call-backs from
`customer service-based phone numbers entered into a Web page; as multiparty
`conference calls, with voice links and data sharing, initiated also from a Web page;
`and in the process of reviewing and paying bills. The key is to blend rich, Internet(cid:173)
`based content with a voice service. An example of an emerging application that
`illustrates such innovation is online gaming. lnnoMedia and Sega Enterprises are
`integrating lnnoMedia Internet telephony into Sega Dreamcast game consoles to
`allow game players worldwide to voice chat with each other while playing games.
`This device can also be used to cost-effectively place calls in more than 200 coun(cid:173)
`tries through InnoSphere, InnoMedia's global network. For example, the rate from
`the United States to Hong Kong will be US2 cents per minute, from the United
`States to the United Kingdom it will be USS cents, and from the United States to
`j apan, Australia, and most of Europe, it will be US9 cents.
`Another example of an interesting new VolP application is Phonecast, a media
`network of Internet-sourced audio channels for news, entertainment, and shop(cid:173)
`ping, available to telephones. Created by PhoneRun and WorldCom, Phonecast is
`modeled after television and radio broadcasting, and it allows callers to create a
`personal radio station and direct it by using simple voice commands. This is the
`first of a series of innovative content and service partnerships, assembled to form a
`comprehensive voice-portal product line.
`
`VoiP Service Categories
`There are several main VolP service categories:
`
`•
`
`• Enterprise-based VoiP-ln enterprise-based VolP, whether for the LAN or
`WAN, specialized equipment is required at the customer site.
`IP telephony service providers-These providers are generally involved in
`toll-bypass operations. They do not require specialized equipment at the
`customer site, but they may require additional dialing procedures to gain
`access to the network. Currently, multistage dialing is one of the problems
`we still face: You have to dial a seven- or eight-digit number to gain access
`to your ISP, and then you have to dial a string of digits for the auth entica(cid:173)
`tion code, and then you have to dial the string of digits corresponding to
`the number you want to reach. Single-stage dialing will remedy this situa(cid:173)
`tion in the very n ear future.
`• Converged service providers- These companies will bundle together
`voice, data, and video services.
`• Consumer VoiP-Consumer VolP is generally geared toward consumer
`connections over the public Internet.
`
`APPENDIX C
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`

`VoiP
`
`355
`
`VoiP Network Elements
`VoiP may seem like rocket science compared to conversations, but the concept is
`really quite simple: Convert voice into packets for transmission over a company's
`TCPIIP network. Two characteristics determine the quality of the VolP transmis(cid:173)
`sion: latency and packet loss. Latency is the time it takes to travel from Point A to
`Point B. The maximum toleran ce for voice latency is about 250 milliseconds, and
`it's recommended that the delay be less than 150 milliseconds. Small amounts of
`packet loss introduce pops and clicks that you can work around, but large amounts
`of packet loss render a conversation unintelligible. With too much packet loss, you
`would sound like you were saying "Da dop yobla bleep op bop," because little
`packets with much of your conversation would have been lost in congestion and
`could not be retransmitted while working within the delay requirements of voice.
`Hence, packet loss with VoiP can cause big chunks of a conversation to be lost.
`(We will talk about ways to resolve that a little later in this chapter.)
`VoiP gateways have allowed IP telephony applications and new, innovative
`VolP applications to move into the mainstream. Other features that have helped
`the development of VoiP are Internet telephony directory, media gateways, and
`softswitches, as well as telephony signaling protocols.
`
`Vo/P Gateways
`VoiP gateways bridge the traditional circuit-switched PSTN and the packet(cid:173)
`switched Internet. Gateways overcome the addressing problem. A couple years ago,
`for two VoiP users to communicate, they had to be using the same software, they
`had to have sound cards and microphones attached to their PCs , and they had to
`coordinate a common time during which both would be online in order to engage
`in a VoiP session. Gateways have made all that unnecessary, and now the only
`requirement is that you know the user's phone number. Phone-to-PC or PC-to(cid:173)
`phone operation requires the use of only one gateway. Phone-to-phone operation
`requires two gateways, one at each end.
`VolP gateway functionality includes packetizing and compressing voice;
`enhancing voice quality by applying echo cancellation and silence suppression;
`dual-tone multifrequency (DTMF) signaling support (that is, touch-tone dialing);
`routing of voice packets; authentication of users; address management; administra(cid:173)
`tion of a network of gateways; and the generation of call detail records that are
`used to create bills and invoices.
`To place a call over a VolP network, the customer dials the number the same
`way as on a traditional phone. The edge device, the VoiP gateway, communicates
`the dialed number to the server, where call-agent software-
`that is, a softswitch(cid:173)
`determines what is the appropriate IP address for that destination call number and
`returns that IP address to the edge device. The edge device then converts the voice
`signal to IP format, adds the given address of the destination node, and sends the
`
`APPENDIX C
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`signal on its way. If enhanced services are required, th e softswitch is called back
`into action to perform the additional functions . (The softswitch is also referred to
`as a Class 5 agent because it behaves like a local exchange or a Class 5 office.)
`There are two primary categories of VolP gateways:
`
`• Gateways based on existing router or remote access concentrator (RAC)
`platforms- The key providers here include the traditional data networking
`vendors, such as 3Com , Cisco, Lucent, and Motorola. As incumben t equip(cid:173)
`ment suppliers to ISPs, the data networking vendors are capturing the larg(cid:173)
`est percentage of these sales. They represented the majority of VolP gateway
`sales through 2000 because ISPs were buying gateways at a fast rate based
`on the significant wholesale opportunity available to larger carriers.
`• Server-based gateways- These are designed from the ground up to support
`VolP Key providers of server-based gateways include telecommunications
`vendors, as well as companies specifically designed for this business; Clar(cid:173)
`ent, Ericsson , Lucent, NetSpeak, Nortel, Nuera, and VocalTec are among
`the vendors involved. These gateways will overtake router and RAC solu(cid:173)
`tions as incumbent carriers deploy more server-based gateways with exten(cid:173)
`sive call server and signaling capabilities.
`
`More and more merger and acquisition activities will lead to blended solutions,
`causing the distinction between the different types of gateways to blur. RAC- and
`router-based gateways will take on more enhanced call-server characteristics as a result.
`The market segments for the two categories, then, are composed of the following:
`
`•
`
`• Enterprise VolP gateways- These gateways are customer premise equipment
`deployed between a PBX and a WAN device, typically a router, to provide call
`setup, call routing, and conversion of voice into IP packets and vice versa.
`• VoiP routers-Voice cards perform packetization and compression func(cid:173)
`tions and are inserted into a router chassis. The router then directs the
`packets to their ultimate destination.
`IP PBXs-An IP PBX is an infrastructure of distributed telephony servers that
`operates in packet-switched mode and offers the benefits of statistical multi(cid:173)
`plexing and IP routing. We are still in the early days for IP PBXs, although
`they are beginning to emerge as a viable alternative. A key concern is reliabil(cid:173)
`ity. (IP PBXs are discussed in more detail later in this chapter.)
`• Service-provider VolP gateways- These are used to aggregate incoming
`VolP traffic and route the traffic accordingly. The role is analogous to that of
`the local exchange. Challenges include the local loop competition among the
`incumbent carriers, quality concerns, shortage of product, interoperability
`
`APPENDIX C
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`

`

`VoiP
`
`357
`
`issues, the lack of hot-swappable and redundant support, and the lack of Net(cid:173)
`work Equipment Building Systems (NEBS) compliance.
`• VolP access concentrators- VoiP cards fit into an existing dial access
`concentrator.
`• SS7 gateways- SS7 gateways are critical to enabling us to tap into the intelli(cid:173)
`gence services that enhance so much of the telephony activity on the PSTN.
`
`Th ere are many gateway vendors. All gateway vendors share the need for digi(cid:173)
`tal signal processors and embedded software solutions that provide for silen t sup(cid:173)
`pression, echo cancellation, compression and decompression, DTMF signaling,
`and packet management. Th erefore, another very important part of this equation is
`the component vendors. Manufacturers of VoiP equipment need to con tinue to
`make quality improvements in the underlying technology. This includes address(cid:173)
`ing interoperability between different gateway vendors' equipment; improving the
`tradeoffs between cost, function, and quality; and introducing single-stage dialing
`and the ability to dial from any telephone.
`
`Internet Telephony Directory
`An Internet telephony directory is a vital piece of the VolP puzzle, so this section
`talks a little bit about the IETF Request for Comment 2916, also known as ENUM
`services. ENUM services convert telephone numbers into the Internet address
`information required to support all forms of IP-enabled communication services,
`including real-time voice, voicemail, fax, remote printing, and unified messaging.
`In other words, ENUM is a standard for mapping telephone numbers to IP
`addresses. DNS translates URLs to IP addresses, and EMUM uses the DNS to map a
`PSTN phone number (based on th e E.l64 standard) to the appropriate URLs.
`ICANN is considering three proposals for the . tel domain. The applicants are
`NetNumber, which currently runs the Global Internet Telephony Directory (an
`implementation of ENUM that is used by IP-enabled platforms to convert standard
`telephone numbers in to Internet address information) , Number. tel, and Telnic
`based in the United Kingdom. The ITU is trying to advance an implementation of
`the IETF ENUM standard under the domain el64.arpa. In this implementation,
`control of telephone number addressing on the Internet would be distributed to
`the more than 240 national public network regulatory bodies that administer tele(cid:173)
`phone numbers for the PSTN.
`
`Media Gateways
`Media gateways provide seamless interoperability between circuit-switched, or
`PSTN, networking domains and those of the packet-switched realm (that is, IP, AIM,
`and Frame Relay networks). They interconnect with the SS7 network and enable the
`
`APPENDIX C
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`handling of IP services. They're designed to support a variety of telephony signaling
`protocols. Media gateways are designed to support Class 4, or toll-switch, functions,
`as well as Class 5, or local exchange, services. They operate in the classic public net(cid:173)
`work environment, where call con trol is separate from media flow. They support a
`variety of traffic-
`including data, voice, fax , and multimedia-over a data backbone.
`Enhanced applications of media gateways include network conferencing, network(cid:173)
`integrated voice response, fax serving, network, and directory services.
`As shown in Figure 11.12, media gateways fit between the access and core lay(cid:173)
`ers of the network, and they include several categories: VoiP trunking gateways,
`VoiP access gateways, and network access service devices. They provide service
`interconnection or intercarrier call handling. The trunking gateways interface
`between the PSTN and VoiP networks, terminating trunks associated with SS7 con(cid:173)
`trol links. These Time Division Multiplexed trunks carry media from an adjacent
`switch in the traditional circuit-switched network, and the adjacent switch gener(cid:173)
`ally belongs to another service provider. (Depending on the agreements between
`service providers, these are also referred to as cocarrier trunks or feature group D
`trunks.) The trunking gateways manage a large number of digital virtual circuits.
`The access gateways provide traditional analog or ISDN interfaces to the VoiP net(cid:173)
`works; they are devices that terminate PSTN signaling and media, and they connect
`to PBXs, as well as to traditional circuit switches, such as the Class 5 and Class 4
`offices. With network access servers, you can attach a modem to a telephon e circuit
`
`Softswitch
`
`IP
`phone
`
`POTS
`phone
`
`ISDN PRI or T-1
`trunk TOM G.711
`
`Figure 11.12 VoiP network architecture
`
`POTS
`phone
`
`POTS
`phone
`
`APPENDIX C
`
`AT&T, Exh. 1003, p. 320
`
`

`

`VoiP
`
`and p rovide data access to the Internet, so that you can attain managed modem ser(cid:173)
`vice by using cocarrier trunks.
`
`Vo!P Softswitches
`Call-control intelligence is outside the media gateways and VolP gateways; it is,
`instead, handled by a softswitch, also referred to as a media gateway controller or call
`agent. The softswitch implements the service logic. Tt controls external trunking
`gateways, access gateways, and remote access servers. Softswitches run on com(cid:173)
`mercial computers and operating systems, and they provide open application pro(cid:173)
`gramming interfaces.
`A softswitch is a software-based, distributed switching and control platform, and
`it controls the switching and routing of media packets between media gateways,
`across the packet backbone. Softswitches provide new tools and technologies to build
`services in a more productive Internet-based service creation environment. Operators
`are advised to adopt a "service separation" strategy and to distribute applications
`throughout the network, avoiding the monolithic closed system that is similar to the
`circuit-switched environment. We can use application servers to partition enhanced
`telecommunications services and to determine what interface protocol to select for
`facilitating interoperability between the softswitches and the applications servers.
`The softswitch functionally controls the voice or data traffic path by signaling
`between media gateways that actually transport the traffic (see Chapter 10). The
`gateway provides the connection between an IP or ATM network and the traditional
`circuit-switched network, acting a lot like a multiprotocol cross-connect. The soft(cid:173)
`switch ensures that a call's or a connection's underlying signaling information-auto(cid:173)
`matic number identifiers, billing data, and call triggers- are communicated between
`the gateways. Softswitches must reuse intelligent network services through an open
`and flexible directory interface, so they provide a directory-enabled architecture with
`access to relational database managemen t systems, and to Lightweight Directory
`Access Protocol (LDAP) and Transaction Capabilities Applications Part (TCAP)
`directories. Softswitches also offer programmable back-office features , along with
`advanced policy-based management of all software components.
`The softswitch is a very important element in the new public network. lt is
`what enables the media and trunking gateways to communicate with the underly(cid:173)
`ing infrastructure of the PSTN and thereby to draw on the service logic needed to
`support telephony activities. In addition, softswitches will be able to reach to new
`application servers on which new generations of applications have been designed
`for new versions of enhanced services.
`
`Telephony Signaling Protocols
`New generations of signaling and IP telephony control protocols are emerging,
`and their purpose is to con trol the communication between the signaling gateway
`
`APPENDIX C
`
`AT&T, Exh. 1003, p. 321
`
`

`

`360
`
`Chapter 11
`
`Next-Generation Network Services
`
`and lP elements. Since the early days of exploring the nature of VolP and creat(cid:173)
`ing devices to enable it, a number of telephony signaling pro tocols have been
`considered. Some of the contenders h ave been H.323, Internet Protocol Device
`Control (IPDC) , Signal Gateway Control Protocol (SGCP), Multimedia Gateway
`Control Protocol (MGCP), Multimedia Ga teway Control (MEGACO), Session
`Initiation Protocol (SIP), and IP Signaling System 7 (lPS7). Many of those con(cid:173)
`tenders have combined, so this section focuses on the ones that have the s tron(cid:173)
`gest presence and potential today.
`
`H.323 The lTU H.323 version 2 specification is based on ISDN standards and
`limited to point-to-point applications. Version 2 requires multipoint control units
`(MCUs) to manage multiple sessions. H.323 version 2 provides much of the foun(cid:173)
`dation for exchange of voice and fax messages. The advantage of H.323 is that it is
`the most mature of the telephony signaling protocols, so many vendors offer it and
`vendor interoperability is good. On the other hand, H.323 is not as robust as some
`of the newer entrants, so other protocols on the horizon might eclipse H.323
`before too long.
`
`MCGP Bellcore and Level 3 merged their respective SGCP and IPDC specifica(cid:173)
`tions into MCGP In MCGP, softswitches provide the external control and manage(cid:173)
`ment, so MCGP is becoming a good way to connect an lAD to a gateway.
`
`MEGACO MEGACO is also called H.248 and it is anoth er emerging ITU stan(cid:173)
`dard. MEGACO describes how th e media gateway should behave and function.
`
`SIP SIP (IETF Request for Con~ment 2543) is an application-layer control, or sig(cid:173)
`naling protocol, for creating, modifying, and terminating sessions with one or more
`participants. SIP is used to set up a temporary session, or call, to the server so that
`the server can execute the necessary enhanced service logic. These sessions may
`include Internet multimedia conferences, Internet telephony, or multimedia distri(cid:173)
`bution. Linking caller ID to Web page content can link the status of a mobile phone
`with instant messaging. Members in a session can communicate via multicast or via
`a mesh of unicast relations, or by a combination of these. This is increasingly popu(cid:173)
`lar as the protocol between softswitches and application servers.
`
`LDAP LDAP is the standard directory server technology for the Internet. LDAP
`enables retrieval of information from multivendor directories. In fact, LDAP 3.0
`provides client systems, hubs, switches, routers, and a standard interface to r