VOICE 2001 Pr otocol War s Th r eaten VOIP Future

Larry Hettick

Instead of fighting over SIP and At WorldCom, distinguished engineering H.323, vendors should member Dr. Henry Sinnreich couldn’t disagree more. “H.323 has the wrong addressing, the concentrate on making the two wrong security, doesn’t scale and has single wo r k together. points of failure,” he said. “It is extremely complex and has a heavy footprint. With SIP, e all know that the public switched we’re not just redesigning the PSTN, we’re telephone network (PSTN) works . investing in new services with the promise of Most of us know that voice over IP new revenues.” W (VOIP) works. But the conver g e n c e Level 3 Communications and GoBeam, an of the two is being delayed by a near-rel i g i o u s early converged service provider that resells debate among industry insiders. Level 3 VOIP services, also weigh in for SIP. At the heart of the controversy is an either/or “H.323 is the PSTN, and SIP is the PSTN choice between the H.323 and SIP prot o c o l s . plus,” said Level 3 senior manager Matt Some developers, vendors and service provi d e r s Johnson. ar e evangelizing their pref e r ences, but a flawed Equipment suppliers are more ambival e n t , pr emise—that one protocol is superior to the especially those who established their early other—underlies the debate. In fact, both VOIP business with H.323 gateways. Tod a y , st a n d a r ds bring positive elements to the table, vendors like Cisco, Clarent, Commworks and and work is getting under way to make sure that Radvision support both H.323 and SIP. both will operate in the networks of the future. Acc o r ding to Michelle Blank, marketing VP Fighting protocol wars at this stage of the at Radvision, H.323’s capabilities allow carriers game does nothing for either the H.323 or the to make money today. “If you ’re a large servi c e SIP factions, and it casts doubt and uncerta i n t y pr ovider with a need for hundreds of over customer perceptions of VOIP and thousands of VOIP ports today, you must use co n v erged services. In a market with billions of H.323,” added Ofer Sha p i r o, Radvision senior dollars at stake, equipment suppliers and vice president for business devel o p m e n t . se r vice providers should be doing all they can to At Commworks, Houman Mod a r r es, fully integrate both of these protocols, and to di r ector for IP telephony, claims that the traffic educate customers about the efficiency and new mix users send across his company’s equipment se r vices that converged PSTN/VOIP networks is split about 50/50 between H.323 and SIP, but can offer. he acknowledges that the company is “ver y high on SIP, because a majority of our servi c e Who’s Pushing What? pr ovider customers are beginning to deploy it.” The battle between Session Initiation Protocol By comparison, Cisco is “strategically agnostic” (SIP) and H.323 has been brewing for several rel a t i v e to the protocols, said Alec Hen d e r s o n , years now. While SIP has been gaining ground VOIP product marketing manager to servi c e since the IETF standardized it in 1999, H.323 pr ovi d e r s — “ although our customers rarely are. ” La r ry Hettick is vice systems, which were introduced in 1996, are pre s i d e n t , co n s u l t i n g more widely deployed (see “Protocol Primer: Why Choose Sides? with Tel e C h o i c e H.323, SIP and Megaco/H.248,” p. 65 and Ser vice providers have good reasons to select (w w w. t e l e ch o i c e. c o m ) , also “Too Many VOIP Standards,” in BCR, either H.323 or SIP. The early VOIP adopters a consulting fir m that June 2000, pp. 64–69). used H.323 gateways to bypass traditional cat a ly z es cha n g e in AT&T chose H.323 because it was the most ci r cuit-switched paths and offer inexpensive te l e c o m mu n i c at i o n s mature protocol, according to Ann Machi, international long-distance service. Mor e business and product manager for VOIP. “It does what we rec e n t l y , domestic providers have shown interes t ma r keting strate gie s . want to do for our retail and wholesale in VOI P , but they prefer SIP as a platform for He can be rea c hed at customers,” she said, “especially for legacy ne w services, such as unified messaging, click to lh e t t i ck @ integration with our existing network and the talk and others. As for the incumbent local te l e ch o i c e. c o m . customer premises equipment at the edge.” ex change carriers, their lack of interest in VOI P

64 BCR’s VOICE 2001 / SEPT2001 VOICE 2001 is understandable: toll bypass efficiencies are not incumbents like Nor tel and Avaya have chosen im p o r tant in the local exchange, and new to “IP-enable” their installed base of PBXs with VOIP-enabled services are not important in a H.323 transmission gateways, and left the monopoly environment. traditional call control and feature sets in place. Carriers can’t As a practical matter, service providers can’t For these vendors, SIP remains a future option. af f o r d to fully equip their networks with gear for Newer PBX vendors, like Sho r eline Commu- fully equip their both VOIP protocols. They can successfully nications and Cisco, who lack an installed base to networks with mo ve from one technology base to another, as upgrade, seem more focused on SIP. “While we many did who started with analog cellular st a r ted with a prop r i e t a r y software load we call both protocols ne t w o r ks and then moved to digital, but the ‘sk i n n y ,’ we have since included SIP, a SIP call transition can be slow, complicated and costly. agent and MGCP software,” said Hank Lambert, Equipment suppliers, who want to sell those Ci s c o ’s enterprise VOIP marketing direc t o r . upgrades and alternatives, have ever y reason to “I n our arch i t e c t u r e,” Lambert continued, “a remain agnostic. And since both SIP and H.323 call agent like Cisco’s Call Manager can provi d e ar e used today in different service provider ‘sk i n n y ,’ SIP or MGCP as needed by the ne t w o r ks, vendors who want to sell VOI P ne t w o r k, and can include updates as differen t equipment will simply have to support both. st a n d a r ds are needed. The Call Manager can act The major exception to that rule is as a proxy to translate between multiple traditional PBX vendors, who have an easier st a n d a r ds as these standards evol v e. H.323 is st r a t e g y . Their core business value comes from possible, but we haven ’t had sufficient demand the feature set their PBX makes possible. Hen c e , to include it as an option.” Pr otocol Primer: H.323, SIP and Megaco

he amount of traffic carried by IP-encapsulated using HTTP, which increases the pool of development “protocols” has now eclipsed the amount of circuit- resources. T based voice traffic by nearly two-to-one, according to “SIP was designed by those who were big believers in Vertical Systems Group. In the 10 years since this shift was the Internet and Internet technologies,” explained Radvi- projected, PSTN network experts have been looking for sion’s Shapiro. “Their first concern was to bring voice over ways to converge the PSTN with packet-based networks the Internet, and then enhance for value-added features like like the Internet. multimedia.” The first such design emerged from the ITU-T’s efforts Houman Modarres of CommWorks agrees. “The SIP to standardize videoconferencing in 1996. It was H.323, model follows the Internet model for creativity. It is open entitled “Visual Telephone Systems and Equipment for and lightweight—a model that is created for adding fea- Local Area Networks that Do Not Provide Guaranteed tures and applications in an open architecture.” Quality of Service.” Subsequent additions, spurred by the Like H.323, the SIP architecture also contains four fast-developing Internet, moved to include standards for main elements, but they don’t exactly map one-for-one to packet telephony and wide area networks in the H.323 the H.323 architecture. They include: family. n User Agent, an endpoint that communicates either as a “H.323 was originally created for multimedia, and then peer or in a client/server relationship with other agents. enhanced for voice” noted Radvision’s Ofer Shapiro. “The n Proxy Server, which makes requests for User Agents. enhancements—features like call hold, call transfer, call n Redirect Server, which closely corresponds to the role waiting—were driven by traditional telephone philosophy. played by an H.323 Gatekeeper. The H.323 standards developers asked: How do we offer n Registrar, which works with the Redirect Server to redi- these PSTN capabilities on the Internet?” rect calls to the current location(s) of users. H.323 specifies four elements designed to interwork About the same time SIP was being developed, Media with the PSTN. They are: Ga t eway Control Protocol (MGCP) was also being n Terminal, which provides a multimedia codec developed for use with both SIP and H.323. MGCP sepa- (coder/decoder) user interface to other H.323 system rates call control (signaling) and media control, and initial- elements. ly was designed to function internally between the media n Multipoint Control Unit (MCU), which controls ses- g a t eway controllers (MGCs) and the media gatew a y s sions with three or more users. (MGs) in “decomposed”VOIP network architectures. In n Gateway, which provides the interface between the cir- the MGCP model, the MGC handles call processing cuit-switched and packet-switched network. between the PSTN and an IP signaling device—like an n Gatekeeper, an element that provides network manage- H.323 gatekeeper or a SIP server. ment and call control functions. The standardized derivative of MGCP is the joint The newer Session Initiation Protocol (SIP) was intro- I E T F / I T U ’s Megaco/H.248. This protocol set offers duced by the Internet Engineering Task For ce (IETF) in enhancements to MGCP, such that the media gateway con- Ma rch, 1999. SIP was designed with many familiar troller can also control multimedia and multipoint confer- characteristics borrowed from protocols like Hyp e r text Tra n s - encing enhanced services. Megaco/H.248 also offers fer Protocol (HTTP). SIP applications can be developed improved syntax for more efficient message processing

BCR’s VOICE 2001 / SEPT2001 65 VOICE 2001 implementations of H.323 FIGURE 1 Functional Architecture and SIP to interwork across these layers is a big challenge—interworking different vendors’ equipment across architectural boundaries among the PSTN, H.323 and SIP is even more complex. Because H.323 gatewa y s have been deployed as “VOIP network islands”— i.e., matched pairs at either end of point-to-point links—they have operated basically at the transport layer. They don’t need to interoperate with other VOIP islands, and they can rely on the PSTN or a PBX to provide call control and value-added features (e.g., stutter dial tone and call-waiting “beeps”) . But without call control and service layer interoper- ability, these islands can’t Source: Clarent, 2001 be connected, even though this represents an essential requirement. Jean-Francois Mule, Clarent’s director for In other words, incumbent PBX vendors, like standards and architecture, noted, “Not only incumbent service providers, have largely elected do large corporations need to connect to multi- to support H.323 as an efficient enhancement to ple carriers, but when corporations integrate their embedded base, with some new feature multiple IT networks, they need to keep their integration. And, like the newer servi c e existing [pre-integration] infrastructure. So the pr oviders, new entrants to the PBX market have enterprise needs proven interoperability.” mo r e broadly accepted SIP as the protocol for an Mule views the progression of interworking expanded services focus. in three phases. “First, you have publication of the standards. SIP and H.323 are both Why Interoperability Is Key published standards. Next, you have profiling. H.323 gateways have made VOIP a useful, The work for profiling these standards is “save-money” application for international long currently in progress in the IETF. Then you have distance providers and private network interoperability testing.” operators, while SIP-based PBXs are beginning According to Mule, testing is under way to appear in customer premises. Yet a mass between vendors on each protocol separately, market for VOIP won’t take off until vendors and between vendors’ H.323 and SIP and service providers can get their implementations in several test labs, including implementations to interoperate—with each some sponsored by interexchange carriers and other and with the PSTN. Making H.323, SIP by CableLabs. In addition, the International and the PSTN architectures work together is Softswitch Consortium, an industry group with also the key to pushing VOIP beyond current more than 193 member companies, began service suites and into new services, and while interoperability testing in June. progress has been made toward interoperability, Modarres of Commworks stated: “We’ve much hard work remains. been in SIP and H.323 interoperability tests The PSTN, H.323 and SIP have slightly with companies like Cisco and Clarent. The different architectural approaches, but they all basic features all work fine—features like call perform the same logical functions. Figure 1 connectivity, Automatic Number Identification shows the three basic, functional layers they (ANI) and basic call treatment. Some vertical share: transport, call control and intelligent features like leaving voice mail also work. What services. Getting different vendor gets more difficult are features like

66 BCR’s VOICE 2001 / SEPT2001 VOICE 2001 communications between messaging costs in the last few years. But while the applications servers.” gateways created efficiency by packetizing and “More difficult” is a nice way to put it. The compressing voice calls at the transport layer, road to H.323, SIP and PSTN interoperability SS7 created efficiency with a new call control Claiming either needs to be followed for each of the three layer to better manage the transport. layers. Although transport interoperability is An added benefit of SS7’s call-control SIP or H.323 is largely complete and call control is making capabilities was the introduction of some $20 better raises good progress, interoperability at the intelligent billion in new service and feature revenues, services layer has a long way to go. For exam- from offerings like Caller ID, 800 number doubts about IP ple, the several varieties of instant messaging, portability and pre-paid calling. But these telephony all of which are Internet-based, work fine with revenues couldn’t be realized until the carriers SIP, but none work yet with H.323. interconnected their SS7 “island” networks.

Can We Learn From The Past? Conclusion Still, it’s important to keep developments in By arguing that one protocol is better than perspective. As Mike Gaines, marketing another, service providers and IP telephony director at IP service control point (SCP) vendors introduce fear, uncertainty and doubt maker SS8 sees it, “The process is unavoidable (FUD) about IP telephony. This could slow and not entirely negative. Even SS7, a widely- user adoption, denying everyone the effi c i e n c y used standard, has different implementations and benefits that interoperable VO I P se r v i c e s and variations. For example, there are no 800 co uld offer. [toll free] services available between the United Customers don’t want to have to make a States and Asia, yet I can roam with my cellular choice between technologies, nor do they want phone in both.” the complexity of multiple systems. “End - u s e r s Gaines makes a good point. The cellular want to be able to use any device, from any- roaming he describes is only possible using wh e r e, at any time,” asserted Radvision’s Mic h e l l e multiple subscriber identification module Blank. “They don’t care about the underlying (SIM) cards, or with “tri-mode” or “tri-band” pr otocol as long as the technology works.” The cell phones. These phones can accommodate good news is that multiprotocol and the multiple frequency ranges, analog and interworking gateways are emerging from digital transmission and different signaling companies like SS8 and CommWorks. capabilities used in different cellular phone The PSTN, H.323 and SIP can work systems. And it is possible to call an American together as complementary and value-adding 800 number from Asia—but only if the caller network technologies, and can serve the end first accesses a U.S.-based SS7 network (e.g., users who will benefit from their integration. AT&T Direct). In other words, basic H.323 brings efficiencies to the PSTN, and transmission and call control incompatibilities SIP brings opportunities for new services. To in the cellular and international SS7 networks best serve the enterprise, emerging VOIP are being solved today only with more technologies must combine transmission- intelligent phones or by user intervention. efficient services to reduce the cost of So, one way to solve interoperability among telephony and create better communications the multiple VOIP protocols would be to services, regardless of protocol manufacture phones and other “VOIP terminal adapters” that could either “roam” or provide a Companies Mentioned In This Art i cl e gateway between incompatible VOIP network protocols. But let’s hope this is not the AT& T (w w w. a t t . c o m ) industry’s “final answer.” If we want to move Avaya (www.a v a y a . c o m ) VOIP forward, to give it the same ease of use Cisco (www.c i s c o . c o m ) as the PSTN, the service provider networks Clarent (www.c l a r e n t . c o m ) must provide VOIP protocol interworking just Co m m W orks (www.c o m m w o r k s . c o m ) as they provide today’s interworking between North American T1 and European E1 GoBeam (www.g o b e a m . c o m ) networks and between North American SS7 International Softswitch Consortium and European CCSS7. (w w w. s o f t s w i t c h . o rg ) There’s more to the SS7 story that might Level 3 Communications (www.l e v e l 3 . c o m ) interest service providers today. Recall that SS7 Nortel Networks (www.n o r t e l n e t w o r k s . c o m ) was initially deployed as an efficiency play. It Radvision (www.r a d v i s i o n . c o m ) saved interoffice trunking—the expense of Shoreline Communications establishing a circuit between two phones if the (w w w. g o s h o r e l i n e . c o m ) called party or intermediary trunks were busy—in much the same way that H.323 SS8 Networks (www.s s 8 n e t w o r k s . c o m ) VOIP gateways have saved interoffice facilities WorldCom (www.w c o m . c o m )

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